I would move the AFC housing back if you havent already and/or back out your zero boost screw completely. You should not be able to create enough boost on these revs to even move the AFC. This fueling is done at the zero boost position and and by the governor. If the governor springs are enough to overpower the rack spring, it will over fuel more than it should on zero boost shots.

 

See, somebody knows....

 

The AFC housing was already set back as far as it would go in the OEM position and I left it there for this installation. The zero boost set screw is already set at the minum point before the OEM spring starts floating so I left it there. I would hesitate to even completely back out the AFC with the TST springs which would place the spring preload pressure on the AFC's silicon rubber diaphram. That constant pressure would be bad for the diaphram and would cause it to creep back as it stretched and it could ultimately cause it to fail. Better to use the zero boost set screw to limit the diaphram movement to a safe range.

I just received issue 60 of the TDR register and in there Joe Donnelly gave the case for twin turbos and outlined the limits of a single turbo on page 96. To quote him:

"As you increase the horsepower from the factory setting you have to size our turbocharger so that drivability is adequate with responsiveness and low smoke, yet a power increase is supported. As the power increase gets bigger and bigger, the compromise becomes more significant. We accept slower spool up and the need to moderate the accelerator pedal to keep smoke down. We also accept that the turbo ends up smaller than would be ideal...."

I had to move from a 12cm turbo housing to a 14cm housing to reduce my EGT temperature while towing my 5th wheel trailor. This tracks with the compromises that Joe is talking about. Accordingly my problem appears to be a fuel/air balance problem at high RPM/Boost during accelleration. I have taken two 200+ mile trips, without my tralor, since I did this installation and had no problems under steady state run conditions. It was only on acceleration under load where fueling got ahead of the turbo resulting in smoke. This tracks with what Joe Donnelly is saying. His solution is to combine the quick response of a small turbo with the higher air capacity of the larger turbo to increase the transient and run response of the turbo system. As he points out it is a costly solution however, in the long run he has nickel and dime'd his way past the cost of a well designed twin turbo from a vendor like BD.

I have yet to try the system with my trailor. At this point I hope the system will work well. We shall see.

 

Thanks for the update - sounds kinda like what we said at the start - you need more air.

The BD Towing Twins are supposed to be great for towing. BUT, like you said there is substantial cost involved. Many guys are fabbing up their own twins using a HX on top and a S400 or something similar on the bottom. Yeah, this would not be tested and balanced like one of the "diesel shop" sets of twins, but it will give you a while lot more air to clean up the emmissions as well as a huge performance kick in the pants. You will likely need some head studs and o-ring/fire-rings etc. Why not do twins you already have a good tranny which really is the starting point for twins.

 

When I did the spring install and AFC foot modification, I did not observe the same "stretch" you described with the unit set for minimum fuel at zero boost.

However I do agree, as would any with mods, that the fuel is the easy part. Getting your boost air flow to match your fueling is the tradeoff of lag, flow and overall performance. Compounding stretches out the useable air map of the primary turbo and fills in the holes for spooling vs. all out flow. I can drive with little smoke, but its just a little hard to keep up to traffic waiting for boost. Consiquently, my turbo is also a little small and chokes me out at high RPM runs (read 1500 F temps ).

Again, the fueling should not be harsh enough at zero boost to cause large amounts of smoke.

 

I don't know if you worded this wrong, or thought wrong or something, but moving the plate forward (toward the radiator) is going to increase fuel and smoke. That could be part of your problem.



My recomendation for a smoke free 180hp truck would be this
1. make sure you valves are adjusted properly
2. make sure pump timing is set close to stock
3. #8 fuel plate, in stock position (or possibly a #6)
4. Afc housing in stock location
5. Smoke srew in enough to take up the slack on the afc rod
6. then fine tune your acceleration smoke with the various afc springs and spring tension (probably stock spring)

Other thoughts....
The banks plate I have a pic of looks very similar to the #5 plate and the maximun EPA certified plate for a 180hp truck is a #8 (EPA certified to me would mean no smoke). Now don't get me wrong on this, I don't think EPA should be able to tell us how much HP we should be allowed. But that might be a nice smoke free plate, and combined with your other mods should make for a nice towing truck.

Hope this helps....Josh