NHC250 needs more power

[jwaller]

those pistons would make good ashtrays. I recall many a burnt/cracked piston as a counter top ashtray in the old auto parts stores of times past.

ya they are nice and big. I've got plenty of sbc pistons I killed with too much boost and not enough fuel.

 

[spicergear]

I bored out the inside of one of those pistons and used it as a cup holder in my one truck a time ago-

 

[m139h2otruck]

I have been following this thread for a while, since the M812 is a Cummins. A local trucker/engine builder here, built a hypo 855 Cummins a few years ago with the help and advice of the guys in PA. They figured that they were getting nearly 1000 hp out of a stock block engine with a compound turbo, special fuel advance and and special pump. When I questioned him about RPM and head work, the only thing he said was that pistons are the key to high HP. They were using special factory pistons made specifically for the higher temps and pressures of the compound turbos. RPM limits were about stock @ 2100-2200. Heads and valve changes were minimal. He ran this engine in an older Pete for a few years, but it was hard on u-joints and rearends. Claimed it would spin the tires loaded @100,000# going up hill in the rain as the boost came up!

I guess my short point to a long story is that it seems that the pistons are more or less the weak link in these engines as long as you don't raise the RPMs.

 

[jwaller]

I ran the truck just now on the way to work and it's good and bad news.

Good that I am under the 1200 max temp but bad in that I'm not that far off.

I was only able to make 4th gear max rpm loaded pulls bc of the roads I was on but it shouldnt matter which gear I was in.

max egt was 1050-1075F@2100rpms with a sustained long uphill pull on several ocastions.

So I wont be able to get much more power from this thing if I stay at the heretofor reccommned 1200degrees.

 

[DaveP]

you will still notice quite a difference when you run it up to the max temp.

 

[WillWagner]

Try another 1/4 turn and see what it does. Keep in mind, the ambient has alot to do with it.

 

[jwaller]

you are right. but I havent touched it yet. I simply ran it stock to see where I am at. I will try tomorrow to make an adjustment with the screw. that provided I can get to it.

 

[D'cheat]

Any updates how how this affected performance?

 

[jwaller]

ya. none. when I got her loaded down it appears my pump was already maxed out. I pull 1200deg on long pulls when loaded. now if I were just bobtailing all th etime I could run more fuel but not when loaded.

I've now moved on to adding a turbo to get the power I need.

 

[MidnightDuramax]

How do you tell if it has a PT pump or not? I have a 1970 M818.

 

[vinny-socom1]

Thanks for the updates and pics!! I lost this thread and missed a couple of posts

Vinny

 

[m16ty]

How do you tell if it has a PT pump or not? I have a 1970 M818.

All Cummins powered 5-tons have the PT pump.

 

[PowerstrokeNC]

How about a turbo with only 3-6psi? Ought to give another 100#tq huh? Maybe save some bread and get a big cam 350 or 400 Cummins...may even be able to find one with a Jake on it--

This is exactly what I have been thinking, just a little push of air to get better throttle response , pulling on grade etc. nothing too wild that starts sacrificeing metal bits..... Anybody do this?

 

[bearboley]

A NTC290 is just a NHC250 with a turbo and a bright and shiny 290 will pull 80,000 around just fine. Its a can of worms when you start makin power with those old small cams they like to stretch head bolts when you lug them and burn pistons when you pull them lack of charge air cooling would be my guess. If you got ur pump off pull the throttle shaft and replace the button with a small number cummings parts dept will have them and add a couple high rpm shims in the back of the pump that will increase you fuel pressure and rpms. I've driven a few that would dead rev 2400 rpm with no troubles. You will be good to go. But after I told you this I have a 816 thats a dog and I just drive it sure I could make it a 400 if I wanted to but that little trans. and driveline won't take it for long. That driveline my look heavy to some but as far as class 8 trucks go it actully not.

 

[Floridianson]

Don't know if anyone has checked there rail pressure but I have mine at 180 psi. on one of the motors. Think the book called for 172psi.

 

[quickfarms]

subscribed

 

[goodguyzy]

also

 

[dezert ratt]

my tach is broken in my 818 and im new to the nhc 250. when i am accelerating am i gonna over rev the motor? i understand downshifting and overrevving and downhill overrevving but what about just on flat ground? reason i ask, ive been driving carefully and a couple times it felt like the motor stopped making power at a certain rpm.

 

[73m819]

You hit the governor, you really need to FIX the tach

 

[dezert ratt]

Darn tachograph, ill check it out asap