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Quote:
Originally Posted by rhphotord
Can any one give me what is considered a safe comfortable rpm range for a stock 42 flathead? Running a 4:11 gear set presently and rpm seems high at highway speeds. Love to install 3:78 gear set but not in the budget as of yet unless one falls into my lap at the right price.
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You can calculate the engine rpm, it is fairly simple math, all you need is the rear axle ratio (which you have) and the rear tire diameter.
RPM = (Rear Axle Ratio x MPH x 336.13) / Tire Diameter
As an example
(4.11 x 65 x 336.13) / 29 = 3096 RPM
That is not that may RPM. Original Torque/HP curves go to a bit of 4,000.