what blower size would you install on top of tall deck 640 cu.in engine to receive 10 psi boost.?

Best not to spin a roots blower over 8,000 rpm for any length of time. Whips up more heat than boost.

At 6000 motor rpm, you can overdrive 30%.

An 8-71 at 30%over will give around 14 pounds of boost in a 640. An 8-71 at 15% over will give around 9 pounds. At 1:1 is will be about 4 pounds.

A 10-71 at 1:1 will do about 7 pounds in a 640. At 10% over will do around 10 pounds.

A 14-71 at 1:1 will give you probably 10+ pounds.

These are just guidelines. Each motor, how well its heads flow, carb size, cams, etc will affect the outcome.

I'd say a 10-71 is minimum for that motor, but you could really stretch an 8-71 and make it work.

timucin, I have a 621" BBC with a 14-71 blower and I get about 9 psi boost (at 6,300 rpm) running 12% over. I would run a 14-71 on anything bigger than 600". Hope this helps.

Keith

what the heck are you build'n now




did you get that Hemi car you were looking at?

I had a 460 ci and went with a 8 71 and wished I WENT LARGER . You can always slow them down,Less heat .Bigger better

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