If I want to add a supercharger to my engine how do I calculate the flow rate? I have worked out that my 400 engine at 95%VE and 7000 rpm needs around a 1000 cfm. Do I start by specifying how much boost I want, or do I aim for a specific HP? For example one supercharger I looked at has 1175 cfm 775 HP.

Thanks

 

Following up on my own post, one approach might be: pick a maximum boost, for example 7.35 PSI :-) Does this increases the flow by half? So does that mean I need a supercharger that flows 1500 cfm? Is this the same as making the engine 50% bigger? It looks like they give similar answers.

Cheers

 

Hmmm, not much response, either a really dumb question or nobody knows. In case anyone is interested it looks like I'm on the right track. One pound of boost adds about 7 - 9% power. You can calculate the flow from the pressure ratio, which is 14.7 + boost / 14.7, multiply that by the N/A flow rate. So either of my approaches above work.

Cheers

 

I doubt you will find many maps for compressors for superchargers, assuming centrifugal. I dont know why that is but the speed of the wheel is basically fixed via pulley/gear ratios and rpm.

I would start with HP goal and assume a VE and estimated CFM per hp required using various engine math calcs. Engine cfm demand varies depending on the build and how well matched the combo is.

You can also follow turbo math which uses lbs/min of airflow for a hp value. Then back calculate CFM that way assuming air conditions/converting to standard condtions.

A half decent 400" motor will make 750-800 hp on 12-15 psi depending. Bigger heads/cam may make that with less boost. It doesnt take much to make 2 hp per cube on boost with a 400" motor.

Also note that a blower that makes 15 psi on a smaller motor with a set of heads/cam for that motor, may only make 10 psi on a larger motor with different heads/cam because of the CFM demand changes. Boost is a measure of restriction as well so less restriction will show less boost. However that larger motor on 10 psi could very well make lots more power than the smaller motor on 15 psi.

 

Thanks Mr Orr, I thought you would have some insightful comments.

Cheers