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AFC Spring Question
- Thread starter Old Smoky
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It would depend on alot of different things Mike.
A star wheel that was near the top of the threads, which puts more pressure on the spring would lose some of its spring rate over time and would need more psi before bottoming out. A newer or less mileage truck would have more spring rate also. Most likely very small amount of difference. Could be 1 or 2 psi diff.
One would have to mark the pin with grease and put back in, test on bench with 1 psi increments and take out after each 1 psi increase to it showed bottoming out. Or test in truck by driving it slowly but again looking at boost gauge and increments of only 1 psi at a time, pull out each 1 psi increase etc. Until bottoming out. Or hook up air with adjustable regulator to pump while still on truck and do as above, either way it would take some time.
Again it depends on starwheel adjustment too. I do know even with the starwheel all the way out ( to the top and almost falling off threads and smoke screw all the way out too ) I could bottom pin out no problem.
mark
A star wheel that was near the top of the threads, which puts more pressure on the spring would lose some of its spring rate over time and would need more psi before bottoming out. A newer or less mileage truck would have more spring rate also. Most likely very small amount of difference. Could be 1 or 2 psi diff.
One would have to mark the pin with grease and put back in, test on bench with 1 psi increments and take out after each 1 psi increase to it showed bottoming out. Or test in truck by driving it slowly but again looking at boost gauge and increments of only 1 psi at a time, pull out each 1 psi increase etc. Until bottoming out. Or hook up air with adjustable regulator to pump while still on truck and do as above, either way it would take some time.
Again it depends on starwheel adjustment too. I do know even with the starwheel all the way out ( to the top and almost falling off threads and smoke screw all the way out too ) I could bottom pin out no problem.
mark
Ok, I want to play with this one too... ... .
I always thought that over time, with heat and repeated cycling something like a spring lost its elastisity. In other words it would sag or give way easier, and fail to return to original position with any accuracy,,, kinda like a leaf spring does. Yes/No??
Did I misunderstand your post mark? I read it to mean that it got more resistant to deflection/travel as it got older.
With current metalurgical standards, it would take longer to see this happen but still, it should be the natural result of fatigue.
On another thought... .
Why couldn't you measure the total available vertical decent length on the cone, then... . replace the smoke screw with a threaded in attachment that had a measuring device (like a dial indicator sort of thing). You could slowly apply air pressure until you reached the full predetermined "available vertical decent length"? This will give you a psi # based on your current starwheel setting.
Is my thinking off on this or have I over looked something here?
If this would work you could then start with your starwheel all the way down and work your way up in, say, 1/4 turn increments to see the varying results of increasing spring pressure on the AFC housing.
At the present time my full fueling comes on at about 9-10 psi but that doesn't give a full accurate reading on what " full deflection" (if I can call it that) is and at what psi.
Jump in here people.....
Bob.
I always thought that over time, with heat and repeated cycling something like a spring lost its elastisity. In other words it would sag or give way easier, and fail to return to original position with any accuracy,,, kinda like a leaf spring does. Yes/No??
Did I misunderstand your post mark? I read it to mean that it got more resistant to deflection/travel as it got older.
With current metalurgical standards, it would take longer to see this happen but still, it should be the natural result of fatigue.
On another thought... .
Why couldn't you measure the total available vertical decent length on the cone, then... . replace the smoke screw with a threaded in attachment that had a measuring device (like a dial indicator sort of thing). You could slowly apply air pressure until you reached the full predetermined "available vertical decent length"? This will give you a psi # based on your current starwheel setting.
Is my thinking off on this or have I over looked something here?
If this would work you could then start with your starwheel all the way down and work your way up in, say, 1/4 turn increments to see the varying results of increasing spring pressure on the AFC housing.
At the present time my full fueling comes on at about 9-10 psi but that doesn't give a full accurate reading on what " full deflection" (if I can call it that) is and at what psi.
Jump in here people.....
Bob.
There is an easier way to test the spring tension.
All you need is a drill press, a digital scale for weighing mail or small articles and a dial indicator.
Basically you set the spring on the plate of the scale under the drill press chuck. Then line up a dial indicator to measure how much the spring moves vertically. Typically on the top of the press or top of the chuck feed.
To measure, just apply pressure with the drill press chuck, measure the force and the distance. This will tell you the spring tension or the force per inch (or thousandth of an inch) that is needed to compress the spring. You may have to test the full compression of the spring if it has different tensions half way through or something.
After you have that number, you just need the area of the diaphram, and you can back calculate the pressure to compress the spring.
Tell me if this doesn't make sense.
At my former employer they had a setup just for this type of measurement, but it was all digital. A little easier than this little project. I may be able to do this on a day off here and go in to test my spring. It would only take a few minutes.
J-eh
All you need is a drill press, a digital scale for weighing mail or small articles and a dial indicator.
Basically you set the spring on the plate of the scale under the drill press chuck. Then line up a dial indicator to measure how much the spring moves vertically. Typically on the top of the press or top of the chuck feed.
To measure, just apply pressure with the drill press chuck, measure the force and the distance. This will tell you the spring tension or the force per inch (or thousandth of an inch) that is needed to compress the spring. You may have to test the full compression of the spring if it has different tensions half way through or something.
After you have that number, you just need the area of the diaphram, and you can back calculate the pressure to compress the spring.
Tell me if this doesn't make sense.
At my former employer they had a setup just for this type of measurement, but it was all digital. A little easier than this little project. I may be able to do this on a day off here and go in to test my spring. It would only take a few minutes.
J-eh
Wow guys, this is great. You all have good points. I thought someone would throw out 10 psi or something, but this is better. I agree that with different depth/tension settings, the pressure required to bottom out the pin would differ. So, it would be different for every rig. The minimum and maximum settings should be consistent, however.
If one did some testing and found a certain boost level where they wanted full fueling, a custom spring could be made to make this possible. But this would be particular to each vehichle, because of different setups. Keep the ideas coming.
Mike
If one did some testing and found a certain boost level where they wanted full fueling, a custom spring could be made to make this possible. But this would be particular to each vehichle, because of different setups. Keep the ideas coming.
Mike
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Bob, no i didn't mean the spring has more tension as it gets older. IT HAS LESS which will make it travel farther with less psi.
My point i was trying to make was everyones springs and setups are different. So what makes one tick doesn't make all the others.
Sometimes you guys make things too complicated.
LOLIf your starwheel adj isn't cutting it for you, and you need less spring tension for sooner fuel, just heat spring with oven or what have you or if you need more spring tention... stretch the spring alittle.
mark
mark,
Ahhh, ok, I actually read it twice and still really figured I was missing it...
I haven't yet given thought to using heat to reduce spring temper or what ever, but I think that we have that already built in... . the starwheel does exactly that. I suspect that all you'd really change is the initial response time, if you were to mess with the spring itself.
Your supposition about "..... what makes one tick..... " etc is right on.....
You should have seen the 'twisting and turning' I went thru to clear aircare last week..... poor guy at the testing station kept killing it, everytime he put it in gear... . course I had to " explain " high efficiency TC, etc. . (to cover for detuning)
Took the poor guy 3 tries to get it to run and cycle the test to stay in the parameter band for a successful test.
I passed by the way, but not by much... . my opacity was 24. 99 and a 30. 00 is max allowable...
Its worth noting that my 2002 test with stock injectors read 4. 9
Hmmmmm, more fuel !!!
Bob.
Ahhh, ok, I actually read it twice and still really figured I was missing it...
I haven't yet given thought to using heat to reduce spring temper or what ever, but I think that we have that already built in... . the starwheel does exactly that. I suspect that all you'd really change is the initial response time, if you were to mess with the spring itself.
Your supposition about "..... what makes one tick..... " etc is right on.....
You should have seen the 'twisting and turning' I went thru to clear aircare last week..... poor guy at the testing station kept killing it, everytime he put it in gear... . course I had to " explain " high efficiency TC, etc. . (to cover for detuning)
Took the poor guy 3 tries to get it to run and cycle the test to stay in the parameter band for a successful test.
I passed by the way, but not by much... . my opacity was 24. 99 and a 30. 00 is max allowable...
Its worth noting that my 2002 test with stock injectors read 4. 9
Hmmmmm, more fuel !!!
Bob.
Oh boy, what a can of worms you opened up here. But a very good one. All of the ideas posted here will work. But the one that will work best is the one using an installed spring-air pump-and scale.
Now if you really want to dial it in, go to a spring supplier with your spring spec's and an idea what you want. After all, springs come in many different rates and installed hights. Just figure out what you want it to do and do it.
I do this with M/C ignitions and carbs. Even suspensions need a wide range of spring rates.
I think you just came up with something for me to think about and try to dial in.
Man, my wife is gonna hate you. he he
-dave-
Now if you really want to dial it in, go to a spring supplier with your spring spec's and an idea what you want. After all, springs come in many different rates and installed hights. Just figure out what you want it to do and do it.
I do this with M/C ignitions and carbs. Even suspensions need a wide range of spring rates.
I think you just came up with something for me to think about and try to dial in.
Man, my wife is gonna hate you. he he
-dave-
Geezzz I luv it when a plan comes together and you don't even know it was a plan to start with... ... BTW, was that my idea that you liked???
Bob.
Bob.
Ok, I'll be the one that throws the monkey wrench into things (maybe). We're all assuming that the spring is linear (that the resistance is the same on all points during it's travel).
If the spring is non-linear, measurement of it's spring constant now becomes an exercise in determining a function, not a constant.
So, I suppose it's easier to assume that the spring is linear. Most likely is anyway, given the application. Right... ?
If the spring is non-linear, measurement of it's spring constant now becomes an exercise in determining a function, not a constant.
So, I suppose it's easier to assume that the spring is linear. Most likely is anyway, given the application. Right... ?
$. 02 worth of engineering input. . . . . . For the range of motion, the spring rate should be considered linear. In reality, spring rate is not linear, however for modeling puposes and over small ranges of motion, linear modeling will work.
Finally, spring rates will change with time, however the amount of change is dependent upon the number of thermal cycles and mechanical cycles that the spring sees. Theretically, if the spring material never enters into the plastic deformation region of its material stress strain curve and does not exceed its matrix transition temperature, then no change should take place, However, in reality, the spring rate will typically decrease. Will it be enough to have an effect on the system by the time all other wear parameters are taken into account? An interesting side test would be to determing the spring rate from a used unit and the spring rate of a new spring.
Finally, spring rates will change with time, however the amount of change is dependent upon the number of thermal cycles and mechanical cycles that the spring sees. Theretically, if the spring material never enters into the plastic deformation region of its material stress strain curve and does not exceed its matrix transition temperature, then no change should take place, However, in reality, the spring rate will typically decrease. Will it be enough to have an effect on the system by the time all other wear parameters are taken into account? An interesting side test would be to determing the spring rate from a used unit and the spring rate of a new spring.
Realizing that our springs have undergone different temperature changes, up/down cycles, and have been set at different pressures, maybe starting with a new spring would be best, as hdm48 suggested. This would put everyone on the same page for comparisons sake (well, much closer anyway). If a spring that would work well for most everyone could be found, slight adjustments could be made for personal preferences.
What would you guys like to go with? Shorter, taller, shorter and stiffer, taller with less tension? Maybe a spring for different driving conditions, empty, towing, racing, etc. ? Again, slight adjustments can be made with the star wheel without dramatically changing the characteristics of that spring.
Mike
What would you guys like to go with? Shorter, taller, shorter and stiffer, taller with less tension? Maybe a spring for different driving conditions, empty, towing, racing, etc. ? Again, slight adjustments can be made with the star wheel without dramatically changing the characteristics of that spring.
Mike
Oh boy, here we go.
First, Bob, yes, it was your idea I was talking about. But don't be going and getting a swelled head. You'll never fit in the cab again.
I do believe using a spring in it's aplication and applying air at a measured amount using a scale to measure travel is by far the most accurate.
If spring "rate" is an issue, one can always get a "progressive" rate spring. I use these on a lot of high performance street machines (motorcycles). I don't use them on racing bikes because I need to know the exact rate for tuning.
But, something like this would work in our pumps. Mark K. and I are going to be playing with a VE pump to work with my twin turbo set-up soon and I think I just might get a few springs to try too.
I lay awake at nite dreaming of stuff like this. Now I've got one more thing to think about.
I hate to admit it, but, I love this stuff.
-dave-
First, Bob, yes, it was your idea I was talking about. But don't be going and getting a swelled head. You'll never fit in the cab again.
I do believe using a spring in it's aplication and applying air at a measured amount using a scale to measure travel is by far the most accurate.
If spring "rate" is an issue, one can always get a "progressive" rate spring. I use these on a lot of high performance street machines (motorcycles). I don't use them on racing bikes because I need to know the exact rate for tuning.
But, something like this would work in our pumps. Mark K. and I are going to be playing with a VE pump to work with my twin turbo set-up soon and I think I just might get a few springs to try too.
I lay awake at nite dreaming of stuff like this. Now I've got one more thing to think about.
I hate to admit it, but, I love this stuff.
-dave-
While I was playing around with my spring, I thought I would test the pin that rides up and down the diaphragm cone. I cycled the throttle linkage a few times, and it didn't come out of its hole. I sprayed some WD-40 on it, and gently pushed on it with a small screwdriver, and it still wouldn’t move.
While I was at school today I grabbed a VE injection pump off of a 4BTA, and experimented with it. All I had to do was open the throttle up all of the way once, and the pin came all of the way out. I know there is no easy way to pull the pin to check and clean it, so I am unsure of what to do. What doesn't make since is that I can see the "whiteness" mark riding all the way up the cone, and can now make 30psi boost. Do you guys think that something needs to be done, or it's ok and the pin is just afraid to come out in the daylight when I am looking at it?
Mike
While I was at school today I grabbed a VE injection pump off of a 4BTA, and experimented with it. All I had to do was open the throttle up all of the way once, and the pin came all of the way out. I know there is no easy way to pull the pin to check and clean it, so I am unsure of what to do. What doesn't make since is that I can see the "whiteness" mark riding all the way up the cone, and can now make 30psi boost. Do you guys think that something needs to be done, or it's ok and the pin is just afraid to come out in the daylight when I am looking at it?
Mike
Hey Mike,
Don't worry as your pin is working fine. When i checked your pin and adjusted your diaphram, things were fine. Normal. The pin is leaving marks on the concentric pin which shows its working.
Your getting there alright. I'll have to watch out for you soon.
mark
Don't worry as your pin is working fine. When i checked your pin and adjusted your diaphram, things were fine. Normal. The pin is leaving marks on the concentric pin which shows its working.
Your getting there alright. I'll have to watch out for you soon.
mark
re: hdm's comments on spring progressive spring rates... . Can we follow this along a little further...
First is there any merit in considering the alteration of this component at all?
Since the starwheel itself is, in effect, a spring adjustment specifically designed to do that job ( as I understand it's function) Would making physical changes to the spring itself be a redundant change?
I can envision how a "progressive" spring would work in terms of resistance increasing with deflection, but not the other way round. Unless the aim is to set the starwheel low to have a quick onset of fueling and then the progressive nature of the spring causing a slowing of the rate as the AFC dropped, needing higher boost, what other purpose would this serve? If this was the aim of the change, then would you not serve the same purpose by easing the starwheel back up, then increasing 'full fueling' (keeping in mind that this adjustment directs a larger portion of the total fuel increase to the low/mid range) which would result in heavier initial fueling (like the low starwheel setting) and then have the stiffer starwheel setting slow the travel rate due to being set higher?
(No one has mentioned delivery valves on our pumps either... )
Would there be any theoretical benefit to lowering the starwheel all the way down and using a progressive spring for the entire AFC deflection control function?
Also, when I was trying to get my smoke screw to a true "neutral setting", that is, absolutely no pressure on the AFC, I found I had to back the screw right up into the housing body. Then, take a dremmel with a 3/16ths round fine stone, and grind away some of the inside casting were the smoke screw protruded from. Even at that there is still a slight pressure on the AFC from the screw end/nut in the center of the AFC diaphram since I assume its contacting the underside of the smoke screw housing outlet.
I did notice that my "witness mark" on the cone showed that the fuel pin was reaching a little lower on the cone when at idle condition.
One last thought, ... is there any difference as to were the boost tube draws its boost pressure? Would drawing boost from say, the inlet horn instead of the manifold make any difference in response?
Ok, that's alot of thinking out loud. Does someone want to pick at it and scrap the none issues and work on the applicable ones???
Bob
First is there any merit in considering the alteration of this component at all?
Since the starwheel itself is, in effect, a spring adjustment specifically designed to do that job ( as I understand it's function) Would making physical changes to the spring itself be a redundant change?
I can envision how a "progressive" spring would work in terms of resistance increasing with deflection, but not the other way round. Unless the aim is to set the starwheel low to have a quick onset of fueling and then the progressive nature of the spring causing a slowing of the rate as the AFC dropped, needing higher boost, what other purpose would this serve? If this was the aim of the change, then would you not serve the same purpose by easing the starwheel back up, then increasing 'full fueling' (keeping in mind that this adjustment directs a larger portion of the total fuel increase to the low/mid range) which would result in heavier initial fueling (like the low starwheel setting) and then have the stiffer starwheel setting slow the travel rate due to being set higher?
(No one has mentioned delivery valves on our pumps either... )
Would there be any theoretical benefit to lowering the starwheel all the way down and using a progressive spring for the entire AFC deflection control function?
Also, when I was trying to get my smoke screw to a true "neutral setting", that is, absolutely no pressure on the AFC, I found I had to back the screw right up into the housing body. Then, take a dremmel with a 3/16ths round fine stone, and grind away some of the inside casting were the smoke screw protruded from. Even at that there is still a slight pressure on the AFC from the screw end/nut in the center of the AFC diaphram since I assume its contacting the underside of the smoke screw housing outlet.
I did notice that my "witness mark" on the cone showed that the fuel pin was reaching a little lower on the cone when at idle condition.
One last thought, ... is there any difference as to were the boost tube draws its boost pressure? Would drawing boost from say, the inlet horn instead of the manifold make any difference in response?
Ok, that's alot of thinking out loud. Does someone want to pick at it and scrap the none issues and work on the applicable ones???
Bob
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Well I was thinking about the progressive spring tension, but the spring is about 2 - 2. 5" long and is only pressed about . 5" on the pin. So that being said, the spring tension is for intents and purposes linear. The pre-load on the spring will determine the, (for lack of a better term) break-over point for the fueling curve.
The preset of the spring with the Star wheel affects your mileage. What I have done (just watching the boost gauge and the tail pipe) is up the spring pressure to keep any fueling above 5-6 Psi. I have done this because on empty cruise at 75 Mph, I am at 5 Psi boost. I don't want excessive fueling there, but if the boost goes up over that break-over point, lets have it >LOL...
I think "gutting " the AFC is not a educated solution (sorry, trying to be political here) it has a purpose. I personally don't want to have smoke pouring out of the pipe while I'm tootin through town. I want the truck to react with the pedal and when I floor it there is some lag up to the magic 6 psi, but then the smoke comes and the needle peaks. .
I use my truck as a daily driver, so I am not out to drag race. You big power guys probably want a different fuel curve, because you have the other goodies to go with it ie. turbo enhancements.
Thoughts??
J-eh
The preset of the spring with the Star wheel affects your mileage. What I have done (just watching the boost gauge and the tail pipe) is up the spring pressure to keep any fueling above 5-6 Psi. I have done this because on empty cruise at 75 Mph, I am at 5 Psi boost. I don't want excessive fueling there, but if the boost goes up over that break-over point, lets have it >LOL...
I think "gutting " the AFC is not a educated solution (sorry, trying to be political here) it has a purpose. I personally don't want to have smoke pouring out of the pipe while I'm tootin through town. I want the truck to react with the pedal and when I floor it there is some lag up to the magic 6 psi, but then the smoke comes and the needle peaks. .
I use my truck as a daily driver, so I am not out to drag race. You big power guys probably want a different fuel curve, because you have the other goodies to go with it ie. turbo enhancements.
Thoughts??
J-eh
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