I start doing testruns on my project Flathead with a Volvo overdrive gearbox with a S10 3. someting rear, so far I got 60 miles/h with only 2000 rev's and it still pulls. I must say a lot of fun, the smile is not of my face for a while...
With the right gears and tire size, I would say around 2000 rmp would be nice for a flathead. I had a full race 296 Merc flathead that was balanced in the 70's and it would come alive at 4000 rpm and still pull at 110 mph. Never should have sold that one.
60 MPH and 2000 RPM is nice I have found driving highway speeds the flathead likes to be up to about 2200 RPM pulling a good highway gear the engine will pull along nicely at well over 70 MPH. Rear end ratio in my halibrand with a C-4 is 280. Running a five speed with a .78 overdrive rear ratio in my halibrand is a 319 in fifth gear the final drive is 246 ratio. Many miles with smiles for sure.
Here is some calculators for mph, OD, tire size etc etc. http://www.nitrousexpress.com/oldwebdocs/hpcalculators.htm
Thanks all you guys for the input, last week I put a broadband lambda sonde in the exhaust for measuring the fuel/air ratio and it sits nicely around 14.3 all the way, accelerating and cruising. Here is a pic from the Flathead/Volvo combination.
How heavy a car? The one in your avatar? I have been thinking about this setup for my '51. I believe I would have to go to a little lower (higher numerically) rear. Anyone have any thoughts or experience with this?
I have a similar setup to Mean Lean using a GV O/D behind a Ford toploader. Using a 4.11 rear axle gear, in O/D becomes 3.21 About 2400 rpm @ 65 mph w/ 29" tire