Boring Out Carbs

my kawasaki carb hero is also quite a Holley carb guru also,had problems with a stroker 415" small-block chevy a few years ago that wasnt running up to par ,he gave me this formula after seeing the 850 i was running turned out 500 cfm and some change was all this motor really needed at 5000rpms,went from being a sluggish tank to a real stoplight missile! :evil: he told me the .85 is an average realistic efficiency to aim for on a decent set of gm heads now we just need to figure out a realistic efficiency for a kawasaki head and convert the rest to metric! goodluck,happy wrenching!

wireman wrote:

heres that carb formula i was talking about for figuring cfm !rpm x displacement x .85(efficiency 85%) divided by 3,456 =cfm requirement ,now can one of you mathematician types with the sliderules built into your glasses figure out how to convert this from inches and cfm to centimeters and mms? goodluck,happy wrenching!

Post edited by: wireman, at: 2006/01/16 00:21<br><br>Post edited by: wireman, at: 2006/01/16 00:22

What are motorcycle carb flow rates measured in?

Your formula to calculate CFM using CC for displacement would just be:

RPM * displacement * .6102 * 0.85 / 3,456

So for a 650 at 9,000 RPM that's:

9,000 * 650 * .6102 * 0.85 / 3,456 = 87.08 CFM

The .6102 comes from converting from cubic centimeters to liters (1,000 cc = 1 L) and from liters to cubic inches (1 L = 61.02 ci).

Do bike carb makers publish flow rates? What units do they use?

wow ,now if we can figure out how carb flow is rated well be on to something here! :woohoo: