Engine/Transmission (1994 - 1998) waste gate theory

[DValentine]

I hooked up a pressure regulator in between my intake manifold where the boost elbow was and the steel line going to the turbo. I did this to be able to regulate the W/G on the fly. My question stems from the fact that when I open the valve, per stock cummins set up, my boost drops and the egt's go UP.....



I have not messed with the W/G only put on a turbo mount Pac Brake. I just seem weird to me that the gate opens and egt's go up. Boost drops 22 pounds which makes sense to me.



Am I looking at the system wrong? Understanding the system wrong?



I was hoping to reduce egt's while towing my 5er on long hills, and then letting the boost rise on the flats. Hoping to have the best of both worlds.



Dave

 

[fox]

More pressure opens the wastegate. That in itself will not raise EGT's.

 

[DValentine]

Yeah, the boost pressure is on the intake side of my regulator, when closed and nothing on the W/G head. When pulling a good hill with the 5er, in 4th... . at 35 pounds boost, with the regulator closed I see 1100 degrees (pre-turbo). I open the regulator , letting boost to the actuator, boost drops to 22-23 pounds and the egt's climb fast to 1400 or above. This is at 2500 rpm.

I just can't figure out why, when the w/g opens the temps climb so fast. I figured it would have been opposite.

Thanks,

Dave

 

[Bob4x4]

You have less air flow through the engine at low boost

 

[WDixon27]

less cooling air with more then stock fuel and it will get hot and blow black smoke, if you want/need to cool it down you need less fuel or more air

 

[DValentine]

I agree with the statement that with the wast gate open, with less boost, I am over fueling. I just don't see a whole lot of smoke.

Thanks guys.

 

[BigEasy]

less cooling air with more then stock fuel and it will get hot and blow black smoke, if you want/need to cool it down you need less fuel or more air

Exactly. My question tho, has always been is the cylinder temp actually higher, or is just taking longer for the fuel to burn, actually putting more fire into the manifold... nearer the pyro probe?

I have never been a fan of wastegates at all... they are simply a compromise to let one turbo fit all applications.

 

[Missouri Mule]

You need all the oxygen you can get going up hill!

When the boost is up that means the engine is working hard.

If you want to open the waste gate open it going down hill or on the flats.

 

[cerberusiam]

Exactly. My question tho, has always been is the cylinder temp actually higher, or is just taking longer for the fuel to burn, actually putting more fire into the manifold... nearer the pyro probe?

Both. Under load and higher rpm there is more burn time in the cylinder which raises the cylinder temps. Lack of oxygen slows and extends the burn time so its hot in and out of the cylinder. Added air keeps the temps mostly in the cylinder with the accelerated burn time plus robs temps to heat the added air.



You have to be careful with added air and fuel when the EGT's stay in a usable range. Cylinder pressures and temps are a lot higher than the EGT's indicate.

 

[DValentine]

I see that my thinking was backward. Glad to have the conversations. That is what I like about this forum.



D

 

[Joseph Donnelly]

A discussion of turbocharger wastegates can be found in TDR Issue 59, p. 95. If load, fueling, and rpm do not change when the wastegate opens, egt and backpressure will go up due to the lessening of drive pressure on the turbine wheel. The lower drive pressure will reduce boost pressure as well.