mooktank

Next mod I really want to do is the piston lift pump but I can't find a good source for parts. I've been talking to a guy directly from cummins northeast but he seems like he really doesn't want to help me. This is the only bad thing about cummins I think. You can't get parts like you can for a ford or chevy engine. Kindof a pain.

JimmieD

Curious how much of a performance increase you got from this: dramatic? Amazing? Fair? Ho-hum?

mooktank

Well it's noticeable for sure. The new turbo kicked it up a lot when I upped the fuel a little. I would like to hit a dyno soon and see how it really is.

mooktank

I just put on my piston lift pump yesterday. I didn't need the tube which cost me a good $30. If anyone wants it let me know so you won't have to buy it from cummins.

Now I just feel safer. It runs just about the same I just am not worried about blowing an injector pump as much. Now it's time to do the gov spring and some injectors.

JimmieD

Hey, Mook, I'm thinking there might be a little something that's being overlooked here. Don't quite know how to explain it, but that never stopped me before

This is a 4BT, not a 6BT. The exhaust is what spins the turbo up and in order to do that the exhaust has to complete the trip so to speak, as in blowing out the pipe. The 4BT is missing 2 exhaust pulses because of 2 less cylinders compared to 6Bt, at whatever rpm or load. That's a 33% loss of pressure against turbo's exhaust impeller and also less pressure to pump the exhaust out the tube. That could be why Cummins specd. the 4BT to use 6BT's H1C turbo and what amounts to a performance exhaust at 3", equivalent to a 4.5" on a 6BT. That's one reason I'm going to an HTT Stage II on my 4BT, to address these possible problems of 2 less cylinders.

Can't really use 6BT as a reference for what's 'Normal' for this turbo and fuel combo even though they share the same engine design. Volumetric efficiency is only the same per cylinder, not overall! Strange as it seems you might need bigger exhaust and smaller exhaust housing with a better wheel in order to even spin your new high pressure/volume turbo? Does that make sense? It's sorta like 2 of the guys never show up for work on the turbo crew....

mooktank

Well I'm not sure about a 33% pressure decrease. It may be close to that. But it's not just pressure that makes a turbine work. It's enthalpy which involves pressure and temperature.

I wouldn't go ahead and assume a 4.5" exhaust on a 6bt is the same as a 3" on a 4bt. It makes intuitive sense but I would look into it more...

I'm keeping the turbo I have now anyhow so it doesn't matter. I couldn't fit a bigger exhaust unless I wanted to run it through the hood. I may even need to oval mine a little where it goes between the engine and frame for clearance. It vibrates at certain RPMs and edit me off to no end.

Overall I think the turbo will flow plenty of air now and I'm moving on to my fuel side of the equation.