OB's and RMB's
05-07-2006, 06:28 PM
#1
Racer
Thread Starter
OB's and RMB's
If you do nothing else to your 928, get rid of that rear muffler. Not only do you lose some weight, but the resulting sound is glorious!
Anyone who has been on this form for any length of time is well aware of the Rear Muffler Bybass (RMB) available for the newer cars. (ie , the ones with dual pipes all the way back) Nothing is currently on the market for the Old Buggers (OB's), but that doesn't matter since making your own RMB for these cars is easy.
There can be many variations on this theme, but here's what I did.
Buy a twin pipe extension available at most any auto parts store or on line. Mine came on line from Summit Racing. They have more variations than you can imagine. The pipe into the rear muffler is 2.5 inches in diameter, so that is what your extension has to be. I went with 2.5 single inlet, twin 3.0 inch outlets. A twin 2.5 inch is also available which is closer to the stock outlet size and might be preferred by some.
Find a muffler shop that does custom work. Not hard, I don't think.
Have them remove the stock muffler, cut off the plate that bolts the muffler to the single exhaust pipe and bend up a tube that will be welded to that plate on one end and to the twin extension on the other end. When these three pieces are in place on the car and everything is lined up and looks like you want it, have the welder tack everything together. What works well is for you, the customer, to position the parts just as you want them while the guy with the torch tack welds them together. That way, you get exactly what you want and the shop is sure you won't complain that it's not right since you did the alignment.
The twin extension cost $44.00 and the local shop charged $79.00. Best money I have spent so far.
I was concerned that the sound would not be right, given that the car companies go thru exhaustive testing to tune their systems. But somehow, it turned out fine to my ear. Not too loud, not boomy, not annoying on a long drive...just right. Roll down the windows and enjoy the concert or roll them up and enjoy your long distance GT. Perfect!
Anyone who has been on this form for any length of time is well aware of the Rear Muffler Bybass (RMB) available for the newer cars. (ie , the ones with dual pipes all the way back) Nothing is currently on the market for the Old Buggers (OB's), but that doesn't matter since making your own RMB for these cars is easy.
There can be many variations on this theme, but here's what I did.
Buy a twin pipe extension available at most any auto parts store or on line. Mine came on line from Summit Racing. They have more variations than you can imagine. The pipe into the rear muffler is 2.5 inches in diameter, so that is what your extension has to be. I went with 2.5 single inlet, twin 3.0 inch outlets. A twin 2.5 inch is also available which is closer to the stock outlet size and might be preferred by some.
Find a muffler shop that does custom work. Not hard, I don't think.
Have them remove the stock muffler, cut off the plate that bolts the muffler to the single exhaust pipe and bend up a tube that will be welded to that plate on one end and to the twin extension on the other end. When these three pieces are in place on the car and everything is lined up and looks like you want it, have the welder tack everything together. What works well is for you, the customer, to position the parts just as you want them while the guy with the torch tack welds them together. That way, you get exactly what you want and the shop is sure you won't complain that it's not right since you did the alignment.
The twin extension cost $44.00 and the local shop charged $79.00. Best money I have spent so far.
I was concerned that the sound would not be right, given that the car companies go thru exhaustive testing to tune their systems. But somehow, it turned out fine to my ear. Not too loud, not boomy, not annoying on a long drive...just right. Roll down the windows and enjoy the concert or roll them up and enjoy your long distance GT. Perfect!
05-07-2006, 11:40 PM
#3
Administrator - "Tyson"
Lifetime Rennlist
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I took both rear mufflers off my 81 a few years ago, sounds great.
05-07-2006, 11:43 PM
#4
AJK,
Check the archives and you should see pictures of mine. Sounds identical to yours except mines cost a little less.
Klim,
Any changes after the cat will have no effect on the emissions (except sound).
Dennis
Check the archives and you should see pictures of mine. Sounds identical to yours except mines cost a little less.
Klim,
Any changes after the cat will have no effect on the emissions (except sound).
Dennis
05-08-2006, 08:33 AM
#6
Rennlist Member
For a truly refined - but edgy mechanical music from a 16v with the single pipe system, leave the muffler in place. Punch out the cat internals and reinstall - cost $0.
At P-car gatherings, guys hang around the '80 just to hear it start up.
The S4 with RMB/GT resonators is very nice - but doesn't come close to the rich tone of the 16v, especially on throttle lift.
At P-car gatherings, guys hang around the '80 just to hear it start up.
The S4 with RMB/GT resonators is very nice - but doesn't come close to the rich tone of the 16v, especially on throttle lift.
05-08-2006, 08:41 AM
#7
Supercharged
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I have to agree with Garth. The 16V'ers do sound nicer IMO. It's hard to describe, but the 16V just sound racier. The 32V sounds too mechanical.
There's a guy here in MI that has an 82 Weissach. Now he does have Euro cams which helps a bit, but with his headers, no cats and a borla muffler, his car sound like the biggest baddest sport bike you can imagine. *CRISP* does even begin to describe the note! Very nice. I envy his exhaust!
There's a guy here in MI that has an 82 Weissach. Now he does have Euro cams which helps a bit, but with his headers, no cats and a borla muffler, his car sound like the biggest baddest sport bike you can imagine. *CRISP* does even begin to describe the note! Very nice. I envy his exhaust!
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05-08-2006, 03:18 PM
#9
Inventor
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Note that only 78 and 79 have the bolt on rear muffler. It would be easy enough to have some of those plates made to make bolt-on RMBs for those cars, I wonder why no vendors have offered it.
It's the unburned gas from less efficient 16V combustion, creating an afterburner effect. 
On mine, one of my favorite sounds is the intake roar (no airbox lid), when I git on it.
I have a 3" single with a Flowmaster 50 and 40, and it's decently quiet just putting along, but once it comes 'on cam', the sound is tremendous, and all drag race challengers I've had give up when they hear it - even though I know some of them should be more powerful than my little 273.
Originally Posted by AJK
...cut off the plate that bolts the muffler to the single exhaust pipe and bend up a tube that will be welded to that plate on one end and to the twin extension on the other end...
Originally Posted by Andrew Olson
It's hard to describe, but the 16V just sound racier
I have a 3" single with a Flowmaster 50 and 40, and it's decently quiet just putting along, but once it comes 'on cam', the sound is tremendous, and all drag race challengers I've had give up when they hear it - even though I know some of them should be more powerful than my little 273.
