Cummins 4BT & Diesel Conversions Forums banner

Boost Compensator Adjustment?

11K views 12 replies 5 participants last post by  Dougal 
#1 ·
I have been playing with my boost compensator adjuster in an effort to get more boost sooner(lower rpm's). I've checked the aneroid for leaks, and it appears good. My question, as you adjust the screw in or out, which way lowers the rpm for boost? Is this a suttle adjustment? I've screwed it in and it seems better, but how far can you go? So far a little black smoke, but very little. I have also given about a 1/4 turn more fuel to.

On the altitude side, I have just a small hose going to a clean air source inside the cab. Is there any thing else on this aneroid to connect? Is there any adjustments?

Thanks

Doug
 
#3 · (Edited)
I think it was Erik who posted this manual page some time back


Note there are a few typos - there are 2 item 19's (the control rack and diaphragm) in the diagram. The list below the diagram has the control rack as 18, but in the the description above both control rack and diaphragm are both 19. The full load screw is 18 in the diagram but is left out of the list below and description above.

Edit: my IP doesn't have a boost compensator or aneroid so I have no experience. I assume you adjust item 21 through a slot in the boost compensator housing.
 
#4 ·
Thanks guy's for the advice. I read my FSM, but was not sure which way did what. I have been slowly working the adjustment inward, and performance is improving a little. I have minimal blake smoke. I was now think of trying a little fuel screw also? As long as the rpms are up, she pulls good, but a right turn in 3rd gear around town and it's a real dog until the turbo builds some boost. I can get about 12 lbs max boost. I have egt and boost gauges, what do you think about a little more fuel.

Thanks

Doug
 
#6 ·
You hit on it, I have the stock non-wastegated turbo.

Will a stock 4BD2 waste gated turbo model bolt on (mounts+oil and water coneections)? I saw a brand new 4BD2 wastegated model for $400 US. I would like more/better low end power, is there a turbo you would recommend? I not looking for a racer, just better low end driveability with as much stock reliabilty and parts availabilty as possible.

Doug
 
#9 ·
I'm going to adjust the boost compensator some more before a turbo change. It feels better the more I screw the adjuster inward. I wonder if maybe more fuel would also help?

Also, the altitude aneroid has a barb fitting on it. I have a hose going to a clean air source inside the cab. Is this correct? I could not find anything in the FSM on how it shpould be connected.

thanks,

Doug
 
#10 ·
...Also, the altitude aneroid has a barb fitting on it. I have a hose going to a clean air source inside the cab. Is this correct? I could not find anything in the FSM on how it shpould be connected.
Doug
If it is a 4BD2T, then the hose went to an electrically-controlled valve that was operated by the electronic box (QOS II). The other side of the valve went to a vacuum line. Under normal operation, the altitude compensator would be open to the atmosphere, as you have it now. When the QOS II determined that the engine was running too hot (water temp), it would switch in some vacuum to the altitude compensator making it think that the engine was at a higher altitude than it really was and therefore reducing the amount of fueling with the end result that the engine temps would hopefully go back down. A clever way to limit overheating!
 
#12 ·
We spend a fair amount of time at 7500' (2500m) and go up to around 11,000' (3650m) so I should keep it. I knew how the the stock set up worked for the alt aneroid, but wanted to make sure since all the stock temp/valve parts were removed.

There is an adjustment on the altitude aneroid, any ideas or suggestions on any adjustments on it?

On the fuel screw adjustments, any thoughts on adjusting it to give more fuel to help spin up the turbo earlier for better low end? Or is a new turbo in my future?

Doug
 
#13 ·
Yes more fuel will help spin the turbo up. But it will cause more smoke off boost and that part of the rev range may still be too hot EGT wise to use other than accelerating through.
I guess you'd need a sensitive vacuum gauge to adjust the altitude compensator. Make sure it's open at normal atmospheric and starts to close up after that.

Here's a useful altitude vs pressure table.
http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top