more indepth AFC modifcation, and tuning....

W

wdimig

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Aug 2, 2006
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ok after reading the p7100 information thread, more specifically the rack travel thread that has the information on modding the afc, i removed the AFC, and the plate that i had just put in, and lost power with, i got a chance to pull the AFC apart. here's what i did, and found while in there. i removed the arm, and took enough material off of the face of the arm to flatten it where it makes contact with the rack arm, i ground off about 1/4" of material off the leading edge of the barrel where the AFC arm slides on the shaft, and i switched the washers. now the one washer is flat, that is on the backside of the diaphram(pressure side), and the washer on the non pressure side has a raised edge all the way around the washer, you can see how this will add a small amount of rack travel by just switching the washers. i took it a step further,i ground the edge off the front washer that is now going to be on the pressure side of the diaphram. i did this because there is almost 3mm of travel that can be gained rearward(twoards the back of the housing not the front). the edge of the washer is ground off that is hitting the housing. you then have full control of the position of the rod with the rear coarse smoke adjustment rod that on the outside of the housing. now i plan on running the afc all the way forward, but still want to have good smoke control, i now have a additional 3mm of extra travel that can help control smoke, and make the AFC even more adjustable. after doing all this i got the AFC backtogether, and applied boost pressure to get full travel, i found that the AFC arm never makes contact with the housing in the front where i ground the 1/4" of material off. i was under the impression that it would, so i took eveything back apart to find out why it wasn't making contact, the washer that is on the front of the diaphram(non pressure side) is making contact with the housing, therefore unless you grind some material off the housing where the washer is making contact, you will never get more travel. the only way to get more travel would be to grind more material off the face of the arm where the rack travel arm makes contact with it, but doing that will loose some ability to control smoke down low. now im thinking that once the AFC is back on the pump, and slid all the way forward, i will almost have full rack travel, i have a stock rack plug, that is why i say almost full travel. it should be at least 18-19mm of travel. so the AFC is back on the truck, now all i need to do is play with the starwheel, and find a good combo to limit some fuel before about 10-12psi, and after that hopefully the turbo will lite very well. i wasn't albe to take any pics while i did this, i hope i explained eveything good enough so that if anyone else that wants to do this can. also sorry for the long post. enjoy!

wes
 
I found the same thing too, the diaphram (sp?) hits before the barrel
 
How much material did you nee to grind off of the housing to acheive clearance?
 
I always space that leading washer up on the shaft to the point that the stud only goes through the nut about half way
 
Forrest Nearing said:
I always space that leading washer up on the shaft to the point that the stud only goes through the nut about half way
Click to expand...


Of course won't that allow your off idle smoke to be higher, as the arm would be farther forward?
 
Maybe I am thinking of the wrong nut. I was thinking of the nut on the outside. Not the one on the diaphram.
 
cool, I don't know what the relationship/ratio between lever arm travel and rack travel is, so I just shoot for as much AFC travel as possible :o
 
well got to do some more driving today, i tightend up the afc spring alot more, and i am very pleased with the results, smoke is alot less just putzing around, and when you mash the go pedal, you can actually feel the engine want to rev up and make power almost immediately, and the turbo catches up alot faster, before there would be a delay, and just alot of smoke, now i see smoke, but it is very controllable, i still can blacken out the road behind me at will, but the way the truck runs now is alot better. it almost feels like i went down a turbo size(s366-s364), and i have convinced myself now that i am going to downsize the turbo to a 64/71/13SS(has a 66/65/14cst. on it right now), and then i can really start to have some fun. i only wish that i had done this afc mod, and start to tune it along time ago. eveyone that is on the fence about doing this, dont be, it takes no time, or skill to modify the afc, and you will be glad you did.

wes
 
anybody have some pics??? ...smokem... i need to do something bad. cuz my smoke is crazy.

thanks
Joe
 
If you have A LOT of fuel, like I do and need a considerably stiffer spring to slow the fuel down I may have a solution.

I put a vavle spring (from a VW) in my AFC..it starts to move at around 20psi and takes 65 ish to fully compress.

I have yet to mess with the amount of travel (I did choose not to swap the diaphram washers as the thick one was hitting the housing, defeating the purpose), as I have still WAY too much fuel as it is.
 
has anyone calculated the intalled height for the afc spring?

washer flipped

starwheel ff

wheel 50% to the rear

etc ?

how about the area of the diaphram ?

wes, you have to know what that is

thanks, don
 
i measured aprox. 13.5mm of travel once i had done the mods to the afc, that is from the arm full back to full forward, now there is some travel fo the arm before it makes contact with the afc arm, i dont know how much that is, im guessing about 5mm or so, id like to know how much rack travel i have with this setup, it should be as much as possible with the stock plug. i did not measure the sping height, but it is a stock spring, soo if anyone has that measurement can you post it.

wes
 
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