Next week I'm getting a full header back exhaust done. Car is a 2004 completely stock. Here in South Africa our cars remained 2L, so I guess it's an "AP2 2L".

My questions are:

1) I'm going for a dual exit and I'm offered a 70mm or 76mm system (that's 2.7" or 3.0"). I'm not informed enough to make a decision. I'd like to hear opinions/pros/cons from S owners other than just the opinion of the shop making and installing it for me. Would one be louder; affect power delivery etc?

2) The cat is coming out (test pipe is the term?) and I've read that this can cause a CEL? The installer says he'll address that, but I'm interested to know what causes it and what the solution is?

3) The vehicle is stock, the exhaust will be the only mod. Is a tune recommended after having the system fitted, and is there any risk by driving the car without a tune if one is needed?

Thanks for the input.

 

1) the choice between 70mm and 3" is up to you, without a tune there will be minimal difference in power between stock/70mm/3" sizing. 3" will likely be the loudest option

2) He will likely put an extende oxygen sensor bung that will place the oxygen sensor further away from the exhaust gasses flowing through the pipe, thus sensing "cleaner" air. Many aftermarket exhausts and test pipes like the Berk one do this

3. You don't need a "tune" unless you want more power.

 

1) The differences between 2.75" and 3" for a N/A setup will be minimal. The 3" may be slightly louder.

2) Some exhaust "headerback" systems that use a test pipe instead of a CAT come with a built-in bung for the secondary O2 sensor. This secondary sensor is what causes the CEL when using a test pipe; so long as there's a bung in the test pipe for this to go into you should be fine. My Berk exhaust for example came with a bung already welded in.

3) I would say a tune is only necessary if you have an 06-09 S2000. A "headerback" system that uses a test pipe will always lean out a cars air/fuel ratio slightly, and the 06-09 S2000s already come relatively lean from the factory. If you have a 99-05 I wouldn't worry about it (honestly even if you have an 06+ I may be over-estimating the problem, someone else may need to confirm this).