ptuomov

In a 90-degree cross-plane V8, the half orders are what causes the low-frequency "rumble". If you run equal-length 180-degree headers or equal-length 8-1 headers, the half orders cancel and the engine sounds like a flat-plane V8. Some people like the rumble sound, some people don't.

Drone frequencies at cruise speeds are almost always in the 50-200Hz frequency range. Exactly where there depends on the exhaust pipes, rpm, cabin resonance, etc. Easiest way to diagnose the drone is to run a phone app spectrum analyzer and identify the frequency of the objectionable drone sound. Then depending what the problem frequency is, solutions differ.

As you know, my mental masturbation on the exhaust sound topics has almost nothing to do with need. I just think it's fun to try to understand things. I spent a long time trying to understand the crankcase breather system, it was fun and the system works now although it probably wouldn't been just fine with a lot less thinking. So now I'm trying to understand sound, more so than trying design and exhaust.

Approximately equal length 4-1 headers and a Y-pipe that you have sound pretty good straight of the bat. This is because at low rpms, the pulses don't crowd each other out in the collector and the half orders cancel. At high rpms, the half orders no longer cancel but at high rpms it's supposed to be noisy by my understanding of your tastes. It's going to scream at high pitch at high rpms and high load, because there's not turbine or muffler there.

Todd Tremel's exhaust is also going to sound good. The half orders don't cancel quite as well as with 4-1 headers, but the turbos take out the high frequencies about as well as an additional packed muffler would. Then he's got three Borla mufflers in there, so not much over 200Hz and nothing above 500Hz is going to get thru that. The 50-200Hz frequencies get mostly thru in that exhaust based on my understanding, it's a low sound that comes out if I've understood the acoustics of it correctly. The connecting pipe sections are unequal length and the lengths are not integer multiples of each other, so I wouldn't expect it to drone either.

That Todd Tremel's exhaust arrangement doesn't quite work for me, because it lets thru a lot of low frequencies at low rpms and with some load. John has to make mine even quieter at low rpms, because I have to climb a steep hill home in the middle of our little neighborhood. So my situation is a little unique.

95carrera

180 degree headers sound the best. I would hate to spend the money for cross pipe only to hate it. This is my daily driver, wish I could hear some real world examples as I suspect you tube video on PC speakers doesn't accurately represent it.

bureau13

Good info, that makes sense. I actually like both engine sounds to some degree...

Regarding the phone spectrum analyzer, that's a great idea. I never thought of that.

Speedtoys

Did it, fixed it.

https://flic.kr/s/aHsjx2c3mg

ptuomov

Some sound relevant Engine Masters episodes. I think these strike the right balance between entertaining and informative. I think the usual magazine article tests are pretty much useless but these are at minimum fun and at best some of the side comments on sound are probably informative.




And one additional one that I'm watching right now. It's lower production value than the Engine Masters episode and it also tests a set of mufflers that are arguable large enough for the engine. Once you are large enough or oversized, the peak power is similar across mufflers. At low rpms, the mufflers make a difference and that by my logic is because of the exhaust resonance tuning. That is, some mufflers look like straight pipe and some mufflers look like a big plenum to the pulses, and that causes variation in power below the peak torque rpm. Not much sound related info there, unfortunately:

Andre The Giant

The first video where they test the difference between straight pipies, h-pipe, (what is on the original 928) and the famous X-Pipe is interesting. I am wondering where does this leave the claim of 928Motorsport's X-Pipe with gains of 26 HP ? At this point I am debating whether the cost of purchasing an X-Pipe for HP gain is worth it. Yes the sound might be cooler, but at that cost !

ptuomov

I'd either contact Louie Ott or look at his web site thru the way back machine. He ran a lot of H, X, and Y pipe tests.

For me, it's a sound vs performance trade off. The good news is that anything that is naturally quieter makes for a better noise vs. power trade off overall.

I could believe that compared to no crossover, H takes out a decibel, X takes out two, and Y a little more than the X does. Dennis Kao run a single dump pipe from Y and that seemed to have worked out well. For really high powered cars, you probably want to divorce the single center pipe again to use maximum available space for mufflers.

Andre The Giant

I thought it was Carl Faussett which produced the X-Pipe at 928 Motorsports ? Am I confused ? Louie Ott is the person with the stroker engine ?
https://www.performance928.com/home.html

ptuomov

I mentioned Louie Ott because he did a bunch of back to back testing, bothered to write it up, and isn't trying to sell you anything exhaust related at this point. Informed and not conflicted.

http://web.archive.org/web/200409050...ss_parent=1125

http://web.archive.org/web/200409051...ss_parent=1125

Porken has also done a bunch of testing with S3 and exhaust options, so you might want to PM him and ask what he thinks the gains will be.

Andre The Giant

WOW, thank you very much. I now have other subjective data to base myself on ! Yes I did purchase Porken's authority chip for the S3 and have not been able to install yet, but hopefully soon !

beran earms

Please, lets keep this thread active! I was considering the x for some time now, but after the first vid., I agree, lot of $ for sound. Any additional info would be great.

ptuomov

There's 928 specific knowledge and testing results out there, I wouldn't go with generic videos in this decision making. Still, correctly sized exhaust pipes, a large cross-over (H, X, or 2*Y) in the center, and three large straight-thru perforated core mufflers will in my opinion give the best power-noise tradeoff in any car, including the 928.