991.2 manual GT3 - question about change in engine sound
07-15-2018, 06:48 AM
#46
If there is a performance difference between open and closed exhaust flaps, it has to be to the advantage of open flaps. A lower static back pressure can never be a bad thing for volumetric efficiency and scavenging, rather the opposite. And add to that, I think the flaps are probably anyway too far downstream to have an meaningful effect on the dynamics of the gas exchange.
Open valves should be better in high rpms, hence it opens also automatically.
07-15-2018, 06:49 AM
#47
I collected my GT3 touring on Friday.
I havent yet driven the car extensively but after first 20 kms, i think the GT4 is louder from inside under 4000rpm with open or closed valves.
And i liked the GT4 clutch; GT3 seems to be too light. Need some more time to adjust.
I havent yet driven the car extensively but after first 20 kms, i think the GT4 is louder from inside under 4000rpm with open or closed valves.
And i liked the GT4 clutch; GT3 seems to be too light. Need some more time to adjust.
07-15-2018, 12:07 PM
#48
I collected my GT3 touring on Friday.
I havent yet driven the car extensively but after first 20 kms, i think the GT4 is louder from inside under 4000rpm with open or closed valves.
And i liked the GT4 clutch; GT3 seems to be too light. Need some more time to adjust.
I havent yet driven the car extensively but after first 20 kms, i think the GT4 is louder from inside under 4000rpm with open or closed valves.
And i liked the GT4 clutch; GT3 seems to be too light. Need some more time to adjust.
To me, the GT3 clutch is like an on/off switch that is super light.
07-15-2018, 12:38 PM
#49
Rennlist Member
Exhaust mute valve bypass
https://capristoexhaust.com/product/...-oem-capristo/
07-15-2018, 01:33 PM
#50
I felt the same way when I switched from the GT4 to the GT3. It’s took me a little bit of time to get used to the GT3 clutch pedal effort and point of engagement. I’m still getting used to it but it’s getting better and better. At this point with about 800 miles on the GT3 I like the GT3 clutch better. Also for me it felt like the GT3 engine is much stiffer with delivery miles compared to the GT4. You’ll notice the GT3 changing quite a bit as it goes through break in period. No comparison between the two engines for me anyway at this early stage. GT3 feels completely different in a good way.
07-15-2018, 03:31 PM
#51
Drifting
I felt the same way when I switched from the GT4 to the GT3. It’s took me a little bit of time to get used to the GT3 clutch pedal effort and point of engagement. I’m still getting used to it but it’s getting better and better. At this point with about 800 miles on the GT3 I like the GT3 clutch better. Also for me it felt like the GT3 engine is much stiffer with delivery miles compared to the GT4. You’ll notice the GT3 changing quite a bit as it goes through break in period. No comparison between the two engines for me anyway at this early stage. GT3 feels completely different in a good way.
07-16-2018, 03:04 AM
#52
Burning Brakes
So higher back pressure (i.e. more pumping work, i.e. losses) on lower rpm should give higher torque? I disagree, and I have a hard time understanding the theory behind that.
07-16-2018, 06:29 AM
#54
Racer
07-16-2018, 08:02 AM
#55
I found the following video (see below); I haven't yet seen the other one linked above. If I understand correctly, it is actually not back pressure but the velocity of the exhaust gases getting out as they pulsate their way forward in the exhaust system. It seems that the length of the exhaust system is quite important and by playing with the length, you can optimize the output for certain rpms. It is clear that backpressure is the wrong terminology for this.
It would be interesting to see a cut model of the GT3 exhaust and see if the valve is really making a bypass at higher rpms.
07-18-2018, 05:24 PM
#56
Burning Brakes
Yes. Static back pressure and tuning of pressure waves (with pipe lengths, diameters, collectors' positions etc) are two very different things. I did my Master Thesis in 1995 on the subject (or more accurately: "A study of instationary, compressible flow in turbocharged internal combustion engines”)... Forget about the "turbocharged" bit - the theories and physics are the same for N/A engines.
07-30-2018, 09:37 AM
#57
Intermediate
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Could not help noticing the reference to change in exhaust note. I have a 991.1 C4S with PSE, and I recently noticed a change in the exhaust note when the sports exhaust is switched on. Seems to have more a of a rumble to it, more or less overnight. Just wondered if anyone had any thoughts? Car only has 14k miles. Thanks!