MFI now fitted - muffler recommendations?

[obrut]

Hi all,

Finally had MFI fitted to my RS replica last week. Just starting to tune it now. This is a new 7R cased RS spec-ish 2.7 but with 10.5:1 pistons and GE80 cams (twin plugs installed too but distr set up not finished).

My present exhaust is early 911 heat exchr's with a 2in 1out Monty muffler (3" outlet). The muffler itself appears almost totally hollow.

I recall reading somehere that MFI prefers some back pressure - anyone got any first hand knowledge or recommendations?

Cheers - Ryan

[Steve@Rennsport]

Ryan:

Monty makes a specific muffler for MFI-equipped cars. That's the one you want.

[jluetjen]

Obrut and Steve;
My concern is that you really don't have an "RS" spec motor since you have 10.5:1 CR and GE80 cams. In that regards you almost have more of an RSR then an RS. I wonder if the normal "MFI" style muffler which is designed for S's and RS's may not be any better for the engine then megaphones are for an S, and have similar flat spot issues. My thought is that the classic "Flat spot" caused by sport mufflers or megaphones on a stock MFI car is the result of the exhaust harmonics changing the fuel requirements at a certain rev range. Using a "stock" muffler and 3D cam on an engine which is significantly different from a stock engine will most likely not deliver "stock" results.

What will be the use for your car and engine? What % track and what % street? What spacecam do you have installed in the MFI?

[obrut]

Steve: thanks, i'll check with the monty guys

John: the space cam is 2.7RS and the car is only used for track and tarmac rallies (see www.targa.org.au - IMO one of the best car events in world)

[Matt Holcomb]

Ryan,

My mechanic won't let me use anything other than the factory, 2-in, 1-out muffler ....


Matt Holcomb
MFIWDP
1974 911 Carrera 2.7 (RoW)
Dedicated Homepage
Engine Rebuild Homepage
Pelican Gallery Profile

[Tim Walsh]

Matt,
What does your mechanic (and John G.) think of the factory sport muffler? I've heard they're MFI friendly and with near (or more) 10.0:1 compression I'm thinking about making mine one since it will sound really mean.

[Matt Holcomb]

Tim,

My mechanic (John G.'s son-in-law; John G. passed away last year) thinks that the sport mufflers are too noisy.

Now, I don't mind noise per se, but when he says "noisy", he means that they're illegal for most of Australia's racetracks.


Matt Holcomb
MFIWDP
1974 911 Carrera 2.7 (RoW)
Dedicated Homepage
Engine Rebuild Homepage
Pelican Gallery Profile

[Fishcop]

Ryan, have you thought about a Supertrapp style of muffler... ( I had a couple on my old Ducati), I've seen them on a few cars. By adding and removing spacer discs, the back pressure (and noise) can be adjusted to suit tuning.

Just an idea

[obrut]

John - I've seen a few setups like that, its a definate possibility down the track.

What about a couple of hot dogs?? - they were all the rage on torana's in geraldton in the 70's...

Cheers - Ryan

[campbellcj]

Another couple of options are the Burns / Coast Fabrication "cans'" or the Phase9 setup. Both are reported to get the car well under 100dBA and are lightweight, but I have no personal experience with either.

Most folks seem to agree that the stock 2-in/1-out or modified 2-in/2-out setups (and other "sausage" variations like the Monty) are very tough to beat, though.

I seem to keep coming back to a slightly debaffled 2-in/1-out stock type muffler as being the best overall sound vs performance compromise for most street driven cars. The factory clearly did their homework...