Flathead V8 REDLINE RPM

J

JAKEFORD

Senior Member
With all the experts on board I have a question regarding the speed limit for the Ford Flathead V8.

In the old days we revved these engines beyond belief. They actually screamed, especially in trucks with low ratio rears. But somehow they seemed to last with no block cracks or other defects. There is no sweeter sound than a V8 pulling a heavy load up a hill in first gear.

But now they are rare or becoming rare. So what do you think the max rpm should be to preserve integrity? I am thinking of highway runs.
 
If your cruseing long distance with stock engine I'd say 2500 that's where the torque is, you might wind it up to 3000 to pass a car but no need drive to drive like that all day long. Walt
 
So my car runs 2800 RPM at 57.. 2900 at 60. You think I am running it too fast? 3000 seems like it is running too fast for my comfort but just below seems to be a sweet spot. Should I slow it down?
 
My avatar roadster has 3.54s and with the tires I have I am at 3000 at 65 mph. I believe the engine is built to take that continuously but maybe a bone stock one would be happier at 2500
 
It's time to buy JWL's book, there are dozens of dyno runs that show the rpm and torque curves of stock and modified engines. Having raced these engines I don't believer there is a limit to the rpm you can run the engine. A stock or mild engine doesn't produce much power. a good engine in perfect tune will produce aprox 80 HP with out gen and fan at 3200 after that it's all down hill. No mater what you do to the outside of the engine (Except supercharging) it won't produce 100 HP (239 engine) Yet it has almost as much bearing surface as a 350 Chevy.
 
deuce_roadster said:
My avatar roadster has 3.54s and with the tires I have I am at 3000 at 65 mph. I believe the engine is built to take that continuously but maybe a bone stock one would be happier at 2500
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Yea, I was talking about a stock engine, but if your running a hot engine with a cam all most 3000 will be your sweet spot. My 40 I'm running a 276, hot track cam, tight heads, 4 97s straight linkage, T-5, 9in. with 350 gears, on the pike at 60mph 2000 rpm, BUT, you kick in the butt and it's lazy, but drop it into 4th and when it hits 28-3000 it kicks you right in the butt, and will it 5000 so quick it's unbelievable. I red like the tach at 4000 but it goes past so quick if I don't pay attrition. Walt
 
I don't think they have a red line; they'll run outta breathe way before they reach destructive revs.
 
JAKEFORD said:
With all the experts on board I have a question regarding the speed limit for the Ford Flathead V8.

In the old days we revved these engines beyond belief. They actually screamed, especially in trucks with low ratio rears. But somehow they seemed to last with no block cracks or other defects. There is no sweeter sound than a V8 pulling a heavy load up a hill in first gear.

But now they are rare or becoming rare. So what do you think the max rpm should be to preserve integrity? I am thinking of highway runs.
Click to expand...

A stock engine in good shape will run 3000-3500 all day.
A slightly modified engine, will stand an ocassional blast to 5500 for a long time.
An all out drag engine with 100% nitro will make maximum power between 6500 and 6800 and will usually be turning a little over 7000 through the lights.
An all out circle track engine will turn 7000 twice a lap for many race programs.
 
I think we may have the answer in a book by Roger Huntington. Copyrighted in 1951 by Floyd Clymer. This book was given to me 25 years ago by a guy who is now in his 80's. Note that there is no use of the word flathead, because it is about ford v8s. The last text on the last page has a poem regarding the engine's redline....
 

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For most engines and most people, revving up becomes a waste of time LONG before you reach any sort of mechanical limit.
A stocker is going to pretty much drop dead at about 4,000, and unless you love listening to useless whirring noises you will know it's time to look for another gear.
A typical mild streetable rod might move that up to about 5,000, then there's lots of room between the number and the stuff Pete gets into as money, wild parts, and secret tech is poured in...
Worst I ever drove was a borrowed '38 pickup...it went into terminal valve float at about 2800! I'm pretty sure that that engine had been violently overheated a few times and the valve springs cooked into the tensile strength of oatmeal. Almost lost a stoplight drag to a Volvo! Never heard of flathead valve float before or after...
The V8 60 might be an interesting exception...look at the factory dyno chart on that: At the point where Ford ended the chart, the power curve was still going UP!!
 
In 1935 the Autocar magazine in England got 72mph out of the new V8-60 Fordor - that was the early 4 main oddity which only had a production run of about 3000. With 4.77 rear end that was about 4200rpm. I've read that racing 60s in the US would pull 7000 all season.
 
I've been told (and I believe) that a Flattie cannot rev high enough to grenade itself, probably because of breathing difficulties and the only things that can feasibly grenade would be throwing a rod or disintegrating a piston. The valve train has nothing to crash into and high revs probably cause valve float which will also limit revs.

That being said, all engines are going to have a "sweet spot" in the torque curve which is basically a redline because it's kind of useless to rev beyond that point. You can gauge yours by the seat of your pants. When the engine stops pulling hard on acceleration, that's your redline.
 
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