2.2S engine - MFI or PMOs?

[304065]

The RSR used MFI, early "electronic" systems like D-Jet are unsuitable for performance applications.

Any "period" modification throws the door open wide enough to spend about $50K. . .

[jkarolyi]

The ultrarare '83 911SC/RS also had MFI very similar to the old cars...and this was from an era when decent electronic systems (Motronic) were available. No denying the MFI's prowess on the race track for many, many years.

[Grady Clay]

Michael (Pelican hillsprint),
First, WELCOME to the Forum.
You will find a lot of help here.

Yes, YOU can make your MFI work perfectly well for your intended purpose.
Just like everything else in a competition car, you want it working perfectly.

Since perfect idle and emissions at idle are not usually most important with a racer, the condition (wear) of the throttle bodies is not paramount. Worn throttle bodies are the bane of getting most otherwise OK Mechanical Fuel injection systems to function perfectly.

There are two distinctly different directions for you to consider: using what you have (2.2S original MFI) and the ideal (most competitive – cost secondary) systems legal for “pre-1975” rule.

This second choice might include a ’74 Carrera RSR 3.0 engine type 911/75. It came with MFI but the racing version for use with 910 cams and has slide-valve throttles rather than butterfly type. In stock (endurance racing) form, these were 320 hp @ 8000 rpm. With some ‘tweeking’ more power is there. This is very spectacular performance in a lightweight (sub-2000#) 911. The only problem is the cost would make a dent in the National Debt – if you could source the parts.

Your 2.2S MFI can be the basis for almost as spectacular performance and to most eyes appear original and unmolested. Your MFI, fan shroud, tin and most else will easily fit on any pre-’75 911 engine. If you aren’t limited by displacement, you can build a 74.4 x 102 mm engine (3648 cc) that looks similar to your 2195 cc engine. Of course you can change from your 9.8:1 CR to above 10.5:1. Twin ignition helps and can be not obvious to the casual observer. Your MFI can be made to accommodate an engine of this size. This is a suitable choice if you can have an engine that “appears original” within the rules.

In stock, original form, your 2.2S MFI is a pretty potent engine with 180 hp @ 6500. Depending on the rules it can be ‘improved’ noticeably. Even today, I wouldn’t hesitate to take a well prepared 2.2S, drive from Denver to Daytona and race 24 hours. Baring a crash, I would expect to drive home.

I agree that the MFI adds 10 hp, maybe more. I can tell first-hand back-to-back that MFI has better throttle response than carburetors – particularly in extreme situations like sudden (almost instantaneous) throttle opening.

The difficulty quantifying ‘throttle response’ is it is a transient, time-dependent phenomium. I’m sure that we could quantify it for our almost 40-year old MFI if we had access to the current instrumentation at Weissach.


Any of these engines YOU can build DIY. This Forum can help. There are vendors that can perform all the operations you may need to out-source. Everything you are considering has been done before. Learn from others success and don’t repeat their mistakes.

Best,
Grady

[Flieger]

Mein Lieblingsmotor:

2,5 liter (90mm bore Nickasil cylinders x 66mm stroke crankshaft)

MFI with low injectors, Magnesium intake runners, and velocity trumpets. (make sure your closed-throttle fuel shutoff relay,solonoid,and microswitch work for best throttle response during engine-braking)

911 transaxle 7:31 final drive ratio, Airport 1-5 ratios

twin-ignition

high compression ratio

ported + polished heads with high rpm valvetrain components

These are nice, also: