why does pulley size relate to boost different from one car to the next?
why does pulley size relate to boost different from one car to the next? I don't get it, I thought that the more free flowing system you have the less boost you would make. So when I got my procharger I got the pulley that should be good for 9psi on a stock engine. I figured I would make less boost because I have a very free flowing setup and a large cam with a good amount of overlap. It ended up boosting to 12psi at 5700rpm and was still going up. It was the 4.13 pulley. There are guys on here making less boost than me with even smaller pulleys? I ended up switching to a 4.25 pulley to hopefully stay under 12psi. It will be nice to be able to easily make more boost when the block is built for it but for right now I need to stay on the lower side. Does anyone have any ideas on why my car would have made so much boost on only a 4.13? It probly would have made it to around 14psi by 6500rpm maybe even more. Did I just have the wrong pulley or is that more boost than normal for this size pulley?
Originally Posted by 02NBMFormula
i believe that boost is referenced at 9lbs at 6000rpm, if you spin it up higher, it will make more boost
Quick break down of my car: fast 90mm intake, nick williams 90mm tb, qtp 1 3/4" long tubes, true duals 3" to the X and then 2 1/2" out the back with no cats and straight through mufflers, lq4 untouched truck heads with dual valve springs, 232/234 .598/.598 on 112lsa cam and I'm not sure if gears matter but they are 4.11s. Then the supercharger is a D1-SC with 3" pipe to the large front mount intercooler then 3 1/2" to the tb.
Last edited by rufretic; May 23, 2007 at 11:19 AM.
yeah that doesnt make sense at all. from what ive read (been researching prochargers for a little while, should get one this summer) good exhaust (which you have), lower comp heads (also that you have) should lower boost. im sure that someone from epp will chime in with the magic answer
First off most boost gauges arent very accurate, second altitude has a lot to do with how much boost you will see, third the number of bends and IC piping also makes a difference. I am pretty much within 1psi of what I saw (same pulleys) with 10:1 compression, Z06 cam, hooker cat back and stock valves/heads as I am now with 9.2:1 compression 230/240 115 cam, 4" straight through exhaust and AFR 225 heads but I'm running 14mph faster in the 1/4 - dont always believe what you read 
What size crank pulley do you have?
What size crank pulley do you have?
Originally Posted by kp
First off most boost gauges arent very accurate, second altitude has a lot to do with how much boost you will see, third the number of bends and IC piping also makes a difference. I am pretty much within 1psi of what I saw (same pulleys) with 10:1 compression, Z06 cam, hooker cat back and stock valves/heads as I am now with 9.2:1 compression 230/240 115 cam, 4" straight through exhaust and AFR 225 heads but I'm running 14mph faster in the 1/4 - dont always believe what you read
What size crank pulley do you have?
What size crank pulley do you have?
One other thing I thought of was the air filter going into the procharger is very free flowing and I could see how that would add more boost than the stock procharger setup. It's just a 4" 90 to a large air filter.
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^^There is your answer^^ the stock supplied ATI hat and filter are pretty restrictive. I pick up 3psi, and 90 rwhp with mine off. I'll bet if you put the stock hat and filter on, you'd see 2~3 psi less.
But you are correct, the freeer flowing heads, intake, and exhaust should make less boost than the stock ones...
But you are correct, the freeer flowing heads, intake, and exhaust should make less boost than the stock ones...
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Verdad Gallardo One day I'm going to figure out how people pick up 3psi by taking the inlet off because I sure dont. I dont pick up a thing, not even with the F1A..
I think the ATI is a 7.625 crank pulley, that sure seems like a lot of boost with a 4.13 pulley on a D1SC. I see 15psi with a 7.25/3.7 at 7000rpm which is 59K impeller with the inlet hat on or off, you are seeing the same boost with a 7.625/4.13 @ 6500rpm which is 49K impeller speed. Doesnt really make a lot of sense but just try the 4.25 and work up - better safe then sorry..
I think the ATI is a 7.625 crank pulley, that sure seems like a lot of boost with a 4.13 pulley on a D1SC. I see 15psi with a 7.25/3.7 at 7000rpm which is 59K impeller with the inlet hat on or off, you are seeing the same boost with a 7.625/4.13 @ 6500rpm which is 49K impeller speed. Doesnt really make a lot of sense but just try the 4.25 and work up - better safe then sorry..
