Afc tuning with twins.

blackcloudCTD95

blackcloudCTD95

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Oct 16, 2007
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After I got the oil pressure figured out and drove the truck home I realized I have way to much low end fuel. I put a different afc spring in the pdd 35-45 psi spring and I slid the afc housing back a bit. With afc live I can control the smoke very well, but I lost mid end and top end( to the point where I'm in od and lug it I have hardly any smoke and the truck does acclerate) I have the housing in the right spot for low end ( not full foward)

My question is does anyone know of a softer spring I can put in the afc that moves easier with boost? Should I try the pdd stock to 35psi spring? To me is seems like the spring is too stiff :bang
 
Is it binding? Im not a fan of the afc springs sold online. I like inner valve springs.
 
have you tuned the AFC with shop air to get an idea on what its doing?
 
Slide the afc back forward, then bring back the pre boost screw all the way out. Look at it off the truck and sometimes you can grind on the back of the housing (Where the pre boost screw is) and get it to come back further. I'm not familiar with their spring but some springs have to have the star wheel backed off all the way to let the foot travel the full way forward, to get the top end back. Or the spring binds before full travel.
 
It's a longer spring I know than the stock one and the tst spring. I set it up per the instrctions of power driven afc live install. Star wheel foward towards the radiator. Smoke screw to where it barely just touches then 1/4 turn after it touched. Afc housing all the way back then slide it towards little bit.

I have not benched the afc since I got afc live.. this morning I was rather pleased with performance I slid the housing up a tad before I went to work but I got the low end smoke again.
 
turbo2332 said:
Is it binding? Im not a fan of the afc springs sold online. I like inner valve springs.
Click to expand...

Inner intake spring of what motor? 12v or do you mean governor spring I have read that, people use one of the governor springs in the afc after they stretch it a bit
 
Inner springs from old air cooled VW's are the ticket. Full travel around 50psi initial movement around 20. Take whatever springs you choose to test and compress them in a vise. Compare that measurment to the stocker fully smashed. They need to be equal or smaller than the stocker to work right.
 
I've been using the inner spring from a big block Chevy aftermarket set. Picked them up from a machine shop buddy, I cut about 1 coil off and they fully open at about 45psi and the only spring I've found that travels fully without coil bind, even with the star wheel preloaded against it.
 
blackcloudCTD95 said:
It's a longer spring I know than the stock one and the tst spring. I set it up per the instrctions of power driven afc live install. Star wheel foward towards the radiator. Smoke screw to where it barely just touches then 1/4 turn after it touched. Afc housing all the way back then slide it towards little bit.

I have not benched the afc since I got afc live.. this morning I was rather pleased with performance I slid the housing up a tad before I went to work but I got the low end smoke again.
Click to expand...

If you are happy with how it runs now other than low end smoke, leave everything the same but pull off the afc and look at what's keeping it from coming back/retracting further. There is room in the back housing with a little grinding on the back housing, among other ways to get it to come back more. Then use your regulator deal to tune the rate it opens from there.
 
jasonc said:
If you are happy with how it runs now other than low end smoke, leave everything the same but pull off the afc and look at what's keeping it from coming back/retracting further. There is room in the back housing with a little grinding on the back housing, among other ways to get it to come back more. Then use your regulator deal to tune the rate it opens from there.
Click to expand...


Back housing where the pre boost set screw sits?
 
There sure is a fine line from driveable taking off from a stop and being embarrassed LOL. Before I left for work this am I had to slide it foward a bit because of it had a hard start. And I barely moved it and got that low end smoke back. But it's better than the first go around.

I'm going to ask my co worker he has old vw beetles I'm sure he'll have a valve spring.
 
Not a no start.. it was a prolong . Slid the afc foward and it fixed it. Idk?. I know I'm going to have to write down all the changes so I don't forget what I already did.

There really isn't many threads about spring stiffness for twins. I guess it comes down to driving preference I like to drove more low to mid end. While by brother drives like an ads LOL
 
So after reading and confusing my self..I'd like for max fuel to come in around 40-45 with my driving habbits so my spring i have now should be good

I have the pre boost touching then 1/4 turn after that. The afc is in the middle maybe a little back from the middle star wheel with no tension on it all the way foward. Where should I start tomorrow tightening up on the star wheel ?
 
Desired spring stiffness, length, and preload will very GREATLY depending on injectors, delivery valves, injection pump, and turbo flow. The "fuel curve" will need to be fine tuned based on those options to match the turbo output. Definitely no one size fits all. That's why PDD came out with AFC live.
 
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