I did a search and found too little information to have a concensus. My 50 flathead is said to be 110 hp @ 3600 RPM and 200 ft. lbs. of torque @ 2000 RPM. I have 4.27 gears. I never had a tach with my 3 spd with OD. That ****** went on me and now I have a question for the 700r4 that replaced it. The question actually has more to do with the engine. At what RPM should I have the ****** shift at? Also, what is the maximum RPM you should run a stock flathead at? Thanks in advance for any input.
I have a 255 with a c4 and run 2000 rpms at 55mph,2500 at 70mph. I still have good pulling power on the hills,running 278 gears 205/75/15 tires. I think you would want that in 3rd gear.
I have a Locker shifter and most of the time I shift it by hand.I guess about 3k at most and its quick and no mis shifts.I have no kick down yet so shift it by hand.
The rpm at which it shifts will vary with throttle position/engine load. If you connect the throttle valve (TV) cable correctly, and there is a correct geometry to it, it will work fine without you having to do anything. Ray
I beleive my TV cable is set up correctly and yes there is only one correct setting. It is not something you adjust. However, from what the ****** shop told me there is still the governor to match to the engine and rear end. The shop owner asked me what I want RPM's I want to rev to. I'm no expert and am totally confused. I'm just trying to get some RPM values so the next time I talk to him I can get some clarification what exactly he meant and give him an answer.
Anybody else have any input? I'm guessing it would be around 3600 RPM since it should still be pulling up until then. Yes? No?
I would say that about 4,000 is maximum useful speed on a completely stock FH, maybe a touch lower for a 255. After that it can't get enough air and only noise increases. Mildly hopped, maybe 5,000, wild who knows...ask Pete! Stocker has a very broad and flat torque curve and will pull hard from off idle to whenever it runs out of breath. Numbers would be for full throttle shift, you would want lower for part throttle driving. Rev limit is based on air flow capacity, lower end is generally good for a lot more than stock engine can usefully reach.
Thank you Bruce. That more answers my question. I'm not up on autos, but I have some numbers when I talk to the shop. I know the 700r4 isn't traditional and might have quirks, but I have also been told it will feel at home behind the flathead. We'll see. I had the ****** sitting around when the stock 3sp fell apart.
Another thing...think about torque peak as low throttle shift point, power peak or a bit past that for full throttle. On a 255 flathead that gives you some wiggle room as torue curve is so wide and flat the peak is hard to place. Revs much above power peak on a stocker are worth nothing because output just drops dead without more carb and cam.
Most engines produce max hp around 80-85% max rpm. I would think you would want an auto to shift at max hp and hopefully only drop to max torque.
Here are a couple of stocker curves I posted a long time ago: More dusty numbers from the past: Found a 59A chart, looks the same as the prewar chart above with just very slightly higher numbers. Also has BMEP, compression, fuel, and friction curves--a very busy sheet of paper. Here's a '51 Merc graph reduced to words. The '52-3 got a hotter cam, but don't have numbers for that engine: 1951 Merc engine: RPM Torque HP 500 178(!) not shown 1000 190 37 1500 202 58 2000 206 77 2500 200 94 3000 187 107 3500 170 112 4000 147 110 I'll repeat prewar Merc here for comparison: 500 152 15 1000 171 33 1500 180 50 2000 182 70 2500 178 84 3000 168 96 3500 153 102 4000 138 103 That's all they wrote... Looks like that stack of Merc cranks is worth keeping! All flathead folk should run out and buy the current repro of my favorite childhood book, Roger Huntington's "How to Hop Up Ford and Mercury V8 engines" from 1952. It has lots of engineering charts of stock and modified engines. Also, my various USA and Canadian Ford service bulletins have numerous dyno charts, some with other info as the 59A chart I mention. Bruce Lancaster View Public Profile Send a private message to Bruce Lancaster Send email to Bruce Lancaster Find More Posts by Bruce Lancaster Add Bruce Lancaster to Your Contacts
I have a 39 ford 255 mecury and c4 2.78 gears,and a 52 ford f1 with a 302 and c4. That 302 will shift out at high rpms and much quicker. The 700 r4s were for 305v8 and much higher rpms. The flathead is not the same and never will. I guess its were you drive,getting out of my driveway i have to get up to 55rpm quick.Then I have to hills, that i can take at 2k rpm at 55 mph. I,m not trying to beat the guy next to me at a light in the city. My drive train is out of a Granada 2.78 gears and 250, 6 cylinder,When building it I thought the flathead would be good replacement.
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