Competition afc mods

[Devan Manis]

how exactly do you mod the AFC for more forward movement of the arm, can you grind the upper part to allow more fuel in the upper range, but still keep the "foot" for smoke control? or are there better ways to do this? We put some 370's in my brothers 12v with zero plate and afc slid forward as far as possible and i thought it would smoke a ton more under load, i know that after we mod the afc we need to do the rack plug, but i wanted to know for the afc for know. I was reading a thread where jim fulmer was talking about it, but it was kinda vauge. we are racing in Vegas this weekend, and want to get his truck run'n nicely. thanks for your help.



On Edit: if any one wants to join us in Vegas we will be happy to meet you there, on friday night at the strip.

 

[Signal73]

one way to get slightly more is switch the 2 diaphram washers around in the housing. Play with it with some regulated shop air you'll see what I mean, the 1 forward washer has a lip on it which hits the housing stopping it about 1/8" from forward.



Im sure others will be along with some insight also...

 

[Jim Fulmer]

You do not ever need to grind on the AFC's arm's (foot) for more forward travel, what you may have to grind on the forward part were is slides but this is all dependant of the plate position. Swap the AFC washers as said above and make sure the AFC spring tension (star wheel) is not too tight... ... . I don't mean loosen it all the way... ... . regulated shop air will tell you when X is going to happen.



There is no such thing as a smoke screw or wheel, but there is a star wheel that preloads the spring to make the tension higher. The AFC springs in say a 180 pump takes about 20 psi of air pressure (shop or boost) to collapse it, you can make that a little higher or little lower based on spring preload tension, but if you get the star wheel to tight it will limit travel because you will put the spring into coil bind.



If you or anyone else controls the smoke level with you foot, you are now the AFC and it's not working to your advantage. The absolute worst thing I have ever read about a P-Pump is taking the plate out and gutting the AFC..... makes no since. When you figure out how an AFC works and what all you can do to it you realize it is only a communication tool between you and the pump, the plate controls the total amount and when it happens based on RPM... . the Governor arm position tells the pump at what RPM to an extent. All of these need to work together for proper tuning and it takes some testing to get it right.



Jim

 

[MCummings]

i thought it would smoke a ton more under load,

How much it smokes under load is dependant on how much air you have. It sounds like you have enough air. If you want more smoke, try going to Laser DV's, and jacking the timing wayy up.



Merrick

 

[Bobcat698]

This is definately a modification that works. There is NO need to gut the AFC or remove the plate. . Here is my setup with everything at full forward, with the AFC modified and the rack plug installed:

-Click here to see Video



Read: TO MUCH FUEL! I cranked the starwheel tighter and slid the plate back a bit. . truck runs much better and spools better on the street.



This is a stock 180 pump with just 4k springs + whats in my sig. . Pro Street 66 charger pushing 52lbs of boost.

 

[wildmanben]

holy smoke man. I bet the EGTS got a bit toasty there.

 

[Joseph Donnelly]

There are two things you can change/modify easily that limit rocker travel (fueling) in the pump via AFC. One is the cup washer on the side of the diaphragm near the spring. You can replace it with a flat automotive "body" washer of the same outside diameter and with the same (8 mm) hole size. The other is the shaft part of the AFC "foot" that slides on the round shaft. Remove the screw from the front of the afc and you can pull the shaft out (it is sealed to the housing with a captive o-ring). Remove the "foot" assembly, and grind off a little of the end, maybe 1/16" to 1/8" or so. You can replace the stock rack plug at the front of the pump with one that has a "deeper" cavity, but the ones that are available from Bosch would allow more than 21 mm rack travel, so you must use the torque plate to positively stop rack travel if you do that. Actually, fueling from that much travel is coming in too late, and you will find that the stock plug is OK. I found that less travel than it allows was optimum with the 913 (215 h p) P7100 pump.

 

[Devan Manis]

Its a 180 pump with 370's and 4kgsk and timing 16degrees. I don't want more smoke under load, necesarly just want the most possible power with what we had, and i think the afc not moving far enough is probably what is holding us back for now. I under stand how the afc works, and realize its a good tuning tool i've just never had one apart, and was wondering if this is something i could do with basic hand tools before the race. Ohh and thanks for the help.

 

[MCummings]

Bobcat698.



Why does the video say no traction bars,,, but there appears to be traction bars on the truck though...



Merrick

 

[Bobcat698]

Bobcat698.



Why does the video say no traction bars,,, but there appears to be traction bars on the truck though...



Merrick

The traction bars were there, but non-functional as they were ratched-strapped to the frame.

 

[Signal73]

where the boost line enters the afc there is a brass fitting that has a tiny orifice which allows air to enter the afc and actuate the diaphram. is there any benefit to drilling that out to a bigger size, or does it not matter with air psi?

 

[zstroken]

where the boost line enters the afc there is a brass fitting that has a tiny orifice which allows air to enter the afc and actuate the diaphram. is there any benefit to drilling that out to a bigger size, or does it not matter with air psi?

Only thing that would do is change the rate at which the AFC foot moves. Is the orifice smaller than the hose that feeds it? If it isn't then the hose is the limit. Like I said it would just affect the rate. Once the AFC is full forward, the velocity of the air goes to zero and you have no pressure drop. Now if you have a bad diaphram then it would help.

 

[Signal73]

yeah its small compared to the hose feeding it like a thick needle size would be a way to describe it. mebbe Ill hog it out...

 

[zstroken]

Well opening it up would allow the AFC to move faster, and the only way I can see it helping is if you had a leak in the diaphram. The only time you have a pressure drop is if there is air velocity.

 

[Signal73]

diaphram is in good condition, had it apart recently.

 

[Jim Fulmer]

yeah its small compared to the hose feeding it like a thick needle size would be a way to describe it. mebbe Ill hog it out...

I've got money that it doesn't change a thing... . yes I did it along time ago!



Jim

 

[Signal73]

wont waste my time then. Thats why I asked

 

[Jim Fulmer]

Heck I drilled out the hole and ran 1/4 plastic tube to it like the Valet, Hobbs switches ect use.



I personally thing the best tool to have is the hand air regulator, I even have it setup to use with a little air tank I carry with me along with the spare parts ben, tools ect. Works really good for AFC checks, wastegates, switches ect.



Jim

 

[Signal73]

So Jim, when will your P-Pump book be published?

 

[FDavid]

For all out power where smoke isn't a concern, wouldn't removing the "foot" lever out of the AFC be the way to go?