NHC250 needs more power

[jatonka]

Chiming in with maybe useless informatrion here, but I'm going to try to help those who will listen. Cummins 855 engines, also known as NHC 250, and others, do NOT turn over 2100 RPMs and live long. Ask any real Cummins mechanic, don't trust me. Of course, I've been around Cummins and owned them since 1969 and haven't ruined one yet. But I'm not a Cummins mechanic. Leave the motor alone, add more gears. plain sense. JT out

 

[Gamagoat1]

JT.
You are absolutely correct. These are fine engines if they are treated the way they were designed. I shudder every time I see someone say they drive at 65 MPH or turn 2400 rpms with one of these. The 816 is governed at 52mph. Don't know what or when mine went but it started knocking at about 45mph, and you see what I have.
With a rebuild of #3 and #4 it will last as long as I have it if treated right.

 

[BobS]

If you are interested in increasing the HP from any of the 855CID Cummins engines, talk to Diesel Injection Service (Pittsburg Power guys) and read the cautons and "hop up" articles they have posted on their website. Bar none in the NAFTA area-no one knows more than these guys about "what if's" and the 855's.

http://www.dieselinjection.net/BRUCE/index.html

Best regards,

Bob

 

[jwaller]

OK ,
Here's what happens when the fuel is turned up on the NHC250 in a M816.

how high was the fuel turned up in this motor? and the max rpms was also increased?

I have an EGT that will be here friday and I am going to see where I'm at with EGT before I touch the pump and think about giving it more fuel.

 

[Gamagoat1]

It looks like no more than a full turn above nominal setting.
I think someone down shifted and over sped the engine to break the rings. But the high temp evidence is there also.

 

[AMGeneral]

Ok,Just wanting to clarify here and not step on anyones toes,I appreciate all the info and the pictures. I too have quite a lot of time and expierence with diesels,both on and off road,Cat,Cummins and Detroit Diesel,From 2/53 Detroits to the V1710 and 3412s we use at work.I'm not trying to turn my 816 into a race car(by any means)possibly my hippo and elephant comments were slightly off color.I keep my truck at 50 mph or below and it's NEVER overrevved,The only reason I have contemplated rasing the governer limit to 2450 is to compensate for the large jump in gear ratio between 3rd and 4th gear associated in the 800 series trucks.This will be the only time this rpm is reached in this truck.After reading my earlier post I also realized I typed in 1 turn out of the screw when actually it was only 1/2 a turn(typing error on my part).Once again not wanting to step on anyones toes or offend anyone here and if I have I apologize up front,just trying to clarify the reason for the post.

 

[Gamagoat1]

No Problem here.
I guess I'm getting old, just hate to see these trucks and systems abused.
The stuff coming up from surplus, in the future, will not hold a candle to these. (If the Govt. lets us buy them.)

 

[TheBuggyman]

I just called Diesel Injection and a tech there named Gary told me that if I wanted more power then I needed to buy another style of engine!

I suppose that they do not want the liability of turning up a 250.

But my truck needs just a TAD more power to pull those hills with the 14.00R20's,
could someone explain in detail what was done in the post that talked on adjusting the "screw 1/2 turn"? 15 or 20 more HP would be fine I suppose.......

 

[DaveP]

I dont want to cook my 250 either. i just needed to make it possible to pull a decent load. i dont over rev or let the exhaust temp get high. but if it does cook that will give me the incentive to plop in the 335 (with jakes) with the 13 double over trans that i have been tripping over. then the possibilitys open up a bit more. i like the power of the 400's but they are thirsty so ill stick with the little 335's when the time comes. maybe the M819 will get the 400 since it will be pulling a little more weight.

 

[jwaller]

my egt came today. it will go on in the morning. then I can see where it sits stock.

please somebody tell me where this screw is and pics would be great. I've turned up the fuel on the deuce so I'm not a total noobie but I havent done anything but pmcs on the 5T.

 

[DaveP]

my egt came today. it will go on in the morning. then I can see where it sits stock.

please somebody tell me where this screw is and pics would be great. I've turned up the fuel on the deuce so I'm not a total noobie but I havent done anything but pmcs on the 5T.

are you talking about drilling out the throttle shaft plug?

 

[AMGeneral]

Ok,Below is a picture af the Cummins PT pump on my 816 and the area in question.The aera just to the right of my finger is the end of the throtttle shaft,usually this shaft end is capped off with a lead,brass, or plastic ball,the screw in question is directly behind this.But as Will Wagner said,these engines aren't piston cooled,don't get real over zealous with the fuel.I would go 1/4 turn at a time counter clockwise,drive then repeat keeping the exhaust temp under 1100 if it was me.I only did 1/2 turn out over stock and my 816 runs noticeably better,but it's still a 36,000 lb truck so not expecting 625 hp preformance here.Also black smoke looks cool but it's just unburned fuel going out the pipe,I'd keep the exhaust to a point where it's noticeably black but not blotting out the sun black.Just my

 

[WillWagner]

Be careful. Cylinder kits aren't cheap! Also remember that the Small Cam followers are a weak link. When you jack up fuel pressure, it loads the injector pushtube and follower alot more. Pins like to break. Worse case scenerio, pin breaks, pushes out the side of the follower, sticks a valve follower, bends a pushtube and puts it down in the bottom, gets hung up on the crank and holes a block either externally vented or smacks the main oil rifle and ruins the casting that way...or...pin breaks, blah, blah, hangs a valve open, piston/valve contact, breaks a liner, piston gets stuck in the block at the crevice seal, bends the rod and then takes out the block. Seen both failures! But then again, seen ALOT of Small Cams that are dragsters with no problems.

 

[jwaller]

its all a crap shoot. I might get luckly with 1/2 turn and be happy and it last forever. I might go 1.2 turn and it might not make it till the end of the week. I've blown my fair share of dragmotors to know.

 

[jwaller]

thanks for the pics. I couldn't for the life of me figure out where ppl were turning these things up.

 

[timntrucks]

lets keep this post going as i want to hear about jwallers temps, maybe before and after? with the 1/4 turn, im thinking about turning my m816 up some Tim

 

[jwaller]

I will have results tomorrow. I had to finish some other stuff with the truck today.

I did look at my pump and I have a steel plug in there. so it wont be as easy for me to get to that screw but I will prevail.

 

[WillWagner]

jwaller,
when you drill the ball, be careful when the drill does thru the ball. It pushes against the screw and turns it in. Then it's kind of like starting over 'cause you don't know where you started.

 

[OPCOM]

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.

 

[redass73]

is there a standard for the screw. (say 3 turns out from seated) or anything similar. wanted to check mine .
I would love to see a pics of a turbo set-up on the 250.
thanks
rick