Scion iQ Performance Exhaust Preview

Concept cars are almost always fun, even when the concept is based on a tiny little commuter car like the soon-to-debut Scion iQ. The truth is, a car doesn’t have to be fast to be fun to drive – and a 100hp little street rod is definitely not going to be fast – but by all accounts a tuned-up iQ can be very fun.

Check out this tuned-up version of the iQ that made an appearance at the recent Tokyo Auto Salon:

Performance is more than just straight acceleration

The engine in this concept is only 1.3 liters, and in the factory-tuned configuration it manages a meager 90 hp. However, add a Gazoo Racing supercharger to this car and you’re working with 126 hp.

Sure sure – 126hp isn’t a lot either – but think about that increase as a percentage. The supercharged iQ has 30%+ more horsepower, yet it still weighs about the same. In the words of an Edmunds.com InsideLine reviewer, a less powerful version of the car above offered “Plenty of grip, not much roll and an alert front end” that ” make this iQ an infinitely chuckable little warrior.”

Not a bad review.

Of course, we like to talk about exhaust systems here, so let’s just mention a couple of things about the exhaust system images below:

What's wrong with this picture? (HINT: There are one too many exhaust pipes showing)

While it’s definitely neat to look at, there’s simply no reason to have a dual exhaust system on a tiny little 4cylinder like this one. At best, this is just a waste of money meant to make the car look better. At worst, it hurts real-world performance.

How can a dual exhaust hurt performance, you ask? Because exhaust system must provide a small amount of back pressure to facilitate cylinder scavenging, which means that exhaust gases are basically “sucked out” by the exhaust system. If you remove all back pressure from the exhaust, there’s not scavenging effect. If there’s no scavenging, a small amount of exhaust gas remains in the cylinder during the intake stroke, which reduces engine efficiency (and therefore performance).

Another example of an unnecessary dual exhaust

In other words, back pressure is a good thing (at least in small amounts). If you want to maintain sufficient exhaust system back pressure, you’ll want to match the size of your exhaust system to the power output of your engine. We’ve got a nice exhaust system pipe size chart that shows you how to calculate exhaust system size using engine horsepower. The appropriate size for a 126 hp engine? 2″.

This over-sized exhaust tip might just be for show.

In defense of these concept builders, it could be that the dual exhaust systems we’re seeing with giant tips like the one above are actually just “show” parts. More than one builder has been known to add a non-functioning piece of equipment just to look good, so it’s possible the stock exhaust pipe hasn’t changed. It could even be that one of the exhaust outlets we see above isn’t actually hooked to the engine.

Wouldn’t that be funny?