MFI: Switching between stock and sports muffler

[Haasman]

I am sure technically one should always re-adjust the MFI, but how important is it? If say I wanted to run the sports 2-outlet muffler for several hours of driving?

[Chuck Miller]

No definite answer Haasmen, all depends on your particular set up….

My experience was the two times I bought and installed sport mufflers on my stock 2.4S I needed to richen the main rack about 2 clicks to try to make it run smoother on the bottom. Neither sport mufflers ran perfectly smooth on the bottom and mid-range, but both gave me a little more on the top end. These were both single exits; one a AJ sport, the other a Monty stainless MFI… both sounded great, both ran slightly better on the top, both took away my bottom and midrange, both were sold….

Never tried a two exit sport (although I figure it would be about the same) and never tried a sport muffler on my 2.7RS rebuild.

Hope this helps

[Haasman]

Thanks Chuck. I am sure the sports muffler has a bit less back pressure but not experienced enough to make the call. I do find it interesting that some cars run the "3 pipe" mufflers with the ability to remove 2 caps (sports) or leave 'em on and let the exhaust exit out the traditional way on the left.

I wouldn't want to burn any valves etc. Thought since it is about at max and hour job, R&R it might be a fun way to go.

[Kris Clewell]

slight hijack....How does CIS take the same situation since it doesnt have an o2 sensor? time to bust out the allen tool?

[Rick Cabell]

I have experimented with many differant mufflers over the years on 69-73 MFI cars. The results have been that the cars run best with a stock muffler.

[Haasman]

Rick, I agree. The stock muffler is the best all around way to go .... but that sports muffler just sounds great!

[69Sman]

I have experimented with many differant mufflers over the years on 69-73 MFI cars. The results have been that the cars run best with a stock muffler.

Never found ANY sport muffler to have much sport in it. A toltal misnomer.

[Chuck Miller]

I have experimented with many differant mufflers over the years on 69-73 MFI cars. The results have been that the cars run best with a stock muffler.

Amen to'dat bruda.....

[mobius911]

Check out this thread at Pelican. Some good explanations on why a car may experience a flat spot, but various people reported different results.

[Mr9146]

Ray Crawford did a number of dyno tests with various mufflers available on the market a few years ago. The Leistritz single-out sport muffler produced the best results. Do a search and you will find the thread.

Additionally, it's been my experience that carbureted cars are far more "elastic" in their response to muffler changes. They can be tuned for the "sport" portion of the sport muffler and I have seen a few instances on the dyno where there was an actual increase in performance. However, it's not like you're going to see 10 or 15 hp ... we saw MAYBE 5hp from the muffler swap and tuning.

Stock = Awesome

Porsche tends to get it pretty right the first time. They have a bit more $$$$$$$$$$$ for the R&D.