If you put headers on and a catback exhaust won't the stock cat be a choke point and limit the potential of your exhaust system? Would it be even worth it to get headers if you keep the stock cat? Would the stock cat put some backpressure on the system letting you retain some low RPM torque? Any intelligent replys would be greatly appreciated

Actually the CAT is not a choke point but the piping before it is. Modern cats cause little restriction.

Yes, a header is benificial, even with the cat in place. The Weapon R header is the best design I have seen for these cars but it is not released yet. It has the longest primary tubes and best collector design. The DC header is considerably better constructed than the stock header but the pipes are still way too short for real performance-I heard they made 5.4 hp more than the stock piece.... pretty sad really.

Contrary to what many have said here, back pressure does NOT increase low rpm torque and lack of back pressure does NOT decrease low rpm torque. Old wives tales from mis information. Exhaust is all about velocity with out restriction. If the pipe size it too large you loose the velocity thus loss of torque. Too small of pipe and you have lots of velocity but also restiction which looses power. It's like "Goldie Locks".... Too big, Too small, Just right!!! Engines that respond postitively to more back pressure have too large of piping. The increased back pressure is a band aid but they would make even more power with the correct pipe size.

2.25" from header to bumper with a matching cat would be about the max for these engines unless it's boosted.

ken

believe it or not, or catalytic converters are not as choking as you think. Get a high flow cat by any company and it is about the same size as ours! :shock: It took me two months to find a smaller high flow cat, that still passes smog. And I'm in cali where the smog laws are KING! :D

I have re-done about 7 scions with a manifold back system, including my own and found out what the pipe diameter is on our stock systems. The down pipe from the hedder to the cat will fool you. Looking at it may show about a 2 1/4inch pipe, but if you were to remove it; you would find a happy little 2in pipe inside of the down pipe!

And as far as what kdanie said, he is right. Bigger piping must be done correctly or you will lose both high and low end power. Not to big, not to small. 2 1/4in pipe is perfect for our little boxs.
Sorry so long,
Stylis :D