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

I think lightened flyweights and different control springs also help extend the speed range of the space cam, but just speculation on my part.

Lighter weights, stronger springs, or tightening the springs slows the rate the sensing stylist moves across the space cam side to side.

If the operating range of a motor is say 6800 rpm with TQ peak at say 4500rpm the weights are heavy and or the effective spring rate light so the space cam can move to the end of its rpm range by 6800rpm.

If the operating range is 8000rpm, the weights are lighter and the effective spring rate higher so the space cam moves along its range slower.

No amount of change in springs or weights will expand the range of TQ levels it will support. That is done by how deep the space cam is carved. (Or by adding larger plungers.)

Stock MFI pumps can be adjusted with the existing weights and springs for up to around 7300 rpm or so.

The stylist reaches the lowest part of the space cam at TQ peak which is where it supplies the most fuel per stroke.

Move where the TQ peak is going to be and the advancement rate will probably need to be adjusted.

Thus, if one uses a T pump and TQ peak unboosted is close to stock the stock space cam and settings should remaing the same.

The LDA would add the extra fuel that is needed in support of the increase in VE that comes with boost. Off boost drive-ability would remain as stock.

In some ways it will be easier to get the MFI pump to work well and maintain part throttle drive-ability on a motor with stock cam & displacement that is turbocharged, assuming the addition of an LDA, than it would be if the motor was to remain normally aspirated and see a bump in displacement as that would increases gross total TQ expected and require a different space cam.
Old 01-12-2010, 09:08 PM
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