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06-11-2015, 10:31 AM | #1 |
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cruising speed rpm
Running 60 MPH my engine is turning 2800 RPM. Is that too fast for the old girl or am I OK?
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Tommy |
06-11-2015, 10:45 AM | #2 |
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Re: cruising speed rpm
I believe a lot of people consider 2000 to 2500 ideal for a flathead, 2800 would not be far off.
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06-11-2015, 10:55 AM | #3 |
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Re: cruising speed rpm
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06-11-2015, 12:15 PM | #4 |
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Re: cruising speed rpm
That should cause no problems.
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06-11-2015, 12:29 PM | #5 |
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Re: cruising speed rpm
Will be fine, you could drive to the sun and back a few times at that rpm.
Martin. |
06-11-2015, 03:44 PM | #6 |
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Re: cruising speed rpm
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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. |
06-11-2015, 04:32 PM | #7 |
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Re: cruising speed rpm
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. |
06-11-2015, 04:50 PM | #8 |
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Re: cruising speed rpm
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. |
06-11-2015, 04:56 PM | #9 |
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Re: cruising speed rpm
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. |
06-11-2015, 05:31 PM | #10 | |
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Re: cruising speed rpm
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06-11-2015, 05:51 PM | #11 |
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Re: cruising speed rpm
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 |
06-11-2015, 05:56 PM | #12 |
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Re: cruising speed rpm
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. |
06-11-2015, 06:38 PM | #13 |
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Re: cruising speed rpm
Whatever changes or so called improvements I make our 38 std. on 3.78 diff always seems to settle down at an easy 55 mph.All cars are a little different I guess. Geoff
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06-11-2015, 07:42 PM | #14 | |
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Re: cruising speed rpm
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06-11-2015, 08:55 PM | #15 | |
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Re: cruising speed rpm
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06-11-2015, 09:18 PM | #16 |
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Re: cruising speed rpm
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.
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06-11-2015, 11:05 PM | #17 |
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Re: cruising speed rpm
I am new to the flatheads. Can you tell me if my 1940 ford 2 dr deluxe would typically have a 378 gearing or a 410 rear end ratio ? I like to drive right at 60 mph.
Ron |
06-12-2015, 07:15 AM | #18 | |
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Re: cruising speed rpm
Quote:
Whichever it's got 60 should not be a problem. Martin. |
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06-12-2015, 07:27 AM | #19 | |
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Re: cruising speed rpm
Quote:
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. |
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06-12-2015, 09:29 AM | #20 |
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Re: cruising speed rpm
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).
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