Thread: FE Ford RPM question

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I'm trying to get some ideas.........

Right now I run a 352 w/ 390 heads, cast iron intake with a holley carb, little lumpy cam (and has PLENTY of power through out the rpm range) & a 3 speed auto trans. in my 1962 Unibody truck.

I'm not sure of the rear gear but I'm running a P295-50-15 tire that is aprox. 26" tall.

At "speed" I'm turning 2800 rpm's (my spedo says 70mph - but that is suspect) or so but it feels like it could use a 4 gear. When I rpm down to 22-2500 it appears that the world is passing me bye.

What "safe" range RPM can I turn this motor to for every day driving??

Any info will be appreciated.

Regs

Originally Posted by REGs

I'm trying to get some ideas.........

Right now I run a 352 w/ 390 heads, cast iron intake with a holley carb, little lumpy cam (and has PLENTY of power through out the rpm range) & a 3 speed auto trans. in my 1962 Unibody truck.

I'm not sure of the rear gear but I'm running a P295-50-15 tire that is aprox. 26" tall.

At "speed" I'm turning 2800 rpm's (my spedo says 70mph - but that is suspect) or so but it feels like it could use a 4 gear. When I rpm down to 22-2500 it appears that the world is passing me bye.

What "safe" range RPM can I turn this motor to for every day driving??

Any info will be appreciated.

Regs

2800 shouldn't hurt it. i dont like anything over 3200 on a long trip. i have ran as high as 3600, but didn't like it. sound like you might have a 4:10 gear. get behind someone that you know how fast they are going and then you can get a better idea of what you have. a 4 speed won't help your problem, because the 3 and 4 speeds are 1:1 in high gear.

IThanks.

I was thinking a O/D unit??

Regs

I agree with It1s10.
2800 rpm shouldn't hurt.

I run my 462" Buick at 3000 rpm at 70 mph on the desert highways.
Sometimes up to 3200 rpm on a 5-10 mile run.
Speed limits here are 75 mph on many of the desert highways.

The big Buick engine is fairly short stroke (3.9") all things considered.

Any chance you could go to a 28" tire?
That would get your rpm down about 5-7%.

Mph = rpm x tire diameter divided by 336 x axle ratio.

You can roll things around in the formula to decipher your axle ratio.


Or . . . you can mark the driveshaft, mark the tire, roll the tire one revolution and count driveshaft revolutions.
EG: tire turns once, driveshaft turns just a touch over four indicating a 4.11 or so ratio.
This is pretty accurate if you pay attention.

Use your head as well.
Don't get under the car to do the counting, you should be able to do it from the side.
A couple of helpers, one behind the wheel to operate the brakes as required and one to push the car - engine off - will make life easy.
Safety first above all other things.

If you don't have a locking differential, you can jack up one rear wheel, rotate it one turn and count driveshaft revolutions.
EG: a small amount over two driveshaft revolutions indicates a 4.11 diff.

Originally Posted by REGs

IThanks.

I was thinking a O/D unit??

Regs

that would work. you need to find out what gear you have before you do anything. search one of the gear co. web sites and they will tell you how to do it. i hont have that info. right now, but maybe someone else has.