what is the max boost of my s-trim? also i have the stock crank pulley on the car but vortech worked it over for me. right now i'm running 8lbs of boost so if i wanted to go to 12lbs would i have to get a bigger crank pulley or do i upgrade to a bigger blower hub pulley that bolts to the crank pulley?

 

The stock Vortech blower puller that piggybacks to your crank pulley is 6" diameter. Vortech makes a 6.6" and a 7" pulley. You can also reduce the size of the pulley mounted to the blower head. The S Trim comes with a 3.3" pulley. There are several pulleys that go down to approxiamtely 2.7" diameter.

You can also gain boost by making your tubing more efficient. I gained a pound of boost by eliminating the dryer ducting and adding a Brad Brand solid intake tube (prevent collapsing of the intake tube restricting flow).

Keep in mind that you don't want to overspin the blower as you run the risk of the impeller smacking into the housing. I believe Vortech's website has a formula to determine impeller rpms. Also at some point the blower becomes inefficient generating more heat than boost. That's why people step up to T and YS Trims.

 

yes i have the brad brand tube,and a 3.12 pulley on the blower.

but what is the purpose of going to a bigger crank pulley for the blower?

 

Vortech offers a 6.66" crank pulley and a 2.75" blower pulley. This is the steepest drive ratio they offer. LJ ran in the 9.9 range at 140 mph with the 6.66/2.75 combo on his S-trim feeding a 383, making 10 - 12 psi.

ASP sells a 7" crank pulley and Reichard sells a 2.5" blower pulley.

 

Max. boost depends primarily on three variables. The max CFM of the blower, rpm where you want the boost to peak, and the displacement of the motor. You can ROUGHLY estimate it as follows.

CID*rpm/3,456*(.9) = engine airflow requirement
((blower CFM/airflow required)*14.7) - 14.7 = boost

So, if you have a 350 and an S-trim (1,000cfm) and want to make peak boost at 6,000rpm:

350*6,000/3,456 = 607*.9 = 546
1,000/546 = 1.83*14.7 = 26.9 - 14.7 = 12.2psi is the approximate max boost at 6,000rpm with 1,000cfm.

You select pully sizes to spin the blower to close to max impeller speed at the rpm where you want the power peak (primarily determined by the cam).

Anything which increases VE will increase power but decrease boost. Lower VE will increase boost but decrease power. Anything that interferes with the blower ouput (especially inlet restriction) will decrease blower CFM and decrease boost and hp. An engine with a larger CID will see less boost and make about the same peak power as a smaller motor if the blower is maxed out. However, it will have a fatter torque curve and go quicker. Increased air density (cooler, drier, higher barometric pressure) will increase hp, lower air density will decrease hp.

Rich

 

F'n perfect.

 

Did I just get a compliment from a Pro??

Rich

 

Most deffinitely a compliment.

 

yes i heard you lose some boost or hp depending on the motor setup. i'm going with a forged 355 with a ZZ9 cam.

 

I don't remember the exact specs for the ZZ9, but I don't believe it was intended as a "blower" cam and in any case, it's a pretty old design. There are better choices.

Rich

 

Fixed.

I agree with Rich, there's better cams out there than the ZZ9 for a blown motor.

BTW...

ZZ9
Duration at .050 212 226
Gross Lift .483 .520
Lobe Separation 112

 

That cam does not match up well with a centrifugal SC and the rest of what you have planned. You will be giving up both hp and torque with it. Pick another cam, IMHO.

Rich

 

okay guys, then please help me out with a blower cam then?? i want something that behaves as close to stock as i can. and is a fair price.

 

When I get home I'll check the specs on the cam I have. If I remember correctly it was intended for a similar blower setup. I'm still debating on whether or not to go turbo so it might be for sale here shortly.

 

okay.. is it a custom grind blower cam?