What can I expect if I change to an 8 inch crank pulley?

[RoadW3@aol.com]

I have a 7 inch now. I am thinking of switching to an 8 inch. I know the boost will build faster, which is what I want. I am starting to see boost about 3300 to 3500. I would like it to build lower in the powerband, the thing is I dont want mondo boost up top. I have a 3.5 and a 3.25 pulley. Would I need a 3.75 or 4 inch to make sure I dont build alot of boost up top? What I mean by alot is 14 pounds or more. I have a stock block and am running 93 pump gas.

Thanks,
Eric

[frdfandc]

I would go with the 8" crank and the 3.75 blower pulley. That should help boost build up a little faster, but should also keep boost in check. I would input the crank/blowe pulley size into the spreadsheet and that should give you an idea.

[silvergts1998]

Here's a formula to figure out the rpms you will be spinning the blower.


Dia size of Crank Pulley * 3.54 / Blower pulley size * RPM you shift at= RPM you spind your blower.

Hope this helps. I think 55,000 RPM is maxing out the Novi 2000

[Hustler]

So right now this is what you are spinning the blower to:

7 inch crank divided by a 3.50 inch blower pulley X 3.54 X 6000 rpm = 42480
7 inch crank divided by a 3.25 inch blower pulley X 3.54 X 6000 rpm = 44783

8 inch crank divided by a 4.00 inch blower pulley X 3.54 X 6000 rpm = 42480
8 inch crank divided by a 3.75 inch blower pulley X 3.54 X 6000 rpm = 45312
8 inch crank divided by a 3.50 inch blower pulley X 3.54 X 6000 rpm = 48548

So as you can see the 8/4 would be the same as the 7/3.5 setup you have as far as impeller speed. An 8/3.75 would put you a tad faster than the 7/3.25 setup. The question is, how much boost are you seeing with the 7/3.25 setup, with a 8/3.75 you are probably going to see atleast 1-2 psi up top is my guess.

[RoadW3@aol.com]

Chris, those are my calculated impeller speeds. Right now I am running the 3.5 inch blower. I did take it a hair past 4K tonight and I was 7-8pounds and rising. So I am thinking this might be a 14 pound combo or more. I did buy a 3.75 blower pulley just in case I needed it. It builds boost faster then with the 7 inch combo, and when the boost comes on it climbs fast. It literally shot to 7 pounds from 2 or 3.

Eric