3.6 CA conversion muffler experiments under way!

[BarryJB]

Originally Posted by 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

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

[Bill Verburg]

Originally Posted by BarryJB

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?

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

[Jaskas]

I have at the moment an electric cut out on the right outlet, to cut down the noise, like this:

Even when the other outlet is shut it does not cut the noise enough at 4500 rpm

Here is the original setup:

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.
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.

[BarryJB]

Originally Posted by Jaskas

I have at the moment an electric cut out on the right outlet, to cut down the noise...

...I was wondering if this kind of solution would work with a one long muffler.

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...

[Jaskas]

Originally Posted by BarryJB

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

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.

Originally Posted by BarryJB

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.

This is offcourse worth trying.

[BarryJB]

Originally Posted by Jaskas

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.

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!

Originally Posted by Jaskas

This is offcourse worth trying.

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

[BarryJB]

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.

[Bill Verburg]

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

[BarryJB]

Originally Posted by Bill Verburg

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

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...

[Jaskas]

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:



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




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

[Tom '74 911]

Hi - that's an interesting solution.

Where did you source the cut out valve from?

Thanks,
Tom

[Jaskas]

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