AFC question

Cam73

Cam73

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Joined
Sep 15, 2007
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106
Hey guys-
I did the basic AFC mods today (didn't get to drive it yet) but have some questions regarding what I found trying to set travel with shop air... I searched prior to posting w/o luck.

I cut about 1/4" off the barrel (didn't touch the face of the afc foot), ground the washers flat and backed the pre-boost screw out until it just contacts the end of the rod, not to limit any rearward travel. I did not stretch the spring.

The plate was not pulled or set up any kind of jig to replicate the relationship between the afc foot and fuel plate so my foot travel concerns might be moot in the end but...

50 PSI of shop air was placed on the diaphragm first to see how far the foot would travel and the location marked. Next I turned the air down to 30 and started with the star wheel. With the starwheel cranked all the way towards the front of the truck I could not get the foot to travel to the max mark @ 30 psi. It was roughly 1/4" away. It took 40+ psi for full travel. Probably more boost then the current setup makes. Any chance the arm is clearing a FF #100 plate?

Anyone reaching full fuel with the stock spring with under 40psi?

Am I doing something wrong? Is it time to time find the bag of stock gov. springs? Although the afc foot doesnt feel loose, will the low tension setting make things smokey down low?

Thanks, hope I'm not *bdh*
 
Your on the right track, a stock 215 spring is quite stiff and if you use a Gov spring it is about the same thickness but longer, a 180 spring (biggest one in an AFC spring kit) should be about 25-30 psi. It may take some looking but a small diameter washer or two under the inside spring will add more forward travel and allow you to have the AFC further back to limit low end fuel.

I seriously doubt your going to get it to work with the plate Full forward and a 215 pump doesn't need that much plate, cut it back to 3/4 and I'll bet you don't loose any power......granted I'm arm chair tuning here.

Jim
 
Jim Fulmer said:
Your on the right track, a stock 215 spring is quite stiff and if you use a Gov spring it is about the same thickness but longer, a 180 spring (biggest one in an AFC spring kit) should be about 25-30 psi. It may take some looking but a small diameter washer or two under the inside spring will add more forward travel and allow you to have the AFC further back to limit low end fuel.

I seriously doubt your going to get it to work with the plate Full forward and a 215 pump doesn't need that much plate, cut it back to 3/4 and I'll bet you don't loose any power......granted I'm arm chair tuning here.

Jim
Click to expand...

Thanks Jim

I drove to work this morning with zero smoke and a stiff pedal which I can understand since the pre-boost screw it all the way out. It was slow to spool but would still max out the scale on the commander (CR MAP sensor) at 41#. I'm going to assume when people say after AFC mods, the only thing that needs adjusting is the star wheel when it is set up w/ a lower tension spring..

Is the fuel plate position true with all 215 pumps or just in a mild set up like mine? I read a lot about guys chasing all the rack travel they can get from the plug on back.

I've got a S366 charger going on soon so I'm most worried about getting the afc to a point where it will be tunable for what the big charger needs.
 
If you have no smoke and it is slow to spool you have got the bottom end figured out, now add pre-boost 1/2 turn at a time till it doesn't smoke very much but the turbo comes on quicker.......I can make my truck lag like that from too little fuel.

Jim
 
Really depends on whats done to the truck for fueling, If its all stock and just a plate, you will benifit from a lighter AFC spring Bosch makes one and they are around $35. When you ad larger injectors and DV's things change and you do not need as much low end fueling so you will go with a stock AFC spring like ones in 215 pumps or a Gov spring as Jim mentioned.
 
Thanks for the help guys!

I'll have to do some more tuning when we get some dry weather. Hard to really load it. The truck was starting to light the power tire (yes, it has an open diff. :bang) around 40-45mph in the wet. Slow to come on but clean and strong when it does. The smoke at WOT looks a lot like the haze it makes at idle from the .020 HG and timing (from what I've been told).

Right now the truck has 370s, 4K Gov. springs, 100 plate, o-ringed head and a little bit of tuning from a dude up in Stanwood. Think his name is Bill but looks kinda like lance bass if you ask him :hehe: 5 speed, 3.5s and 37s

Any chances the pre-boost will be the real kicker when the 366 goes on? I've read about the start hot, stay hot theory from heavy low end fueling.

I'm excited to throw the big turbo on, then maybe some 024s and then put the killer b in to feel the changes.
 
just turn the pre boost fuel screw in like jim said until it just barely smokes if you take off fast. if you run out of screw to thread in, back it back out and turn the starwheel forward some more. keep repeating the process until you find where you like it best.
 
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