RPM's @ 70 mph ? - JeepForum.com

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post #1 of 21 Old 03-12-2014, 05:04 PM Thread Starter
1bucknrut
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RPM's @ 70 mph ?

cj7 with quadratrac & TH400 auto trans, 3.54 gears with stock 304 pushing 33 x 12.5 tires, My rpms run at 3000 rpm at 70 mph, That seems high to me but wanted to ask if that's normal since its a quadratrac, I've owned it for 15 years but never driven it over 30 since it was my hunting rig,

Thanks Buck

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post #2 of 21 Old 03-12-2014, 05:11 PM
UBERK
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Sounds a bit high...

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post #3 of 21 Old 03-12-2014, 05:16 PM
skizriz
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Is your speed going by GPS? With the tires, your speedo will be off. Mine will run at about 2,200 at 60 mph. I had the same setup, with 35" tires.
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post #4 of 21 Old 03-12-2014, 05:17 PM
yellow85cj
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Are you sure you were doing 70? If the speedo gear was not changed with the larger tires, the speedo would be incorrect.

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post #5 of 21 Old 03-12-2014, 05:32 PM
Stormpaw
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I don't know anything about automatic transmissions or the Quadratrac, but Novak has some useful calculators. It seems like you should be reaching 70mph around 2500rpm.

Of coarse, your speedometer will be off if you did not change the driven gear in your transfer case to match your tire and axle gear ratio combination.

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post #6 of 21 Old 03-12-2014, 06:00 PM
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http://www.grimmjeeper.com/gears.html

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post #7 of 21 Old 03-12-2014, 06:50 PM
Truck633
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Tell me more of this 70 MPH thing???


I think I may have heard of it.

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post #8 of 21 Old 03-12-2014, 08:56 PM
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What are you using to tell you that you are doing 70 mph?
Because I'll bet you ain't at 70.
LG

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post #9 of 21 Old 03-12-2014, 09:38 PM Thread Starter
1bucknrut
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Ok I didn't change the speedo drive gear so the gauge wouldn't be correct, so I took my gps liked skiwiz inquired about and this is what I have
gps 65 mph gauge 58 rpms 2500
gps 70 mph gauge 63 rpms 2700
gps 80 mph gauge 70 rpms 3100

So does this sound liveable if not what would be your recommendations to lower the rpms at those speeds, Not that im going to be driving it 80 but 65-70 on semi basis
UBERK on that chart what speed is calculated at ?

I will be changing out the gear on the speedo soon

Buck
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post #10 of 21 Old 03-12-2014, 09:47 PM Thread Starter
1bucknrut
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Quote:
Originally Posted by Truck633 View Post
Tell me more of this 70 MPH thing???


I think I may have heard of it.
Could you clarify your response
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post #11 of 21 Old 03-12-2014, 09:50 PM
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I would be tickled pink with that. for some reason according to my tach with my th400/d20 combo with 3.54's on 35's im turning about 2850 at 55 mph
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post #12 of 21 Old 03-12-2014, 10:02 PM
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Quote:
Originally Posted by 1bucknrut View Post
Could you clarify your response
srsly?


It was a joke..


If I ever hit 70, it would be like a Delorean at 88

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post #13 of 21 Old 03-12-2014, 10:08 PM Thread Starter
1bucknrut
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Quote:
Originally Posted by holliewood61 View Post
I would be tickled pink with that. for some reason according to my tach with my th400/d20 combo with 3.54's on 35's im turning about 2850 at 55 mph
Well holliewood61 that are some words of encouragement on my end

Buck
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post #14 of 21 Old 03-12-2014, 10:14 PM Thread Starter
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Quote:
Originally Posted by Truck633 View Post
srsly?


It was a joke..


If I ever hit 70, it would be like a Delorean at 88
I thought that might have been the case after I thought about it a minute, no harm no foul

Buck
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post #15 of 21 Old 03-13-2014, 03:33 AM
Matt1981CJ7
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Quote:
Originally Posted by 1bucknrut View Post
Ok I didn't change the speedo drive gear so the gauge wouldn't be correct, so I took my gps liked skiwiz inquired about and this is what I have
gps 65 mph gauge 58 rpms 2500
gps 70 mph gauge 63 rpms 2700
gps 80 mph gauge 70 rpms 3100

Buck
Buck,

Something is a little off with those numbers. The percentage difference between GPS speed and gauge speed should be the same at all speeds.

That said, your engine should be quite comfortable at 2500 RPMs. A slightly larger tire would lower the RPMs some, but would also lower the power and mileage. I think you're about right where it's at.

Matt
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