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Mechanical Fuel Injection Pump for Early Porsches

The Mechanical Fuel Injection set up on early Porsches was allegedly derived from the need to fly upside down. In the Second World War aerial combat developed into serious forms of aerobatics and there was an advantage to be had by those pilots who could manage their throttle and therefore acceleration, irrespective of the position of the plane. Traditional carburetion was inadequate as carburettors rely on gravity to keep the float chambers filled. Trust the German engineering cadre to come up with a solution. Their Messerschmidt aircraft could pull negative G’s thanks to this technology and the British Spitfires could not follow their trail without stalling their carburetted engines.

The constant fuel pressure combined with excellent fuel atomization, leading to a maximum fuel burn ratio in gasoline engines, had Mercedes, Porsche and later BMW, apply this expensive and complex technology on their race and production cars. MFI was overtaken by Electronic Fuel Injection only 20 years after it showed up on cars, but remained the system of choice for race cars for a decade more. The reliability of the mechanical plunger system versus the relative lack of experience with EFI, saw this sytem used even on turbo charged Porsche 935’s.

Entering the Slotemaker curve to the left, the carburetted 3.0 liter engine just dies due to the lateral G forces

When we ran Woodstock through the Slotemaker curve at Zandvoort it lost power, simply because the G forces at around 100 mph in this left hand kink drained the float bowls and all we could do was wait for gravity to kick back in and allow fuel to pass back into the carburettor channels.

Of course there are modifications available which largely counter this effect, but we decided that it was enough.  Having driven my 2.4E through the same curves with no no problem, MFI was the way forward to us, particularly as we feel that the MFI engines just pick up better.

To many Porsche enthousiasts the MFI system is tantamount to high expenses and great complexity. PMO carburettors have become a popular alternative on engines which were originally designed to run on MFI. However, we should explore the reasons why. It has been due to lack of parts and know how on repairs and adjustment that MFI has lost its luster. The system itself remains superb on any classic 911 performance engine for street or track and the throttle response is just unparalled as you could have heard in the brief video in my previous post.

We now have access to all of the know how and parts required to run an MFI engine reliably.  We have found out that any early Porsche/Bosch pump can be converted to any spec, as long as you have the right parts; which we do. So the myth of only being able to convert 2.2 pumps to high performance spec is dead. For more information on these repairs and conversions you should feel free to write to us at info@twinsparkracing.com.