What muffler?

[Matt Holcomb]

I think I've got a buyer for my 3", single-outlet Monty. I advertised it because my mechanic once said that the Monty is too restrictive. But people are now telling me that the OEM mufflers are the best for MFI engines -- less back pressure?

I was under the impression that a twin-outlet Dansk -- or even megaphones -- would do the trick.

Can anyone tell me what muffler would be a perfect match for my engine?

For those who don't know, I have a 911/83 engine (RS 2.7; MFI), but with 11.3:1 JE pistons and GE-60 cams.


Matt Holcomb
MFIWDP
PRVC
BOHICA
1974 911 Carrera 2.7 RoW
1974 Ford Falcon GT coupe
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[dd74]

From what I've heard concerning MFI engines, the stock muffler is what should ultimately be used. Anything else could involve idling problems, lack of low-end torque, among other issues.

However, I don't know how that might apply to your engine since it's been so heavily modified (over a stock 2.7 MFI). Maybe you might want to try a stock MFI muffler first, see how things run, and if it seems too restrictive, modify the muffler with a second outlet to see if you get any more power. Or rig up a similar exhaust to those used on 2.8 RSR engines. That might work if your engine has close to the same specs as they.

[Matt Holcomb]

dd74,

Dansk make a replica RSR, twin-outlet muffler. I think I'll give one of those a try, first.

Thanks for the reply.


Matt Holcomb
MFIWDP
PRVC
BOHICA
1974 911 Carrera 2.7 RoW
1974 Ford Falcon GT coupe
Dedicated Homepage
Engine Rebuild Homepage
Porsche Owners Gallery Profile
Pelican Gallery Profile

[911nut]

Originally posted by dd74
From what I've heard concerning MFI engines, the stock muffler is what should ultimately be used. Anything else could involve idling problems, lack of low-end torque, among other issues.

If that were true the factory wouldn't have run megaphones on MFI race engines.
Less backpressure is better, period.
Matt, there are a lot of positive statements posted here on the bb about Monty stuff. I'm sure there are Monty detractors, too.
About the only way to be sure you have a low backpressure muffler is to make your own.

[RoninLB]

I don't take notes on MFI stuff.. but I believe some restriction in the MFI muffler is important.. plenty of guys around here know about this.. and the Monty is less restrictive on a MFI than what's needed.. gotta keep bumping till at least Monday .............Ron

[HawgRyder]

It amazes me how the "old wives tales" live on long after the old wife has died!!
Since when is back pressure good?
Engines run best when the cylinders fill with nice fresh gas/air mix.....not when half the jug is filled with old burned exhaust gases.
But...if you guys insist on cutting down on horsepower and torque for the sake of old wives....far be for me to interfere....LOL
Bob

[pwd72s]

Originally posted by HawgRyder
It amazes me how the "old wives tales" live on long after the old wife has died!!
Since when is back pressure good?
Engines run best when the cylinders fill with nice fresh gas/air mix.....not when half the jug is filled with old burned exhaust gases.
But...if you guys insist on cutting down on horsepower and torque for the sake of old wives....far be for me to interfere....LOL
Bob

Hawg...this old wife is still alive, thanks. And it's true. The MFI is calibrated, tuned if you will, for a certain level of back pressure. Yes, the factory ran open exhausts with MFI on the track...and the MFI on those cars was set up FOR an open exhaust, at considerable cost & time. If you do run an open exhaust on a street tuned MFI car, you WILL develop a flat spot...with me, S cams, S MFI, the flat spot happened at around 4,000 RPM. I went back to a factory muffler, and acceleration improved, as timed with a stopwatch, and the flat spot was gone. This flat spot is more noticible in the smaller displacement engines, 2.4 and lower. I gave the twin pipe sports muffler to a guy who had a carbed 911T...he claimed it helped him, but I don't know if he used a stopwatch, so it may have been the added noise making him think he was faster. Don't know about the current Monte mufflers, but guys with MFI who bought the early ones suddenly had "$750 paperweights" as one guy put it...There was a lengthy string about this on the Early S Registry board, but since the server has changed there, I can't find it now..the theory was that with the S cams high overlap, the less restrictive exhaust somehow upset the fuel/air mix....since 4,000 is near the peak efficiency of the S torque curve, the theory made sense to me...and my stopwatch bore this out. 0-100 was approx. 1/2 second slower with a twin pipe sports muffler, compared to stock..

[HawgRyder]

I still beg to differ....
If you were to put the engine on an engine dyno....and test in the condition as if the beast were still in the car (pipes stock size and length)...you would find it's not the back-pressure that gives the flat spot...but in fact a reduction in scavenging at that RPM.
I concede that it is very subtle...and most ppl do not have access to equipment with a fine enough variance to get it correct...but persistance pays off.
I usually cheat...by looking at what the factory did with their racing engines (they had lots of $$)....
It's a small point really....and it breaks down to what you can afford...and what you like in the way of noise.
This should get a large response....LOL
Bob

[pwd72s]

Originally posted by HawgRyder
I still beg to differ....
If you were to put the engine on an engine dyno....and test in the condition as if the beast were still in the car (pipes stock size and length)...you would find it's not the back-pressure that gives the flat spot...but in fact a reduction in scavenging at that RPM.
I concede that it is very subtle...and most ppl do not have access to equipment with a fine enough variance to get it correct...but persistance pays off.
I usually cheat...by looking at what the factory did with their racing engines (they had lots of $$)....
It's a small point really....and it breaks down to what you can afford...and what you like in the way of noise.
This should get a large response....LOL
Bob

Gawd, are WE both off base Bob...I too, thought this would get a response. Maybe we should insert a pic of a babe in a thong about now..

[RoninLB]

Originally posted by pwd72s
Gawd, are WE both off base Bob...I too, thought this would get a response. Maybe we should insert a pic of a babe in a thong about now..

I got a legal bikini pic.. only a few sprouting hairs.. is it legal around here.. it is funny.. guaranteed to crack everybody up ...........Ron

[KTL]

Since I don't know diddly about MFI.........

Here you go. Tasteful looking San Diego Chargers cheerleader from a wacky football webpage:

[pwd72s]

Uh, legal? In what country or locality? "Community standards". you know....

[Vipergrün]

Matt, how about this one from AJUSA good reviews on the boards and a good price.

http://www.ajusa.com/cgi-bin/inventory/view_product?prod_id=0000000035&part_number=AJR 100 184

They also have one in SS.

[Vipergrün]

Whoops, sorry for posting off topic folks, I thought this was a muffler thread. Obviously I was wrong

[pwd72s]

Originally posted by bb80sc
Whoops, sorry for posting off topic folks, I thought this was a muffler thread. Obviously I was wrong

I clicked on the link...the muffler in the pic sure looks like the one I gave away...and the price listed is the same I got for it...$O.O...seems like a fair price to me.

[RoninLB]

Originally posted by HawgRyder
It amazes me how the "old wives tales" live on long after the old wife has died!!
Since when is back pressure good?
Engines run best when the cylinders fill with nice fresh gas/air mix.....not when half the jug is filled with old burned exhaust gases.
But...if you guys insist on cutting down on horsepower and torque for the sake of old wives....far be for me to interfere....LOL
Bob

OK... I used improper words.. I wrote "restriction in MFI muffler is important".. I should have wrote that a tuned MFI muffler is important.. so sorry for the confusion.. so, not an expert on MFI, but I believe the MFI is a simple system that doesn't have any sense of the air flow thru the induction.. it doesn't know the engine load.. but it does know the pedal position.. so, the MFI is built to the power of a good condition engine.. probably the Monty screwed up the exhaust tuning.. and then again, maybe exhaust tuning the MFI to prevent uneven fuel mixture thru various rpms is an "old wives Tale".. don't know..........Ron

[HawgRyder]

In a perfect world....and I do mean PERFECT...all engines would perform to the top of the chart.
Unfortunately...the world is flat...no wait...wrong subject....I mean the engine is flat...no wait...the engine has flat spots in the torque curve...yeh...that's it.
OK...if the cylinders filled with fresh mixture every time....and the ignition was firing at just the correct micro second every time....and the exhaust was scavenging correctly at every RPM range....then we would all be happy.
In fact none of that really happens....and it's because of those cheerleaders....or something....we have to blame it on something..and it's certainly not our fault.
We slave to keep these little beauties running to the best of our abilities....so now we can blame the darn cheerleaders....
What was the topic again?
Those pictures have rotted my brain....LOL
Bob

[RoninLB]

[QUOTE]Originally posted by Matt Holcomb
[B]
Can anyone tell me what muffler would be a perfect match for my engine?

For those who don't know, I have a 911/83 engine (RS 2.7; MFI), but with 11.3:1 JE pistons and GE-60 cams.


Matt Holcomb


Hey Matt,... don't know the answer.. way over my head.. but when I was eyeballing mufflers,[ before I decided I wanted a Monty, LOL ] I found this shop in California, US that had a big rep with mufflers.. I would contact Pressler Parts and see what Happens .............Ron