Safe speed
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Senior User
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From: New Mexico
Safe speed
I have a 390 with new process 435 with 4.10's. No rpm gage, its screaming by 50 but ive ran it at 60 a couple times for about 10 miles. Do you guys like number dummy think that is ok and it wont hurt the motor? It doesnt overheat at all.
Fleet Owner
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From: NorCal
I've got pretty much the same configuration but with 3.50 rear gears (and 35s) and at 3,500 RPM it is screaming for mercy. Get yourself a Sun SuperTach II at Autozone for about $45 and it'll provide the information you need. I have my redline set at 4,000 RPM just cuz there's no need to go any higher than that.
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If you have a 28" tire, you would be turning 2460 rpm at 50 MPH, about 20 mph per 1000 rpm.
If you have a 31" tire, you would be turning 2222 rpm at 50 MPH, about 23 mph per 1000 rpm.
Our '66 wagon with 390 2v and single exhaust sounded like it was going to come apart when shifting out of first at 40 mph. That was at approx. 3542 RPMS...... Wonder how they ever got one to 4400 rpms for the supposed peak power of 265 horse.....
Your motor should run for years at 2500 rpms.
If you have a 31" tire, you would be turning 2222 rpm at 50 MPH, about 23 mph per 1000 rpm.
Our '66 wagon with 390 2v and single exhaust sounded like it was going to come apart when shifting out of first at 40 mph. That was at approx. 3542 RPMS...... Wonder how they ever got one to 4400 rpms for the supposed peak power of 265 horse.....
Your motor should run for years at 2500 rpms.
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From: New Mexico
Ok thanks a lot for the imput guys.. sounds like I have to get a tach, maybe this seems obviose, but where do I hook up the tach? Is it a pretty big deal to put one in?
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IF the op can post his tire size, we will know the revs without a tach.
As for installing a tach, it's usually a hot, ground, the lights and the negative side of the coil or a sender that clamps on to a plug wire.
The tach will have instructions with it, or if you buy it at a yard sale, you can go to the manufacturer's web site and get instructions, if it is at all current.
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From: New Mexico
4.10s, 95 MPH and 5500 RPM would require a 24 inch tire.....
IF the op can post his tire size, we will know the revs without a tach.
As for installing a tach, it's usually a hot, ground, the lights and the negative side of the coil or a sender that clamps on to a plug wire.
The tach will have instructions with it, or if you buy it at a yard sale, you can go to the manufacturer's web site and get instructions, if it is at all current.
IF the op can post his tire size, we will know the revs without a tach.
As for installing a tach, it's usually a hot, ground, the lights and the negative side of the coil or a sender that clamps on to a plug wire.
The tach will have instructions with it, or if you buy it at a yard sale, you can go to the manufacturer's web site and get instructions, if it is at all current.
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32 inch tire, 1:1 high, 4.10 axle, 50 mph = 2153 rpms, plus torque converter slip--maybe a couple hundred rpms.
At 60, 2583.
Approx 23 mph per 1000 rpms.
You should not be screaming at 50 or 60 mph.
Does your trans shift twice?
At 60, 2583.
Approx 23 mph per 1000 rpms.
You should not be screaming at 50 or 60 mph.
Does your trans shift twice?
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From: New Mexico
Its a standard 4 speed np 435
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Generally classic truck V8's can handle cruising at low 3000's RPM. My 400 does OK there. That should be 70-75 MPH with 4.10's and 32" tires. Yes its spinning faster than a modern OD unit but it should take it fine. Your original tires were probably smaller (29"?) so your spedo is off. Check speed wit.h a GPS to be sure and calculate RPM accordingly.
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Senior User
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From: New Mexico
Generally classic truck V8's can handle cruising at low 3000's RPM. My 400 does OK there. That should be 70-75 MPH with 4.10's and 32" tires. Yes its spinning faster than a modern OD unit but it should take it fine. Your original tires were probably smaller (29"?) so your spedo is off. Check speed wit.h a GPS to be sure and calculate RPM accordingly.
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Joined: Jun 2010
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From: Iowa
4.10s, 95 MPH and 5500 RPM would require a 24 inch tire.....
IF the op can post his tire size, we will know the revs without a tach.
As for installing a tach, it's usually a hot, ground, the lights and the negative side of the coil or a sender that clamps on to a plug wire.
The tach will have instructions with it, or if you buy it at a yard sale, you can go to the manufacturer's web site and get instructions, if it is at all current.
IF the op can post his tire size, we will know the revs without a tach.
As for installing a tach, it's usually a hot, ground, the lights and the negative side of the coil or a sender that clamps on to a plug wire.
The tach will have instructions with it, or if you buy it at a yard sale, you can go to the manufacturer's web site and get instructions, if it is at all current.
My brother-in-law has a 72 Chevy with 4.10s and turns the same rpm's with the same tires? I would just get a tack and know what its doing.