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Ok i been digging into afc on this truck i bought in july its been tinkered with so lookin into what has been done i have tuned most things on the afc before but never messed with smoke screw much, i took cover off and it was screwed in flush with the lock nut is that good or bad? where should it be at i dont need the smoke i just want the most power, thanks
 

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the smoke screw is not going to give u a ton of noticeable power all it is is an adjustment of pre boost fuel, thats where the smoke comes from. i would say that its a personal preference mine is turned to where i can still see it through the hex nut on top of the afc and with a #0 plate boost elbow intake and a straight 4inch she runs pretty good.
 
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Ok i been digging into afc on this truck i bought in july its been tinkered with so lookin into what has been done i have tuned most things on the afc before but never messed with smoke screw much, i took cover off and it was screwed in flush with the lock nut is that good or bad? where should it be at i dont need the smoke i just want the most power, thanks
I have questions about this as well.

I understand the smoke screw to be a stopper on the backside of the rack travel which makes the minimum fuel allowance adjustable meaning that this is where you tell your truck the least amount of fuel it will be getting during off boost fueling. Where the starwheel reduces or increases the rate of the spring (increasing or decreasing the ease of fueling off boost through the fuel pedal), I believe the smoke screw to help as a forward assist bringing the rack travel closer to its full travel.

I think you need to find that area where the adjustment doesnt overfuel your engine (black smoke) nor where its not starving for fuel. People have suggested identifying an adjustment that most quickly ignites the turbo.
 

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Do we know (at stock) where the screw sits in relation to the diaphragm inside? I would think these trucks having this adjustment available come with some preboost fuel added by preload from the screw? Is it safe to say that a smoke screw that is adjusted away from the diaphragm is not the optimal fueling to ignite the turbo at its earliest point.

In attempt to dial in my smoke screw, I assume the best method is to just lightly touch the screw to the diaphragm and then start with small 1/2 turn adjustments inward against the diaphragm?

Where should the starwheel tension be during smoke screw adjustment to best identify the results of tuning the smoke screw?
 

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Is it safe to say that a smoke screw that is adjusted away from the diaphragm is not the optimal fueling to ignite the turbo at its earliest point.
It's different for every set up. Even the same set up in different vehicles will not have an identical, optimal pre-boost setting. Most vehicles with stock injectors/delivery valves/turbo will need some pre-boost.


In attempt to dial in my smoke screw, I assume the best method is to just lightly touch the screw to the diaphragm and then start with small 1/2 turn adjustments inward against the diaphragm?
Yes. Make sure you hold the pre-boost screw steady while tightening the nut, otherwise as you tighten the nut, it will also tighten the pre-boost screw.


Where should the starwheel tension be during smoke screw adjustment to best identify the results of tuning the smoke screw?
The star wheel adjustment does not effect pre-boost fuel settings/adjustments. They are independent of each other. If you are smoking heavily before the turbo lights, you have too much pre-boost fuel. If your turbo lights well with a haze and then begins puking smoke (considering you have no fuel plate), your afc spring does not have enough tension on it. It should either be tightened up or replaced with a stiffer (and longer) spring.
 

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Most vehicles with stock injectors/delivery valves/turbo will need some pre-boost.


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More than what is typically delivered from the factory? I keep reading about the "Sweet Spot" I assume that this is not a factory setting?
 

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More than what is typically delivered from the factory? I keep reading about the "Sweet Spot" I assume that this is not a factory setting?
I ran my stock turbo for 2 days. When I got the truck, the compressor wheel had damaged fins so I gave it to my buddy who rebuilt it. I then picked up the turbo in my sig.

With this turbo, my afc full forward, 4k gsk, no plate, TST medium afc spring and fresh 5x.010 injectors, my pre-boost screw is turned in 2 full revolutions after contacting the diaphragm. I'll add more till it starts smoking prior to spool up and then back it off a little to find that sweet spot. As of right now with the 2 full revolutions, I have no pre-boost smoke.
 

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I ran my stock turbo for 2 days. When I got the truck, the compressor wheel had damaged fins so I gave it to my buddy who rebuilt it. I then picked up the turbo in my sig.

With this turbo, my afc full forward, 4k gsk, no plate, TST medium afc spring and fresh 5x.010 injectors, my pre-boost screw is turned in 2 full revolutions after contacting the diaphragm. I'll add more till it starts smoking prior to spool up and then back it off a little to find that sweet spot. As of right now with the 2 full revolutions, I have no pre-boost smoke.
I am mostly stock. I do have a #100 plate which I understand should not have any impact on the preboost. I did put in 3K GSK which I will assume warrants tuning to the preboost?

So we r to assume that preboost comes set at optimal preboost fueling levels from the factory, but some (not all) modifications require preboost adjustments to bring the fueling back to optimal levels after the mods have taken them out of spec?
 

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If I had a completely stock truck, I would absolutely take the time to tune the afc.
 

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I am planning to bench test the AFC spring rate with shop air to ensure no binding and to give myself a starting point, of about 35 psi (which is the low end of what I am producing). I am then going to start with the pre boost screw about 1/4 turn past contact with the rail. Any thoughts on my starting points?

Better suggestions?
 

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You need a longer afc spring to set up an afc properly. The stock one is only ~28mm. It will bind (WAY) before you get full travel.

The TST springs are 38mm long. They're honestly not firm enough for my application but are the correct length.

EDIT: Video I took - Here's how the heavier of the two tst springs reacts to compressed air. Like I stated, it's too softly sprung for me.

 

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You need a longer afc spring to set up an afc properly. The stock one is only ~28mm. It will bind (WAY) before you get full travel.
I have not made modifications to increase rack travel. It will still bind? Is the AFC not intended to recieve enough boost to make the full travel? is this why it binds?
 

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I have not made modifications to increase rack travel. It will still bind?
The stock afc spring will bind because it is too short.. The bound up spring will prevent full travel.

Is the AFC not intended to recieve enough boost to make the full travel? is this why it binds?
Again, in a stock afc.. The short afc spring will prevent full travel.


Random note on afc washers: If you grind the afc washers thinner (or install thinner washers), you will 9 times out of 10 have to add more pre-boost. That's because the thinner washers are allowing the afc to return to its resting position a greater distance before the washer mods... which nets less pre-boost fuel therefore the need to add more.
 

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Man I am testing this AFC on the bench with the air regulator at 35 PSI and I have to tighten this thing all the way to get it to hold against the compressed air. Not what I was expecting at all. Should I expect this from a stock spring?
 

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Are you runnin 35lbs of boost on a hx35?
 
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