Options for higher top speed?

[patracy]

You can do governor springs and get a few more rpms. Which will equate to a higher top speed. The engine will happily rev into the 3000s but the drivetrain is only good for around 2800 or so. The truck really isn't designed for speed. You won't be happy going up hills with higher gears. A few turns on the fuel screw and a few hundred more rpms really breathes life into the truck though.

Just to clarify things for those following along. The 8.3 can rev at 3K. The NHC250 will not. (Well, it will, but not long...)

 

[jasonjc]

I had a 12.50r20XL blow out about a 1sq foot chunk of side wall doing 55!

 

[Csm Davis]

You know,...I have wondered about the potential for this happening. Has anyone heard of these tires actually coming apart due to high speed??

My Frankencab goes 72 on flat ground and I have had it up to 78 going down grades here in the Appalachians on I77...especially driving it back from GA.

I have the 14.00x 20's Goodyears.

Yeah I have but call Goodyear and ask them about it.

 

[Gunzy]

Best option for higher speeds? Buy a commercial OTR truck. Military stuff is NOT designed to run at current highway speeds. That is the reason when you see convoys they have lead/follow trucks with "CAUTION" signs.

 

[Alexsha]

Half the fun is going at you own pace.

And 55 in one of these trucks seems a lot faster when you need to stop quick!

 

[98G]

Half the fun is going at you own pace.

And 55 in one of these trucks seems a lot faster when you need to stop quick!

Yes, and as one person's signature says "I have never had so much fun driving so slow"....

 

[BrainP]

I agree, when I drove it home for the first time I was cruising at about 60mph and was happy with the speed. im just trying to get the rpms done. I live outside of town a ways and travel on country roads to get to the hardware store. it would be nice to have a lower rpm on these flat roads. I not try to speed so much as just cruise, guess I should have worded it differently.

 

[Baradium]

I did not start this thread but this is what I have . 1967 M52A2 with 11.00 20 tires when it had the multifuel it ran good at 46 miles per hour now with the Mack 673 it runs about 39 MPH with the non over drive transmission . if I change to the over drive 6453 it will help some how much ? I have looked at the back rearend to find a ratio some numbers but not 6,44 maybe the gears where changed to 8.88 any thoughts ?

If there is a tag sometimes the numbers are the teeth on ring and teeth on pinion, divide out and you get the ratio. Keep in mind this is experience with civilian axles, I haven't tried to find tags for gear ratios on a military vehicle before... hasn't been an issue. Even if you do find a ratio from numbers on a tag, that doesn't mean they were never changed etc.

 

[topo]

Thank you for the information . On the tags I looked at I was looking for 6.44or 8.88 I will look again . 39 MPH seamed slow it having 6.44 gears .

 

[73m819]

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.

A 939 transfer case is already a overdrive unit, the 39 and the 809 series is 1 to 1

 

[Ford Mechanic]

A 939 transfer case is already a overdrive unit, the 39 and the 809 series is 1 to 1

I have been told this before and didn't catch what was meant then.

What your saying is the high range in the t-case is a od ratio not 1:1? The trans also had a od ratio for the top gear?

 

[ThatXJGuy]

I did not start this thread but this is what I have . 1967 M52A2 with 11.00 20 tires when it had the multifuel it ran good at 46 miles per hour now with the Mack 673 it runs about 39 MPH with the non over drive transmission . if I change to the over drive 6453 it will help some how much ? I have looked at the back rearend to find a ratio some numbers but not 6,44 maybe the gears where changed to 8.88 any thoughts ?

My ENDT-673 powered M-62A1 does about 49 at 2,000RPM with the overdrive transmission. Never heard of the 8.88 gears honestly so I always assumed it was the 6.XX ratio but I could check. It handles and brakes very well at this speed on the 11.00-20s it has on it and I would certainly like to find something to help it go a little faster. Just like 65 at 2,000 so I can comfortably cruise in the upper 50s without revving it up so high.

 

[topo]

Thank you for your information ThatXJGuy. I will be looking for a overdrive transmission.

 

[Csm Davis]

I have been told this before and didn't catch what was meant then.

What your saying is the high range in the t-case is a od ratio not 1:1? The trans also had a od ratio for the top gear?

Yes in the M939 series the transfer case is overdrive.
The transmission is Not.

 

[Ford Mechanic]

Thanks for clarifying

 

[Jayco36REQS]

My 923A1 cruises between 68-70mph on the gov... I drove it from Dayton OH -to- Orlando FL and cruised it on the gov the whole way... and this while towing a M796 Bolster trailer, and fully loaded truck and trailer. I had the tires aired up to 85psi, and it drove great, handled great, braking was still really good.. (YES... I had to use them a few times for idiot drivers.. ****, NOT like you can't see this thing!!...LOL)

Personally, with the tall sidewalls and handling characteristics of these trucks... I doubt I'd want to go much faster, especially with a load... unless your trucking through the desert on flat roads! lol As it's been stated, these trucks are interesting when emergency handling comes into play.

The only things I've done to mine is a #22 fuel pill, shimmed the pump, turned the fuel screw 3/4 turn, and added a fuel line to the back of the motor.... It starts great, runs smooth, and scoots right along. I have plans for a turbo still, (that project got put on the back burner due to my move to FL). Once I get moved into my new house, and get the building built, I'll put the turbo on and play with the fuel a little more to control the EGTs, and help with the steep hill slow-downs. Ohh, and add a dump cylinder for the bed. lol

Good luck with your truck... and don't let others talk you out of something.. It's your toy.. play with it, and see what makes it more fun for you! But just make sure your safe to yourself and others out there... so you are around to play another day! Cheers!!

 

[ThatXJGuy]

You guys are making me want a 900 series for their top speed. My trucks could never achieve those speeds, not for lack of power but for lack of gearing or RPM.

 

[ke5eua]

Yes in the M939 series the transfer case is overdrive.
The transmission is Not.

So if I drop a 900 series transfer into my 818 I will essentially have a double overdrive?

 

[ThatXJGuy]

Which transmission's top gear is the tallest? The overdrive Spicer or the Allison?

 

[Csm Davis]

So if I drop a 900 series transfer into my 818 I will essentially have a double overdrive?

Yeah it has been done, i forget who.