760Li V12 exhaust mod experiment

so I tried the whole Mufflerman mod on my 760Li. I know I mentioned it before but I have an update.

here's the complete story

http://mwsmith.smugmug.com/Cars/760L...04237969_iiNZ5

The end result is: the pipe I attached so I could use the stock valve and have a quiet idle, was way too restrictive to let the V12 sound come out, with all the proper overtones of a V12. It sounded like a buzzy V8, both in and out of the car. I mean, the valve "worked" and all, but the sound was like an anemic 745. I do not have a video of this.

I just decided, "heck with it" and removed the pipe, since it was mounted with a flange I welded on, and drove around like that. now THAT sounds like a V12.

Here's a little sample movie with my wife trying to blip the throttle. Put headphones on to hear the full effect.



now THAT sound is more like the V12 wail I was going for. I decided to just try driving around with a 2.5" gaping huge hole in my exhaust.

You know what? not that loud at idle, and very nice note when accelerating, both in and out of the car. It does get a strange wooshing noise going up high, probably the gasses banging into the rear bumper as they exit. So yes, it's totally ghetto and needs to be tamed down a bit.

I still want to incorporate a valve for idle to really quiet it down and direct it out the back with some 2.5" to 3" pipe.

The stock valve is too small to do what I want.

After much searching, found this:

http://www.apexi-usa.com/products/?id=5326

which are meant to be actuated in the cockpit with a cable. It will not take much to weld on the vacuum actuator from the stock valve and have a valve big enough to pass those V12 gasses (and overtones!)

Originally Posted by mws

I mean, the valve "worked" and all, but the sound was like an anemic 745.

btw: what I mean is: a 745 that not in good shape, not that all 745s always "sound" anemic in general. I like the sound of 745s, I wish 760s had an aggressive sound when accelerating as well.

as far as the exhaust goes and that whistle, you might want to get an elbow or something for it since there's a good chance it'll slowly melt the rear bumper and deform it.

IMO you should cut the whole exhaust system off and get a magnaflow muffler as the stock exhaust (quiet muffler) and then get the apexi valve and attach an elbow to it and call it a day. Better exhaust flow, better sound and it'll look good from underneath too.

EDIT: just listened to the video, sounds good but it lacks that growl that a V12 gives off. I wonder what straight pipes would sound like on the 760... hmmm I might have to disconnect my exhaust one day...

Originally Posted by csmeance

as far as the exhaust goes and that whistle, you might want to get an elbow or something for it since there's a good chance it'll slowly melt the rear bumper and deform it.

I'll do something soon, not too worried, though, the entire area is armor-clad with heat sheilds

Originally Posted by csmeance

IMO you should cut the whole exhaust system off and get a magnaflow muffler as the stock exhaust (quiet muffler) and then get the apexi valve and attach an elbow to it and call it a day. Better exhaust flow, better sound and it'll look good from underneath too.

I've worked with Magnaflows before. If I used one, I would just use one on the main exhaust and forget the valve. The only thing is, it would be fairly loud all the time, like it is now. I like the idea of using the stock muffler for super stealth and just a straight pipe with valve for WOT.

Originally Posted by csmeance

EDIT: just listened to the video, sounds good but it lacks that growl that a V12 gives off. I wonder what straight pipes would sound like on the 760... hmmm I might have to disconnect my exhaust one day...

yeah, it's very VERY baffled and muffled. There's a pre-cat off each header, then a large and long resonator muffler on each header tube before the two header pipes go into one big, long and cavernous catalytic converter. That cat sums the two together and comes out the other end as one huge 3.5" pipe. By that time, going thru two cats and a resonator, it's already really quiet. One of my pals made a joke I should have two valves and have one come off each header right after the pre-cats and dump under the car

Originally Posted by mws

yeah, it's very VERY baffled and muffled. There's a pre-cat off each header, then a large and long resonator muffler on each header tube before the two header pipes go into one big, long and cavernous catalytic converter. That cat sums the two together and comes out the other end as one huge 3.5" pipe. By that time, going thru two cats and a resonator, it's already really quiet. One of my pals made a joke I should have two valves and have one come off each header right after the pre-cats and dump under the car

Wow, I only thought there was only 1 cat cast into the header and that's it along with a ton of resonators. I contacted Hamann a while ago for the sports headers w/o cats and they never responded. I might call up an authorized dealer and see what they can do. The design makes it look very restrictive as it is:

Originally Posted by csmeance

Wow, I only thought there was only 1 cat cast into the header and that's it along with a ton of resonators. I contacted Hamann a while ago for the sports headers w/o cats and they never responded. I might call up an authorized dealer and see what they can do. The design makes it look very restrictive as it is:

oh, no doubt, but the problem is, (without looking at the service manual, but knowing OBD2) the ECU would code if it does not see the proper signal before and after the pre-cats. There needs to be some kind of pre-cat--plus the primary and secondary O2s, before and after the pre-cats-- to not code. I've made headers in tight engine compartments before. What a pain!!!! It's bad enough without also trying to support the OBD2 stuff.

Originally Posted by mws

oh, no doubt, but the problem is, (without looking at the service manual, but knowing OBD2) the ECU would code if it does not see the proper signal before and after the pre-cats. There needs to be some kind of pre-cat--plus the primary and secondary O2s, before and after the pre-cats-- to not code. I've made headers in tight engine compartments before. What a pain!!!! It's bad enough without also trying to support the OBD2 stuff.

Well the O2 sensors before the cats can stay where they are on a new set of headers. On the set after the cats, all you need is a set of spark plug bungs to pull the sensor out of the stream of the exhaust. That way it'll think the cats are working properly! Common trick used on many cars!

Originally Posted by csmeance

Well the O2 sensors before the cats can stay where they are on a new set of headers. On the set after the cats, all you need is a set of spark plug bungs to pull the sensor out of the stream of the exhaust. That way it'll think the cats are working properly! Common trick used on many cars!

That large center "cat" I said I saw while under the car? not cat at all



#1 is the "Center muffler" I thought it was a large cat (from underneath, it looks like one). hmmmmmmmmmm..... I am thinking they are chambered/baffled. ie: steel walls impeding gas flow and directing flow around them. More like the rear mufflers.

and the pre-cats are the only cats on it. So it has 1 cat and 3 mufflers per "side" so to speak.

here's the "front" mufflers as they call them. They are likely perf tube resonators, like a magnaflow or even an old cherry bomb.

In all honesty, I would think that a new set of headers and some pipes straight back (duals that merge into 1 right before the axle) and then into a dual muffler setup (performance and quiet tip) would make probably add a decent amount of power. All of those mufflers probably restrict the flow of all the exhaust gases a great deal and the same with those headers! I'd think something that was equal length tubes into a solid collector for all 6 would work well enough. I wonder if there are any headers for the 328 that we could modify for our cars...

Originally Posted by csmeance

In all honesty, I would think that a new set of headers and some pipes straight back (duals that merge into 1 right before the axle) and then into a dual muffler setup (performance and quiet tip) would make probably add a decent amount of power. All of those mufflers probably restrict the flow of all the exhaust gases a great deal and the same with those headers! I'd think something that was equal length tubes into a solid collector for all 6 would work well enough. I wonder if there are any headers for the 328 that we could modify for our cars...

The 328 idea "might" be good for starting one bank of the V12 but not the other (wrong direction). The flanges from the header on a 328 might be useful to get the job started on the other bank of the V12. Having flanges to start a headers project is 80% of the battle.

While the are not pretty, I have a bit of experience prototyping and using headers for a couple cars:

the non-turbo Z32 300zx. Which these headers basically did almost nothing to add power. In fact, having full-length headers (about 36" long) reduced torque in a few areas. The problem is, not being able to tune them and try several sets until you get the right length and size. These were then cut off, and I had some flanges made so I could try to add different ends to the headers to try to find the right combo. I never finished the job. It was a waste of time.



the GM 3400 DOHC motor transplanted in a lowly Pontiac Fiero. What a tight fit. and these were equal length, and full-length as well.

http://fiero*****fiero-tdc/members/mw...ers/index.html

[IMG]http://fiero*****fiero-tdc/members/mws/headers/Rbank1.jpg[/IMG]

these headers worked better because I also changed the intake radically and adjusted the cams. I achieved a 38% gain in power, which was really good for a NA motor.

http://fiero*****fiero-tdc/members/mws/intake/index.html

[IMG]http://fiero*****fiero-tdc/members/mws/intake/240hp.JPG[/IMG]

It would be difficult to be able to tune headers to know what to do with VANOS and Valvetronic.

That said, some sort of short, tubular manifold would be better than the log. So that "would" alleviate some restriction.

I think the only mufflers restricting anything are the "Center" and rear mufflers. The front mufflers are just perf-tube and replacing them with straight pipes would just add more ratty noise, from my experience.

Originally Posted by csmeance

Well the O2 sensors before the cats can stay where they are on a new set of headers. On the set after the cats, all you need is a set of spark plug bungs to pull the sensor out of the stream of the exhaust. That way it'll think the cats are working properly! Common trick used on many cars!

What are spark plug bungs? I need to trick my 2nd O2 sensors on my 911

Originally Posted by sanhonda22

What are spark plug bungs? I need to trick my 2nd O2 sensors on my 911

Here you go:
http://www.energeticforum.com/renewa...n-foulers.html

people do this so the car will not see the full emissions and thus think the cat is working as it should.

I've got a video of my 760 stock exhaust:


I wanted to put cutouts on my car after cats but i realised there is no any space for that, so i decidet to put it between middle and rear muffler and i was very impressed i could make so easy modification but the problem is i cant hear a lot of difference between my stock exhaust and exhaust modification like mws did. Or its just video quality?

Originally Posted by Rostman

I wanted to put cutouts on my car after cats but i realised there is no any space for that, so i decidet to put it between middle and rear muffler and i was very impressed i could make so easy modification but the problem is i cant hear a lot of difference between my stock exhaust and exhaust modification like mws did. Or its just video quality?

When I drive, I can hear a nice, ghost-like "whirrrr" sound up to about 5000 RPM or so, and then it drops off and the lower more growly V8 sound kicks in up to redline. I like the Ghostly Wail as I call it. I'd love it even more if it went all the way to redline. The tone and volume of the sound is exactly what I wanted, I just want it through the whole rev-range.

BTW: in order to get rid of the whoosing air sound I welded up a flange and a 3" dump-pipe with a turn-down that goes under the car to the rear bumper. Still makes the V12 wail, but no flute-like air whooshing noise.

Do you hear that more high-pitched engine wail like I am describing, while driving? If so...I am pretty convinced you could simply cut the rear mufflers off completely (replace them with a nice 3.5" dump pipe) and get basically the same sound as you and I have now. The rear mufflers and the second to last muffler system, the big one that looks like a shielded pillow, I believe, do the most muffling. If I were to mod the system further I would want to see what it sounds like with just straight pipes from the round, can-shaped resonators, all the way to the bumper. Leave the resonators on, but remove everything behind them and replace with pipe. If I then got too much bass, I would add a large chambered muffler like a Flowmaster or a Spintech. I know, sounds like I just committed blashpame, but they do a good job of preserving mid-range sound, and removing pulsing, thumping bass. No one needs to know it's there.

Originally Posted by mws

When I drive, I can hear a nice, ghost-like "whirrrr" sound up to about 5000 RPM or so, and then it drops off and the lower more growly V8 sound kicks in up to redline. I like the Ghostly Wail as I call it. I'd love it even more if it went all the way to redline. The tone and volume of the sound is exactly what I wanted, I just want it through the whole rev-range.

BTW: in order to get rid of the whoosing air sound I welded up a flange and a 3" dump-pipe with a turn-down that goes under the car to the rear bumper. Still makes the V12 wail, but no flute-like air whooshing noise.

Do you hear that more high-pitched engine wail like I am describing, while driving? If so...I am pretty convinced you could simply cut the rear mufflers off completely (replace them with a nice 3.5" dump pipe) and get basically the same sound as you and I have now. The rear mufflers and the second to last muffler system, the big one that looks like a shielded pillow, I believe, do the most muffling. If I were to mod the system further I would want to see what it sounds like with just straight pipes from the round, can-shaped resonators, all the way to the bumper. Leave the resonators on, but remove everything behind them and replace with pipe. If I then got too much bass, I would add a large chambered muffler like a Flowmaster or a Spintech. I know, sounds like I just committed blashpame, but they do a good job of preserving mid-range sound, and removing pulsing, thumping bass. No one needs to know it's there.

I dont wanna a lot of bass at all. Why do you leave this valve in the exhaust? May be, if you put it out it would be much beter?
Whats happend if remove middle muffler? I'm looking for something not so loud with V12 tones

Done. But still its not so loud, I do not fill a lot of difference when the muffler was there
I think in a few weeks i will take off mid muffler.

Originally Posted by Rostman

Done. But still its not so loud, I do not fill a lot of difference when the muffler was there
I think in a few weeks i will take off mid muffler.

my experiments showed that the open pipe needs to be 3" or so, to get any sound out of it.

Originally Posted by mws

my experiments showed that the open pipe needs to be 3" or so, to get any sound out of it.

I'd allready done a new mode. Cut the muffler and put a straight pipe n it. Sound is incredible.