Pulley Selection V2 SI

[greenvf]

hi all.....
just about done changing out the Powerdyne bd11a on my 360 Chrysler for a V2 SI that i have just purchased. The powerdyne was not going to give me the boost i want.
Anyways what i would like to know is what head unit pulley to use for say 12psi boost @ say 6000rpm, 7" crank pulley, 3.5 rear, auto. i have a couple of spare pulleys from the powerdyne, but they are 2.7 and 2.9. think they may be too small.

cheersP1010441.JPG

[vinces427bb]

welcome to the site.
looks like it packaged under the hood well.
what kind of boost are you getting now before changing pulleys??

[greenvf]

about 6, but that was with 6" crank pulley and 2.7 on the head unit.

[vinces427bb]

Powerdyne bd11a has max impeller speed of 38,000rpm with an internal step-up ratio of 3:1;
therefore 6psi-boost with 6" crank pulley and 2.7 on the head unit = only 21960 blower speed @ 6000rpm-engine speed =122% overdriven
with 7" crank pulley and 2.9 on the head unit = only 25380 blower speed @ 6000rpm-engine speed =141% overdriven
with 7" crank pulley and 2.7 on the head unit = only 28620 blower speed @ 6000rpm-engine speed =159% overdriven

wallace has many calculators on this site.
http://www.wallaceracing.com/blower-od-calc.php
this one can tell you the %-of UD/OD ratios of the crank/blower pulley, then times by the rpm and times by the 3:1 step-up ratio to end up with the blower speed at engine rpm

you can spin the blower much higher than you are now with the 7''crank and either 2.7/2.9''blower pulleys
providing the max-blower rpm and set-up ratio i used are correct