jay-leon

I have a 2016 PGTS. Recently on the track when I braked for a curve, I heard 3 or 4 loud backfires. This happened many times after it first started. Is this normal? The dealer couldn't find any thing wrong.
Any suggestions or advice would be gratefully appreciated.

balazskontes

those popping sounds are what make that car great vs. Turbo cars!
Turn off the sport exhaust and he car will become quiet and then you'll miss it and turn it back on! :-)

mdosu

You're doing it right. lol. That's Porsche Vario-Cam doing it's job! I'm actually surprised a stock GTS with stock cats will pop and crackle.

I heard and felt it on a stock 991.1 TT which likely have very aggressive cam tuning. It feels amazing when you lift off and it cracks along with hearing the blow-off valve divert the air, plus a unsettling fluttering from the excess spooled air in the intake system (but that's for another thread!).

Backfire you're hearing is the excess combustion process in your exhaust system due to running rich and/or aggressively tuned overlapping cams (for performance reasons). Adjustments made by the car's engine management unit to use more fuel during high throttle applications and adjust cam timing causes incomplete combustion. Combustion isn’t complete before the exhaust part of the engine cycle. When the exhaust valve opens on that cylinder, the extra air allows the unburned fuel to explosively burn and the popping noise of a backfire is heard through the entire exhaust system. If you run catless, you'll at this point see flames also shoot out.

It's amazing, have you attended a Weathertech/Tudor IMSA or a PWC race event before? The backfire and crackle on those racecars = orgasm.

balazskontes

The cam in the GTS, amongst other parts is from the Turbo-version of the same-sized engine. Hence the beauty of the sound that aren't muffled by the turbos!

jay-leon

thank you all for clearing this up. I will NOT turn off the sport exhaust!!!

mdosu

Again, Sport Button probably adjusts throttle sensitivity, which might adjust cam timing, or at least create situations where overlapping exhaust cams open earlier.

It's not a exhaust piping thing, which adjust valves in the muffler area of the exhaust, that's what gets louder exhaust noises.

jay-leon

Doesn't the same thing happen when you start the PGTS?

mdosu

I don't know, I don't have a PGTS. But likely shouldn't. On idle or consistently low engine speeds, intake/exhaust cams shouldn't overlap much if at all, or you'll get rough idle

mdosu

Don't take this as an insult, but here's a really good simple visual and explanation how cams work and also how overlapping cams work.

It's the overlap (earlier, quicker opening) of exhaust cams that's creating the backfire you're hearing. But again this what Vario-Cam is designed to do. Because Racecar.

http://auto.howstuffworks.com/camshaft.htm

Now you can tell your wife and friends all about it as you will find it all very fascinating.

GVA-SFO

Yes, the "sport-plus" button of our cars is a kind of "manual" version of the VW software : when you are in Normal, ..you pass the emission control, but when you are on Sport-Plus, the emissions are "different" and ..the MPG too !

ROTFL, big time !

AndrewP

Good explanations here. I love the exhaust overrun on downshifts, whether in Sport Plus, Sport or Normal. When I had my 991.1 TTS on the track the exhaust overrun was noticeable (Sport Plus), but does not compare to the PGTS or the 991 GT3. I'll stick to NA Porsche engines as long as possible. FWIW, it is sounding from press reports of exchanges with Porsche engine people that the next PGTS will unfortunately be turbo charged. No doubt the sound engineers tune the exhaust note as much as possible and still remain compliant, but NA sound and torque curve are what I prefer. Not as fast as turbo models, but on roads quite fast enough.

LexVan

I think it also has something to do with the DME overfueling the car on throttle lift to aid in the snap crackle and pops.

Lots of this with the 991:

https://rennlist.com/forums/991/9500...d-farting.html

ELMEL

My PTTS makes very loud popping and backfire sounds as well. I drive it in Sport Plus almost all the time and love it.

balazskontes

that's great! When i test drove the Turbos, for me, they weren't as pronounced. Glad that yours make those beautiful sounds.