Pulley size and resulting boost

[Race Grandpa]

Dumb question:

As the pulley gets larger the boost gets higher.

However, in my way of thinking the smaller the pulley the shorter the pulley belt SO would not a shorter belt, which has less distance to travel (vs belt for larger pulley) create a higher RPM?


:stupid:

[bambam]

bigger pulley and you get more boost. How many lbs of boost you running now grandpa? 10 ?

Buck

[pumpkin]

The belt length has nothing to do with the drive ratio.
Example: You could have a 4" on the crank and a 2" on the SC, or reverse them and put a 4" on the SC and a 2" on the crank. Belt length would be the same, but the SC driven speed would be totally different.
JD

[Race Grandpa]

bigger pulley and you get more boost. How many lbs of boost you running now grandpa? 10 ?

Buck

Just got the SC installed and putting it on the dyno on Tuesday. Will post my results on Wednesday.

If the Autometer Boost gauge is fairly accurate, It should be slighty over 11.

[Tom @ Fast Forward]

If you divide the crank pulley (110) by the SC Pulley (65) you will get the ratio. For example:

Crank = 110
SC = 65
Ratio = 110/65 = 1.774

Engine RPM x RATIO = SC Speed.

7000 x 1.774 = 12,418 RPM SC speed

[Race Grandpa]

Tom,

Thank goodness that this calculation only requires division.

This has given me the confidence to work on other forumlas that determine belt load, etc.

My objective is to learn as much as you have forgotten.


Curious, what are the maximum size of pulleys that one could go to without causing some problems. And what might those problems be. (Working on Tom's take home test.)

[Tom @ Fast Forward]

Paul,

You have it all wrong. It is not the pulley size that causes problems, it is the belt size. As long as the belt is too long to spin the supercharger, you will not have any problems (or power). It is only when the belt fits properly that problems begin. ;-)

As soon as I get back I will check my FAX to see if the notorized permission slip is there to allow you to purchase a larger pulley. ;)

[pat conlon]

If you divide the crank pulley (110) by the SC Pulley (65) you will get the ratio. For example:

Crank = 110
SC = 65
Ratio = 110/65 = 1.774

Engine RPM x RATIO = SC Speed.

7000 x 1.774 = 12,418 RPM SC speed

Hey Amigo, check the batteries in your calculator.
110/65=1.692(7000) = 11,846rpm

[pumpkin]

Good catch. Looks like Tom was thinking of a 115mm.
jd

[Tom @ Fast Forward]

Da@##$%^m PDA! Even 115 doesn't come out right. Guess that is the penalty for doing it on a PDA while driving and posting here at the same time. Next time I'll pull over to the side of the road. ;)