Hi, is there some kind of formula to figure out what size supercharger to use? for a Whipple screw blower?

The 1st formula for me was cost then effective rpm,HP goals,carbs or injection to start.

This will be 370 cubic inches, mechanically injected, really crappy ports. 6500 rpm limit. The only priority is maximum peak horsepower. Low end, midrange, street manners are irrelevant. I have been told that a screw blower is best for this. But what size?

What is your hp goal?700?

700 to 750. The more the merrier!

Yeah, they got them 2.2L 2.4L and then I think it jumps to 2.9L and then the big 4.0L and then the biggun 8.0L...

What's really cool are the dual 2.2L or 2.4L setups....Those look wicked. And none of them are cheap.....

Most of the under 4L use an intercooler.The 2.9L will make 850 hp but may need the cooler to do it.

Might as well call the manufacturer and get the full dope. Without a lot of info on what you are putting the blower on, no formula is worth a hoot. Most kits i see for new 5.0 mustangs run about 7200/8000, and you might need things like an injection and timing controller plus fuel system.

The blower speed is also a variable, too low with large blower = poor low speed efficiency, too high wtth small blower = higher pumping loss
More comments on my site here: http://victorylibrary.com/mopar/blower/blower-choices3.htm

Thanks for the replies. I've tried to contact Whipple but got no response. I think they're only interested in selling big dollar kits for the popular engines at this point. This is going to be a custom one off deal on a oddball engine. There are places that refurbish these Whipple blowers and sell them for a whole lot less than new, and allow you to build your own kit. That's what I'm thinking I'll do. It will be intercooled with a water to air intercooler between the blower and the intake ports.

Boff, you say too big of a blower hurts low end. That doesn't matter on this engine. The only thing that matters is peak power. In this instance is there such a thing as too big?

Screw blowers are also known as Lysholm, Opcon Autorotor, Sprintex.
Some samples of blower capacity vs. application: http://kennebell.net/products/

My Viper has a 2.4 making 10 pounds of boost was 646 hp at rear tires and over 700 ft pounds at 2500 rpm. Its a blast on the street.

For rough numbers just assume you get 100% efficiency with a blower size and then figure out the blower speed and how many cfm you need to fill the engine,
If peak numbers are what you are looking for I would go procharger.