AFC Shimming for greater rack travel

[HEMI®Dart]

Piers touched on the subject once.



Piers wrote:



"Yep, without the afc housing all the way forward you're missing some rack travel = power One can even take the afc housing apart and install a shim so you can get more rack travel. The 215 engines came with their afc housing shimmed from the factory, but not the 160 or 180hp engines".





Has anyone shimmed a 160, 175, 180 HP pump AFC housing to pick up a few HP?



Where in the AFC does the shim go?



#ad

 

[SlyBones]

Well I am not the god of 12v's, but it seems to me that the AFC housing only needs to be far enough forward to allow the governor lever to have full travel on the plate.



-- At that point the plate is limiting the travel not the AFC housing.



-- The more forward the plate position the more this can be a problem. A plate in the stock position I doubt has a need to be shimmed. If you housing is back close to the stock position.



-- Seems to me what moving the plate forward really does is change the starting position of the governor lever when you first hit the throttle. -- You are changing the position of the little arm that sticks down from the housing. At low boost thats the limiting factor. AS the boost builds and pushes against the diaphram, it moves the arm, until finally it moves far enough that the lever hits the plate. -- In essence you are controlling pre-boost and low-boost fueling, rate of travel, etc.



-- Shimming would be for those who keep the AFC housing slid back for less lowend smoke and better economy, and have the plate slid forward. I think the AFC housing may not allow the lever to travel all the way, in this case.



OK enough lecture. In the area where the spring and the diaphram are located, there is a cupped shaped washer that holds that in place. Pink in the drawing. Replace that with a flat washer.

 

[Deezul1]

Good pic of pump works too.

 

[HEMI®Dart]

I found it



The 215 pump AFC's have a . 040 washer that seats on the shoulder of the long stud that goes thru the center of the afc spring. It's about the same O. D as the stud.

 

[Cummins Corvette]

Couldn't you just lengthen the holes, so it could go forward some more?

 

[SlyBones]

HEMI,



Where is that in the picture? or is it.



In the pic the spring is pink. Has the star adjuster on one side and a large round ( pink ) washer on the other side. In the pic the diaphram movement is being stopped when the large washer comes in contact with the pins sticking out. By changing that washer to a thin flat washer, you get that little bit of extra diaphram movement. -- Thats was I was referring to.



Is this it, or is there another trick?

 

[JohnE]

Hmmm;

I do recall the talk of a washer in the manual stack up when changing the AFC springs.



Is it easier to add the washer or regrind the AFC stop to match the new fuel cam? The washer should only be significant under no or low boost. If things are ideal the "light springs" or "adjusting the star wheel" should retract the AFC foot once you get boost. Sliding the housing should already move the AFC stop behind the fuel cam nose under low and/or no boost sitations.



Has anyone tried removing the entire guts of the AFC and just let the governor lever and fuel cam control the smoke?



-John

 

[Cummins Corvette]

Well I got curious and went and took the AFC housing off of my truck and took it apart. The arm that goes down into the pump by the plate wasn't getting full travel; it was limited by the cup shaped washer on the spring side of the diaphram. I put a thick washer on the stud before I put the big washer, then the diaphram, other washer, and nut. The arm is getting full travel now. The slider is almost making it too the other side of the housing. It was stopped short about 1/8" before. I will go for a drive and see if it helped anything.



I also found out that the cap on the back of the housing has a screw under it that does the same thing as sliding the housing forward. It adjusts the point at which the arm stops when boost goes down. If you turned that thing way in and slid the housing all the way forward, you could get some SERIOUS SMOKE!!!

 

[SlyBones]

Notice when you look at the top of a plate the channel down the center. This is the slot where the AFC arm moves to when boost pushes it out of the way. Depending on plate position either the back of the plate or those little pins against the washer are what limits AFC arm travel.



If its possible to slide the AFC housing all the way forward so the arm is fully "retracted" at no boost, the the spring, diaphram, washer and all that is doing nothing. Is already out of the way. The governor lever is allow to move straight until it hits the plate.



If the plate position is stock lets say, and the housing is 1/2 the way forward. The arm is not fully retracted behind the plate. So when you hit the throttle, the governor lever starts to move. It moves till it hits the arm. Then it stops and stays there until you get boost. Boost starts pushing against the diaphram moving the arm back until its retracted behind the plate. At this point the lever is now riding against the plate. -- In this situation more that likely the back of the plate is the arm stop because the housing has enough travel even stock.



Now lets say ( like this would ever exist ) the plate is all the way forward and the housing is barely moved forward. Same as above you hit the throttle, the gov lever hits the arm, the boost comes up and starts pushing the arm. The arm moves all the way till the washer hits the pins and stops travel. At this point IF the arm is not fully retracted behind the plate, the the AFC housing is limiting rack travel because the AFC does not have enough over all travel. Now we would need to make mods so we can get more arm travel so it fully retracts and the gov lever hits the plate.



So am I full of crap or what? And if not, then where does this washer of HEMI's fit in?



EDIT, I see Chris posted while I was typing this long and boring response. Yes that gives it more travel. But do you need it? I dont know how much travel these have. But just for example lets say stock it move 1 inch. And now you have 1-1/8 inch travel. If the position of the plate and housing was such that the arm only needed 1/2 inch for it to fully retract behind the plate, what good did it do?

 

[Strick-9]

Slybones,



Stock truck w/ stock camplate, you're right. You don't need to worry with AFC travel. People wanting more MIGHT need to.



When I got my new 913 pump in from Pier's, I spent two days making modifications to it before I installed it. The better part of one day was work on the AFC housing alone.



There is a LOT of stuff to be done in there. Get a set of calipers, and start measuring stuff. It's a LOT easier to do with the pump off the truck, but that's too time consuming for most.



There comes a point as we continue to add rack travel that other factors need to be taken into consideration. In my opinion only HEAVILY fueled rams need to worry with this.



But in the last week my truck has lost 6 MPH in the quarter and I can't figure out why, so what do I know?



-Chris

 

[HoleshotHolset]

I hope your transmission isn't eating itself.....



This is gasser theory, but could be true..... too fat of a mixture has slowed me down many times in gassers. Lean and just at the extreme verge of detonation makes the most power..... thankfully, I detonate all the time now and I don't have to worry about that anymore... !! (Until the 'BIG BANG' occurs... . )



Matt

 

[Cummins Corvette]

Well, it didn't help any. At least I know that the afc arm isn't holding the rack back any. I now have a much better understanding of the afc though. BTW, it only has about 1/2" of travel. Now mine has about 5/8", but to no point. The arm definitely isn't out of the way with the housing moved forward, buy if you want it out of the way, just take the cap off of the back and loosen the locknut, and turn that stud in all the way. That will do it for sure, and give you major smoke!

 

[Strick-9]

Wow! the AFC only has 1/2" of travel?

I thought the pumps were capable of 21mm of rack travel?

Are you saying the AFC only allows 1/2" or 13mm of rack travel?

Something doesn't add up?







Good find!



-Chris

 

[HEMI®Dart]

I get what you are saying Sly.



I just want to make sure the AFC arm is out of the way (fully forward) not hindering rack travel. I am running my cam plate all the way forward. This is a big reason for this question.



The . 040 spacer on the 215 HP Pump AFC's apparently gives the arm a . 040 head start forward.



Either I'm dreaming, or my AFC has that spacer already? I could swear I saw it.



By judging my dyno results last Dec, I think the AFC dog is far enough forward at full boost so the rack is on the torque plate, not on the AFC arm.

 

[HEMI®Dart]

Strick-9,



What are you going to do for a Turbo? I have a stock HX-40 too, but have been babying it. I know I could break it at will. I'm either going to get Piers's new HX-40 or Kurts B-1 Turbo. 500 buck price difference between the 2.