Quote:
Originally Posted by Flieger
Displacement is not the most important factor in pump tuning. The horsepower determines how much fuel and air is needed to be combusted. 2.5 short stroke motors are often found in racecars making more horsepower than a 2.7RS spec. They are stressed more and use high compression, of course.
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I do not think the pump's delivery is correlated to HP directly or very much.
It is correlated directly to air flow per stroke and thus is more correlated to displacement and thus bassicaly to Torque.
Mess with air flow per stroke and you mess with the the pumps ability to fit a motor.
Thus, it should be easyer to adapt a T pump to an E cam that makes almost the same TQ but dose so higher in the RPM range than is would be to adapt it to a 2.7. Stretching it to a 2.5 where the peak TQ stays close to the same point in the RPM range would probably be the easyest of the possable builds in referance to the using the existing pump.
A "T" pump can maintain balanced AFR's at idle and up to a peak TQ of up to about 150# of TQ.
The difference between the high and low spots on he space cam determine the range of TQ it supports. A 2.7RS space cam is cut into deeper than a T cam as it needs to deliver enought fuel to support fueling at idle and up to 200# of gross TQ. Thus, the RS cam supplys about 33% more fuel at peak TQ and the space cam is cut about 33% deeper to achive this.
If you try to readjust a T pump it to support a 2.7 that makes 170# of TQ compared to 148# for a stock 2.4T the bottom is probably going to end up very fat. Adjusting the rack dose not increase fueling as a percentage. It gets increased in the gross amount along the hole range.
That is, if you need to increase fuel delivery to support 20 more # of TQ at at WOT it is gong to deliver enough fuel for another 20# at idle. This could end up being a 50% increase in fuel at idle. Some of this can be adjusted around to a small degree using the link to the pump and with the air bypass screws but probably not that much.
The centrifugal weights determine at what RPM the max fuel is delivered.
The shape of the space cam then sort of fine tunes the deliver to fit the shape of the TQ curve.
It is probably easer to support building a motor that makes more TQ at a different rpm (more HP) than more gross TQ if it is signifficant. Thus if one wanted to use a T pump on an E or S build it might ge doable by tightening up the springs on the weights in the pump to delay peak fueling to the later peak TQ point. However, the shape of an S space cam is a lot different than a T's so there will probably be points along the curve where things are off some.
The pump dose not care about increases in TQ from better timing and higher compression. Thus, 2.4T motor set at 10/1 with twin plugs would probably be able to use a fresh T pump quite with out compensation even thought the motor is making 10% more TQ.
At least this is what I belive so far.