MFI or Webers?

[davidbir]

As I am in the very early stages of planning a RS replica I thought now is the time to ask the experts: How big a difference in 'driving feel' is there between MFI and Webers on a 2.7?

[leadrsa729]

I have a 72' S motor that I put carbs on instead of modifying the MFI as well to match. I am kicking myself because of it. I will definitely be putting the MFI back on someday.

[Steve@Rennsport]

Both can be made to work VERY well but MFI will cost more.

[RWebb]

looks like it doesn't have to be a perfect replica or you would not consider carbs...

you are in a rel. cold area - do you drive much at altitude also?

MFI has altitude compensation & cold start injection...

someone hunted down some factory info & posted it somewhere here re a few more ponies from MFI

BUT, besides cost, MFI puts more wt. on the rear of the car -- that pump was designed for diesel tractors -- it is a heavy chunk of steel

many people will tell you that MFI has a magic feel* to it - but in every case where I've inquired of an owner, the feel cannot be distinguished from placebo effect

* often seems to be related to throttle response

I think it is interesting that Steve does not come out and say that MFI has much better throttle response than carbs...

[davidbir]

Thanks for the responses. As I said in my other post, I am looking for the RS driving experience-if Webers will provide that then that may be the way to go-cheaper and as RWebb points out, lighter.

Perhaps Steve at Rennsport or Dave at TRE or John Walker or....can offer more advice/opinion?

[BURN-BROS]

The weight difference really isn't that much. The entire system will add aprox. 5 to 7 pounds over a set of carbs.

As far as throttle response, carbs can have great throttle response but only with a mild set of cams. MFI does not require manifold vacuum like carbs, so throttle response is great.

A Mod-Solex 2.7 is also a great driving experience.

[lateapex911]

Whats a "A Mod Solex"?

I have a 2.7 with PMOs and a Solex cam, SSI. etc.

I WISH I had the fortitude, (And the cash at the time) to go MFI when I did my rebuild. (My MFI needed conversion/setting up for my new larger engine, when I was dealing with a broken 2.4., it was $$$). MFI has come along way recently, as there is much less of a 'black magic' to it, and sources and information have become much more readily available. 10 years ago, that wasn't the case.

If I were doing it again, and had the $$, I'd go MFI.

That might be more of a romantic answer though.

[BURN-BROS]

Originally Posted by lateapex911

Whats a "A Mod Solex"?

I have a 2.7 with PMOs and a Solex cam, SSI. etc.

I WISH I had the fortitude, (And the cash at the time) to go MFI when I did my rebuild. (My MFI needed conversion/setting up for my new larger engine, when I was dealing with a broken 2.4., it was $$$). MFI has come along way recently, as there is much less of a 'black magic' to it, and sources and information have become much more readily available. 10 years ago, that wasn't the case.

If I were doing it again, and had the $$, I'd go MFI.

That might be more of a romantic answer though.

A Mod Solex refers to the Cams. A Mod Solex has a lobe center of 102 deg. instead of the factory 97deg(IIRC). This bumps low rpm torque and also gives you a better top end.

Other than the lack of MFI, how do you like it? Would you step up to S cams or????

[RWebb]

re wt. diff.

the pump itself is North of 16 lbs.

plastic manifold are light but are a fire hazard - I'd use Mg ones and powdercoat black if I were doing it

also I assume a multi-kilobuck Motec EFI setup is out of the question?
- that can give you a lot MORE than the RS driving experience...

[lateapex911]

How do I like it. It's a long sad saga, and my racing has back bunered it endlessly.

In short, when my mech/builder finished it, I was out of $. So he sold me a set of Webers cheap, and when I picked it up, it just didn't run right. Popping backfing, etc. He tuned and changed jets, etc for a couple hours, and it got better ways, but wasn't right.

It seemed like fine tuning, so I brought it home, and kept at it. Still, I never got it right, and eventually decided that the shafts must be leaking, etc, and just bought PMOs.

Which did the exact same thing, LOL. I've checked for vacuum leaks etc, etc a million times, been though the ignition system, replaced it in it's entirety, and so on.

Still - does - it.

I've become convinced that I'm going to have to look deeper. I started a thread a bit ago on the subject and there were a couple of "Sounds like the cams aren't timed right" comments.

So, as soon as my racing shop work gets caught up, I'll dive into that.

Sorry for the long, and no commital answer! It runs well when it's floored over 4K to 7K. How's that?

[RoninLB]

my carbs are set up as good as it gets with zero issues and max available power

if time ever comes for a 3.4 it's going to have MFI

[Tom '74 911]

There are some interesting opinions from those who went down the carb route regarding their desire to use MFI for the next go around. Why? Is it performance, mystique?

I've always assumed that carbs would be a bad choice for me as I live at altitude and drive from 4000' to 8000' - am I correct in that assumption? I have recently zeroed in on comments from some who have had their carbs set up by a pro (like Steve W.) and their cars run fantastically well. I could never get my carb'ed KTM 300 EXC 2-stroke dirt bike to run great everywhere, all the time out here - does the same hold true for a 2.7 w/PMOs?

[zotman72]

I live at alititude. My 2.4 MFI S rocks but then I have local mechanic who is a MFI wizard. Several of my vintage racing buds have carbs on their 2.2S engines and they are constantly futzing with them. I recently raced with PCA here in at our new track, nobody could pull me in my class (alright they had CIS ) on the straights as my engine response out of the turns was so good-- in the turns well that was a different story (skinny tires!). I love my MFI and would not ever consider running carbs on my engine. When MFI runs right, it is amazing. YMMV

[RoninLB]

[QUOTE=Tom '74 911;4907046]

regarding their desire to use MFI for the next go around. Why? Is it performance, mystique?
---------- MFI throttle performance response. Carbs & cam package have a much smaller response window. Max power don't matter except for fuel/air ratio. It don't matter how it gets there.

I've always assumed that carbs would be a bad choice for me as I live at altitude and drive from 4000' to 8000' - am I correct in that assumption?
------------- I'd avoid carbs. CIS is better that I expected at altitude or better said changing altitudes.


above only my non pro experience

[RoninLB]

Originally Posted by zotman72

When MFI runs right, it is amazing.

same take from my limited experience