briggs animal racing engine

[greg]

these engines produce 8 or 9 hp stock how much mph do you think they will run

[kkuenemann]

Your speed depends on more than just engine horse power. You need to know the rpm's you are willing to turn the engine, the number of teeth on the clutch or TAV gear (driver gear), the number of teeth on the axle sprocket, the pitch of the chain, and the circumferance of the rear tire. For example:
12 tooth driver, 68 tooth axle, 12" dia tire(34" tire circumferance), and 4000 rpms will give you a speed of:about 22.7 mph.

try this link to estimate speed by changing the variables:
http://www.compgoparts.com/TechnicalResources/SprocketCalculator.asp