POLL: Carbs or MFI?

[X-Faktory]

I bought it as a roller, engine out, tranny out, but numbers matching. It came without the intake/MFI bits and I expect that was due to the infamous cold-start/fire starter system. During the resto process, I searched long and hard to find the correct parts and rebuild them for this 71E................ This is my 1st MFI....I like it!

[HughH]

Mine is MFI from new but for the last 12 years or so has the RS space cam to go with the 2.7 barrels and pistons and E cams

I echo the need to have someone who really knows the system to look after it properly (thankfully I have - thanks Mike) but when it is working well it is fantastic.

Another thing that gets overlooked (but shouldn't be if you read check-measure-adjust) is that ALL the parts of the system need to be in good order to get the best out of MFI.

I recently noticed the difference when I had my throttle bodies redone and taken out to S spec. It turned out that there were small air leaks on the face of the throttle bodies where they meet the engine as well as the usual wear in the butterflies etc and a couple of clogged air holes. I knew that we had to do the throttle bodies because it was hard to get the engine to idle smoothly and we had to set the MFI richer than optimal to counter the airleaks - I just did not realize how much effect that the worn throttle bodies were having.

The difference when the engine was put back together is amazing - it will idle smoothly down to below 500rpm (although it is now set above that) and is extremely responsive and smooth in power delivery from there right up to 7300 redline. I cant remember any other maintenance fix (including rebuilding the MFI pump) that has produced such a marked change in the responsiveness and smoothness of running. My mechanic says it is now so smooth that it feels like EFI instead of MFI!

[Allen Henderson]

MFI IS a great system when the major elements are working right and not worn. IMHO, a lot of pumps have been rebuilt unnecessarily when what was really needed was to rebuild the throttle bodies which do wear for sure. That is not to say if you are going from 2.4 to 2.7 you don't need a new space cam..you do. My '72 had about 77k miles and the throttle bodies were worn. Back then I had Eurometrix, which at that time was located in Campbell CA, rebuild my throttle bodies. Engine ran great and back then, our cars had to pass tough California emissions and mine did...however it did need some tweeking to get it in spec.
A challenge to ANY MFI system rebuild is a. cost and b. the fact that it needs to be matched to the engine can't easily, like Webers for example, be modified to match a hotrod engine. High butteflies and Slide-valves on the other hand are, also, totally cool but best suited for race-type engines. Not to mention, expensive! All this IMHO. Thanks.

-Allen-

[edmayo]

Rick, I have two 72 S's both with MFI, only way to fly!!

[TEC69E]

Well, I always seem to find myself in the minority camp and this time will be no different. The first motor I built was my hot rod 2.5 with PMO's. And having never dialed in a porsche engine of any sorts before I felt PMO's were going to be the best choice for a newbie. And they have proven to be the best choice in my opinion. Once I worked through the normal tuning issues . . . fuel pressure, float bowl fuel level, idle jets, main jets, venturis . . . I love them. I know exactly how to tune them based on the results I want to get. Bigger mains and venturis and the motor pulls like a freight train all the way to the rev-limiter . . . or step down a size on both and it's the best daily driver a guy could ask for. And all this can all be done by me (a rookie, backyard mechanic) in a matter of a couple hours with predictable results. BTW, I also just completed a 2.7 RS spec. build with MFI . . . and yeah, MFI is a different beast. But for now (at least until the MFI is dial in) for the thrill of driving . . . I prefer the 2.5 with carbs.

[fryardds]

MFI

From back in the day (circa mid 70's) and currently.

[fryardds]

And on the other steed brought to you by Matt Blast and Gus.

[BBausser]

Nothing wrong with PMO's

[kh911]

My '73 911S still has it's MFI. The injection pump was 'refreshed' by Gus @ Pacific back in the '90s.

[boba]

I just love the MFI on these cars. As has been stated they have to be well set up. Once they are, they are bulletproof. Great fun to drive. I am fortunate to have one of the best at setting these up nearby, Ed Mayo.

First a stock '69 E 2.0
...and a not so stock 3.2ss in a '72 T tub.