[obrut]

I've been chasing a flat spot in my MFI 2.7 RSR-ish spec engine for some time now. Yesterday we pulled the stock 2-in 1-out muffler off a 2.4T that I recently acquired (BISHOF ?? brand, 911 part no.) and put it on the race car.

The car had a BAD 3000-4000 rpm flat spot which made it impossible to use full throttle in this range (ie. headbutt the steering wheel bad). Now you can snap it open at 3000 rpm in 3rd and it pulls smoothly to redline. It still has a little hesitation at full throttle around 2000 rpm but i put that down to the GE-80 cams. I'm at the track next weekend and will then know if the top end is affected - I suspect it won't from how the car now drives generally.

Just goes to show you shouldn't mess with the original set up too much - particularly with MFI.

We then bolted the 2-in, 1 HUGE outlet sport muffler onto the CIS 2.4T engine - fantastic. Nice raspy note, no flat spotting and it feels like a few more hp.

I am now convinced that MFI engines need back pressure (whereas low comp CIS motors don't).

All in all a great days work.