2.2S engine - MFI or PMOs?

[hillsprint]

I'm building a car for "light" competition work, it will be fitted with a '71 2.2S engine. The sort of events it will be aimed at, a tractable engine will be more of an advantage than outright power.

What do you think stick with the stock MFI kit or go for PMOs?

[RSBob]

There is no stock MFI for 2.2s only 2.4s, unless you want to have one special-built. You may want to go with PMOs. MFI has better throttle response through the range. PMOs look cool and are more appropriate to your vehicle.

[hillsprint]

Thanks,

Sorry I should have said this is a Euro engine, so it has the MFI system on it. The car is based in Ireland.

The MFI system currently needs set up and there are no experts close to hand. Does the MFI go out of tune through time or once it is set up it stays in tune ?

The thought of PMOs are that they are potentially easier to set-up, there is a lot of local knowledge on Webers etc, and should stay on song for quite a while

Regards

Mike

[daepp]

If there were no 2.2 MFI's, what did the 71 S's have for induction?

[356RS]

Remember, MFI started in 69 for the production 911 E & 911 S.

[curtisaa]

Originally Posted by RSBob

There is no stock MFI for 2.2s only 2.4s, unless you want to have one special-built. You may want to go with PMOs. MFI has better throttle response through the range. PMOs look cool and are more appropriate to your vehicle.

Huh ??

[boba]

Once you get the MFI dialed in it should be rock solid. Follow CMA (lots of documentation on this site) and you should be able to set it up.

I would say my 69E is dialed in (Thanks to Ed Mayo) and I just got back from a 4300mi trip that went from sealevel to over 10,500 ft and it never missed a lick. This included a track day a SOW.

Lots of big grins.

[RWebb]

Originally Posted by RSBob

... MFI has better throttle response [than PMO carbs] through the range.

Is this true?

[boba]

Originally Posted by RSBob
... MFI has better throttle response [than PMO carbs] through the range.

Originally Posted by RWebb

Is this true?

How do you measure that? OH YEAH, seat of pants.

Are yours calibrated?

[zotman72]

Geez it would seem there was a shortfall in someone's understanding of Porsche history with regard to MFI on early street 911s. That said, if your MFI is dialed in and works, keep it. CMA will help it stay that way. When MFI gets out of whack, you will know it. I had my '72 2.4S MFI set right now for two years (thank you John Eisenbud) and it is a pleasure to drive. Carbs can not match it for throttle response, if someone says they do, most likely they have carbs instead of MFI. YMMV

[Zeke]

Originally Posted by RSBob

There is no stock MFI for 2.2s only 2.4s, unless you want to have one special-built. You may want to go with PMOs. MFI has better throttle response through the range. PMOs look cool and are more appropriate to your vehicle.

wrong.

To answer the question, the PMO's (not old Webers) might be the ticket to reliability with performance and an easy setup and tune. MFI is good stuff, but unless it's in great condition, I think a brand new carb would be my choice.

[RWebb]

Originally Posted by zotman72

... Carbs can not match [MFI] for throttle response, if someone says they do, most likely they have carbs instead of MFI.

Ok. But how did you derive your opinion?

Did you drive cars with the same engine displacement AND cam profile back-to-back?

I accept seat of the pants impressions, but would like to know what they are based on.

And, do you think the throttle response is superior throughout the rpm range, as rsbob stated above? Or only at high rpm?

[zotman72]

Fair enough Randy. My experience was ancedotal, on the Pueblo racetrack, side by side one, my 2.4 S MFI and another longnose 911 equipped with a 2.4S weber carbs, coming onto the front straightaway. I pulled away in third starting @ 3.8K and continued on with fourth gear acceleration as well. I was at least three car lenghts ahead when I hit the braking zone. Granted maybe my car was in a better tune but... Nor I do not have the dyno information to support my assertion, just one empirical data point. However there was a reason Porsche went to MFI for racing from carbs too. YMMV

[RWebb]

Thanks - one data point is better than 0.

I wonder if the other car had S cams....

Part of the reason P AG began using MFI was... emissions - according to Frere -- and it makes sense.

re: racing -- emissions wouldn't apply directly as a reason, but if the class rules required the stock fuel system it might then apply indirectly.

I've only driven a MFI'd 911S once - a '73 -- it didn't seem to have magic throttle response, but may not have been set perfectly, who knows.

[GrantG]

I love MFI - that's my vote!

[Flieger]

MFI is better. High injection pressures give better fuel atomization and a better cylinder charge. Injectors close to the chamber give more precise control of the fuel and better throttle response throughout the rev range. Porsche found they picked up both horsepower and fuel economy (depending on driving style) with MFI racecars.

[RWebb]

sure - but how much better?

that's my question. Can you feel the [claimed] difference in throttle response?

Ive heard people go on and on about it but never get anything close to even the most minimal methodology that would be used in a real experiment.

There is also a cost: you've got that big heavy pump slung out there and it's noisy.

[GrantG]

Originally Posted by RWebb

sure - but how much better?

that's my question. Can you feel the [claimed] difference in throttle response?

I've never conducted a controlled experiment, but I have never driven any 911 that feels as responsive to me as the two MFI-equipped 911's I've owned.

I would think there are some good opportunities in Oregon to try a well-tuned MFI car, but if not you're welcome to visit

[304065]

Properly set up MFI delivers 10 hp more than carbs. For that reason it is the only choice for competition.

[zotman72]

Last night I went through my extensive Porsche library John for that exact figure (10 more hp than carbs) but could not find it. Where did you find it? I think it was in reference to the the '72 2.4T engine, US tuned MFI vs ROW carbs. Oh, Randy the injection pump is probably not more than 5 lbs, equal roughly to the extra weight of the carbs over the MFI intake stacks, who knows? On that straightaway incident, my friend's 2.4S engine was a real one that had been converted over to carbs, my S engine was one I built up from my original T with the right S components. Finally Randy we have to get you into an MFI set up 911. Come to Denver next summer when our new track is open, my car would be available for you.