AFC simplified

Smokem

Smokem

Turbler
Joined
May 10, 2006
Messages
5,565
Pre-load adjustment
Spr4-1.jpg

This will determine the off idle quantity of fuel injected before manifold pressure overcomes the spring pressure.

Starwheel
Spr5.jpg

Increases or decreases spring tension.

Lever height adjustment
Spr3.jpg

Eccentric movement, counter clockwise raises the lever, clockwise lowers the lever.

AFC lever
AFC013.jpg

Removing 0.100" from the marked area will provide full travel.
 
160/175/180hp spring on left, 215hp middle, TST on right.
Spr7.jpg


In the following picture I compare two springs that began as the same. The spring on the right was heated and stretched to achieve the open pressure desired.
Spr2.jpg


160/175hp governor spring on left, 180/215hp governor spring on right.
Spr6.jpg
 
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Spring choice will vary depending on peak boost pressure, and the desired fuel curve. Many of the springs shown will vary in pressure, and can be modified with a little heat to achieve the correct open pressure.

Both stock AFC springs are much too short to be of much use. The TST light/medium springs are the correct length and ~ 20/25psi accordingly. The light stock spring can be stretched to increase open pressure to ~ 30psi, and the heavy stock spring can be stretched to increase open pressure to ~ 45psi. For higher pressure applications, such as twin turbo setups the governor spring works quite well, however the shorter spring from the lower hp P7100's comes up a bit short in free length, and is quite high as far as open pressure is concerned.
 
The washers on the diaphragm should also be modified, or replaced to increase travel. I always set the AFC lever adjustment as low(clockwise) as allowed to prevent the governor arm from hanging/binding. I also always adjust the starwheel to the full travel position and modify the spring accordingly to prevent coil bind issues.

The two things to take into account when adjusting the AFC after reassembly will be it's location when mounted front/rear, and the amount of pre-load on the AFC lever. Every setup is different, and there is no magic number here, trying different locations and pre-load adjustments will be needed to fit each individual case properly.
 
Great stuff!! Pictures always help me a ton.

I love your write-ups and truly appreciate it!!

Thanks,

Garrett
 
How does modifying the lever height affect the fueling? Is full fuel achieved when the barrel on the afc arm hits the back of the afc housing or is there a certain millimeter of travel the afc arm needs to move (19-21mm)?
 
Altering the lever height does not affect fueling, but aftermarket governor springs lower the governor arm's relative height to the other parts. Full fuel is when either the washer, or barrel contact and stop movement of the lever.
 
Unmodified AFC washers
Spr8.jpg


Modified AFC washers
Spr9.jpg


I typically turn the collar down on both washers on the lathe as you can see in the second picture. If you are looking for washers to replace the stock pieces, they are 1.575"/40mm in diameter, 0.060"/1.5mm thick, with a internal diameter of 0.325"/8.25mm.
 
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