3.6 CA conversion muffler experiments under way!
 

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:
http://forums.pelicanparts.com/uploa...1341717121.jpg

Naked test install:
http://forums.pelicanparts.com/uploa...1341717444.jpg

One side, dressed & made-up (goth black):
http://forums.pelicanparts.com/uploa...1341717722.jpg

What it's like now (with 6" extensions added to tips):
http://forums.pelicanparts.com/uploa...1341718145.jpg

That's pretty neat. Keep us updated!

Nice job! Looks somewhat like mine, though I currently have no valance...M&K 1-in 2-out GT3 muffler
http://i291.photobucket.com/albums/l.../IMG_0272s.jpg

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

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 ;)

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

My solution using Bishoff HEs.

http://forums.pelicanparts.com/uploa...1341773897.jpg
http://forums.pelicanparts.com/uploa...1341773907.jpg

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?

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.

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...

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.

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 :)

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.

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.

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.

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
http://forums.pelicanparts.com/uploa...1343350743.jpg
http://forums.pelicanparts.com/uploa...1343350768.jpg

It looks terrific; simple and elegant. But a bit low for a street car, maybe?

Bill, have you any recollections of reasonable road-car muffler solutions on the stock 993 cat setup?

I know might be wasting my time/$ even trying. There are many the threads here where you and others have contributed fascinating images and comments on 3.6 conversion exhausts, but the challenge for me is to try some things not seen that aren't, well, ridiculous.

So just playing around, starting with the most basic of gleaned 3.6 mill exhaust heuristics (plumbing sizes & lengths and so on) and the overriding constraints of limited asymmetric free space, heat and at least some nod to installation ease... would be delighted (serendipity welcome) to figure or stumble into a good CA legal solution that isn't too much of a compromise on performance (say = or better than stock 993 muffler), as well as satisfying at least some esthetic & visceral sensibilities. Something of the Bose ilk - cheap drivers and cunningly folded tubes came together nicely for them. May have been a bit of engineering research involved there ;)

when it's in a 993 chassis sure, when it's in a 911 chassis it's much harder, especially if you want to keep the cat

the 993s use side mufflers behind the rear wheel right where a 911 has an oil tank, I've seen 964s w/ side muffler too, but they also have the forward mounted oil tank.

Slickest I've ever seen was on a 964 C4 RS/LW but it had no cat.

Steve Weiner had/has a pic of a 3.6 in a 911 chassis on his site w/ a modified oe bannana, very slick and i'll bet very nice sounding but again no cat

I have at the moment an electric cut out on the right outlet, to cut down the noise, like this:
http://i216.photobucket.com/albums/c...8032011170.jpg
Even when the other outlet is shut it does not cut the noise enough at 4500 rpm :(

Here is the original setup:
http://i216.photobucket.com/albums/c...s/IMG_6269.jpg
Soundclip of this: Just testing the new throttle cabel system ;) - YouTube



I was wondering if this kind of solution would work with a one long muffler.http://i216.photobucket.com/albums/c...austmodded.jpg
If you want to keep the noise down, keep the valve closed. It does cut down on power quite a bit... But gives nice backpressure though. I think ideal would be to use a vacuum operated valve, which would open when under load.

Hi Jaskas,
Simply adding a second cut out to the left end of the cat would make it a LOT quieter :)

One thing I did not try was simply adding full-car-width long tailpipes to the cat outlets. Plenty of room for both of them to pass each other over/behind the cat, and wrapped or heat-shielded too too. There is no question from much reading that lengthening tailpipes (of right size - told magic diameter for 993 engines is 2.25in each side) will make an engine quieter, even without mufflers.

BTW your present setup and sketch concept wouldn't work at all with the later Gillet 993 cats as the flows from the two banks are kept separate by a blocking plate in the center of the cat - so closing the cut out would completely block the left header. But with earlier Bischoff cats, where the l/r bank flows collide/mix together in cat center and can head for the atmosphere either way, it would tend to leave the left side stagnant and the right side working double duty. It also cuts total cross-sectional area in half, so it would be a performance hit.

But for a mainly drive-to-the-track-car, it might be worth a shot, but wouldn't you need to put either a much larger diameter pipe on the left, where the cat and muffler combine - or a separate tailpipe on the left end of the muffler - or you'd be choking the engine even with the cut-out open. And open, the disparate lengths and different flow dynamics of each side may introduce undesired effects - different rpm/torque/power curves on each bank.

On a mainly street car doesn't look like it would be a good idea for such a cut-out-equipped (or permanently welded-in-muffler) setup, re the performance hit.

Adding a left-side fender cooler this week, then will get to extending the tailpipes, sort of like this dummied-up Photoshop image. There's just room with a bit of lower valance tweaking so it will look close to a normal 3.2-type two tailpipe install. Not sure if the tip area will exit rear or angled yet, have to see how it all goes together. At least then trying different muffler types that will fit will just need the two 180's, a mounting tab and one v-band clamp welded to the ends. I would like to try and retain what is essentially (apart from the cat/combining area) a symmetrical dual system to achieve the goals - CA street legal, daily-driver-livable - not too loud but great sound, and is no worse or (please!) better than a stock 993 muffler setup re performance...

http://forums.pelicanparts.com/uploa...1343734504.jpg

Left-right mistake... Yes i have a e-cutout on the left side allready as in the pic. But is not quiet enough. And it does not block the the left bank totally.... The cat was from a -97 tip engine. I have also noticed that the cutout affect the power.

This is offcourse worth trying.

No not at all your mistake I was referring too, I didn't even notice anything! I was attempting a little humor - that if you put and closed cut outs both ends of cat it would certainly be VERY quiet (as in not running).

For the record, I am definitely left/right challenged, as all my copilots (amateur rally navigators, friends, GFs, colleagues, etc) can testify with a variety of tales, such as in my head, all set up for a nighttime 90R in 50m, quite alarming when my idea of R once every so often turns out to be what everyone else calls L... any car control I have at all I attribute to dealing with such surprises!

The odd thing is I've not found any threads where people have tried either this or the approach I'm trying with conversions... and it's not like anyone has said "I or someone else tried those ideas and they didn't work and here's why" and when I started this thread I expected to get shot down BTDT style. I suppose it depends on car's uses, driver's priorities, and whatever street or track rules and regulations apply.

The longer tailpipes on the cat, I'm guessing, based on my results and playing around so far, will still be very loud, but might be enough to take the edge off compared to just the short tips enough for your purposes; some add resonator tips which AFAICS are good for no more than a dB or so. It seems any of the silencer/insert devices are either only good for a dB or two, or reduce power too much if they are configured to be good at noise reduction... removable setup on latter may be a workaround for a mainly track car.

It's pretty easy & cheap to test the long tailpipe idea, get your local shop to make up bent bell-ended pieces long enough to emulate what installed length would be and shaped so you can temporarily fasten and hang them off the rear - bit of discretion as to when and where to drive around like this though! My local shop here in US took scrap pieces of 2.25in pipe and made up four half-dozen bell-ended straight and two 45 degree pieces in about 5 minutes, asked for a dollar each (dropped him a $20 anyway), then I bought four double bell-end pipe joiners at the store (≈$20 total) which is what I'm using to try things out lengthwise before getting anything made professionally.

Great you posted the video clips, I'm still trying to get those out as my saga progresses.... maybe THIS week :)

I got a better iPhone SPL this week, claims to be calibrated for use with iPhone 4 built-in microphone, and compared pretty equal to RS unit. At 20 inches just off axis with approx. 10 inches total tailpipe per side after each Magnaflow, was getting dBA numbers of 96 at idle and not really much different at 3krpm. Temporarily adding another 14 inches per side and driving around definitely kills all the external drone-like effects between 2-3krpm, makes the car much quieter outside, AND inside with windows up or down, and knocks SPL readings down to 95's.
That is close to the intended final length of about 24 inches of 2-1/4-in tailpipe per side, with side (corner) not center outlets. Still retains same great sound, just no booming/droning.

Sorry haven't posted any YouTube clips yet, have to reshoot as I have no simple way to remove ID & landmark info :)

I'll endeavor to do shoot some more, also with the mufflers removed (cats only), to show what difference the twin Magnaflows actually make.

The 993 cat in any of it's iterations makes foe a very poor muffler, some will need to retain the cat for legislative reasons and I feel sorry for them, but if you can go catless the nicest solution I've seen is a banana plumbed to the 993 headers

here's an example from Rennsport systems
http://forums.pelicanparts.com/uploa...1343870478.jpg

http://forums.pelicanparts.com/uploa...1343919430.jpg

Bill,
How I wish such were options for possible my car! Maybe I should move to AZ or TX...

Going stock-catless is out of the question for me, hence I started this thread - this is specifically to see if I can come up with an easily & permanently post-73 CA legal 3.6 conversion road car that doesn't do worse hp/torque (and hopefully a bit better) than a stock 993 set up, without unacceptable noise levels. Many here have used their 3.2 HEs, cat and muffler to get by CARB & DMV - the parts are OEM if not the right year, and they sometimes get away with it - which is also quiet, but chokes the motor somewhat.

As you see I have retained the stock 993 HE's & cat, added two wrapped Magnaflow mufflers up behind the bumper, and I'm presently about to extend the tailpipes to reduce some low frequency booming which is apparent at idle some low-rpm (lugging loads) with short tailpipes. The car is subjectively already WAY quieter than just the cats, which is utterly unacceptable to me as a daily driver re noise. Lengthening the tailpipes on the Magnaflows definitely refines the sound; also stopped the slow-about-town triple chirp shock alarm triggering (there's a particularly sensitive car parked evenings three miles away...)

Visual rules in CA mean big hassle if you try to change ANYTHING from the air intake(s) thru the cat outlet(s), including engine management, breathers and so on. All that has to be - and _look_ - stock for the engine's model year. No-one that makes (or has bothered/can afford to do so) any of the trick Porsche header/cat/muffler 3.6 conversion-compatible solutions has got CARB approvals.

Nonetheless some folks, either through luck, persistence or brilliance (or all three!), have got cars through without strictly adhering to this - and got the coveted approval sticker - others risk it and may end up with a load of hassle, or change stuff out every two years. No fun.

In searching here and elsewhere, I found no-one who'd tried adding any type of mufflers to the stock 993 cats, except one person who'd moved the oil tank and put in slightly reshaped 993/964 cans in very low at the back... I don't think resonator tips qualify... so I'm just trying stuff I haven't seen anywhere else.

Noise level is down, it sounds good, and I have an improvement path. Whether I've choked performance - will get dyno'd with cats only and with the longer tailpipes installed, once I have that setup ready, to see if I've done any good, or just crippled this 64.07 in getting it everyday-acceptable quiet. I don't mind if it's a bit sporty :)

Drawback to this approach is you have to drop the cats and muffler as one to remove the bumper overriders to allow bumper removal, and a rear-ender would probably nail this stuff some. But it goes up and in with bumper installed. So far it doesn't get that hot back there - maybe RUF-style perforated bumper/valance later...

Installing driverside oil cooler kit and upgrading A/C at the moment... reduced to exhaust pondering a few days...

Hi again, here is my latest exhaust version. This solution does not have a cat though.

The goal was to achieve a silent exhaust when cruising. When you floor it, vacuum drops and the exhaust flows nicely and the sound is... enough. A bit too much maybe.
DIY-PSE i call it.

When the valve is closed i pass the local track noise limits as well. Which is a huge plus. One muffler is capable to handle about 280 hp. If you would put another one to replace the valve you would have a quite and well-flowing exhaust.

Some pics:

http://i216.photobucket.com/albums/c...ps9a2f10ac.jpg

The muffler is Dynomax. The fitment inside the bumper is really thight.

http://i216.photobucket.com/albums/c...pse3c77eb0.jpg


Sound check in the Finnish countryside:
Porsche 911 3.6 exhaust test - YouTube

Hi - that's an interesting solution.

Where did you source the cut out valve from?

Thanks,
Tom

I bought i from us ebay. Not so sure about the valves quality. Some parts fell out after first test...