Hi all, just hoping for some input on my engine. I have a '91 KW T800 with a Big Cam 4 that has about 65,000 miles since a major out of frame overhaul. It's basically a BC3 at this point as it has been upgraded to a high flow cooling system. The overhaul was done by the previous owner, well paid for by the previous owner and done at a very reputable shop. It was built using parts from Pittsburgh Power and is supposed to be making 600hp. It's running oversized injectors and a HT4B turbo. Now, this thing runs great, pulls hard, starts easy all that but the egt's run a bit warm and I get conflicting answers from PP and other drivers I've talked to. Maybe it's nothing to worry about but I just want to make sure this thing's running right and will last me a long time. So here's what happens:
Hard pull, 80,000 lbs egt's are 950 - 975, 27 boost psi, and 135 psi fuel pressure, 2,000 rpm
Moderate pull, 80,000lbs egt's run about 850, 35 psi boost, 210 psi fuel pressure, 2,000 rpm
Pittsburgh is telling me my egt should be 800 with 37 psi boost and 215+ psi fuel pressure.
I can get those numbers if I'm empty in high gear and then floor it but that's it. They think I have a boost leak but I cannot find one anywhere in the system. They're next guess is leaking/overfueling injectors.
A local shop here just said it's going to run warm with the bigger injectors and just to keep the egt's below 1,000 and it should be fine.
So anyway, I'm thinking about having the injectors tested or maybe replaced to try and get the egt's down a bit but I'm not totally sure it'd be worth the trouble/expense at this point. I feel like I'm overthinking this but like I said earlier, just want to take care of my truck.
Please Help me with my Big Cam Cummins
Discussion in 'Ask An Owner Operator' started by Ryan.W, Jan 26, 2023.
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Last edited: Jan 26, 2023
Mattflat362 Thanks this.
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I don't think you're the first person to get conflicting answers from PP.
Part of this depends where your pyrometer is set up.
I think about 900 post turbo is where you want to be. Those pistons are aluminum and heat is the enemy. 950 to 975 sounds like too much to me. I would drop the gear when you get to 900. Maybe that's all you have to do. Turned up engines are going to have higher egts and you need to know when to back out of it.
You also mentioned you want this engine to last you a long long time. A 600 hp big cam generally speaking is not going to give you the longevity of a stock engine or an almost stock engine, irregardless of what PP will tell you. Of everything I know about these engines 475 to 500 horsepower is about the line. Beyond that you're adding and subtracting. Adding horsepower and subtracting longevity.
@OLDSKOOLERnWV has a monster turned up big cam. I'm sure he can give you more information on how to make it last or what you should be looking for.Mattflat362, OLDSKOOLERnWV and haycarter Thank this.
To make boost there has to be Fuel….
EGTs seem fine just try not to hit over 1,000degrees for more than 5secs. The amount of Secs at high egts will destroy alum. Pistons. A quick pull of 1,100 degrees for 2-3seconds ok but with longer pulls damage engine in the making. You’re fine in my opinion.
If you’re a bit worried about it Try a Water/Meth injection system. Every time it hits a set EGT degree it will dose an keep everything cool.
I think You would be better of asking your question in the Mechanics Sub Forum...
Heavy Duty Diesel Truck Mechanics Forum
My advice (for what It's worth) is to turn the wick down to about 425-450Hp...!!!Dino soar Thanks this.
600 hp on a Big Cam…Hmmm.
If you want it to live, about 500 hp from a Big Cam is what you want. And don’t lug it…. when lugged the wrist pin bores will crack, and eventually that crack makes its way to the top.
What CPL is the engine & pump calibration?? What size injectors?
If it’s got big injectors it’s going to run on the warm side, you won’t be able to drive it carefree without watching that pyro.
I’m at times over 100,000 gross, and can’t complain about power from a dinosaur, but I’m not close to 600 anymore either…..jamespmack, Mattflat362, beastr123 and 3 others Thank this.
I agree, 900 after the turbo is about all you want. And dropping a gear is always your friend….beastr123, Dino soar and GreenPete359 Thank this.
Jubal Early Times Road Train Member
You are trying to pull in too high of a gear. That’s evident but the fuel pressure drop. If you can’t accelerate while climbing you need to drop a gear. That will bring temps down and fuel pressure up.
Pulling a hot big cam at 2000 rpm is getting low, time to change gears. Needs more rpm.
So I'll try to answer a few things:
I'm not 100% that it is making 600hp that's just what PP claims it should be making with the injectors/turbo combo.
I'm pulling grades in 1st gear, high range (I guess technically 11th as it's a 15 speed) going about 30mph. I can definitely pick up rpm's if I give it more throttle. What rpm range should I be pulling grades in with this motor?
I don't know what size the injectors are or how the pump is calibrated currently.
CPL# 1280 Pump Calibration Code# 4556
Thank you for the replies so farJubal Early Times and Mattflat362 Thank this.
My opinion, start the pull at almost max rated RPM. Pull it down to 1850 and downshift.
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