[pitman]

I have a '72 Road runner which has a rebuilt----- (STOCK)----- 1971 ---- 440 CI engine in front of a 4 speed manual transmission. The rear end is a 391 ratio which translates to a HIGH RPM at highway speed.

Can anyone tell me what the RED LINE for a 1971 440 engine would likely be????

I have not driven it enough to see if it will overheat with this RPM in a long distance drive---but since it makes it's most horsepower and torque at ( I THINK ) 4600 RPM--I wonder what rpm at a constant speed is safe!!!!????

Thanks in advance to anyone with this knowledge!!!!!!


Pitman

[ted sweet]

how hight of rpm at what speed? i have driven my 70 challenger6 hrs to carliske turning about 3600 the whole way.

[pitman]

Our speed limit is 75 MPH---driving at 80 MPH my Tach shows an RPM of 5500!!! I assume this is an acceptable rpm to maintain without harm!!!!

Thanks for the reply---any further thoughts????

[ted sweet]

sounds more like a defective tach or you really have 4.56 or higher gears.

[Rusty_OToole]

5500 is too high for sustained driving. You must have some real wild gears in the rear end. Or your tach is from Jupiter.

If it really is revving that high you will know it. The engine will sound like it is trying to jump through the hood.

Would suggest you invest in some lower (numerical) gears.

To find out what ratio you have jack up the car with one rear wheel off the ground. Make a chalk mark on the rear universal and on the rear end. Make a similar mark on the tire at the top, and a matching piece of tape. Turn the rear wheel exactly two turns and count the turns the driveshaft makes.

When one wheel is stopped and the other turns, the driveshaft turns half as many times as when you are driving.

[keiser31]

I have always liked 3:23 rear gears in MoPars...good highway gears.

[DeSoto Frank]

If I remember correctly, big-bock MoPars (standard consumer variety) redlined between 4200 and 4400 RPM.

I think your tach is out of whack... my '41 De Soto with a very tired flathead six and 4.11 gears spins about 3,200 RPM @ 60 mph....

My 1960 Chrysler , with RB-383 big-block, Torqueflite, and 2.93 rear turns about 2200 RPM @ 60 mph.

If you want your engine to last, I wouldn't subject it prolonged speeds above 3,600 to 4,000 RPM.

Fuel economy plummets at speeds above 2500 - 3000 RPM.

I would definitely avoid revs over 3000 rpm until the engine is completely broken-in ( 1,500 miles ?).