12 valve q's
03-18-2009, 12:50 PM
#1
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12 valve q's
I've searched and have found lots of great tech info here, thanks. There are still a few things that are not clearly outlined, and I'm looking for some clarification from someone more experienced than myself. My questions are about the function of the GSK, fuel plate, star wheel, and afc. What exactly is the function of each, and how do adjustments relate to each other and performance? If I have it correctly, the fuel plate is the fuel delivery curve, but moving it forward or back does exactly what? The afc tells the IP what the boost is, what does moving it do? The GSK limits rpm, I think mine is a bit higher than 3K. The star wheel controls the amount of fuel at a given amount of boost. Correct? My truck was a Ca truck, with #10 plate and 3k spring, tuned for no black smoke. I'm looking to educate myself on the function of everything before I go sliding things back and forth. I do have gauges, yet to see 1100 degrees, or 32 lbs of boost. I apologize if this is here and I missed it searching. SD
03-18-2009, 02:53 PM
#2
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Fuel delivery is ultimately controlled by the rack. The rack slides back and forth. The further is slides, the more fuel the pump will inject. The governor arm is connected to the rack by springs and linkages, so for our purpose, the further the gov arm is forward, the more fuel is injected.
The shape of the plate is essentially the fuelling curve at full throttle. A 10 plate, for example, brings more fuel in to the mid rpm range, and then begins to defuel as it reaches higher rpms. This occurs whether the plate is full forward, full rearward, or somewhere in the middle. The same profile is followed. Moving the plate one direction will increase the amount of fuel able to be injected at any given point. If the plate is moved forward, the gov arm can move further forward before contacting it, it means the rack is also moved further forward, which means more fuel. The opposite is true if the plate is moved to the rear.
The AFC is the Aneroid Fuel Control. It increases allowable rack travel based on boost pressure. It has a foot that is right beside the fuel plate, that slides forward because of boost pressure working on a diaphragm. The foot is usually much further to the rear of the plate, so teh gov arm will contact it before the plate, except when at high boost. Sliding the housing forward will allow the gov arm to move further when no boost is present. This is where lots of black smoke comes from when someone pins it from a stop. Moving it to the rear does the opposite, reduces the amount of pre-boost fuel.
In the AFC, the foot is moved by a diaphragm that is acted on by boost. There is a spring inside forcing the foot to the rear, which the boost must overcome to make it move. Moving the starwheel to the front reduces the preload on the spring, allowing the AFC foot to move at a lower boost pressure. This affects the low boost fueling characteristics. Tightening it up increases the preload, requiring more boost to move the foot to allow the pump to deliver more fuel. There are different springs available to fine tune how far the AFC foot will travel at given boost pressures. There is also a small fine adjustment screw on the back of the AFC (under a small stamped cover held on by two screws) that can be used to move the foot forward inside the housing. That will also increase the preload on the spring inside, so messing with that one will require adjusting the starwheel afterwards to get it back to how it was.
So, in summary:
Plate - limits fuel delivery at full boost (or if no AFC is present) based on the profile and position inside the housing
AFC - limits fuel based on boost pressures and housing position. Housing position limits no-boost fueling, starwheel affects low-boost fueling, springs affect travel of foot based on their spring rates, smoke screw in the back is a fine adjust of foot position.
The shape of the plate is essentially the fuelling curve at full throttle. A 10 plate, for example, brings more fuel in to the mid rpm range, and then begins to defuel as it reaches higher rpms. This occurs whether the plate is full forward, full rearward, or somewhere in the middle. The same profile is followed. Moving the plate one direction will increase the amount of fuel able to be injected at any given point. If the plate is moved forward, the gov arm can move further forward before contacting it, it means the rack is also moved further forward, which means more fuel. The opposite is true if the plate is moved to the rear.
The AFC is the Aneroid Fuel Control. It increases allowable rack travel based on boost pressure. It has a foot that is right beside the fuel plate, that slides forward because of boost pressure working on a diaphragm. The foot is usually much further to the rear of the plate, so teh gov arm will contact it before the plate, except when at high boost. Sliding the housing forward will allow the gov arm to move further when no boost is present. This is where lots of black smoke comes from when someone pins it from a stop. Moving it to the rear does the opposite, reduces the amount of pre-boost fuel.
In the AFC, the foot is moved by a diaphragm that is acted on by boost. There is a spring inside forcing the foot to the rear, which the boost must overcome to make it move. Moving the starwheel to the front reduces the preload on the spring, allowing the AFC foot to move at a lower boost pressure. This affects the low boost fueling characteristics. Tightening it up increases the preload, requiring more boost to move the foot to allow the pump to deliver more fuel. There are different springs available to fine tune how far the AFC foot will travel at given boost pressures. There is also a small fine adjustment screw on the back of the AFC (under a small stamped cover held on by two screws) that can be used to move the foot forward inside the housing. That will also increase the preload on the spring inside, so messing with that one will require adjusting the starwheel afterwards to get it back to how it was.
So, in summary:
Plate - limits fuel delivery at full boost (or if no AFC is present) based on the profile and position inside the housing
AFC - limits fuel based on boost pressures and housing position. Housing position limits no-boost fueling, starwheel affects low-boost fueling, springs affect travel of foot based on their spring rates, smoke screw in the back is a fine adjust of foot position.
03-18-2009, 06:23 PM
#4
Registered User
Thread Starter
Having read that over and over, I'm thinking it would make sense to move the plate forward a bit (#10), and then adjust the star wheel to get some more power. Is this correct? Besides the plate, spring, and 4" exhaust, everything is stock. Thanks. SD
03-18-2009, 06:35 PM
#5
Registered User
http://dodgeram.org/support_pgs/diesel_ix.htm
http://www.cumminsdatabase.com/read.php?id=58
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