How To Calculate Muffler Size and Exhaust Pipe Diameter
If you’re a math wiz and/or an engineer, you’re probably going to like this article and the resources we’ve linked to. However, if you find yourself getting stuck (or bored) with the info below, here are the key take-aways:
1. The factory exhaust pipe diameter is usually a good choice for most vehicles.
2. The muffler manufacturers are doing all the math for us – no need to reinvent the wheel. If they say it will work for your vehicle, it will probably work for your vehicle.
3. We’ve got an easy-to-read exhaust system size table that is good for quick calculations.
Breaking Down The Problem
While we’re not going to go through and list out all the formulas and calculations you need to figure this exactly, we will break down the problem, explain how you would go about figuring things out scientifically, and then leave you with some good quick-and-dirty exhaust system math as well as some interesting links.
The science goes like this…
Conservation of mass, right?
2) To calculate the volume of air the engine takes in, we multiply the displacement of the engine by the engine RPM and then divide by two (it takes two full revolutions for the engine to exhaust it’s entire air volume). We then convert that to volume to mass.
3) To make the calculations easy, you want to assume that combustion is perfect, i.e. there aren’t any byproducts, any unburned fuel, etc. It’s easier to assume perfect combustion and then “back in” to the actual numbers using an estimate after the fact.
4) Since you’re assuming perfect combustion, it’s easy to figure out how much fuel mass is added to the exhaust.
5) Once you know the mass of the exhaust gas, you just figure out how much volume that mass would occupy. Of course, you have to adjust for expansion due to the high exhaust gas temperature.
That’s it! Of course, when you sit down to figure it, you’ll find that getting a good scientific estimate takes a lot of work (which is why we don’t bother with it here).
Quick and Dirty Exhaust System Math
Easy Way To Estimate: Your intake system needs to flow 1.5 CFM per engine horsepower, and your exhaust system needs to flow 2.2 CFM per engine horsepower.
Good Way To Estimate: Take engine RPM x engine displacement, then divide by two. This is the intake volume. Use this same volume of air for the exhaust system, but then correct for thermal expansion (you need to know exhaust temps to figure things out).
Exhaust Pipe Size Estimate: A good section of straight pipe will flow about 115 CFM per square inch of area. Here’s a quick table that shows how many CFM each common pipe size will flow, as well as the estimated max horsepower for each pipe size:
| Pipe Diameter (inches) | Pipe Area (in2) | Total CFM (est.) | Max HP Per Pipe | Max HP For A Dual Pipe System |
| 1 1/2 | 1.48 | 171 | 78 | 155 |
| 1 5/8 | 1.77 | 203 | 92 | 185 |
| 1 3/4 | 2.07 | 239 | 108 | 217 |
| 2 | 2.76 | 318 | 144 | 289 |
| 2 1/4 | 3.55 | 408 | 185 | 371 |
| 2 1/2 | 4.43 | 509 | 232 | 463 |
| 2 3/4 | 5.41 | 622 | 283 | 566 |
| 3 | 6.49 | 747 | 339 | 679 |
| 3 1/4 | 7.67 | 882 | 401 | 802 |
| 3 1/2 | 8.95 | 1029 | 468 | 935 |
NOTE: These numbers are just estimates. All pipes are assumed to be 16 gauge steel.
The table above is probably over-estimating pipe size, but you can see that a 400 hp vehicle with a dual exhaust system only needs 2 1/4 – 2 1/2 inch pipes. Anything larger is overkill.
Useful Links
Great forum discussion that really discusses the details of the scientific calculations: http://www.eng-tips.com/viewthread.cfm?qid=104735
An interesting discussion of header pipe designs: http://victorylibrary.com/mopar/header-tech-c.htm
A good general article about designing the perfect exhaust system: http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index.html
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it was a very good article. i red and i was impressed. it solved my problem to make more efficiently exhaust for racing need. do you have any article about header? size of pipe diameter and how long it can be to give an optimum performance. i’m atuner from indonesia. an in my country, something like this was very rare. i have searched on the web, but found no article that make me delightfull to solve header problem. if you have some, it will make me very gratefull. thanxs before.
@ onyeh,
search for the haynes website and consider purchasing performance tuning for 4 strokes and performance tuning for forced induction. They are EXTREMELY useful and have a great amount of information for real motoring enthusiasts and professional tuners.
This is in regards to this:
“Good Way To Estimate: Take engine RPM x engine displacement, then divide by two.”
My question is… for the engine displacement do I used cubic inches or CC?
thank for an informatic article,
Brian Mizell
Brian – It can be either. Just remember that whatever units you use (cubic inches or cubic centimeters) must be converted to a unit of mass. My suggestion? Stick with metric. Conversions are much easier.
Hello
Great table but it may not be as accurate as you may think as i have a very quiet 3″ system on my 3.0L turbo Nissan skyline with 315kw@all 4 wheel, the problem is it’s 315kw on 15psi boost and 335kw on 19PSI boost, so did a google search for pipe size vs horse power
Kind regards
Geoffrey
Just a quick update
I removed the rear muffler and increased power to 355kw@ all four wheel.
New rear muffler fitted dropped the power to 345kw@ all four
made up a 3″ mandrel bent pipe to replace the rear muffler 350kw@ all four
Now it’s just too noisy
Destroyed my clutch before Christmas so have not played since
best so far is a 11.66 quarter at 201km with street tyres
Hoping to up the power to 400kw@ all four
Great site and helpful
kind regards
Geoffrey
Very informative! I do not understand “overestimating pipe size”. Do you mean I can make more power with each size pipe in the chart? I have a non mandrel 1.75″ system on a Daihatsu Rocky that originally made 94hp with 1.5″ from the cat back. Am I properly sized, it needs all the HP and tq it can get.
Buz – The size of your exhaust system pipes should be matched to the power of your engine. So, if you have an engine that generates less than 100hp, the proper single exhaust tube size is 1 3/4″ . Smaller (like 1 5/8″) is probably just fine (might actually help with low end torque to got to 1 5/8″), but if you go much bigger you’ll actually rob power from your engine.
Also, when I wrote that our chart was over-estimating size, it means that the diameters listed aren’t exact. Instead, they’re rounded to the common exhaust pipe sizes so you can buy pipe…if we just used math to arrive at the diameter, we’d end up with some funky pipe sizes that would be impossible to buy. Hopefully that makes sense (the article is a bit cryptic).
Hi there Jason, Great reading, Im running a 572ci big block chev on a twin 2.5 inch system with an x pipe and flowmaster mufflers(620hp)primary pipe size is 2 inch going into 3 inch collectors i have been thinking about going to a twin 3 inch system but am wondering if i would see any noticible difference in the car as I seldom go beyond 4500rpm on the street(Max rpm 6000)the system is ceramic coated so cost a bit what are your thoughts?
Michael – If I’ve done the easy math right, your big block could pump out nearly 1,100 CF of exhaust per minute at 4500 RPM. If you’ve got a section of pipe that’s only 2″ in diameter, than you’ve got a bottleneck that’s probably restricting flow on your vehicle.
However, dual 3″ is a lot..I’m thinking dual 2.5″ or dual 2 3/4″ is probably enough. Based on all my readings and conversations with people who would know first hand, it’s better to be a little on the small side (2.5″) than too big (3″).
Jason, Thanks for the reply the only 2 inch pipes in the system are the primary header pipes(this is quite a big size primary pipe size as I understand) I think i will stick with the dual 2.5 system as its only a street driven vehicle (I do drive it hard often though)People comment on how awesome the car sounds it currently has Flowmaster delta 40 series mufflers on it but im thinking of trying out the super 44s as i understand they have a deeper tone than the delta 40s(Can you comment on this?)
Michael – I’m sorry I misunderstood – 2″ collectors are quite big. No restriction there.
I can’t comment on Delta 40 vs Super 44′s from experience, but I’ve heard the same thing. My honest opinion, however, is that you won’t notice enough difference to justify the expense. They’re both going to sound great.
Jason, So basically unless im going to run the car at max revs the dual 2.5 inch system will lose nothing to a twin 3 inch system ? and may even be better for low down torque (Although the car makes massive torque anyway) thanks Michael
Michael – You’re going to lose something at 6000 RPM using 2.5″ pipes – the CFM requirements are higher than your current exhaust will allow at that RPM. However, in low to mid RPMs (4000RPM or less) you’ve got more than enough pipe capacity, and just as you say it’s actually a good thing to have smaller pipes in terms of off-the-line performance.
So, if you use the vehicle as described, than you’re better off with your current setup than a set of 3′s…assuming all the assumptions we’ve made are correct.
Hey Michael,
Your set up sounds nearly perfect! the one thing I can think of that will up your horsies across the entire rev range is to try siamesed pipes instead of a balance/cross pipe. Siamesed pipes are basically where the two pipes merge into one pipe for about a foot before splitting again. However on alot of cars it can be impossible to get room for two 2.5″ pipes next to each other at all!! Just a thought
thanks in part to the information you have provided ihave decided to go with a single 3 lnch exaust instead of a 2 or 2.5 inch dual setup all the information i have been able to find says i will gain torqe with a single 3 inch system thank you much
Hi there Jason,i’m running a toyota celica gts with rev at 8700 rpm,1796cc and the car has a valve lift at 5700 rpm.horsepower is 210,What is the best dimension for this car?the car has 3 inch air intake pipe from 2.75 and tuning ecu with lift from 6200 to 5700 and rev from 8200 to 8700 and my exhaust is 2,25 inch!!!nice article it helps my a lot but i have comfused…..
I have a 1993 gmc sierra 5.7 350. I didn’t understand how to do this so i was wondering if you could do it for me. I plan on putting a dual exhaust.Can you tell me which diameter i should get?
Anthony – Is it stock? Factory HP was probably around 250…which means a couple of 2″ pipes should cover it. Now if you start doing mods and crank it up over 300hp, a set of 2.25″ pipes will work.
Hello can u help me whit exhaust pipe size. I got 2,0 16v , 136 HP
car, whit cylinder size 1998 ccm, what size of pipe i have to put on for more power.
Help.
I recently bought a 1975 Mercedes 450SL as a classic but it idles rough. They have replaced plugs, fuel injectors and the catalytic converter in the exhaust system. None of this changed the rough idle. It wants to stall if the idle rpm is reduced below 1100rpm. Now they tell me that the exhaust manifold on the right side of the engine needs to be replaced. I understand that this car uses a “catalyst” as part of the exhaust manifold. Could this catalyst be blocked like the catalytic converter was thereby causing the engine to run rough? There is no missing at highway speeds or over 2000 rpm so I can’t quite grasp what role the exhaust manifold plays in this problem.
Any advice or comments would be sincerely appreciated.
Thanks, Larry
Larry – I gotta tell you I have no idea. However, this guy – http://daveknowscars.com/ – is an MB expert. You might try looking over his blog and seeing if he’s got the answer to your question.
It’s been a few years that i last worked on a old classic merc.
Some of the fuel injection systems are trigerd by an old fashioned points system in the distributor, there s a block of them that comes out of the side of the distributor.
This may help, everyone overlooked the one i repaired and he had been to about 30 different mechanic’s including a merc dealership
Kind regards
Geoffrey
Hey, just wondering if you can help. I have a clevo running 350-400hp, it currently has twin 2′ pipes out of headers. Would there be any advantage upgrading to 2.5′ Thanks
Matt – The advantage in increasing pipe size at your HP rating is better performance at high RPMs.
I cant see where there would be any advantage even at high revs by running a twin 2.5 inch system with only 350-400hp on tap 2 1/4 would be more than enough surely
I tried doing the math but I’m falling between 2.5″ and 2.75″. Was looking at 2.75″ system but would like your advice. I have a 4.2L V8 FSI with 420hp that redlines at 8250rpms. I plan on doing a few bolt modifications that will bring the car around 480hp. What is your suggestion?
HI Justin, See my discussion with Jason above im running 620hp on a dual 2.5 inch system so i think 2.5 inch max for you as a twin 2.5 is good up to 500hp I would run a twin 3 inch on mine if I was taking it to max revs but I seldom go about 4000rpm
Michael,
Thanks for the response. Does the fact that my car redlines at 8250rpms make a difference? I did the calculations with stock numbers and im getting 610CFM which is right on the cusp on 2.75″. I usually shift between 3k-5k rpms but get close to the redline fairly often on my drives. (not a DD car) From factory, it comes with 2.5″ dual exhaust. Do you still think that 2.5″ max is right for me if I plan to do mods?
Hi Justin, I can see no advantage having a dual 2.75 inch system in fact most of the time you would be losing hp and definately low end torque, im making massive torque right through the rev range on a dual 2.5 inch but lose hp at max revs but then were comparing a 4.2L to a 9.3L im producing 500hp at 4000rpm and my system if great even at max revs your not producing more than 500hp. What size header pipes and collecters do you have ?
Agreed! Thanks for commenting!!
Not sure. I looked around for it but couldnt find any dimensions. I know the dual stock downpipes and exhaust pipes are 2.5″. No idea about the header size. I know they are 4-2-1
Justin, dont worry about headers im sure they are fine dont waste money on going to a 2.75 inch system and then end up losing hp and torque the opposite of what you are trying to achieve
justin – I agree with Michael. Better to go with the smaller size if you value low-end torque.
ok guys I need help . Ive got a 67 olds with a 350 ci motor and 455 edelbrock heads. motor should be pushing 460 to 500 hp. I want louad but deep sound and I want the best preformance i can get . if it matters ive got a set of hooker headers on it now. what muffler sould I go with and what size ? and should I go center to center or a off set chambered muffler….. I wandt the sound
thanks guys
Kyle – You can calculate size by looking at the CFM figures on the mufflers or contacting the manufacturers. As for offset vs center to center, I don’t think it makes much difference…but if I had to choose, I’d go center to center.
I have a rammer that melts plastic close to the exhaust. Could the engine be running rich or lean ? Or the mufler is restricted
Could be that the mix is off, but it might also be that the plastic is too close. Is this a factory part that’s melting or an after-market part?
The sizngs are so incorrect it’s not funny.. my car has about 270hp stock and has a 2.5″ with a crush axle back.. even a better (catless etc.) 2.75″ exhaust is good for 330-350hp N/A.. should see 350 *W*HP out of the OEM exhaust even with forced induction.. and that’s with cats in the headers and 4 cats total -_-.. Evo’s run 2.5″ up to about the same and even a single 3″ is fine for 450-500hp
admittedly the OEM exhaust i run is twin 2′s (or 1.75 or something) off the headers into a single at the diff.. but still. you should mention more about the design not neccessarily needing a consistent piping size to the end like this.
I don’t follow your comment – not sure what you’re trying to say.
Also, bear in mind that the article says best way to figure out the proper size is to do the math…the chart is a shortcut.
Sir,
I m interested in silencer . but I am having very little knowledge about silencer . I don’t know how to calculate pipe size and holes maid on pipe of silencer and how to calculate the chamber in silencer and all regarding silencer . I m having esteem car . and I have to modify the silencer and make it more silence instead of noisy . can please guide me for this silencer developing and if there is a book covering my requirements can you please suggest me . I will be thankful to you .
I have a 93 civic about to have 300-350 hp on my d16z6 will i need a 3″ exhaust or can i get away with 2″ 3/4″?
I would go with 2.75 inch rather than 3 on a 4cylinder. It’s better to preserve low-end torque.
hi,i’m looking into a catback system and i’m looking at the chart and were it shows the max hp for a dual system is it true dual from the manifold back with 2 converters and 2 mufflers or is it dual catback?
Kirt
Kirt – As far as the chart is concerned, it’s not specific to cat or muffler back – it’s based on volumetric gas flow rate.
thanks jason, so are we to assume the chart is assuming the flow rate using just straight pipes not taking into account it has any converters,mufflers or am i just totally missunderstanding the chart altogether?
Kirt
Kirt – The chart shows you what approximate size of tubing you need for a specific engine HP, based on the amount of exhaust gas an engine typically produces for any given HP. Since it’s based on the amount of exhaust gas that has to flow through the tube, mufflers and cats don’t matter…it’s just flow.
Think of it as a water pipe – a 1″ pipe is only going to flow a certain amount of water at any given pressure. If you want to flow more water, you have to make the pipe bigger. It also doesn’t matter what you put on the pipe anywhere in the line either. You can add valves and tanks to water pipe, but those things aren’t going to increase water flow because the only thing that matters is pipe size. Make sense?
Jason, yeah it makes sense and thanks again for the explanation…always better to have it explained more in depth or a different way since we all don’t have the same translation abilities.
Kirt
Have cad eldorado with 3″ from engine back! No cat no mufflers with 5 inch outlets! Might loose back pressure, who cares, NORTHSTAR comes to life!!!!!!! Try it, best of both worlds!!!! Thanks kev
So i was wondering what formula did you use to get the pipe area. I want to see what the larger diameters flow. I may have to use a 4″ exhaust to achieve the power goals that i want but i wanted to do the math to make sure.
Jason 2 – Sorry man, I don’t have a simple formula to calculate flow by diameter. It’s actually quite complex, which is why it’s not listed here. If you’re looking for an easy way to calculate pipe area, it’s Pi times the square of the radius (remember Pie – R – Square from school?)
Hey, ok so I’m not fully understanding, this but I’ll tell u my set up and maybe u can help me! I have 2008 dodge ram 1500 with a 287ci motor stock hp 310, stock tq 330 but I have about 40 hp/tq extra of bolt ons. Now I installed a 2.5″ pipe to a y pipe to twin 2.5″ pipes going to five inch tips. I don’t know why but I personally feel like I lost hp/tq after this install? Would it be better to just go single 3″ since I’m steady adding more performance parts also is why I’m asking I’m not trying to rob performance, over sound? Hope I explained this good enough, thanks Donald
I HAVE MORE OF A QUESTION, I HAVE A 99 DODGE DURANGO AND INSTEAD OF THE PREVIOUS OWNER PUTTING THE CORRECT SIZE MUFFLER ON IT HE WENT WITH A MUFFLER THREE SIZES SMALLER. SHOULD I CONTINUE WITH THAT OR GET THE CORRECT SIZE AND WHAT IS THIS DOING TO MY TRUCK?
THANKS 4 ANY SUGGESTION
Jan – A small muffler could be restrictive relative to a normally sized muffler, only it depends on design. If it’s a flow-thru design muffler, size isn’t a huge concern.
Thanks Jason, I guess if its not broke dont fix it.
I have a stock 4.8 gmc sierra with 2 3/4 pipe exhaust. I has told the muffler robs my truck of mpg and horsies. I want to put a new muffler only on and can’t find any after market exhausts that are 2 3/4″ should I replace the muffler with a 2.5″ or a 3″ and when doing so should I keep the 2 3/4″ tail pipe or replace to fit the new muffler. will going from 2 3/4 pipe to 2.5″ higher flow muffler back to 2 3/4″ tail pipe work?
John – I think I’d go the other way (up to 3 then back down to 2 3/4) but I doubt it makes much of a difference either way. Whichever muffler is cheaper.
Having said that, you might check the price of necking up and down vs down and up. Could up that up and down is cheaper.
I’m currently in the process of swapping my 97 Civic 1.6L SOHC engine to a 2.0L DOHC engine approximately (170hp @ the flywheel) and I am in need of a custom exhaust but I want it to be a very quiet exhaust. I will have a header with a 2.5″ collector and I was thinking I could go with a 2.5″ non-mandrel bent exhaust (essentially 2 1/4″ right?) into a restrictive muffler to keep it all quiet. Would it be best to go with a multiple baffle muffler or a turbo style muffler? Also is my exhaust size right or should I smaller or larger?
Thanks,
Jason
Jason – Your plan sounds good to me. I might think about going with a slightly smaller pipe (2.25) that was mandrel bent simply because a smaller pipe will perform better…part of what you’re trying to avoid is having the exhaust gases cool too quickly. If you go with an oversized pipe (even if the bends are a little smaller), you’ll get some of that negative cooling effect you’re trying to avoid. This can reduce low-end power.
As for muffler style, I don’t have any guidance other than to look at Hushpower mufflers. They claim to be quiet yet still high performance. The trouble with after-market mufflers is that they’re almost always loud.
I can get crush bent exhaust for a very good price. Would I hurt my fuel economy and/or power production too much by going with 2.25″ crush bent piping with an 18″ inch resonator and a 2.5″ oem replacement muffler (since it’s going to really restrictive)? Or should I go with mandrel bent exhaust at a bit more costs?
Jason – There’s not a HUGE difference between crush-bent and mandrel-bent tubing, but mandrel-bent is always better. I’d say go with whatever makes the most financial sense, especially if you’re going with the OEM muffler.
Great website, ive been looking for ta resource like this.
I have a question. Ive built a 4 cylinder MGB GT engine 142bhp@ at the back wheels, its a very tuned engine std they were 95 at the flywheel which probably gave 65-70 BHP at the back wheels. Im currently running a 2″ freeflow system with a rear muffler (Moss Tourist Trophy system). Id like more of a low down throaty sound (MG`s tend to sound like farts in drain pipes).
Would a larger backbox help? Or would that two box system have helped with that? Perhaps a 2.5″ system would have been better?
I chose the single back box as I had read somewhere that the rear muffler gives more throat and the front creates a higher pitch?
Thanks really appreciate your input.
Ray
Ray – The very best sound I’ve ever heard out of a 4-cylinder exhaust is fairly muted and likely restrictive. If you’re looking to get good power AND good sound, I don’t have any ideas. I’m not aware of any tricks to make a 4 or 6 sound like anything other than a 4 or 6, at least outside of idle.
I currently have a CRV engine going (approx 170hp at the crank) into my 97 Civic and I was considering a custom dual exhaust (1 3/4″ or 1 5/8″ into a dual inlet and dual outlet muffler. Would the dual exhaust help quiet my exhaust any?
Jason – Probably not. The frequencies that generate the most noise aren’t really attenuated by additional tubing. I’d also say that you’re trading exhaust noise on just one side of your vehicle for noise on both sides.
If you want to reduce noise, a good trick is to point your exhaust tip(s) down towards the ground, and to run them out of the side (behind the wheel) rather than straight out the back.
but would my car be quieter with two 1 5/8″ pipes run into one muffler or maybe two mufflers rather than one 2 1/4″ or 2 1/2″ pipe run into a similar sized muffler?
My goal really is to maximize flow/velocity without too much or too little restriction but most importantly I don’t want my car’s sound to be loud or droning at all.
Jason – If I understand you, you’re contemplating a custom dual inlet and/or dual outlet exhaust. I’m also guessing you have a V6. A dual outlet won’t be any louder or quieter than a single outlet if it’s coming from the same single muffler (see my previous comment, where I was assuming you had a 4cylinder). As for a dual outlet coming from two separate mufflers (i.e. a “true dual” system), than a dual exhaust will probably be harsher than a single.
This is because the V6 exhaust note is inherently unbalanced, as opposing sides of the motor are detonating an unequal number of cylinders at any given time. Therefore, splitting this exhaust up into two completely separate tubes is going to give you a raspier, harsher sound than you’d get from balancing both sides by running them into the same muffler and/or using an x-pipe.
Based on the fact that your vehicle has a relatively small V6 (I’m still wondering if you have a 4cylinder, quite honestly), I’d run a single muffler, single exit exhaust system and then just try to buy a good muffler that isn’t too loud. Hushpower is supposed to be a quiet performance option, but I don’t know if they have anything that fits your CR-V. Good luck!
P.S. If you have a four cylinder, there’s nothing to talk about here…single in and single out is the only way to go. Anything else would be silly.
My car is and will be a 4 cylinder from a CRV.
My line of thinking is that if I split my exhaust after the header then I have smaller pipes which in return I think should be quiter then I add two resonators which in return makes it even quieter then I can two mufflers to each pipe and now it’s even quieter but I was also thinking that I could run both pipes into a dual inlet and outlet muffler and hopefully still keep a quiet exhaust.
Jason – As I’ve said, there’s no benefit to extra tubing. One resonator and muffler will work just as well as two. It’s not a “bigger is better” situation because a 4 cylinder doesn’t pump out enough exhaust to require two of anything. You’re over-thinking it.
I think you misunderstand because I’m thinking smaller pipes versus one larger pipe. Your chart shows that two 1 5/8″ pipes flow the equivalent of one 2 1/4″ pipe and the 1 5/8″ is what I’m getting at.
Jason – I’m not misunderstanding. You want to take the single exit on the stock manifold, split it in two, and somehow reduce the noise level without effecting performance. Unfortunately, it just doesn’t work that way – one pipe (and one resonator and one muffler) is all you need. No amount of tubing is going to reduce noise any further than a good muffler (the frequencies that are attenuated by extra tubing aren’t impactful on overall sound levels), and whatever extra tubing you add will likely hurt performance too (if exhaust gases cool too quickly, you’ll kill your low-end torque). Don’t screw around with it – focus on finding the best muffler you can.
so explain this to me please anyone. if these car geniuses calculate this the why does my suburban and dakota have stock 3 inch exhaust. suburban 454 about 350 hp. understandable. dakota 3.9 v6 180 hp. shouldnt there be a 2 1/4 to maybe 2 1/2 in. please explain.
Rob – Who knows but a Dodge engineer? I could guess that a) only the tip is 3″ or b) that the pipe size from the manifold to the muffler inlet is much smaller, but the fact is I have no idea.
If it helps you, Chrysler is a three-time loser. They went under in the 80′s, then went under in the early 2000′s when Cerebus Capital bought them out, and then they needed a federal bailout. Chrysler didn’t fail on three separate occasions just because they had some bad luck…
thats why the dodge costed 500 bucks. its 3 inch from manifolds to muffler and 2 1/2 out. i kinda wanna do a 2 1/2 all the way through but really how much money do i want to throw away. i mean dodge really isnt what you want to tell people you own but the fact of the matter is its 4×4 and works good 92000 miles and no mechanical problems. MIGHT last another 8000 miles.lol.
Hi
I was just wondering, I have 2000 Mercury Grand Marquie that I bought used but in great condition with only 140,000KM on it. I installed a K&N recommended custom cold air intake with shroud and I also installed a Helix throttle spacer on the throttle body. The car came with a single exhaust from factory so I had a custom dual put on by the performance shop in my area. We cut the original Y and made 2 separate exhaust by adding the left drivers side. We put a regular muffler on the left side and kept the original on the passenger side. The performance was excellent and the car would squeal the tires even with the traction control engaged. We kept the pipes and everthing normal diameter. I missed my performance mufflers ( magnaflows ) that I had on my 1993 mercury 4.6 ltre that I finally scrapped at 357000km. I decided to put the same type magnaflows (tube type) on my 2000 Mercury. The car sounded really deep in tone but when I started driving for about a week I noticed that I didn’t have the same power and my fuel consumption increased. Is this because of not enough back pressure? I am seriously thinking of going back to the normal standard mufflers if this is the cause. The performance guys say sometimes you comprimise power for nice sounds but I am not sure? Any ideas would help. Car runs perfect otherwise. Thanks Darrell
Darrell – There are a lot of reasons that you could feel as if your car is slower and getting worse gas mileage. First, it’s the winter time, which means that fuel economy is always lower (cold engines are less efficient, and winter fuel mixes aren’t as good as summer fuel mixes).
Second, the “butt dyno” – i.e. your personal assessment of power – just isn’t very accurate. It’s hard to tell how fast something is just by feel.
Still, any time you hack together an exhaust system, you risk creating something that doesn’t perform as well as the stock system. This is why I recommend either a) going with a quality after-market cat-back kit or b) working with an experienced performance muffler shop that knows about tuning.
If your current muffler shop says that “you have to compromise power for sound,” find a new shop. That guy couldn’t be more wrong.
Hi Jason.
Thank you for the reply. I just wanted to give you a little more detail to avoid confusion as maybe I didn’t explain enough. The guys that did my 2000 Mercury Grand Marquie are the same custom shop that did my 93 Grand Marquie. They have been doing every type of car out there and have a great reputation as far as their work and critical details involving all their installations. All their systems are welded and in most cases better than factory. They do not install junk but only top of the line products. The comment about sometimes you sacrifice a bit of performance when you change some of the original factory equipment. They did all of this work in the summer and even though the 2000 Mercury I have now feels much quicker than the 93 Mercury, I only seemed to notice the feel of the car being different since I went over to the recommended Magnaflows that were installed. Is it possible that because the 2000 Mercury is more solid and quiet that when I switched exhaust I became more aware of the engine sound which I never really heard with the factory single exhaust. I know when they installed the duals they cut off ( which seems to be standard ) the damper weight that was just after the Y. When the duals were installed and perfectly matched except for an additional new standard muffler and the original factory I was getting a vibration at idol in Drive with the brake on. The opinion of a few custom shops was that I shouldn’t need these weights and even they cut them off when they insall duals. My performance shop thought it could be because of the mismatch between mufflers. I bought new weights and had them installed on both sides of the duals and this solved the problem. I don’t know if the match mufflers would have made a difference without the weights as I never bothered after the problem was gone,
My 93 Mercury also had the original 4 converters removed and we put on the mustang cats (only 2 ) and then took everything to the xpipe and then to the magnaflows (oval ). My 2000 Mercury sounds really good right now but I don’t know if some back pressure is needed as they say most of these cars have tuned exhaust when they are designed and is there any possibility that maybe I have disturbed this equation since installing the magnaflows? Jason I am just trying to figure out if it is me or has the car lost some additional punch that I noticed when I went from the duals ( standard mufflers to magnaflow tube type). We also added an H crossover connection between left and right but it made very little difference. If you get to know how a car runs and feels as we all do after time I’m sure if something changes you will notice it. I felt right after I drove the car away from the performance shop that it just didn’t seem to have the same snap. ( Maybe I’m just losing it but most of the time I have always been correct when something changes in the characteristic of the car that I am use to driving ). This definetly changed something but no one ( other shops ) have any idea? I would like to know if any of your members have ever come across something like this when they modified their cars from muffler changes be performance or otherwise! Thanks Darrell Smith Toronto.
Darrell – I hear what you’re saying, but in all honesty I’d find another shop. Here’s what I know:
1. There’s very little reason that removing the factory exhaust and replacing it with after-market components should reduce power. At worst, it should make no difference…and on a Crown Vic/Grand Marquis, you should be able to add power with an exhaust relatively easily. This “sometimes you lose power” comment is alarming.
2. Connection quality (i.e. how great they weld things) has very little to do with tuning ability or performance.
3. Adding an H-Pipe to a V8 makes absolutely no sense…if you’re trying to get rid of a vibration you could try it, but I would focus elsewhere first.
4. If your car felt fast when you first had it, and is now slower, it could be that the mufflers have become clogged. Did they check that?
5. Swapping out the stock catalytics for Mustang catalytics doesn’t make a lot of sense to me either. Modern cats aren’t very restrictive at all…unless you’re strapping a supercharger onto the engine, you don’t need to touch the cats.
6. There’s a whole lot of rigging and trying going on…good shops don’t need multiple tries to get it right.
Again, for almost all the reasons listed above, I’d say your shop isn’t very experienced. I’d contact your local racing clubs and ask them for a recommendation.
Hi Jason.
I guess there is still some confusion with my explanation so I will try to simplify what has been done.
Just the 2000 Grand Marquie
1. Car was bought with factory single exhaust and was very responsive.
2. Added K&N cold air intake complete kit in summer (good response in performance and much improved.
3. Added Helix power tower to throttle body. (better mid range acceleration)
4. Had factory Y pipe cut and kept original factory right side exhaust complete and factory weight damper was removed.
5. Had left side exhaust installed without H pipe just straight through.
6. Now car had dual exhaust with no H pipe and the only thing different was original factory muffler on right and a new satandard muffler on left side. Car was responsive and only thing that changed was that at idle and in gear there was a small vibration at a certain frequency when stopped,
7. We installed the H pipe at my request thinking that it might help the small vibration but didn’t.
8. I decided to buy the left and right damper weights from Ford dealership andd had them welded on in the same place as the original factory exhaust.
9. Problem solved vibration gone!
10. Car running very well and performing excellent and very responsive accelleration.
11. Missed my nice Magnaflow sound so in about a month later I decided to install the new magnaflow tube type reccommended by Magnaflow for my car.
12. I got to hear them before they were welded in place and was very impressed, Low nice rumble but much louder if you hit the pedal.
13. Drove away after every thing completed and felt the car sounded great but it seem to lack the same punch. I thought maybe it is just me adjusting to the new system but again I can’t explain why the car just doesn’t feel the same.
You are correct in the fact that you can’t measure power and speed from your butt and I’m thinking maybe it’s the difference in the acceleration noise between original quiet mufflers to the magnaflows.
The comment about sacrificing power for sound was taken wrong. What I mentioned to one of the installers was that I felt my gas mileage was a little worse than before with the factory installed single system. His comment was more that like any HP improvement
sometimes you have to sarifice a little more fuel to get more response which makes sense.
I have a lot of respect for these guys and they do have an excellent reputation and I probably drive them a little crazy when I ask them why the car just feels slightly different since all the work. They even test drove it and inspected all the work and said it was running very well for a Mercury Grand Marquie and couldn’t see any problem.
I still love the sound so I don’t want to go back to the quiet mufflers. I also know Grand Marquies love cold weather and perform very well the colder it gets and yes fuel burns better in summer for sure.
Thank you Jason for your feedback and like I say it may just be me.
regards Darrell
p.s. A very Merry Christmas to you and your family!
Darrell – I understand more now. It sounds like you had a semi-customized factory exhaust that you replaced with two high-flow mufflers.
If the Magnaflow mufflers you added were designed for a single-exit exhaust, they’re likely too big for your dual system. THAT could cause the performance to fall off a bit.
I’m having to have a custom exhaust done to my car which will be making around 175hp around 7500rpm. I want a quiet exhaust but not too restrictive. I was thinking about going with an oem type muffler but I figure it will bottleneck the whole exhaust.
Would it be best to go with a 2.5″ piping out to a restricitive 2 1/4″ muffler or go with a 2 1/4″ piping out to a 2.5″ muffer? In other words where’s the best place to put my exhaust restrictions nearer to the header or near the rear at the muffler? Oh all piping will be crushed bent so the actual restriction size will be smaller.
Patrick – If we’re talking about a quarter-inch here or there, it’s not going to matter. I would go with a mandrel-bent system, however, as that does matter. I’ve seen data to suggest mandrel bending is just as important as finding the right size.
My general guidance: the factory exhaust system tubing is very close to the right size. When in doubt, stick with the same size.
very interesting. but how about pipes below 1.5 inches. im building a header for my 1.3l ford aspire motor. and i want it to be maximized for cruise rpm. i know your pipes hp rating were for max hp numbers, and cruise hp numbers are maybe 1/3 of the rated wot for that specific rpm. any idea on what size i should run for my primary pipes?
bryanh – I’d suggest going with the same size as the factory exhaust system – that’s size is usually optimal for less than maximum power.
i cannot let myself believe that factory exhaust is maximized for cruise on any car. we as americans want to go fast, so our cars are designed with flowier than effienct exhaust systems. i may just have to do this test myself with some sort of pipe sizes, like 1.2, 1.1. 1. .9 and .8 inches. itd be a blast building 5 different but similiar headers like that. do you think those size primaries could get me the results that i need. reading about that tri y design got my hopes up a bit on wanting to try that on my car for fuel economy. in that case, can lower torque are lower rpms get me better fuel economy?
There are a lot of factors that go into header design besides tubing diameter.
My suggestion is to find a successful header design on a similar yet larger engine, then scale it down. If you try a bunch of different diameters without considering other factors (tube length from head to collector is really important), you’ll be spinning your wheels.
bryanh actually jason is correct. the stock pipe is optimal for less than max hp. the factory stuff is meant to maximize power for normal driving conditions. although if you still build those headers would you be so kind to post those results so we can see what works and what doesnt? losing hp and torque doesnt mean you will lose gas mileage. alot of the reason people lose mpg with better hp is because the lead foot that comes with the power.
Having got caught up with all the “bigger is better” hype I went with a 3″ dual (with x pipe) exhaust system on my full sized chevy Caprice. I built a 355 SBC that made 400 flywheel HP on the dyno and have a set of tri-y headers with a 2.5″ collector. The system has already been purchased and installed on my car. After reading lots I have a terrible feeling that I made the wrong choice on going with 3″. For one, the car is too loud for my tastes. I actually have a pair of resonators on order that I am going to install in hopes bring the volume down some. Hindsight I would have gone with a 2 1/2″ system, but I dont want to spend another $800 on exhaust.
Can I except to lose a lot of low end power? Any advice?
Taylor – The headers are probably going to impact you more than anything, and they don’t sound like a bad choice. However, the only way to know what impact the dual 3″ pipes have is to test the vehicle with 3″ pipes and then 2.5″ pipes and see the difference. My guess? You’re losing a little bit of low-end torque. How much is hard to say.
Jason, between the headers and crossover the pipes are removable. I believe the drivers side is ~2′ and the passenger is 1.5′. Would it be be beneficial to knock these down to 2.5″ before the 3″ crossover? I picked the headers as they have good low end and midrange power, just not to sure why I went with the 3″ now that I think about it. The guy that manufactures the headers and exhaust system usually recommends people switch to 3″ around the 400FWHP mark. Live and learn I guess…
Forgot to mention I will need to be doing emissions testing where I live next year so I will be adding cats into the “hook up” pipes I mentioned above.
taylor – First of all, cats don’t effect performance nearly as much as people think they do, especially if you purchase racing cats.
As for dropping to 2.5″ before going to the crossover, I’d suggest getting rid of the crossover unless you’re trying to mellow out the exhaust note. Its not necessary on V8′s. That way you can run the right sized pipe all the way.
Still, if this system is all done, I don’t know that I’d bother. The slight loss of low-end torque isn’t going to make much of a difference on the street.
Thank you for your input Jason. And here I thought the crossover was the “way to go”… I think I will just leave it and the next time I build another car will do my research before hand rather than after!
Hello
Love the topic and conversations i have read!!!!!
My question is on a 99′ regal gs 3.8 s/c. Currently stock, but finally have the money for mods. Car is rated at 240hp 280tq, planning on getting custom pcm, ported throttle body with spacer and a whole bunch of little stuff to help reduce the common knock retard issue with this engine. Planning on doing full exhaust, front p log to replace manifold, rear ported manifold, crossover tube, they offer a 2.5″ and 3″ down pipe with and with out cat, prob gonna go with out out cat and an o2 simulator. The only full exhaust replacement i can find is 3″ stainless with muffler and resonator optional. Will probably go with the resonator to kill that annoying rasp 6 cyl are known for. What do you think of the 3″ down pipe with 3″ mandrel bent exhaust, i will be running a smaller pulley not sure what size, guess it depends on where i go with the exhaust. I can buy all the bends and do a 2.5″ exhaust and get the 2.5″ downpipe…….after the mods prob lookin 330hp but with forced induction not really to sure how the math equation helps…..guess i will be around 12 psi, stock is at 8psi and im not sure what size factory exhaust is either. I do know the factory down pipe is extremely restrictive and just that swap alone is good power gains. What do you think……
Frank – There are lots of questions there, none of which have easy answers. Going with an after-market downpipe is smart, but going with a 3″ vs 2.5″? No idea. You can’t really trust the downpipe manufacturer’s dyno testing, but that’s probably what you’ll have to do to get an answer to your question.
As for a single 3″ tube system, I say go for it. That seems about right for a forced induction motor pushing 300hp.
Thanks for quick response, lol….i did get a little carried away i guess. Goin 3″ all the way!!!! Sad part is i just wish it wasnt gonna cost a 1,000.00 for a single pipe set up:(
i’d like to know the minimum pipe wall thickness which should be used so as to avoid drumming/vibration. also would this principle apply to motorcycle exhaust design?
Mihir – I don’t know if tubing thickness has much impact on drone…I’m sure there’s an effect, but I’m not sure that it’s the most economical way to solve these problems on a car (thicker tubing is both more costly and heavier, so using it for an entire exhaust system is economically out of the question).
However, many vehicle exhaust systems are 16 or 18 gauge steel, and I’d guess that this is a good thickness.
Hi,
I have a 393 cleveland with 600hp 7200rpm street strip what do you think??
Hey Jason,
I have enjoyed visiting your site and reading your thoughts. I have a Q for you. I own a ’92 Ford Ranger w/ the 2.3 L, 4 ( and I LOVE IT )! It came w/ a single 2.25 pipe on it. When that wore out, I replaced it w/ a split/dual cat ( 2 pipes @ 2.25″ ) back system and a FLOW MASTER 40 muffler. I desired the look of the “functional” pipes as well as the deeper, and louder tone.
It sounds GREAT when idling and cruising but, when I “get on it” it trumpets because it’s a stock, non loping 4! I am getting ready to lift the body to make room for larger tires. This means, that the exhaust system will have to be adjusted so it looks good again.
This is the time to make mods! I want to use a HOOKER AERO FLOW muffler and 2, 1.25″ pipes. The engine rarely turns above 3000 rpms ( it has a 5 speed ) and am seeking more low-mid power gains.
Later this year, I will bore the throttle body, spacer, port and polish the intake manifold and install higher PSI fuel injectors. This will increase the flow into the motor. Do you think a larger 1.25″ pipe, might be a better choice?
Thank you for your time, just reading this Long Winded letter! I look forward to your input.
Sincerely,
Alan – If you’re most concerned with low-end power, than 1.25″ pipes are likely fine no matter what you do. I’d rather have a smallish system on a rock crawler, b/c smaller pipe diameters create more of a scavenging effect at lower RPMs…they just rob HP at higher RPMS. So, I’d leave it alone if I were you.
PS: In the letter I sent you a few hours ago, I think I may have said, going to a smaller 2.25″ 2.50″ exhaust pipe size. I meant; 2 @ 1.25″ or 1.50″ w/ future performance upgrades. Sorry for the confusion.
Does the chart take in account for standard crush bending or mandrel bend pipe?
Michael – Excellent question. Mandrel bent, if I recall…I’d say crush bends are good for a 1/4 inch “hit”.
I have a colt rodeo 2.4 i (4g64) engine . viper branch 4into1 , and 50 mm pipe with free flow. it has lost power since putting the 50mm , and seemed to be a bit heavy on fuel. it had a 48mm pipe before . would this 2mm make such a difference? what size U recon / the 48mm sounded great and had good low down torque
Brian – Can’t imagine that 2mm would make such a big difference, but if that pipe included a new header, than all bets are off. Changing the header/exhaust manifold can make a big difference, especially if the header/exhaust manifold is tuned for top-end performance.
I don’t have a recommendation for a Colt Rodeo – no idea.
THANKS FOR THE GREAT INFO!!!
Iam thinking of buying an exhaust
for a 280hp inline 6 bmw, its an after market from a company in itally “Ta Technix Sportauspuff “.
The exhaust starts out at dual 2in then to a resonater continues out with dual 2in to another resonater but it comes out to a single 3in to muffler with dual 3in tips.
Would this be an upgrade? or our they just trying to cash in?
Thanks Jason
jose – I’m not sure if the system you’re looking at is worthwhile or not, but there’s nothing about the description that gives me pause.
However, I’d hesitate to buy any system that didn’t come with some sort of expected performance improvement and a dyno graph to support that claim. Meaning, they should say “our system adds up to 10hp – here’s a dyno sheet to prove it.”
Thanks Jason. They claim 30bhp
but no dyno sheet 
. Just wanted your thoughts, and thankyou.
I had a muffler shop splice in a pair of 2.25in magnaflow (11225) on my 2012 mustang 5.0. The pipe is 3in duals but he said I had less than 2.5ID. I know I have a pair of 2.25ID resonators as well. Did this guy just give me one heck of a bottleneck or should the mufflers be ok with my 412hp?
Hagen – I think it’s going to be just fine on the street, but it probably doesn’t help your quarter mile time to go this route. Might even have taken a little bit off (a tenth or two I’d guess).
That’s good to hear. I’ve noticed an increase of lower end tq but haven’t had a chance to make runs or test the top rpm range yet. I do enjoy the added lower end though! Thank you for the info and piece of mind, it is greatly appreciated!
You probably dont remember, but you replied to my comment awhile back. I have a regal gs with the 3800 series s/c, currently stock. We talked about a full 3″ mandrel bent system from manifold through tailpipe and decided sence there was boost involved it was good to go. Do to finances i had to cancel full 3″. From the resonator back it is 2.5″. The down pipe is the most restrictive part of exhaust along with a u bend that was designed for 2nd o2 sensor just past the cat. I ordered a true 2.5″ downpipe without cat and an o2 simulator. I was thinking instead of the 3″ downpipe being knecked down to 2.5″ it would be just as benificial just having 2.5″ all the way. With the pulley ill b putting out 11lbs of boost. This should b an ok setup? I really dont have any plans on very much more, except for the 4″ cai and custom pcm currently on order and mayb a throttle body soon.
Frank – Sounds good to me, but I’d recommend posting this question on a forum for Regal GS (or 3800 S/C) vehicle owners to see if anyone has any specific insights. However, as a general rule, 2.5″ vs. 3″ isn’t likely to make a big difference in the way your vehicle performs on the street. If anything, it will perform better at the lower RPMs with this setup.
It is an interesting topic, But i have a feeling that it does not take into consideration for backpressure that are needed in non turbo petrol cars(too low backpressure = damanged valves and loss of HP). I am currently “making” my own custom, exhaust for my 206 2.0 GTI 159bhp@6700rpm(with the old worn out system) and are wondering if a 2″ is not better than the 2.25″ after the race cat, for the sake of backpressure and decreased volume of the colder gas? Or am i completely on a sidetrack here?
Is there any golden rule on how to calculate the proper backpressure?
Kim – It’s not really about back pressure, it’s about exhaust gas velocity. The heads and ECM are tuned for a specific ideal velocity, and your goal is to make sure the exhaust system hits that ideal velocity figure at the point you want it to.
Quite frankly, the headers/exhaust manifold is far more important here than the exhaust tubing. Does your header manufacturer have a recommendation? If not, you might try to match the size of the stock system, test it, then increase diameter and test again. Testing is the only way to know for sure, as I’m not aware of any good (yet simple) methods for calculating the ideal setup…only if you had the right modeling software like the exhaust system manufacturers do, I bet you could get very close.
Ty for the reply,
You are right, there probably is not any easy way to find the proper backpressure, it is a topic i had no luck finding good info about.
The header i am using is slightly a modified 4-1 from supersprint(from old system), to fit the cat and middle muffler piece. I have a feeling that it is pretty optimal for the car.
I am still unsure if 2″ or 2.25″ is better, but for now i welded on a original middle muffler and it has a 2″ exit pipe.
If i can get info on if a bigger diameter can give alittle more bang for the buck, ill probably swap it to 2.25″
Jason, I see where you said “A good section of straight pipe will flow about 115 CFM per square inch of area” but how do bends in the exhaust pipe such as where it goes over the rear axle affect flow? According to your chart I have my exhaust pipe sized pretty close (460 hp into a dual 2-1/2″ system with an X pipe). The pipes are also mandrel bent. Do mandrel bends present any appreciable back pressure to the system that could skew the results shown on your chart? If so do you think going with a larger pipe (such as a 2.75″) would make up for it, or might that cause turbulence? What are your thoughts on a H or X pipe? Do you think they lower system back pressure any due to each side now having 2 exits to flow through instead of just one? Thanks for your time, Tracy
Tracy – Mandrel bends shouldn’t effect flow too much, as fluids “roll” along the surface of the pipe they’re in. As long as that surface remains smooth, bends don’t have a significant effect…so I’d stick with the suggested sizes.
Crush bent pipe, however, can flow much worse than mandrel bent pipe – as much as 20% according to some things I’ve read. While you could go with bigger pipes to compensate, it’s better to go with mandrel bending.
As for cross pipes (x-pipes, h-pipes, etc.) they’re useful on V6′s for increasing the lower frequency sounds, and some say they work quite well on smaller V8′s from a performance standpoint. However, they have almost no effect on exhaust flow, so my guess is that most cars don’t need them.
I have a 2007 Chevy silverado 2500 HD newer body style with a 364 6.0L it’s a gas truck. I was wondering what aftermarket exhaust system I needed? I have a cold air intake system on it dose it matter?
David – Any of the popular systems will work, only you might think about going with a single side exit rather than a dual, as they tend to produce a little more usable torque (sometimes, depends on the system).
Whatever you do, make sure you buy a system that is tuned to your truck and offers dyno testing as proof.
So what sizing of an exhaust do I need for the truck how it is right now?
I am now changing my entire exhaust system on my truck.
I have a Toyota tundra 4.7 I force 245 crank HP stock
I am putting headers, Cold air intake and electric fan. which gives me around 55HP to the crank. which brings me to est 300BHP
Now this is a V8 so the down pipe is connected through a Y or X.
According to your calculator i should be using a 2″ pipe
now is this the down pipe or the entire system?
because i was thinking 2″ down pipe and into the y then 2.5″-3″ cat back
or into a the X and back out 2″
Adrian – Dual 2″ or 2.25″ pipes all the way back will be plenty. Additionally, if you go with 2.5″ or 3″ duals after the cats, you may find that you lose a bit of power, as the exhaust gases will “backfill” that extra pipe diameter.
Or not – just depends.
I’m also thinking that you should dyno-test before you mount a system, as these accessories don’t always bring the promised power on an older engine.
Good luck.
Ok so what sizing do I need for and exhaust?
Read the post man…