Cummins 855 535hp Rated

[74M35A2]

Probably had an 8.3L or a 250 with two sprinkler boxes.

 

[simp5782]

Probably had an 8.3L or a 250 with two sprinkler boxes.

915 series trucks are real trucks sport. They dont want a small cam or school bus engine to power them.

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[Csm Davis]

It's a morphadite. BC3 and 4 mixture. Used a bc4 oil system, step timing control, bc3 aftercooler, conventional cooling instead of low flow cooling like the bc4. These are rated at that power because they are only used part time and not for prime power, long term running, most likely coupled to a 20-30 kw generator end. Boats are rated this way too, recreational boats will have c series, like in your five tons, rated at 750 hp because they are only used part time, not a lot of hours, the Howells will only take it on a 3 hour tour once a month. Commercial, like a fishing boat, will have less power because it is rated as a continuous duty, meaning it will be on the gas steady for hours on end daily. Same parts, just less HP due to the duty cycle.

Not just the piston squirters.

The older small cam 855's (like the NHC250) suffered from early cam failures when cranked over 400hp. 200psi of fuel pressure after the pump is reliably all the cam will survive.

Compression ratio varies as well but not by much. Anywhere from 14:1 up to either 14.5:1 or 15:1 (can't remember which), higher compression on the lower powered models. The piston material was different as well. The 250 has a mostly aluminum alloy piston while the higher powered models have a more heat resistant alloy.

For a reliable build the small cam NHC250 is limited to about 300hp ish, maybe 330hp if you really watch the EGT's. This is assuming no internal mods and the truck that hauls.

A big cam 855 block on the other hand, 700-800hp can be built reliable in a truck that hauls often.

So Will and Red will a 290 small cam live if I build it up like this 535 hp in a five ton and watch my EGTs?

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[Wildchild467]

You guys are a bunch of tool boxes. That 855 will drag me down the street in flames. The rest of yours, I'm not so sure about....

A worn out LDT-465 with lots of blowby DRAGGED you around.

 

[Wildchild467]

915 series trucks are real trucks sport. They dont want a small cam or school bus engine to power them.

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I'd LOVE a 916 and trailer to match. Zero use for it but it would be lots of fun! That or a Dodge Hellcat. 916 and trailer would be cheaper, but the Hellcat would have the "magnet" inside.

 

[simp5782]

I'd LOVE a 916 and trailer to match. Zero use for it but it would be lots of fun! That or a Dodge Hellcat. 916 and trailer would be cheaper, but the Hellcat would have the "magnet" inside.

They have the new Demon now that is something like 700+hp.

 

[swbradley1]

Off-topic but the Hellcat is 707HP.

Demon, 840HP.

 

[red]

So Will and Red will a 290 small cam live if I build it up like this 535 hp in a five ton and watch my EGTs?

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290 small cam? No it will have a short life if you try to crank it up that high.

A 290 big cam could be built up to those levels but not a small cam.

 

[Csm Davis]

290 small cam? No it will have a short life if you try to crank it up that high.

A 290 big cam could be built up to those levels but not a small cam.

Even if it is in a play toy truck? So the problem is wiping out the cam? 20,000 miles? 200,000 miles? And this will be because of excess fuel pressure over 200 psi?

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[red]

Even if it is in a play toy truck? So the problem is wiping out the cam? 20,000 miles? 200,000 miles? And this will be because of excess fuel pressure over 200 psi?

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Cam itself and possibly the crank bearings at those power levels.

To a certain point you can get the fuel flow by using injectors with larger orifices and keeping the pressure at/below 200psi. Eventually though it gets to where the fuel is just being flown into the cylinder instead of a mist, so poorly mixing with the air/incomplete combustion leading to less power and quickly rising EGT's.

Towards the end of the small cam line Cummins offered a 400hp model. Most common complaints on it are the short life of the engine and needing a rebuild, usually cam failures.

It's the same cost to get those power levels out of a big cam, but the big cam will handle it longer.

As for how long a small cam turned up that far would last used as a toy, can't say. Roll on the throttle easy every time and maybe see 400-600k miles. Or stomp on it once and shear a cam lobe within 50k. Maybe the cam has a minor manufacturing defect or is just fatigued from age leading to a early failure.

Running take out big cam engines are available for pretty cheap, less than 4k. Saw one last month for sale with 300k since rebuild, gen 3 400hp big cam with a head gasket leak sell for 2k. Still ran fine was just dribbling some coolant out of the head gasket by the #3 cylinder.



The other concern at those power levels is the torque going through the transmission/tcase. Once you pass about 330hp with the 855 series engines you're over 1000ft/lbs torque. Unloaded or not loaded real heavy most of the time they should be ok. Cranked to over 500hp gets the engine to over 1500ft/lbs of torque, plan on a trans/tcase upgrade.


The small cam 855's are good motors, but their big cam 855 replacement is better. I'm planning to upgrade the NHC250 in my m816:
Dual fuel lines
Swap the fuel button
adjust the pressure to 200psi
Turbo. Debating trying out a 'small' compound setup with a hx55 with a 11 blade impeller and either ht3b or hx60. With that bottom turbo setup it should spool up very early to help out with the 800 ish rpm drop between 3rd/4th gear. Haven't seen anyone try it yet but the Chinese copies of those turbos are inexpensive.

Have to find out what pump mods have been done to mine before I got it. After installing the EGT gauge found out that it will climb to 1400F and there are shims added to the plunger, will turn 2500rpm while driving. Both are too high. When my motor goes (hopefully after a long life) it will be swapped out for most likely a big cam.

 

[Csm Davis]

Okay well 2-4k might not be hard for some to come up with but I will blow up my 250 first then my 290 buy then I should be to old to care. And hey y'all can have fun holding my beer while I say watch this!

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[WillWagner]

So Will and Red will a 290 small cam live if I build it up like this 535 hp in a five ton and watch my EGTs?

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No

 

[Csm Davis]

No

So Will what do you think the highest fuel pressure should be on a small cam? 200? 190?

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[WillWagner]

So Will what do you think the highest fuel pressure should be on a small cam? 200? 190?

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If you ain't using the truck to pull 80k on a regular schedule, 200-210 will be ok, short trips, parades won't hurt it, BUT, higher than specified rail pressure will break cam follower shafts, roller pins and compromise injector lobes in a very short time. And, if you don't catch the failure, the little pieces parts of the failed cam can and will cut through the filter media, ESPECIALLY if the filter is an old style paper media, and go directly into the mains which in turn goes to the rods and before you know it, the bearings have grand canyon deep gouges in them and you loose a bottom end.

WHY do you need more fuel pressure? Accelerate a bit faster, it won't be that much faster. More pulling power? It is a NA, 855cid engine, it will only do so much without being force fed the air needed to make better, usable, reliable power. All the black smoke out the pipe is just wasted dollars.

But it's YOUR stuff, do what you feel you need/want to do


The above is worst case. I have actually seen this. Small cam 350, overhauled with a new cam and followers, and I was told NOT to touch the f/p. After overhaul, I put it on the dyno to seat rings and check leaks. It put 390 to the ground, keep in mind, normally you get 75-80 % of flywheel rated hp delivered to the ground on a 3 axle truck. Rail pressure was 250 ish. I noted it in my story. It left on a Friday AM. He hauled drywall. 1 trip, LA to Sac and 1/2 way back, and the truck was in the driveway Monday am. All 6 injector lobes were wiped out, some of the worst I had seen at the time. IIRC, 4 of 6 of the pins were broken. When I cut the filter open, the media was full of cam material and the pleats has ripped, The OP regulator had stuck in the up position, meaning it was making 100+ psi op. All the mains were trashed,, #4 spun, the 2,3,4 and 5 rods had spun and the engine was locked up and was now junk.

Just sayin'

 

[WillWagner]

Small cams weren't the only cam eaters, BC2 and 3 MVT engines liked to eat cams and the early L10 was REAL bad, Seen those leave friday and be back monday, UPS had alot of issues with them

 

[Csm Davis]

If you ain't using the truck to pull 80k on a regular schedule, 200-210 will be ok, short trips, parades won't hurt it, BUT, higher than specified rail pressure will break cam follower shafts, roller pins and compromise injector lobes in a very short time. And, if you don't catch the failure, the little pieces parts of the failed cam can and will cut through the filter media, ESPECIALLY if the filter is an old style paper media, and go directly into the mains which in turn goes to the rods and before you know it, the bearings have grand canyon deep gouges in them and you loose a bottom end.

WHY do you need more fuel pressure? Accelerate a bit faster, it won't be that much faster. More pulling power? It is a NA, 855cid engine, it will only do so much without being force fed the air needed to make better, usable, reliable power. All the black smoke out the pipe is just wasted dollars.

But it's YOUR stuff, do what you feel you need/want to doJust sayin'

Okay well the 250 won't be NA for long and I don't want to jack the fuel pressure over 200 if I know it will kill the engine, but I am going to beat on the engine without mercy and I expect it to fail at some point.
Then the 290 formula will get modified and installed, hopefully to last a bit longer. If it doesn't last long enough for me to get to old to want to mess with it then it will probably be replaced by a 8.3l or something.


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[74M35A2]

Yeah! And stay out!