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Old 09-03-2019, 09:29 AM   #1
Lon Jackson
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Default RPM range for 51 merc flathead

What would be the red line on a 51 merc flathead. The engine has Offenhauser heads and edlebrock 4 barrel carb.
What would be a good cruise RPM?
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Old 09-03-2019, 09:55 AM   #2
tubman
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Default Re: RPM range for 51 merc flathead

I have a '51 Merc engine with Edmunds heads, a Mallory dual-point, and a Rochester 2G carburetor in my '51 Ford. When I first put the engine together, I had it on my test stand. I made one run up on the stand to see what it would do. It got to 5500 RPM easily when I lost my nerve and throttled back. In practice, it seems that running it any higher than 4000 when "going through the gears" is counter-productive. When you reach that, it's better to go up to the next gear if you are not in high. Anything over 4000 in my car is too fast. I have 3.55 rear end gears, and the car cruises at 55 mph turning 2500 RPM. It will go 70 easily, but it really likes to sit at 2300-2700.

I have an overdrive transmission and all the extras needed to install it under the bench, and I would sure like to put it in, but without a lift, it's just too big of a job for me. These cars. especially with a engine with a little more "pop" than stock can really benefit from some sort of overdrive (T5 or RTS, for instance, or even a stock setup).

Last edited by tubman; 09-03-2019 at 10:19 AM.
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Old 09-03-2019, 10:36 AM   #3
4dFord/SC
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Default Re: RPM range for 51 merc flathead

My '40 with a 221 flathead, Offenhauser heads, 4bbl carburetor, Fenton headers, and Columbia will comfortably do 70 mph indicated at 2800 rpm. Like Tubman says, 3800-4000 is as high as I would ever want to run it. I should think your set-up should do at least as well.
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Old 09-03-2019, 11:11 AM   #4
Lon Jackson
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Default Re: RPM range for 51 merc flathead

Thanks for the information
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