Jay, Pushing 4,000lbs with that little 223 designed back in the 40s is a lot of the problem.

All manual trannys not overdrive, run 1 to 1 output ratios (tranny output shaft is turning same rpms as engine). You can add overdrive to slow the engine rpms down, but then it may not have the gonads to push it. That is why most small engines had low rear ratios. You have to get the engine power to the rear wheels. There are all kinds of factors on performance, mpg, and mph ratios.

As long as it is in gear, and is in decent shape, you pretty much can't blow it up by mashing the gas. Run it on up to faster speed, it'll just stop gaining before anything bad happens.

Put a 4.6 with auto overdrive in it, and getterdone.

best




John