3.6 CA conversion muffler experiments under way!

[BarryJB]

Comments, criticisms welcomed - still work-in-progress, in cahoots with the talented & thoughtful Kevin at Ed Hansen's muffler shop in Spring Valley, CA...

After endless searching, I couldn't find anyone who has tried this approach, i.e., stuffing wrapped mufflers in over the stock 993 headers & cat. Since I'm in CA, this is largely intended to keep DMV & CARB folks happy and not require some sort of finagling with exhaust components every couple of years... and not set fire to my car.

It all fits up under the stock bumper with room to spare; will add suitably hacked valance once exits are finalized, as definitely going to longer tailpipes running sideways across car (under or over cat/mufflers, TBD), exiting at quarters. Bit sad about this though as IMO the dual center-outs with a valance installed would look cool, even a bit mysterious on a 3.2 Carrera body, but not at the expense of drive-me-&-others-mad noise.

Just adding simple 6" extensions - not too obvious, as in bottom pic - as long as I dared for road use - to the exhaust tips/stubs (as shown in pre- & test-install pics) considerably reduced excessive low-freq & drone-type noise at idle and certain load/throttle positions between 2-3krpm.

It's only a windows-down issue and surreptitious night testing with longer chunks of pipes & bends draped and suspended Heath Robinson style off the rear end ("Oh that... It's an heated bike rack, officer!") continues, to determine optimal length (so far, it seems to be simply that LONGER = BETTER). First thought was maybe tip proximity was primary cause, but the '95 993 cat/collector already mixes the flows like a crossover and quick tests trounced that idea. It will probably do no harm to have them separated though, it might change the shape of the sound footprint from omnidirectional to more fore & aft, and up.

No noticeable heat build-up noted in bumper area or rear of engine compartment, it seems the wrap does its job when overlapped to give 200% coverage (tape is 2" wide on mufflers, 1" on pipes).

Another option after seeing how livable this is (everyday driver) will be to swap out the Magnaflow (2.5" inlet/outlet, 5"x14" can) for Flowmaster HP-2 shorties or custom Spintechs, will all fit same way.

Sounds awesome though, for the moment, especially winding up through gears to max rpm at full chat. But just a bit too loud, once or twice a day during urban errands, like an Army chopper, sets off a triple chirp shock sensor alert... nothing like as loud as many of the H-Ds running around

Naked - pre-install:


Naked test install:


One side, dressed & made-up (goth black):


What it's like now (with 6" extensions added to tips):

[PcarPhil]

That's pretty neat. Keep us updated!

[mclmk8d]

Nice job! Looks somewhat like mine, though I currently have no valance...M&K 1-in 2-out GT3 muffler

[silver911rdb]

That's a real nice looking solution. Would love to see a video post to hear what it sounds like

[BarryJB]

Originally Posted by mclmk8d

Nice job! Looks somewhat like mine, though I currently have no valance...M&K 1-in 2-out GT3 muffler

Love to be able to use that solution! But CA is tough re engine replacement in post '73 cars. I found a FG rear valance (Rennspeed) with no pre-cut openings that is long enough to completely cover existing driver-side side outlet, plus my original, but for now some matt black hit temp paint it's hardly noticeable there's anything missing - not like I have your cool 321 stainless to flaunt, and of course your car is also the perfect color

[BarryJB]

Originally Posted by silver911rdb

That's a real nice looking solution. Would love to see a video post to hear what it sounds like

I'll break out the GoPro and see if I can figure out how to get something up on YouTube shortly...
Cheers!

[Joe Bob]

My solution using Bishoff HEs.

[BarryJB]

Originally Posted by Joe Bob

My solution using Bishoff HEs.

Yes I've seen this your purty car in amongst other things several conversion exhaust threads during my searches. Mark K at Black Forest has done some 3.6 conversions that looked sort of like this, which he has got passed & door-jam stickered by a CA DMV referee. Was your setup ever approved in CA - or is part of the solution to sport Oregon plates? Up there maybe the DMV considers a clean-running &/or nominally-for-year equipped engine upgrade (i.e., suitable non-OEM cat, etc.,) to be approved...

Do you ever bottom out that installation? - in pics it looks, but maybe isn't, rather low. Guessing it sounds awesome - any videos posted?

[Joe Bob]

I passed smog in CA with it....I moved to Oregon for awhile after I retired. Never bottomed out.

[BarryJB]

Originally Posted by Joe Bob

I passed smog in CA with it....I moved to Oregon for awhile after I retired. Never bottomed out.

Thank you, that's promising on both counts. Jae at Mirage did the major conversion work, so I'm still futzing around with the cooling, exhaust and A/C requirements. I hope options like yours are still DMV-viable in case my present efforts to retain the Bischoff HE's &/or cat don't pan out. Mark K told me he's got entirely non-OEM exhaust systems approved in the past, although BAA the stock H/E's aren't bad, especially if you still want heat.

[Joe Bob]

One rule of thumb when dealing with the BAR and DMV. Get any direction you get in writing, with contact information or document statements in a Journal. Try and deal with the same person every time.

Rules can be interpreted differently by different staff. BTDT.....good luck.

[BarryJB]

Originally Posted by Joe Bob

One rule of thumb when dealing with the BAR and DMV. Get any direction you get in writing, with contact information or document statements in a Journal. Try and deal with the same person every time.

Rules can be interpreted differently by different staff. BTDT.....good luck.

My plan is to have Mark K test & vet the whole conversion once it's all debugged & buttoned up before I take the plunge with officialdom, last time we spoke he said there is a particular referee in San Diego that's proved knowledgeable & helpful with Porsche 3.6 conversions.

Who knows what horrors are hidden behind your BTDT, but reading some of the stories on such issues here, I appreciate your advice, and cheerfully accept the "good luck" . If I can get this muffler idea to work, everything else is retained and stock for the engine MY (including functional "check engine" light) so it "should" be a relatively painless process...

[Joe Bob]

IF your guy has done it before and he has a guy he has gone to.....great. But anything that hasn't been looked at or approved before is something that I would get a blessing for BEFORE putting $$ into it and building it.

I worked for the smog nazis for years and I know that efforts, while making sense to the client and the applicant's engineer, can be shot down w/o prior approval. Whimsical interpretation is alive and well when it comes to getting something certified by CARB, BAR, DMV or any other regulatory agency.

When it comes to governmental approval, asking permission as opposed to not and asking forgiveness later doesn't work.

[BarryJB]

Originally Posted by Joe Bob

IF your guy has done it before and he has a guy he has gone to.....great. But anything that hasn't been looked at or approved before is something that I would get a blessing for BEFORE putting $$ into it and building it.

I worked for the smog nazis for years and I know that efforts, while making sense to the client and the applicant's engineer, can be shot down w/o prior approval. Whimsical interpretation is alive and well when it comes to getting something certified by CARB, BAR, DMV or any other regulatory agency.

When it comes to governmental approval, asking permission as opposed to not and asking forgiveness later doesn't work.

All duly noted, and it was such that almost persuaded me to not even go this way and simply rebuild my trusty (up to starting to make odd noises at 1/3 million miles) 3.2. Six months and the 95% of the $ in already, and this is the crux of the (hopefully considered) risk of doing it.

Hmm, until you present the vehicle to them to see what's done so far for them to approve/disapprove, how you can get prior approval before spending and doing? Seems all one can do is read the rules, take a deep breath, do your best, then take care of stuff that isn't OK - negotiate what can be and fix what can't. More $ and more time, sure. I'm utterly upside down with this old car anyway, nothing to do with economic sense. Put off remodeling my kitchen twice now - my priorities bite me every time I cook

Patience and a cooperative non-confrontational approach seem to be factors in most of the success stories... there are quite a lot of post-73 3.6 conversions running around CA now that are now legal (like yours!), so it has and can be done, and that's my wish for mine too...
The saga continues... hopefully not too many more months.

[Joe Bob]

I talked to my BAR referee on a regular basis. Albeit it was ten years ago. He was down the road from me and we developed a good working relationship. Maybe the fact that I was a County Regulator greased the way.....dunno.

My Dad used to run a little burger joint up at a local ski area. We had the Health Inspector come up and he would constantly point out things and say, no good, no good. After 3-4 attempts to correct things he finally asked.....what is good?

Show me where there is an example of compliant construction.....it was finally the right question.

All I'm saying is, these guys do answer the phones and will take a look at drawings via fax or scans attached to an email.

[BarryJB]

Originally Posted by Joe Bob

I talked to my BAR referee on a regular basis. Albeit it was ten years ago. He was down the road from me and we developed a good working relationship. Maybe the fact that I was a County Regulator greased the way.....dunno.

My Dad used to run a little burger joint up at a local ski area. We had the Health Inspector come up and he would constantly point out things and say, no good, no good. After 3-4 attempts to correct things he finally asked.....what is good?

Show me where there is an example of compliant construction.....it was finally the right question.

All I'm saying is, these guys do answer the phones and will take a look at drawings via fax or scans attached to an email.

Ha! As a professional courtesy, perhaps you more readily received helpful feedback rather than blunt "no goods" without further advice... and I have buddies who've got war stories about very confrontational & heavy-handed official home construction and factory inspections... I hope vehicular stuff is less hostile.

My intention was to start with what I've been advised has already passed muster with others, and report the adventure and any issues arising and the remediation process, as have others, in a thread here. It's good to know that some issues may be pursued over phone and with documentation via email, etc.

No-one ever suggested to me that this wasn't a procedure that could become tricky, protracted and expensive, so with cautious optimism, any relief in those areas will put me ahead of expectations, and let me enjoy this car another 13 years or so

[Jaskas]

I have been looking a quiter solution for my 3.6 as well... I have only the cat with tips. I love the sound, but wife and local track authorities dont.

Have you measured the sound level? Or have you compared the sound between the cat only, and with the silencers.

Your solution looks great but im afraid the noise level is still too high.

[Jaskas]

Yep:
Supertrapp testing with Porsche 911 3.6 - YouTube

The test was done with 3500 rpm, the track test is done with 4500 rpm.

Cuts down the power and doesnt reduce the noice enough.

[BarryJB]

Originally Posted by Jaskas

I have been looking a quiter solution for my 3.6 as well... I have only the cat with tips. I love the sound, but wife and local track authorities dont.
Have you measured the sound level? Or have you compared the sound between the cat only, and with the silencers.
Your solution looks great but im afraid the noise level is still too high.

I hope to post a drive-by video clip this weekend (yeh, said that before and didn't get around to it, do have some stuff to edit down now), it does sound great, maybe it will give you some idea of the difference to how yours sounds. Got some more 2.25 pipe bits & bobs last week so may try to dummy up the longer tailpipes in a drivable configuration, get some more readings and driving time. It's really at idle that the low frequency pounding sound is worst and is what sets off the occasional alarm at just low barely open throttle rpm in town; it really seems the longer tailpipes are effective at reducing that and the droning effect mentioned before. We'll see!

It's definitely a work in progress - I'll check noise with a better meter, a Harbor Freight multimeter gave over 102dB at idle with the short stubs as in photo before I added the extra 6 inches, and a tad less after, but there was no definitive info on the type of measurement this was in meter booklet; but it is definitely WAY quieter than with just the cats (and no tips at all!) before we did this. For now my tests are mainly lots of driving around with windows open to assay DFF (drone fatigue factor) and note how often I set off the shock chirps on parked cars.

FWIW, CA DMV noise level spec for street use is not enforced (no funding or something like that) but is I believe 95dBA at 20 inches measured in an open non-reflective space (e.g., big field) at 3krpm.

I got down to high 90's and way less droning-type noises at idle and above just by Heath Robinson addition of more 2.25-in tailpipe (making about 20 inches each side) so if the dummy-up above works I'll have my guy make it real and see how that goes for a while - next will try the shortie Flowmaster HP-2's. Resonator tips may also make some small difference, if I can find any suitably shaped, short and matt-blackable.

No-one seems to like Supertrapps on these engines - a guy in Europe YouTubed a 3.6 cats-with-tips conversion with and without them - not impressive - BAA and as mentioned in above posts, they sap power well before they cut down noise enough. Some say the Car Chemistry style inserts (2.25 and up) work well in the tips for sound, others have tried the cone insert style there instead but homemade seems to be needed for 2.25 pipe as they're made to fit 2.5 and up. Latter reported as free-flowing, 1-2dB effect when used as intended in collector area... former reported to be overly restrictive... so it goes

Many say 1995 993 stock headers/cat combo is quite good; for me it's worth putting out some more time & $ to see if something can be done that retains the free-flowing advantages of that but keeps it livable and legal enough to use every day. Intend to get dyno before-&-after muffler/tailpipe install dyno numbers, once there's something seems worthy of such, and hoping results will avoid needing to proceed to any Plan B.

[Bill Verburg]

It's amazing the difference effects an exhaust can have on different engines

This exhaust was worth a few hp and nice and quiet on a 2.7S but lost hp and made too much noise on a 3.6, displacement, cams intake etc all make the difference