Just wanted some opinions on how many RPMs I can cruise my 239 without causing any problems. Right now I'm turning about 2300 at 60 mph with my 3.25 rear. Not much for a modern OHV engine but how well will a flattie tolerate it? What's a comfortable upper limit? Thanks.

 

I've heard reports of guys running 3500 rpms for extended highway trips. I'm more comfortable keeping mine (merc with 4" stroke) around 2500 which is about 62 mph with my 3.50 rear.

Basically a flathead V8 runs out of breath before it hits the wall rpm-wise. They are incredibly tough and flexible. Your's should last a coulple of lifetimes at 2300.

 

Ive got around 65K on a thundering 286 inch flatty and run it on the interstates regularly at 3300-3600 with the 3.73 rear. Back when it was a stock 239 I still ran 60-65 with it and had no problems.
This is in a car, a 53 Vicky.

If you are going to be driving it regularly Id at least drop the pan, clean it and the oil pump screen. If you got a few extra $ invest in a new Melling M19 high volume pump; available at Speedway and others. This is the same pump that Henry switched to in 51.

 

JD, just curious, are you running a stock 3-speed with the 3.25 rear end? If so, how do you find it taking off from a light, etc.? Would sure be simpler than a T-5...

 

Thanks for the responses. Sounds like 2500 or so is no problem. I guess it's just different to hear an engine wind out the old fashioned way without an overdrive like everything has today. Albuq, it's a stock 3 speed. It sure is no tire burner but it takes off OK. If your flatty is stock I probably wouldn't recommend going any lower than the 3.25 though. Aside from needing a longer driveshaft the 9" swap sure is simple if your lucky like I was and find the ratio your looking for right away.