Thread: MFI in a 930
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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Originally Posted by jcge View Post

Rack movement vs fuel delivery - this is from test plan data for the normally aspirated R3, R3Y & R3Z pumps with 6mm plunger.

Assuming you need to get to 65cc/500 strokes (this figure was posted by Bernie Buschen on his 935 pbase gallery) = 130cc/1000 strokes, you'd probable need to look at a 7mm piston (1.36 times the area of the 6mm piston) to not "overextend" the rack.

You can tell plunger size externally from the ID plate on the pump

PED6KL60... = 6.0mm
PED6KL70... = 7.0mm
PED6KL75... = 7.5mm...

Changing the pistons is a new concept for me and very interesting.

I have taken an MFI pump apart maybe 30 or more times to grind on the space cam for a 2.8 I built.

If a stock MFI pump dose use a 6mm and we move up to a 7mm it might be a good start for a 930 motor.

For example. If we start with a 2.4 pump, increase the piston 1.36 times this sould support a 3.26 which is very close to our 930 motors in displacement.

My thinking is we might be able to use the existing space cams to maintain drive ability.

I think a T pump should support a flatter TQ curve and might fit our purpose. One might be able to use the T, E, or S pump by playing with the spring tensions.

I had a 2.4T, S, and RS cam. The S cam looked very peaky. That is there was not much increase in fuel until the higher RPM. The RS was between the two except it was carved deeper for more fuel.

I found I could tune my space cam a bit by marking it with a felt tip pin, driving the motor in the rpm range I wanted to effect and pull the pump down to see where the stylist road on the space cam. Then grind that area for more fuel.
Old 01-13-2010, 07:54 AM
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