cruising speed rpm
- Thread starter 37 Cab
- Start date
How about installing a Columbia rear end or a Mitchel (sp?) overdrive?
supereal
Well-known member
2500 is the "sweet spot" for the flathead engine. It is the point where the torque and horsepower curves meet. For the times, it was reached in the 50-55 mpg, depending upon tire size and rear end gearing, so it is likely you are in the 3,000 rpm range when you get near or above 60 mph. That pushes the engine a bit, and likely raises the operating temp.
I have a 3:78 rear in my '47, and installed a 30% reduction overdrive to cruise at today's highway speeds of 65-70.
I have a 3:78 rear in my '47, and installed a 30% reduction overdrive to cruise at today's highway speeds of 65-70.
3000 rpm is NOT pushing it a bit, it's not pushing it at all! These engines are not made of chocolate and cheese! And it should not get hotter at that speed either, if it does, you have a cooling issue. A 3.78 will cruise at highway speed no problem without any kind of overdrive.
Martin.
Martin.
The point at which torque and horse power curves meet? At 2500 rpm, using Ford's rather biased dyno figures, horse power is about 80hp, torque is about 170 lb,ft. Not much meeting going on there in my opinion. If your using a Ford print dyno sheet for reference, the two lines do cross on the graph, but look at the numbers each side of the graph, the two figures are hp on one side and torque on the other.
Admittedly the 2000-2800 rpm is a sweet spot due to the max torque is about here, but nothing to do with curves crossing.
Martin.
Admittedly the 2000-2800 rpm is a sweet spot due to the max torque is about here, but nothing to do with curves crossing.
Martin.
Mart
Well-known member
I tend to cruise at about 55 mph, but that is with a 4.11 gear. It's a very comfortable speed, as speed rises, it isn't engine revs that become obtrusive but road noise and wind noise. All cars are different though, my 40 would cruise at a higher speed, 65-70 that had a 3.78 gear and better sound insulation.
Mart.
Mart.
Admiral
Well-known member
I agree! These engines were designed to take a pounding. When new they were worked from sunup to sundown under trying conditions. My car, with a 3.78 rear end, pulls about 3,000 RPM at 60 miles an hour, though I cruise at about 65 on the highway, which is a bit noisy because of the barn-like aerodynamics but whatever, she's happy to do it and is willing to go even faster.
oldford2
Well-known member
Well, all this talk about cruising at 65-70 on the interstates at 3000 rpm.... We have a Mitchell in our 46 (3.78) and 60 mph is about 2600 rpm. Just loafing. But.... this car is not made for those speeds. It is dangerous! When we have to get on an interstate 55 is generally max. Next time some of you are "cruising" at 65 mph, try a very hard braking and see the results vs your modern car. Not good. 50 to 55 is enjoyable and you get to see a lot of thumbs up as cars pass you by. JMO
John
John
Kahuna
Well-known member
3000 RPM to me is too fast, but I don't think there is any harm to the engine even for extended periods. As mentioned, noise becomes a factor.
My 39 std coupe is 4.11 geared and was originally a V8 60 car and I tend to drive it at speeds less than 60 mph.
My 32 Tudor is also 4.11 geared, but has an overdrive that reduces the overall ratio to 3.21.
60 mph is about 2200 RPM. Very comfortable and relatively quiet.
Overdrives are nice.
My 39 std coupe is 4.11 geared and was originally a V8 60 car and I tend to drive it at speeds less than 60 mph.
My 32 Tudor is also 4.11 geared, but has an overdrive that reduces the overall ratio to 3.21.
60 mph is about 2200 RPM. Very comfortable and relatively quiet.
Overdrives are nice.
Admiral
Well-known member
That's why I leave about two miles between me and the guy ahead ... LOTS of following room. And you're right, braking is a real issue with these old Fords, though driving them at ANY speed is dangerous.
flatjack9
Well-known member
By definition, torque and horsepower meet at 5252 rpm only on all engines.
37 Cab
Well-known member
Thanks guys for all the input.. 60 MPH is fast enough for me.. I may do a Mitchell one day but since my car is lowered I would need to modify the floor pan.. Don`t really want to do that as the body on my car is pretty sound and original.. So.. for now anyway... 60 suits me just fine.
3.78:1 would be normal, I'd be surprised if it had a 4.11:1.
Whichever it's got 60 should not be a problem.
Martin.
These cars were made for these speeds. I agree with you on the brakes to a point, no there not as good as new car, but they do the job well enough. I always drive with the idea that every other car is drive by an idiot who's trying to kill me. And drive with regard to my brakes, leaving lots of room in front. It's worked well so far. But I've always driven old stuff daily. My modern car is a 1966 mk1 Cortina.
Are they more dangerous than New stuff? Course they are, but it's a calculated risk I'm happy with. If I want to be as safe as can be, I'd drive a new volvo, that ain't gonna happen before there's snow in hell!
Martin.
JSeery
Member Emeritus
Figure out which one you have, the numbers should be stamped on the center section (assuming they haven't been changed) or you can use one of the one wheel jacked up methods (a search should turn up the method to check that way).