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

[Reddog1]

EGT’s climb quick , a lot of smoke on initial acceleration, spools very quick. (about 27 to 28 PSI), quickly let off pedal (10 pounds boost or more) and turbo will bark.



After hours of searching and reading past Posts (this Forum and others), I think I need to change the injectors and exhaust housing, but would be interested in other thoughts.



I have had the mods listed below for three to eight years, with the turbo being the latest. I have modified and adjusted the AFC several times. I usually haul a 4200 pound slide-in truck camper. MPG empty is typically 17 to 17. 5, with camper 12 to 12. 5. I am very happy with the power.



PDR HX35/40 w/12 cm exh.

boost Elbow

#10 plate (stock position)

370 injectors

Timing 16*

3KGV

60-lb valve springs

Marine Head Gasket (0. 020)

4" muffler & back, (3” turbo through 3-inch US Gear Ex. Brake to 3” resonator)

BHAF

Auto (DTT)

1996, 2500HD, 2WD ‘96

US Gear aux. tran. (underdrive - 4:10?)

3. 54 gears

19. 5 tires/wheels (32-inch diameter)





Wayne

 

[hsmith]

A larger turbo solved my barking issues long ago.

 

[JDKammin]

You need to get a different turbo, then you can get rid of the boost elbow. Also, look into some SDX injectors. The 370's are an OK injector and I am currently using them. They have a wider spray pattern than what should be used with the pistons in our trucks, which can lead to some unburnt fuel. I bought a turbo thru Engineered Diesel and am happy with what they built for me.

 

[Vaughn MacKenzie]

Yep better injectors and bigger turbo would help.

 

[Reddog1]

I think I am limited on what I can do with the turbo, due to my exhaust brake. The US Gear Exhaust brake is the same size as the stock exhaust, so it limits me to a stock down pipe. I think I will have to drop back on the fuel to reduce the EGT.

I am aware of the downside of the 370s. I have been running them for over six years. It is my understanding, one of the characteristics of the 370s is excessive smoke. I don't know how they effect the EGTs. I think dropping to a smaller injector may help reduce the EGTs.

Wayne

 

[Reddog1]

Vaughn MacKenzie, I see your '96 has the Hybrid 35/40 isn't that the same turbo that I have? My pump (180?) is stock. What fuel plateis in your '96? Would the DDP Stage IIs produce less smoke and have lower EGTs?


Wayne

 

[JMcCoy]

Smaller injectors will help, but your real problem is the exhaust. You say your happy with your power. I would sell the exhaust brake and buy one for a larger exhaust. Maybe US gear will just sell you the 4" pipe and butterfly, for a fraction of the total price of a new exhaust brake. A three piece exhaust manifold will also help lower your egts. I would just hate to see all your nice mods go to waste. Keep us posted. Good luck.

 

[Reddog1]

I am happy enough with the power I think I would be OK with less. Exhaust brakes are very pricey. It is my understanding US Gear no longer has the RV line of products, so no help there. I think the exhaust brake is more valuable than the power, depending on how much I have to give up.

I have considered the three piece exhaust manifold, simply because of the potential of shrinkage and damage of the stock one. What do you think I could expect in EGT reduction?

My EGT complaint is related to going up a long hill at 70 MPH, with a 4000 pound slide-in camper in the bed. I can hold the 70 MPH, but the EGTs are just under 1500 degrees. I do not need a great amount of EGT reduction, but definitely need some.

What differences should I expect for changing out the 12 cm exhaust housing for a 14 cm housing? Preferably without (cost) a wastegate?

Wayne

 

[GAmes]

I want to add that the "bark" is really a compressor stall and will aid in the early death of the turbo if you aren't careful. My fairly new to me PDR HX35 will bark a lot easier than the stock turbo did, so I have to be careful on my downshifts when pulling hills while loaded. I too have an exhaust brake so I feel your pain.

 

[Reddog1]

I want to add that the "bark" is really a compressor stall and will aid in the early death of the turbo if you aren't careful.

That is my understanding.

My fairly new to me PDR HX35 will bark a lot easier than the stock turbo did, so I have to be careful on my downshifts when pulling hills while loaded. I too have an exhaust brake so I feel your pain.

Is this typical of the PDR HX35? If so, what is the cure?



My auto will make the turbo bark. I am beginning to think I made a bad choice with the PDR HX35, if the bark has to be tolerated.



Wayne

 

[Driftwood Ram]

Try taking out the silencer ring and see if that helps the "bark".

 

[Reddog1]

I will remove the silencer ring, to see if it helps. I see you removed yours, did it help reduce the bark?

Your signature looks very much like mine, with the exception of the injectors. Do you have any EGT or smoke issues?

Thanks for the suggestion.

Wayne

 

[Missouri Mule]

Taking out the silencer ring just lets the turbo make more noise.

As I recall turbo bark is caused by hard acceleration then suddenly backing off the go pedal. I don't ever recall my turbo barking but the Mule is still stock. Somewhere in one of theTDR Magazines it explains turbo bark.

 

[Reddog1]

It has been my past experience that taking out the silencer ring just lets the turbo make more noise, but if someone has done this and reduced the bark, I am willing to try it.

It is also my understanding and experience, turbo bark is caused by hard acceleration then suddenly backing off the go pedal. I really do not think hard acceleration includes what I think is normal driving. If you do not baby the go pedal, my turbo will bark. Accelerate getting on the freeway, it will bark. Like you, I do not remember my stock turbo ever barking.

My concern is not how or why it barks, as much as what can be done to stop or reduce it. If it is simply the design of the turbo, then I will consider a different turbo. If it can be reduced or eliminated, through adjustments or changing some other parts, I need to know what it is.

At this point, I would not recommend the PDR HX35/40 w/12 cm exh. turbo to anyone. It does spool better than stock, but what is the value, if you have to baby it when you let off the go pedal. I am having trouble understanding what would be the application for it to be drivable.


Wayne

 

[DPashko]

do not let off the pedal suddenly and no more turbo barks. you are stalling the compressor wheel as previously noted by GAmes/ missouri mule. you will destroy your turbo in no time! you are causing it to spin from XX000 RPM to 0 or even forcing it to reverse rotion. No turbo likes a quick relase of the pedal and the more load on the engine the worse it will be. a bigger turbo will help to a certain extent but will still do it depending on your engine load.

 

[Reddog1]

I am well versed on how to make my turbo bark. I also know why it barks. My question is, can the bark be eliminated or reduced with further upgrades?

My stock turbo did not bark, why? I really doubt all turbos bark, why?


Wayne

 

[GAmes]

I doubt that removing the silencer ring would reduce bark, it seems to me that removal could result in worse bark. It is a smooth surface that routes the air into the inlet, with it out there could be some turbulance IMO. I removed mine once long ago and recorded worse mileage, so I reinstalled it.



Newer engines have varible inlet vanes on their turbos. Going back to long ago turbine engine training, Lycoming engines (used in Hueys, Cobras and M-1 tanks) went to variable inlet vanes in the '70s. The result, besides more power, was greatly reduced instances of compressor stalls. In a helicopter a compressor stall whip lashes the entire drivetrain and causes lots of damage. One thing we were trained to do was to decrease power smoothly and that is the cure for the bark we encounter. I don't know how to combat the problem you have with an automatic transmission.

 

[Reddog1]

GAmes, thanks for the info. It does help in understanding.

I am somewhat stumped that with everything I have read, there is no information I can find on how to eliminate or reduce the bark, other than slowing the release of throttle position, with your foot. It certainly brings up more questions to me. The main question is do all non-stock turbos have the same bark issue, and if so is it just not talked about?

I can only see three modifications I have made that should have an effect on my original questions of EGT too high, too much smoke & bark. I installed a #10 plate, 370 injectors and a PDR HX35/40 w/12 cm exh. turbo. I think it is fair to say, if I go back to stock on all of these, I would eliminate the high EGT, excessive smoke and bark. From what I have read, it appears I am the only one complaining about this combination. This makes me wonder if I am missing something in my setup?


Wayne

 

[GAmes]

370s are famous for smoke, so it is possible that a different set of injectors would help there. Do you have a wastegate? I was thinking I might be able to adjust mine to open sooner.

 

[Reddog1]

370s are famous for smoke, so it is possible that a different set of injectors would help there. Do you have a wastegate? I was thinking I might be able to adjust mine to open sooner.

This perhaps the most tangible response I have had so far. Thanks. I too think a different injector would not only reduce the smoke, but might even lower the EGTs.

I am using the wastegate. Without the elbow, I have about 22 to 24 lbs boost. With the elbow, 26 to 28 lbs boost. I cannot tell any difference in performance, smoke or EGT. Do keep in mind, this is from the seat of the pants, and I probably do not see small changes.

I wonder if perhaps I have intimidated many people by expressing three concerns, in one post. I confess my ignorance to a final solution, assuming there is one. I am disappointed with how many post are made recommending mods, when the most basic (in my opinion) questions cannot/or are not addressed by the same people. It kinda suggest there are a lot of people that simply re-post hype, with very little knowledge of what they have. It also suggest they fail to post the negatives of their set-up. Simply stated, it does not do much for their creditability, on their suggestions.

Thanks again for stepping up to the plate, with a constructive suggestion. You certainly do not fit in the "re-post hype" group.

Wayne