8ba RPM

A lot of variables here, but you did say stock 8ba. Most all of the printed max HP ratings were based on rpm ranges between 3200 RPM to 3800RPM.
 
I asked the same question on the HAMB and couldn't get a straight simple answer. Most answers said a flattie, because of breathing limitations, can not rev high enough to grenade itself.
 
I would agree that the real world redline is just the end of the power curve...you reach a point, certainly by about 4,000 in a stocker, beyond which you are just getting a whirring noise and no power. Assuming decent condition, you won't be able to approach destructive speed or valve float.
According to some published lore, the origin of Duntov's idea of making heads for the Ford was his discovery that his heavily loaded '37 Ford used for smuggling in Europe after the war would run up to very high RPM, higher than his prewar French OHC race car, without damage on the downhill parts of his runs. He realized that he had found a platform that could support better breathing...
 
My Mercury Manual says that the 1951 stock Merc engine puts out 112 HP at 3600 RPM. Compression ratio is 6.8 to 1.
 
This is a good time to read JWL's book. During his tests of the stock engine he didn't measure any torque readings after 3700 rpm untill he changed cams. The most Horsepower he could get from a stock 8BA was 80HP and reguardlass of any exhaust, intake or compression changes, could not exceed 100 HP Many of your questions can be answered by reading this bood, which can save you allot of momney when you start your rebuild.

I've run several modified Flathead son my friends Superflow Dyno and found that power falls off rather fast after 4800 RPM. This engine was built for a Hydroplane and would not be suitable for street, Max HP was 175 @ 4650. Just love em!
 
my 286 dragster goes throught the traps right on the rev limiter 5500 every time. My boy shifter into 4th one time at 5500 and he said it still set him back in the seat. Walt
 
Is it true that a new modern engine at the factory is run wide open for several minutes before they install it? Seems awful harsh! Years ago I had heard they ran the new engines by compressed air, which makes more sense.

Shadetree
 
Another source...if you look at the various year factory dyno curves in the service Bulletins, you will see the curves starting to drop like a rock at the point they end the charts. The stock engine has simply run out of air. Curves are shown up to about 4500, by which point they are headed DOWN dramatically. Hot rods I would say commonly add about a thousand, uncommonly a lot more.
Interesting factoid: If you look at a factory 60HP curve, the lines are still heading UP at the point the chart ends...the 60 quite clearly made more power above the point at which the factory chose to rate it.
 
I think the bottom end is good for a lot more than that.
In the Duntov anecdote I read, he found himself running well beyond 6,000 down long hills in a heavily overloaded '37 Ford smuggling car that had to struggle to get the loads UP the same hills at all...supposedly this led him to realize that he had found a cheap and sturdy platform that could handle some serious development upstairs.
His racecar was some sort of little DOHC Frnch sportscar that could not rev nearly that high...
In Duntov's immediate postwar Europe, there were stll tightly controlled borders and each country had a different range of items in short supply...so D stepped up running foods, tobacco, gold, etc. across low country and French and German borders to take advantage.
 
Now...I need to go dig in the basement and compare 221 and 239 prewar curves, just out of curiosity. Since everthing in the flow path was the between 221's and 239's of same year, seems like there should be a tiny difference in the RPM level where torque drops dead...I want to see if there's anything discernable in the dyno charts.
 
Flathead dragster: 296cid, Potvin 425 eliminator, four 97's on gasoline, vertex mag, a lot of valve, port, and head work, stock rods, stock main caps with fabricated steel supports. Told the young (but good) driver to shift around 5500 RPM. It would run the quarter in the high 12's. Then one day he decides to run it out till it stops pulling and then shift. Well he ran it to 7000 RPM before shifting, car went 12 flat. After that, 7 was the new redline. Many races no engine problems or tear downs. Believe it or not, but a true story.
 
flatheads are remarkable, 7000 rpm? that seems very high, but i can believe it. i wouldnt try it with mine, any of you guys push the limit and have one blow? i remember grandpa going down a hill with a load on his truck, breaking with the engine, it was loud and i was about ready to jump ship....gramps just hung on to the wheel and kepted yelling whoa whoa!!!.....thinking back, ...he was better with horses.
 
Bruce your comments on the quick fall off of power is exactly the reason why i have never run any of my engines with tight combustion chambers and high comp. ...after 3000rpm they start to die, no matter what "fruit" is on the engine ...The above is not much use when trying to pass a semi...specially when your halfway past him and somebody is is heading towards you in the opposite direction.?.......The Baron .630 heads plus the L100 cam keeps her pulling easily upto the 5000rpm mark........

Never had problems running stock engines around 3500 - 4000..But i've always balanced the engines......modified or not.......Ya just can't have too much insurance eh ?.............
 
I agree with Bruce the bottom end will take alot more than the breathing will allow. You really cant over rev one. They will run out of air before they blow. The valves will float. Even with a roots blower and all of the port and relief work they will give it up at 5500
 
A FACTORY ANSWER TO THE QUESTION I GUESS ??

HPFLATHEAD.jpg
 
You must log in or register to reply here.
Back
Top