Big Cam Cummins has low power

ya I posted the link for the guys to look into.

Old wrench I hear ya on the new motors. I hope to put a c15 in my 359 some day. I don't have anything against new motors at all. the maintenance is much less and they reliability is light years ahead..lol I just hapen to love 359 petes and most the other old iron

 

I am curious as to what was found out about the original posters engine.

 

Medicineman
I do understand what you mean about the old rigs, the 379 will always be a favorite with most guys, however the 388 is not bad looking. However aerodynamics plays a big part in fuel economy and this day in age that is the name of the game. The C15 is a great motor, but that would be a lot of expense for an older truck.
As for me if I were buying a new truck to run OTR I would be real temped to go with the 387 or the Freightliner Cascadia because of the aerodynamics and the DD15 Detroit, but that is just me. I really don't think that Detroit has anything over Cat but I just like their fuel economy.

 

I agree. If I were to buy new I'd buy a T660 or one of the aero petes. I'd take the detroit if you could get one in a pete of KW. I've always liked the detroits. We had some of the first series 60's in our 379 petes back in the day.
sorry I just can't talk myself into buying a freightliner. especially not the columbia, cascadia century models. after having to work on one of those centuries I swore I'd never buy one. you can't even see the motor without about 4 hours of tearing things apart

 

oh and yes it's allot of expense but it's a truck I don't plan to sell and it's less expensive then buying a new one. I don't like to work as hard as you have to for a new truck plus after my lat business endevor even Guito the bone twister won't barrow me money

 

850 is not too hot but getting to where you need tokeep an eye on it. I'd try the 15 but then start watching the pyro. you can't run these motors as hot as the new motors. 1100 and you'r too hot.
just remember the big cam has injectors driven off the cam. by increasing fuel pressure you are increasing pressure on the cam. there comes a point where you ned to put bigger injectors in as they won't flow any more just have more pressure and they will start to not atomize the fuel good and can wipe out the cam. I'm not sure of where that point is. I don't think a 15 will cause those problems a 10 might though but you need to ask someone who knows more about it then I do

 

Personally I wouldn't go to a 15, remember the idea is to get the optimum fuel air mixture, not see how much juice you can poor into the engine. One of the reasons your pyro will start running too hot is that the excessive fuel will actually be burning in the turbo instead of the cylinder. It sounds to me like you have a very good setup as it is. If it were my truck I would be looking for that perfect balance between maximum power with the least amount of fuel. If she is blowing black smoke, remember that means she is too rich. It has been a long time since I worked on the old pumps but I once thought that the more fuel that I could feed her the better she would run, that just isn't the case.
Medicine man made a good point regarding maintaining the reliability of your engine. You are never going to get that engine to run like the new ones. The thing is now with the ECM we can control the fuel mixture and timing throughout the entire rpm range of the engine. This alone has given the new engines a tremendous advantage both in power and fuel efficiency.

 

Have you had the overhead ran? You are geared way high for that motor, but it still should run better than it does.

Since your pump diaphragm was good, I would go to the next logical thing, which is the valve and injector settings.

If this has not been adjusted in a while then the valves have tightened up and the engine will not have any power at all.

If the engine seems to get weaker as it gets hotter, then that is a good indication of a tight overhead.

Set the valves about .002 looser than specs. This will compensate for the lost clearance when the engine gets hot. You should be able to hear the valves clicking , and when fuel is applied you should get a small amount of smoke and a decent rattle from the engine.

I still don't know if you have a formula engine (1900 max stock) or regular engine (2100 max stock), but whatever your engine is set at, run it in that rpm range. If your pump is set for 2100-2300 max, then the torque settings for the fuel application in the pump are set for 1700 rpm and up. Below that you are not doing the engine any good.

 

This sounds like my rig... my throttle response is ridiculous, very touchy. I also blow black smoke every time I grab another gear, not a whole lot to worry about but some. The plate mentioned around the throttle shaft, is gone on mine so I have every reason to believe that someone turned it up. My question is this; is it turned up too much? When I have the pump rebuilt here soon, will they reset back to factory or something? The motor does seem to run good going down the road, sucks when it is first fired up but I think my check valve is stuck open, anyone know where that is? I am thinking at the fuel filter but who knows.