AFC/Boost Question

RGHodges

RGHodges

New member
I spent some time the other day tuning my AFC to clean up the bottom end smoke a little on my truck. I feel like I have it dialed in pretty well. It runs really clean now and spool up time is the best it has ever been in my opinion. My only problem is that I have lost some power at the same time. I have lost about ten pounds of boost as well. I know that boost doesn't equal power but if I have lost ten pounds then the fuel must not be there. Nothing has changed besides AFC adjustments, starwheel is still fairly loose as well. Setup is benched 913 pump, 5k springs, no plate, 181's, single 71mm charger. Seeing about 45-48 lbs max boost. Truck runs great, just a little low on power compared to before, no boost leaks that I could find. What gives?
 
How did you adjust it? Slide the housing or preboost screw? If you slid the housing, you may have removed a small bit of travel.

Did you pressurize the intake tract? Do you have any drive leaks?

Easy way to tell if you lost fuel, look at the exhaust. Also check afc diaphram. Mine blew through and I didn't find it for about a year, fixed everything else first LOL

Sent from my DROID3 using Tapatalk 2
 
Last edited:
i agree that you probably lost a bit of rack travel through starwheel adjustments, spring change, or the AFC being slid back

sometimes you cant always have the best of both worlds tuning an afc, you may have it tuned perfect for down low, but having the afc full back is like removing 1/4 of an inch of pre-boost screw.... so it will feel better, because the gov arm will be stopped earlier, but it may limit full travel
 
I did slide the housing back about halfway, so I'm guessing that is probably what it is. I will also check the diaphragm just for peace of mind. Thanks for the suggestions guys.
 
did you take some material off the barrel of the foot? you can get more than enough travel even with the housing slid forward to max the rack out.
 
TThe exhaust is a lot cleaner throughout the whole rpm range, but I will sacrifice a little top end power for the drivability I gained.
 
I honestly can't remember if I have trimmed the barrel on the foot or not. I know I did on the pump that was on the truck previously, but I will have to look to be positive.
 
If you do some slight modification the the afc you can run it all the way to the rear and still clear the arm at full rack travel. be carefull how much you crowd it at the back though. With the afc all the way back and the pre-boost screw backed out of the way mine won't rev above an idle when you put it in gear. About 1/2 a turn on the pre-boost screw and it's good to go.
 
Spring choice comes in big when the afc is all the way back as well. Lots of springs will allow good low boost control but bind and not allow full rack with the afc full rack.
 
What spring would you guys suggest? It still has the stock 215 hp spring in it right now, would stiffer be better?
 
if you have a regulator, set it to half and full psi for what you run, that way you can try different springs and see what works perfect, and you can adjust the star wheel perfectly too. I dont think there is one perfect spring, just have to play around with it.
 
RonA said:
If you do some slight modification the the afc you can run it all the way to the rear and still clear the arm at full rack travel. be carefull how much you crowd it at the back though. With the afc all the way back and the pre-boost screw backed out of the way mine won't rev above an idle when you put it in gear. About 1/2 a turn on the pre-boost screw and it's good to go.
Click to expand...

Mine won't even start all the way back lol. Never figured it out, so I just added preboost.
 
RGHodges said:
What spring would you guys suggest? It still has the stock 215 hp spring in it right now, would stiffer be better?
Click to expand...

i have found a 175 industrial engine gov spring works well... but they are not exactly plentiful.

they are good length, and not fully open untill about 45 psi. about half open at 20
 
I have my AFC setup for max travel, and use a light spring on the diaphram. Then I have a boost elbow on the back of the afc and an adjustable needle valve in cab. I can dial it in while driving. Open the needle valve gives you full power, then you can gradually close it all the way to valet mode. With it connected and the AFC off, I used shop air for to make some calibration marks. IE.... full travel @ 40psi, 60psi and etc.
 
That boost elbow is a good idea. I may try to rig up something very close to your set up. Sure beats trying to find a spring that gives you full travel at the desired psi without binding up, which by the way is what was happening in my situation. I ended up stretching the stock 215 spring, and now it doesn't go full travel until north of 65 psi somewhere, which does me no good either. I would like somethimg that goes full travel around 45 psi.
 
You must log in or register to reply here.
Back
Top