By-pass blowers 92 series

Why didn't they use the original style blowers?

The biggest reason Detroit went to a by-pass blower is that it is more efficient. The blower will only allow so much air from the turbo to pass through. Once air box pressure builds the valve in the end plate opens and the increased pressure from the turbo now takes over. The blower robs the engine of power. But is a necessary evil to get the engine started
As to your low end power loss and excessive (black I assume) smoke: Did they change the turbos at the time of overhaul?
Is your hard starting issue with the strbd engine only? Are there 2 different re- builders involved? Is there a throttle delay mechanism involved? Yield links etc...If so may be as simple as rack adjustment.
One question I have for you is: This 83% number what do mean? Because during startup and lower speed (Low air box psi) the blower is actually producing a 100%.

Long story short, no.

Long story longer, the supercharger robs the engine of power at higher RPMs, and cramming more air into it via the turbos causes it to "fight back" (for lack of a better lay term) in two directions which compounds the power loss. The bypass valve allows the blower to unload and, while not quite free-spooling, it is turning without compressing so much air, relieving it of some of the work that is also being done by the turbos. The turbos are far more efficient at higher RPMs than the blower is, so as engine speed increases and the bypass valve opens the intake air is predominantly charged by them instead. 100% blowers were more typically found on NAs, not turbo engines.

At lower RPMs when the turbos aren't spooled up and the blower hasn't reached a certain perssure, the bypass plate is closed and it is a 100% blower.

Do both engines have excessive smoke while throttling up or is just the starboard? If so it is quite possible, even tho the turbos were changed at overhaul they may not be correct. Another words they may not spool up quick enough. The A/R (may still be the same as if your blowers were original) When we would add a by-pass blower to an 8V-92TA for hi-way use we would change the turbo and actually use a 6V-92TA because it had a smaller A/R and would spool much faster thereby minimizing smoke. Food for thought

I don't understand why they changed blowers. But, it could be a turbo that's not right. It could also be a cylinder with low compression, it will do the same thing. Do you see a small sheen of fuel coming out of the exhaust as you're turning the motor over? I had a 12v71TI that was just rebuilt at 150 hours split the tip on an injector and wash the cylinder out and low compression that acted similar. Did they use DD reliabilt injectors at the rebuild? Mine rebuilt in 2008, they put all "new" DD reliabilt injectors and at 150 hours when they had to major the engine again, in addition to the injector with the split tip...... 4 other injectors were deemed to be bad. So 5 out of 12 injectors that were 3 months old and had 150hours of use.....and No water in the fuel or any of that.

I also had a set of 8v92 DDECs with low hours 800ish, and each motor had 1 dead cylinder and they were really really hard starting.....and acted the same way.

I assume this ADDA did not take a compression test of either engine, especially the starboard and he is going on appearance of the cylinder liners and maybe a couple of top rings that he can see. Then you did not have enough air going into the engine. 2nd the rack settings on the starboard engine were not correct, sounds like the port has much more power. I hope they can get this fixed for you, but its a shame that not to many people really know how to work on these engines. BTW who is the ADDA re-builder?

That's essentially correct, but the turbocharged air is not bypassed to the atmosphere, it bypasses into the engine without loading up the blower. This is an increase, not decrease, in efficiency.

http://www.atlanticdda.com/

Atlantic Detroit Diesel Allison is pretty much the only game in town for Detroit service in the northeast, anyone else is an also-ran. As far as I know, they may be the biggest Detroit sales and service company in the nation having acquired many smaller Detroit shops. We were using them since back when they were Bruce GM Diesel.

Hi,

I have not dealt with that particular engine arrgt but have a lot of Diesel Engineering experience including a lot of the smaller Detriots albeit a long time ago.

As posted earlier the Turbos are only going to have any sort of effect on the amount of air provided to the inlet of the gear driven roots blowers when the engine is up and running and has a bit of Exhaust Gas Flow. (These Turbos are purely Exhaust Gas Driven and the blower is mechanically driven via the engines timing gear train)

They will not provide a jot of increase in flow when the engine is being cranked over by the starter motor.

If you have less Air Box Pressure at revs when the Turbos will actually be providing some boost do you have any comparative or Detriot numbers as to what the post turbo and pre Blower Numbers should be?

What are the techs measuring as a pressure drop across the Charge Air Coolers? How does this compare to factory numbers?

1987 vintage (about when the bypass blower engines came on line) 16V-92 TA--

Turbocharger......(2)TW9401 (1.46A/R)
Charge Air Cooling System.......JWAC with boost cooler
Blower type.......100%-relieved-bypass
Blower Drive ratio......2.60:1
Engine Crankcase Vent System....CLOSED [I assume AirSeps are in place here]
Maximum pressure...-6.0-2.9 in. H2O

Fuel Injector/Timing......7125/1.508#

Low idle min.......550rpm
Max No-load......2500rpm

I'd imagine you can have a pre-bypass blower motor or you can have the previous version, but cannot imagine a mixture of the two unless you have a lot of extra time on your hands.

Sort of. There is larger airbox volume because of the "scooped out area" providing space for the bypass tubes and plates, but that should not affect blower pressure at low RPMs. The plates don't open up and allow any bypass until a certain pressure is reached. The higher airbox pressure at high RPMs is because the turbos are no longer limited by the volume that can push thorough the blowers (i.e. when the blowers are "loaded up" - unable to move more volume, and facing positive pressure on both inlet and outlet sides... essentially braking the inlet air). Lower at lower RPMs is relative, it won't be lower than a 100% blower since the bypass plate will be closed and the blower will be sending (nearly) all its pressure into the engine, save for .x% that will be turbulence out at the end of the blower swirling around the bypass valve.

*edit* - This may not be as clear to you as to me, and I will endeavor to address it more completely when I am better rested. Three 4am start days in a row have the brain-to-keyboard function a little bit fuzzy.

Hi,

Thanks for posting back with the results so far.

Lets hope it proves to have solved the problem you were having, I look forward to reading about your next test run.

Detroit Rebuild

Who did you use on the rebuild?
How much and how long did they take?