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Does anyone know how the overrun pops and crackles on deceleration are produced on the NA 991.1 cars? Is it strictly from the exhaust system?
It got me wondering if the GT3s do not do this because of their different exhaust set up.
Then this got me wondering what happens to the overrun sounds if one modifies their NA 991.1 to a center exit exhaust. I know there is at least one gts on here that's done that already.
There is certainly a mechanical element to this as well as an electrical one. Porsche for example will sometimes add fuel on up-shifts and overrun to "flood" the exhaust with un-burnt fuel creating a lot of cracks ad burbles, that is a simple function that Porsche has written into the ECU depending on driving mode etc.
Mechanically, you can increase this by fitting high flow cats and or catbypass pipes. If you think about it, the catalytic converter is there specifically to burn any un-burned fuel before it gets into the exhaust in an effort to reduce emissions. By removing them, you are increasing the chances of that un-burned fuel getting into the hot exhaust and igniting creating the sounds you describe. This will normally net you a really nice pop/bang sometimes on downshifts/upshifts. The borderline excessive crackles you hear nowadays are mostly caused by specific ECU coding to do just that.
I do not expect that changing the 991.1 to a center exit exhaust will have any effect on the pops/burbles since most of that comes from the way Porsche coded the ECU on that car anyways.
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You'd think the GT3 doesn't do it because it's suboptimal process and therefore lowers (if ever so slightly) performance. It's just for "****s & giggles", not something that is in any way useful and replicates suboptimal combustion processes from times when they couldn't do any better.
It's all programming. Note that in normal, they are almost non-existent. In Sport there is more and in Sport plus it's like there is a cannon brigade behind you. The ECU is just choosing to add extra fuel to create these artificial backfires. Personally, and I know I'm in the minority, I think it sounds stupid. I wish there was a way to program it out.
The GT3 doesn't have this because it's not programmed in.
You'd think the GT3 doesn't do it because it's suboptimal process and therefore lowers (if ever so slightly) performance. It's just for "****s & giggles", not something that is in any way useful and replicates suboptimal combustion processes from times when they couldn't do any better.
There is certainly a mechanical element to this as well as an electrical one. Porsche for example will sometimes add fuel on up-shifts and overrun to "flood" the exhaust with un-burnt fuel creating a lot of cracks ad burbles, that is a simple function that Porsche has written into the ECU depending on driving mode etc.
Mechanically, you can increase this by fitting high flow cats and or catbypass pipes. If you think about it, the catalytic converter is there specifically to burn any un-burned fuel before it gets into the exhaust in an effort to reduce emissions. By removing them, you are increasing the chances of that un-burned fuel getting into the hot exhaust and igniting creating the sounds you describe. This will normally net you a really nice pop/bang sometimes on downshifts/upshifts. The borderline excessive crackles you hear nowadays are mostly caused by specific ECU coding to do just that.
I do not expect that changing the 991.1 to a center exit exhaust will have any effect on the pops/burbles since most of that comes from the way Porsche coded the ECU on that car anyways.
I agree, I wish I could get rid of them too. I put a Kline Exhaust on hoping it might minimize but like described above they coded in so now I have POPS and BURBLES in a deeper voice..
It's all programming. Note that in normal, they are almost non-existent. In Sport there is more and in Sport plus it's like there is a cannon brigade behind you. .
Maybe in manual cars, but in my PDK, Sport + is less obnoxious (when driving in manual shift mode).
06-29-2017, 11:47 AM
991.1 overrun (pops & crackles) vs none in gt3
