11 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHHelmholtz resonators in exhaust?
Leading reported evidence
Run 42mm pipe through the outer expansion chambers
Suggestion or failed attempt
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I made some modifications to the muffler by adding a valved section running 42mm pipe through the outer expansion chambers which has really helped, but I still need to deal with resonance at 130hz just over 2k rpm.
Leading evidence: 'Run 42mm pipe through the outer expansion chambers' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Run 42mm pipe through the outer expansion chambers' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I've been working on a new exhaust setup by modifying topgear 991 headers and using a 997.2TT muffler, but I found the setup too loud and with a nasty drone at 2k+ rpm/130hz.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
Maybe take the whole system off, hook it up to a to generator, speaker, and use a microphone at different locations to record and find out where the frequency response has cancellations, standing waves and such.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I think there's something more fundamental than tuning unfortunately; I know Soul use a similar position in their 996TT exhaust for some resonators, but it just doesn't seem effective - if I could measure a noticeable change at any rpm it would give me something to work with, but at present they don't really seem to be doing enough for me to be confident they're doing anything (vs measuring error/differences in engine load etc affecting db).
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
Run 42mm pipe through the outer expansion chambers
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Discussions that contain suggestions
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I made some modifications to the muffler by adding a valved section running 42mm pipe through the outer expansion chambers which has really helped, but I still need to deal with resonance at 130hz just over 2k rpm.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I've been working on a new exhaust setup by modifying topgear 991 headers and using a 997.2TT muffler, but I found the setup too loud and with a nasty drone at 2k+ rpm/130hz.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
Maybe take the whole system off, hook it up to a to generator, speaker, and use a microphone at different locations to record and find out where the frequency response has cancellations, standing waves and such.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I think there's something more fundamental than tuning unfortunately; I know Soul use a similar position in their 996TT exhaust for some resonators, but it just doesn't seem effective - if I could measure a noticeable change at any rpm it would give me something to work with, but at present they don't really seem to be doing enough for me to be confident they're doing anything (vs measuring error/differences in engine load etc affecting db).
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
11 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T072535Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Has anyone had any success with adding Helmholtz resonators to the exhaust? I've been working on a new exhaust setup by modifying topgear 991 headers and using a 997.2TT muffler, but I found the setup too loud and with a nasty drone at 2k+ rpm/130hz. I made some modifications to the muffler by adding a valved section running 42mm pipe through the outer expansion chambers which has really helped, but I still need to deal with resonance at 130hz just over 2k rpm. I've built helmholtz resonators that I've teed just after the cats and before the silencer (before the banks merge) tuned at 65hz based on 3 pulses per bank (I've tried resonators tuned at 130hz too) but they don't really appear to be doing anything. The neck is 1 1/2" and 30cm or so long (with a bend in it and extending inside the chamber for packaging reasons) and the chamber is 4" diameter and nearly 12" long. All my reading has suggested these should have a pretty signifcant effect, but they don't really appear to be doing much at all.
Resonance at 2k rpm @ 130hz
That's a LOT of work put into an exhaust system! I applaud your efforts.
I'd tell you what I'm running, and how it sounds utterly fabulous at every speed and RPM, but I don't think that's what you're looking for. I'm just dropping a note so I can follow your progress.
Maybe take the whole system off, hook it up to a to generator, speaker, and use a microphone at different locations to record and find out where the frequency response has cancellations, standing waves and such.
That's a great idea! It's off the car at the moment so will give it some thought.
I pulled it off the car and refitted a more conventional setup a little while back when I came to a bit of a dead end on the resonators as I wanted to enjoy the car for a while before the winter weather sets in and I don't use it so much; I think it will be a project for me over winter. My latest thinking is to try a x pipe silencer with a larger volume in place of the 997TT box and see how that performs - if I can find someone to build me one or get one off the shelf it wouldn't be hard to hook up, and there's definitely a reasonable amount of room there. It's a tough call as it's pretty good with the 997TT box on otherwise!
I think there's something more fundamental than tuning unfortunately; I know Soul use a similar position in their 996TT exhaust for some resonators, but it just doesn't seem effective - if I could measure a noticeable change at any rpm it would give me something to work with, but at present they don't really seem to be doing enough for me to be confident they're doing anything (vs measuring error/differences in engine load etc affecting db).
If the objective is to cancel the sound waves to lower the DB, I think 90% of the sound waves are just passing by your 90* tap for the Helmholtz , what little bit of sound waves that make it into the 90* tap can only do ~10% canceling even if 100% accurate in the timing...jmo
Maybe! I've more or less zero experience but thought that perpendicular flow is what you're looking for - like blowing over a bottle. It certainly seems the conventional way to do this on car exhausts and from what I'd read a lot of folk get good results with helmholtz resonators and j pipes set up like this. But given this is the only time I've tried this and it's not worked...
I had these in the box about two years ago and sent them back for some other aftermarket mufflers and really wish I had kept these� for reference Holley / blackheart has done the hard work for you in terms of length needed for the drone tube/ resonator on each side or bank of exhaust� these would have been probably to loud for me but to have a mild exhaust and wild exhaust would have been cool! They are now discontinued unfortunately� if someone could make these again I think they would sell well but Holley is not known too well for Porsche parts.
As long as the mouth is adequately sized, it should work. The flow of the exhaust gas has nothing to do with it. Tuning a helmholtz resonator is not straightforward and some trial and error should be expected. Best to build a telescoping arrangement to figure out the optimum volume and go from there.
This is one of mine for my 3.4, works pretty well. A little drone at 3k ish, but the J-Pipe removed most of it. Potentially I could add another curve to extend it a little but these work well for me
A bit of info here:
https://rennlist.com/forums/996-foru...pe-advice.html
This is a source reference. Confirm exact model applicability in the original material.
