Not enough exhaust Back Pressure? Quiet car?

[mtimney]

I just added a P&L header to my BRZ. The car's quite a bit louder than it was before when it just had a 2.5" ISIS cat-back on the car (2nd cat deleted). Actually...it's very loud now. But, the header certainly got rid of the torque valley.

Also, the car's not running as smoothly as it did...even with changing to an appropriate Unichip map to adapt the ECU to this exhaust. It was running fine for a week, but now...not so much even with a few more Unichip maps tested.

I had the car at a muffler shop today to see about adding a resonator to quiet it down just a bit and get rid of a slight rasp and some drone that popped up with the new header. The shop manager said a resonator wouldn't do much and that I should consider adding a 2nd cat back (some super slim new type of high performance cat) to quiet the car, increase back pressure and make the engine run a little better. He thought there was too much 'flow.'

What do you all think of this?

[FR-S Matt]

I think you need a real tune. I'm not driving at all on my header until I get it tuned at the same time.

[WolfsFang]

A resonator will remove the rasp and some drone. How is a tune going to help with rasp and drone? Also there is no proof back pressure does anything.

[grostoine]

Originally Posted by FR-S Matt

I think you need a real tune. I'm not driving at all on my header until I get it tuned at the same time.

I've run it to see if there was any leak, after that I asked for an updated tuned and I'm waiting for it.

[FR-S Matt]

Originally Posted by WolfsFang

A resonator will remove the rasp and some drone. How is a tune going to help with rasp and drone? Also there is no proof back pressure does anything.

This won't touch the rasp and drone. This has more to do with the car not running smoothly. If you want rasp and drone gone, you need cats and a resonator.

Take Perrin for example, the resonated version is pretty quiet. The non resonated version is loud and gets raspy with a header. Have an exhaust shop fabricate a midpipe with a resonator that's smaller than the Perrin resonator but not tiny and keep the cat in the front pipe. That should do the trick.

[IceFyre13th]

So before catalytic convertors were mandatory how do you think we got rid of drone and rasp............hint: similar to a muffler, but called a resonator.

Then we jetted our carburetors, and changed the weights in our distributor and set the dwell and timing with a timing light................thats tuning!!!!

[WolfsFang]

Originally Posted by FR-S Matt

This won't touch the rasp and drone. This has more to do with the car not running smoothly. If you want rasp and drone gone, you need cats and a resonator.

Take Perrin for example, the resonated version is pretty quiet. The non resonated version is loud and gets raspy with a header. Have an exhaust shop fabricate a midpipe with a resonator that's smaller than the Perrin resonator but not tiny and keep the cat in the front pipe. That should do the trick.

Umm the reason the perrin non res has rasp is because there is no resonator in it. I have a borla cat delete and gutted my stock header cat. I only have the stock resonator and I have zero rasp.

[FR-S Matt]

Originally Posted by WolfsFang

Umm the reason the perrin non res has rasp is because there is no resonator in it. I have a borla cat delete and gutted my stock header cat. I only have the stock resonator and I have zero rasp.

The stock resonator is really good and quiets it down big time.

[wparsons]

Adding a high flow cat or resonator will definitely help kill some (or all) of the raspiness, but won't help it run any better.

IMO you need a proper tune for the header, that'll make it run better.

[mtimney]

Thanks, guys. I'll talk with Unichip Jack and see if he has any suggestions on another map that might provide a better overall tune.

I think I've decided to add a small resonator to kill a little of the rasp/drone.

I appreciate the help!

[3000HP]

Originally Posted by IceFyre13th

So before catalytic convertors were mandatory how do you think we got rid of drone and rasp............hint: similar to a muffler, but called a resonator.

Then we jetted our carburetors, and changed the weights in our distributor and set the dwell and timing with a timing light................thats tuning!!!!

I still do it this way :happy0180:

As they stated above, if you add a cat in there you will get rid of the rasp. and it will quite the car a bit.

[Pandle]

I have the p&l header and after I had it installed the car bogged like crazy in low rpm. I sent a log to visconti and as soon as he sent me my new tune everything was fixed.