Low boost question... pulley size to boost calc
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Joined: Nov 2001
Posts: 3,048
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From: Raleigh, NC
Low boost question... pulley size to boost calc One of the guys a question that might be of interest to someone else. He is seeing only 3 1/2 to 4 PSI of boost with a 3.40" pulley. I don't know what elevation his locale is. Perhaps someone else could speculate how the boost level might vary... does anyone here know how to compute a good constant from a known boost and pulley size as I describe here?
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I'd say if you see only 3.5 - 4.0 PSI of boost with the 3.40 pulley, you definitely need the 3.20" pulley.
I don't truly know what the difference would be.
But, going from the 4.10" to the 3.20" doubled my boost (from ~6 PSI to ~12 PSI) and the difference between the two is 0.90". The difference between the 3.40" and the 3.20" pulley is only 0.20".
I guessed (from a proportionate perspective) the 3.40" pulley may have taken me to a little more than 10.5 PSI from the 12 PSI if I'd traded back up.
Instead of ordering yet another pulley (the 3.40"), my solution was to add MAC headers/Y-pipe/cats to lower my boost from 12. It did drop to about 9.5 to 10.0 PSI when I did this.
Using the same proportions, I would guess you might gain maybe 1 to 1.5 PSI of boost by going from the 3.40 to the 3.20 pulley. I could be completely wrong.
What I would really do, if I were you, is tighten the belt more. I have lost up to 2 and 3 PSI by my belt being looser than the tightness where I'd originally found max boost. Tighten it to where you can just twist it between your thumb and forefinger. It won't hurt to do this for a test run. If your boost jumps up, volia! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> , you're fixed! I would then loosen it by one turn until I see it start to drop again.
Try tightening the belt more first.
Let me know what happens... <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
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I'd say if you see only 3.5 - 4.0 PSI of boost with the 3.40 pulley, you definitely need the 3.20" pulley.
I don't truly know what the difference would be.
But, going from the 4.10" to the 3.20" doubled my boost (from ~6 PSI to ~12 PSI) and the difference between the two is 0.90". The difference between the 3.40" and the 3.20" pulley is only 0.20".
I guessed (from a proportionate perspective) the 3.40" pulley may have taken me to a little more than 10.5 PSI from the 12 PSI if I'd traded back up.
Instead of ordering yet another pulley (the 3.40"), my solution was to add MAC headers/Y-pipe/cats to lower my boost from 12. It did drop to about 9.5 to 10.0 PSI when I did this.
Using the same proportions, I would guess you might gain maybe 1 to 1.5 PSI of boost by going from the 3.40 to the 3.20 pulley. I could be completely wrong.
What I would really do, if I were you, is tighten the belt more. I have lost up to 2 and 3 PSI by my belt being looser than the tightness where I'd originally found max boost. Tighten it to where you can just twist it between your thumb and forefinger. It won't hurt to do this for a test run. If your boost jumps up, volia! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> , you're fixed! I would then loosen it by one turn until I see it start to drop again.
Try tightening the belt more first.
Let me know what happens... <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
TECH Apprentice
Joined: Nov 2001
Posts: 301
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From: Woodlyn, PA
Re: Low boost question... pulley size to boost calc I have a P1SC and register 5 PSI with headers, cutout, irreguardless of cats. I have 3.4" pulley. I plan on going down soon to the 3.2" as well, for hopefully 7-8 psi.
One thing I can think of: if you keep your plumbing as short as possible you will register more boost and response.
Aparently there are big diferences between the P1SC and D1SC.
One thing I can think of: if you keep your plumbing as short as possible you will register more boost and response.
Aparently there are big diferences between the P1SC and D1SC.
9 Second Club
Joined: Nov 2001
Posts: 1,445
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From: Bay Area, CA
Re: Low boost question... pulley size to boost calc </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Rock:
<strong>I have a P1SC and register 5 PSI with headers, cutout, irreguardless of cats. I have 3.4" pulley. I plan on going down soon to the 3.2" as well, for hopefully 7-8 psi.
One thing I can think of: if you keep your plumbing as short as possible you will register more boost and response.
Aparently there are big diferences between the P1SC and D1SC.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">100 cfm.
<strong>I have a P1SC and register 5 PSI with headers, cutout, irreguardless of cats. I have 3.4" pulley. I plan on going down soon to the 3.2" as well, for hopefully 7-8 psi.
One thing I can think of: if you keep your plumbing as short as possible you will register more boost and response.
Aparently there are big diferences between the P1SC and D1SC.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">100 cfm.
