Exhaust selection for MFI engine

[deano]

Hi guys,

During my search for an exhaust for my MFI car, I noticed that some 2-inlet exhausts stated 'not MFI' and some didn't say either way.

What are the differences/requirements please, and how can I tell which exhausts are suitable if it doesn't state wither way?

Thanks and best wishes!!

e.g. https://www.design911.co.uk/fu/pt63_398 ... -Mufflers/

Fits:
Porsche 911 S (mech. injection) 2.4L 08/1971-07/1973
Porsche 911 T/E/S (not mech.injection) 2.0L-2.4L 01/1963-12/1973

Fits:
Porsche 911 2.0L -2.40L 1/63-07/73

Fits:
Porsche 911 2.0-2.4L 01/1963-07/1973
Porsche 914/6 2.0L 11/1969-12/1973

Fits:
Porsche 911 T/E/S 2.0L-2.4L 1964-73
Only to be used with SSI or straight through heat exchanger systems

Fits:
Porsche 911 1965-73 Non Impact Bumper Cars

[Lightweight_911]

.
I think it's just a poor description - they effectively are saying that a particular exhaust fits both mfi & non-mfi models.

I don't know why they have limited mfi models to just the 2.4S model - as far as I know any 2-in 1-out rear silencer is suitable for all 2.0/2.2/2.4 models ...

.

[deano]

I think it might be more than just a listing error, but there seem to differences of opinion. Ultimately, it looks like the MFI's might be a little more sensitive to choice of exhaust than the non-MFI cars. E.g. quick searches reveal:

http://forums.pelicanparts.com/porsche- ... haust.html
https://rennlist.com/forums/911-forum/1 ... works.html (this specifically talks about the space cam on the S being more suited to a Sport exhaust, for example....

[Lightweight_911]

.
Those posts relate to twin-outlet 'sport' exhausts & other aftermarket exhausts - my comments relate to 2-i 1-out rear boxes.

.

[deano]

My query applies to 1,2 and 3 outlet exhausts, including Sport exhaust and non-sport.

Seems to be more than just a description error. I think the description for some exhausts that states 'only to be used with SSI or straight through heat exchanger systems' also suggests that not all exhausts are the same.

The safe bet appears to be a single outlet sausage, like the standard OEM exhaust, but I would like to have something a bit more fancy and most probably with 2 outlets, if compatible with my MFI...

- can anyone explain this apparent sensitivity to exhaust choice on the MFI setup, and need to re-tune, and what to look for, or is it just BS?

Cheers!!

[911hillclimber]

My experiences:
1
2.2 T engine, stock on webers, 2.7 carera manifolds, Liestrict 2 in/3 out
tick over 900 rpm open silencer and same with one outlet, centre ones capped.
2
2.4 mech inj engine, S pistons, E cams 180 bhp.
2.7 Carrera 'ssi' manifolds, Leistrict 2 in/3 out silencer.
Capped centre 2 outlet pipes = road friendly noise, tick-over @ 900 rpm, 23 mpg
Open all 3 outlets (for hillclimbs) and tick over @ 900, sounds fab!
3
3.2 engine, stock but with Bob Watson chip in ECU.
SSI headders, Liescrict 2 in/3 out as above.
With centre two outlets capped, tick over 850 rpm, mellow sound. 28/32 mpg
With all 3 outlets open, tick over rises to 1000 rpm, throttle response much improved, quite noisy, goes much better.

Have ran the 3.2/SSi with a Dansk 2 in/1 out and mellow sound, 850 rpm tick over, but boring, hence still using the 35 year old 2 in/3 out silencer.

3 very different engines all driven on the road/hillclimb competition, very little to choose between them all.

[Lightweight_911]

.

For reference, many years ago, I had a high compression 2.7 mfi engine in one of my cars &, at various times, ran it with (at least) 3 different exhaust set ups :

- SSI heat exchangers + std Leistritz 2-in 1-out silencer

- racing headers + 911R/RSR 2-in 2-out 'silencer' (it didn't actually do much 'silencing' !)

- racing headers + stainless steel 'short' megaphones

I never re-tuned the engine between exhaust swaps but never had any problems* or noticed any significant difference in power output.

* it did backfire on the overrun but that was all part of the fun !!

I'm sure if you compared these three set-ups on a rolling road (with a knowledgeable/experienced operator) that you might find some slight adjustments were ideally needed for maximum efficiency but in my opinion they'd be minor (& the difference would not be noticed to the average driver)

.

[911hillclimber]

Andy, do you know if Leistritz still make air cooled 911 silencers?
Last I searched some years back they didn't but made OEM systems for the big names.

My 2 in/3 out is wearing thin after all these years.

[BILLY BEAN]

.

I'm sure if you compared these three set-ups on a rolling road (with a knowledgeable/experienced operator) that you might find some slight adjustments were ideally needed for maximum efficiency but in my opinion they'd be minor (& the difference would not be noticed to the average driver)

.

Agree with Andy's conclusion.

[Lightweight_911]

Andy, do you know if Leistritz still make air cooled 911 silencers?
Last I searched some years back they didn't but made OEM systems for the big names.

I'm fairly sure that they haven't been making any 911 silencers for many years - hence the high prices for s/h ones in good condition.

The demand has even resulted in a guy on the Early S Registry in the US commissioning a small batch to be accurately copied by a high end exhaust manufacturer in Germany.

.

[911hillclimber]

Thanks, I ask as your searches are deeper than mine!
Mine was 5 years old 30 years ago (Husborne Crawley purchase from somebody) and I've had to patch it once, wont take it again.
G.

[deano]

Thanks guys. I think the conclusion is, stick with an original exhaust or buy a different one and hope for the best (+ take it for a tune-up if it doesn't seem to run as well as it did)....

[911hillclimber]

Or talk to Turbo Thomas...

[deano]

Or talk to Turbo Thomas...

Thanks for the tip - wasn't aware of this company....

[Tp81]

Picked this up late. I have a Turbo Thomas that I need to sell. Two in and one out. Stainless steel unit. Ran it on my car for less than a month. Slightly louder than my original so changed it back and have it sitting if I need to replace mine.