Engine/Transmission (1994 - 1998) EGT too high, too much smoke & bark

[Reddog1]

cerberusiam, I am thinking the PDR HX35/40 w/12 cm exh. turbo is a pretty poor turbo, and question what it's application would be.


KB0OU, I am the OP, and if I were too smart for your comments or anyone elses, I would not have ask the questions. I am sure there is more than one thought on my questions. No reason for hurt feeling because you disagree with someone, or they disagree with you. I do not see where anyone intentionally made a flaming post.

I posted; "Could you expand on your post to adjusting the wastegate for less "bark"? If I disconnected the wastegate, do you think that would stop the bark? If pulling up a slight hill, quickly let off the accelerator at 10 lbs boost, my turbo will bark. " My reason was to understand, not for any other reason.

I agree the boost elbow is an adjustment for the wastegate. My question was/is how does the boost elbow differ from adjusting the wastegate?


Wayne

 

[cerberusiam]

cerberusiam, I am thinking the PDR HX35/40 w/12 cm exh. turbo is a pretty poor turbo, and question what it's application would be.

Yeah, in certain situations it has issues. You have quite a bit of fuel when you get after it. When you chop the fuel its gone and the turbine won't support the exhaust flow in comparison to the compressor wheel. Its a problem that exists on a lot of these configurations.

I agree the boost elbow is an adjustment for the wastegate. My question was/is how does the boost elbow differ from adjusting the wastegate?

They essentially do the same thing albeit a little differently.



Boost drives overcoming the spring pressure on the WG actuator. Tighten the adjustment on the WG actuator and it takes more boost to open it.



The boost elbow acts like an orfice in the boost supplied to the actuator. Reduce the orfice size by tightening the screw and it will take more boost to provide opening pressure to the actuator.

 

[Reddog1]

I can't help but wonder if the wastegate is more efficient that the elbow. The elbow is certainly cheaper. If it did the same thing as the wastegate, why would we use a wastegate at all. I must be missing something.

Does your modified HX35 16cm housing have a wastegate?


Wayne

 

[cerberusiam]

I can't help but wonder if the wastegate is more efficient that the elbow. The elbow is certainly cheaper. If it did the same thing as the wastegate, why would we use a wastegate at all. I must be missing something.



Does your modified HX35 16cm housing have a wastegate?





Wayne

You have to have a WG on the smaller housing or the drive pressure gets completely out of hand as does the shaft rpm.



Your not quite thinking of this in the right light yet. The waste gate is a dump valve built into the hot side of the housing. It bypassess the exhaust flow from the turbine wheel directly into the down pipe. Remove the flow from the turbine wheel and it won't generate anymore boost by spinning the compressor wheel.



The WG itself is controlled by an acutator, essentially a boost activated solenoid that pulls a lever to open the WG. One side of the actuator is exposed to boost working against the other side that has a spring on it. As the boost rises it eventually over comes the spring pressure to allow the arm to move and open the WG. If you adjust the actuator rod so there is more spring preload on it it will take more boost to activate it.



The boost elbow does the same thing only it is limiting the amout of boost that actually gets to the acuator. Consequently, if takes nore boost on one side of the orfice to reach opening pressure on the other side.



Both ways, the WG stays closed longer allowing boost to build higher which is a double edged sword as you have found out.



No, the 16's didn't normally come with a WG. Everything smaller did to protect form overspeed. Even then if I hammer it hard enough and dump the throttle fast it will bark. Not like an HE351 but its definitely noticeable especially under load.

 

[KRStone]

You guys let off your pedal sometimes? Huh, never thought of that.

 

[The patriot]

I think you guys are way too smart for my comments but here goes.

The boost elbow sold by TNT etc is a ajustment for the wastegate.

No more comments on the barking turbo, obviously my comments are wasted here.

I just have 40 plus years working on diesels, I don't know much.

The Fairbanks Morris engines I have worked on would overload your trucks and your brains.

You mean "Fairbanks morse" dont you?:-laf

 

[GAmes]

The WG is on the hot side, its only held closed by the spring pressure on the actuator not the boost. The WG opens when boost exceeds the spring pressure on the actuator, it won't open until that happens.

That sure blows my theory out of the water. So what is the noise I hear when I shift gears. The turbo spinning down or the exhaust gas bypassing the turbine wheel?

 

[cerberusiam]

The turbo spinning down or the exhaust gas bypassing the turbine wheel?

Yep, the turbo is still spinning but not enough to support the boost so its bleeding back. Thats typical compressor surge as the compressor speeds up and slows down several times. Depending on the design of the turbo wheels, size of housing, etc, it sounds like a whoosh or a squeal or a wub-wub-wub.



Its better than a bark which is a full blown compressor stall from 10k rpms to nothing. Surge when you shift we can live with, surge at low rpms trying to tow is a huge pain. Bark, aside from scaring the wife and earning you a dirty look, is where you get broken shafts and grenading turbos.



When the turbine wheel comes out of the housing spinning 5-6k it tends to chop things up into confetti. :{

 

[Reddog1]

Your not quite thinking of this in the right light yet.

I agree. I will have to let this soak in, and get it all in perspective. I am sure I will be back to this subject with more questions.

No, the 16's didn't normally come with a WG. Everything smaller did to protect form overspeed. Even then if I hammer it hard enough and dump the throttle fast it will bark. Not like an HE351 but its definitely noticeable especially under load.

With my setup, what would be the result if I replaced my 12cm housing with a 14 or 16?





KRStone - The traffic is getting heavier, so letting off the pedal is a new experience.