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More Power From NHC 250 in M939 Series Trucks With Allison Transmissions

m16ty

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Why would you want a power robbing blower when the turbo works more or less for free? Only blowers that belong on diesels are old Detroits (because they won't run without one). I'd also be interested to see how you would drive a blower on a NHC250. Blowers for the most part are for gas engines.
 

patracy

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Why would you want a power robbing blower when the turbo works more or less for free? Only blowers that belong on diesels are old Detroits (because they won't run without one). I'd also be interested to see how you would drive a blower on a NHC250. Blowers for the most part are for gas engines.
We're getting off track, but there ARE cases where a blower should be on a diesel (Not just a Detroit)...

mms_picture-24.jpg

5.9 cummins. The supercharger allows for instant spooling from idle up. The turbo allows the flow.

If that wasn't enough, Carl has moved from that setup to a supercharged/compound turbo setup.
http://www.youtube.com/watch?v=ER9ddBIseTo
 

jedawson1

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Would the SuperCharge address the hi exhaust temp issue with adding a turbo on the NHC-250? With the lack of oilers, everything I have read says that turbo's (if not well managed) will burn up the pistons on the 250. So my question is, would a supercharger raise gas temps too? I'm not a diesel guy.
 

patracy

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No and the EGTs are controlled by the amount of fuel injected into the engine. The piston coolers do aid in cooling. But if one keeps the EGTs below 1200F everything should be safe.

(I own two diesels that do not have piston squirters that have been turbo'ed)
 

Jayco36REQS

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There are several classes of supercharger... major classes are attached (such as roots style, Eatons, Whipples, KenBell, etc) and non-attached (Paxton/Vortech, etc) The Vortech are like a belt driven turbo. The pros of the Vortech over a turbo is you don't have the exhaust restriction, no parasitic exhaust heat against the compressor, and no lag as it is instant boost since it runs off the crank.
Let's face it.. ALL engines are nothing more than air pumps... the more efficient you can run air in and out of that pump the better the engine is going to run. I've seen many applications of water injection for increased cooling of the fuel-air charge, cools the EGT's and which gives you more power.

If you look at a dyno graph of a single turbo engine, vs a supercharged engine... you will see VAST differneces in the HP and torque curves. On turbos, you have a high spike in the HP and torque curve. With Superchargers torque is flat... like with my 2003 SVT Cobra, I have 16lbs of boost at 2200 rpm under load.

With a turbo you have to build rpm to start getting any boost, and when you load a turbo engine, you have to stay ontop of the power curve or it will be a domino effect of continually losing power due to as the rpm's drop, the boost drops, the torque drops.. which further allows for reduced rpm, and the cycle continues. So for a turbo.. manual transmissions and gearing is critical to keep the engine at optimum torque rpm rage.

This is not the same for supercharged engines... boost is instant maxes out earlier in the rpm range. It's also VERY easy to tune a blower by changing pulley sizes and boost by-pass settings to meet the operating needs. Typically.. a supercharge engine it's easiest to run an automatic trans as gearing isn't as critical as your optimum torque range is a wide band. Ohh and the guys who say a supercharger saps too much HP than it's worth? You've obviously never owned a blown vehicle! lol I've owned both.. and when you hit the peddle... a blower car will instantly push you back in your seat, and the turbo car will slowly accellerate.

Now.. once you get to high rpm and/or long duration running ... turbos start to get more efficient. But honestly.. do we run our trucks a million miles over the road or run at high rpm with little loading? For most of us no.... We want torque for climbing hills, driving in the woods, hauling a load... etc.

So the more I'm looking at this truck.. the more I'm looking at putting a supercharger on it vs a turbo.

Plus.. I actually am one of those crazy guys that like a challenge and to be different. lol
 

Maxgussam

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Well I install the 22 button (stock is 27) have not been on the road yet, waiting to install the pyro., will let all know the results on the raising fuel by the lowering the button number
How did this turn out?
Did you do the "dual fuel line mod" as well?
I am planning on doing both of these mods, and I'd like to know what other's results were.
Thanks!
 

DeuceNewb

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can somebody tell me what the maximum safe rpm, or redline is for the 250? both my trucks have had no stickers on the tach, and the ones i see on gl differ from 2,000 to 2,400. I know the peak power is 2,100 but what about about a safe cruising rpm
 

73m819

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can somebody tell me what the maximum safe rpm, or redline is for the 250? both my trucks have had no stickers on the tach, and the ones i see on gl differ from 2,000 to 2,400. I know the peak power is 2,100 but what about about a safe cruising rpm
the -10 does not lie, 2100 or there abouts is the governed rpm, the 855 is very over rev sensitive, valves float, hit pistons
 

patracy

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can somebody tell me what the maximum safe rpm, or redline is for the 250? both my trucks have had no stickers on the tach, and the ones i see on gl differ from 2,000 to 2,400. I know the peak power is 2,100 but what about about a safe cruising rpm
According to the testing guide by the Red River depot, a maximum rpm of 2400 should not be exceeded for testing purposes. The governer starts to defuel typically around 2000-2100rpm. They will typically free rev to 2350 though. As well as run that downhill.
 

DeuceNewb

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I generally try to keep it around 2k, but i find that it keeps wanting to creep up, crusied for a while at 21, but every now and then going down hill it would just want to go faster and get close to 2300.

guess i'm just trying to convince myself I didn't hurt it
 
Last edited:

Rkrug

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Removed the anti tamper ball yesterday to reveal the fuel screw, turned it a half turn, and it sounds a lot more powerful when revving at idle and accelerates a bit faster to. I was wondering what the max number of turns I should back it out would be, to keep it in a safe range for the engine so I don't mess any thing up.
Thanks
RK




IMG_0878.jpgIMG_0880.jpgIMG_0881.jpgIMG_0883.jpgIMG_0884.jpg
 

stuntmog

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Get some 350 hp injectors, you need a turbo, get pump setup. First pull the pan and see if there are piston cooling nozzles on the oil galley. A Cummins shop could probably tell you by you "CPL" # on L side of the timing cover near the pump. If the motor does not have nozzles, it mat have plugged ports to facilitate install. Also ck on oil pump volume. BA
 

Artisan

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Get some 350 hp injectors, you need a turbo, get pump setup. First pull the pan and see if there are piston cooling nozzles on the oil galley. A Cummins shop could probably tell you by you "CPL" # on L side of the timing cover near the pump. If the motor does not have nozzles, it mat have plugged ports to facilitate install. Also ck on oil pump volume. BA
Stuntmog can you tell us what "CPL" stands for?

My CPL=709, any idea on weather or not I have plugs
or actual piston cooling nozzles installed ?

Engine dated 02-92
 
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