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Options for higher top speed?

Atradies

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Sorry, been away for a bit. M931a2, not so much for more speed, but for a slightly lower rpm while cruising on flat ground. How would a transfer case increase top speed, I thought they where 1:1 in hi gear. Ive got 14.00x20 tires.
Lower the gear on the transfer case the faster the input shat moves which will be you output n 205 cough
 

74M35A2

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Easiest way is to install 16.00 tires and turn up the injection pump. Add an EGT gauge to not melt the engine down.
 
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98G

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Easiest way is to install 16.00 tires and turn up the injection pump. Add an EGT gauge to not melt the engine down.
This ^

With 16.00s on my M925 I don't even see 5th gear until cruising on the interstate.

Thing is, you pretty much need to treat the transmission as a manual. Otherwise the downshift will be late and the upshifts will be early.

A pic, just for general principles -
 

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ProeliatorRex

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Not sure what the previous owner did to my '91 M939 (guarantee they turned the fuel screw up) but it definitely scoots just fine, and cruises easily at 65mph. Its bobbed, and lightened up those brakes will throw you through the windshield if you don't respect them. My buddy is a big diesel mechanic, and he said the Allison in these has another top gear you can unlock.....but I have zero idea if that's true or just rumor as I have not researched it. All I know is that 65 is easy, it might have more but didn't want to spin it to 3k rpm. Not sure I'd really want to send this sucker down the road any faster anyways, especially with how people pull out in front of you these days. Wedged under my front differential isn't a great look for a Prius.
 

162tcat

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Washington
Not sure what the previous owner did to my '91 M939 (guarantee they turned the fuel screw up) but it definitely scoots just fine, and cruises easily at 65mph. Its bobbed, and lightened up those brakes will throw you through the windshield if you don't respect them. My buddy is a big diesel mechanic, and he said the Allison in these has another top gear you can unlock.....but I have zero idea if that's true or just rumor as I have not researched it. All I know is that 65 is easy, it might have more but didn't want to spin it to 3k rpm. Not sure I'd really want to send this sucker down the road any faster anyways, especially with how people pull out in front of you these days. Wedged under my front differential isn't a great look for a Prius.
No additional top gear to unlock. 6cta doesn’t mind spinning a little faster but if you are running NHC 250 keep it under 2,200.


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G744

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If no one stated this, the Mack ENDT-673 is governed at 2100 RPM, whereas the Multifuel is somewhere around 2800. That explains your 30-something speed.

The Cummins 250's were usually set @ 2100 as well. Both those engines used the OD 5-speed.

The multifuel and big 6602 gassers used the straight 5-speed.

DG
 

5tonpuller

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Thompson, Pa
The truck does 53-55 and drives just fine. Bigger tires will make hills a lot slower. Over drive 5 speed will kill the small over the hill in the road. Will turn it into a shift me truck. I was told some time ago that "you need to learn to just enjoy the ride" . At 17 ton 53 year old truck is not going to be a speedy thing. A little better at hill climbing would be nice.
 

simp5782

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No additional top gear to unlock. 6cta doesn’t mind spinning a little faster but if you are running NHC 250 keep it under 2,200.


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They can turn 2700 before the valve springs give out. 2400 rpms unloaded isn't a big deal
 
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