Turning up governed RPM

[Gunzy]

Has anyone turned up the governor on a NHC250? I would like to go up from 2100 to about 2500. I can only get 55mph out of myM923 with 11.00X20s and think at 2500 should be able to get a little more than 60, that would be nice. Any advice would be greatly appreciated.

 

[73m819]

Do you have a SPARE 250 sitting around, if not get one BEFORE you turn up to 2500 being 2100 is the Cummins gov. limit, they will run higher rpm but the higher you go, the shorted the life of the motor, at 2500, the motor has already died, at high rpm, (above 2100) the valve start to float, at aome point hitting a pistion, at that point it is the end of that motor requiring a head, piston/liner kit at the least.

 

[swbradley1]

I have not turned mine up but you know what I like about my NHC-250? Going slow and enjoying the ride. Running the urine out of it isn't in the cards.

 

[wreckerman893]

The "Nifty 250" is built to pull, not to run fast. Turning the fuel to it will cause it to build heat fast and heat (past a certain point) is not your friend.

You also have to remember that the speed is also governed by gearing in the transmission and rear ends.

An Allison out of a M915A2 might get you more speed but since the M915A2's only go about 62 at WOT with a 400 Cummins you might not.

The Allison out of a M915A3 might be geared higher (I never drove them in the Army) but they were a push button setup and you might have issues with cobbling a shifter up.

I have a M927 on loan to me with the 250 and super singles on it and it seems to do a pretty good job. I may take it out on the interstate and see what the top end is.

These trucks are what they are. Sometimes you just have to drive slower and smell the roses.

 

[Gunzy]

Thanks all for the info. That's good to know. I guess if I want a little more top end speed I would be better to go with the super singles. Maybe later as I like the 11.00X20 dual setup.

 

[Julian]

I have two trucks with the 250 and new 11.00x20s and they both run 59 mph at about 2100 rpm. The governor holds the rpm to about 2150 rpm and I get just a little over 60 mph. Your mph will drop as the tires get smaller by the same percentage of tire wear. The speedo in one truck is slow by about 4 mph at 2100.

 

[5tonman1971]

Your best option and cheapest option that won't put added stess to the driveline or engine would be to put the 14.00r20s on it and you will get it to 65-70 deffintly not recommended for sustained speeds. The tires are rated at 55 mph at their full load capacity which is far greater then the truck could handle anyway so you could safley travel at 60-65 mph but again that's on your own will.

I have the 16.00r20s on my m813a1 with the nhc250 and I've gotten it up to 75-80 just to see what it would do. Yes you will loose a bit of your bottom end with a larger tire size but if your just cruising the truck most of its life then it probably won't matter that much to you.

 

[61sleepercab]

Mack trucks used to have a tag on the injector pump warning not to turn up the fuel as "INCREASING FUEL DELIVERY 5% DECREASES ENGINE SERVICE LIFE 20%". I would just enjoy the ride or put larger tires for a little speed. REMEMBER WHAT GOES 80 MUST STOP FROM 80!!
I just pull over regularly when traffic piles up behind me on two lane roads because I do not want to drive white knuckled in a 5 ton.Mark

 

[Karl kostman]

RPMs over the governed limit are NOT NOT NOT the Cummins 250s friend! There are many reasons why its set at 2150 RPM!
KK

 

[Suprman]

You should look into an A2 truck the 8.3 motor will happily rev way past 2100 rpms

 

[Artisan]

68.4 MPH w/ 14:00 20's measured via GPS (M925A1)