what kind of spring

[91bluecummins]

im going to get a denny II fuel pin and what size spring do i need to get or should i leave the spring it stock

[AHineman]

Leave the stock AFC spring in it. People with lots of fuel (big injectors, etc.) run stiffer springs to try to limit low boost fuel.

[unixcowboy]

What kind of stiffer spring ??
I thought the '93 spring was the stiffest you could get from Bosch.

[AHineman]

I'm not the expert, but I've heard about pink & green, blue(I think), and silver springs. I thought silver was the stiffest, but I'm not sure. My spring is pink & green.

[unixcowboy]

Pink & green is the one in mine now.
I just checked it on a homemade spring tester and it shows ~ 15psi to 1/2 compression and 25psi to full compression.
I'd like ~ 10psi higher since I can easily hit 45psi, and with cruise control set at 70mph if I hit a good grade the boost will spike over 25 and stettle in at ~ 18 - 20psi.

[RSWORDS]

I would like to know all the specs too!

[ahale2772]

this is the first time ive heard of preople changing the afc spring id like to know more as well, hav any of you guys tried going on a website like mcmaster carr, they have / can custom order pretty much any mechanical goodie one could want

[BC847]

I've been dinking with the AFC spring mess a little.

My goal was to better control the low/mid boost fueling so as to cut down on the smoke at low boost. I've done a bunch of Googling, Mcmaster-Carr, Graingers, etc and can't readily find anything that's similar in profile, much less with a selection of spring rates.

In the meantime, I've gone and used a turbocharger manual boost controller (MBC) to reduce the boost pressure to the AFC.
With twins, big-honkin IC, 3" plumbing, a cam, ported head, etc, I've got just shy of 60psig at the intake log. I've set the MBC to provide about a 2-to-1 ratio ~ 40psig boost gives 20psig to the AFC for example. Further fine-tuning is done with the star-wheel.

I've found however, running a fuel-pin like Denny-T's sorta screws with it. I'm thinking a fuel-pin like the M&H M3 would be better suited.


That's all I got.


(The above may not have anything to do with what the original poster was talking about. )

[1STGENFARMBOY]

What about puttin a spacer in the afc housing insted of changing the spring

[AHineman]

I knew I had read about these before, didn't want you guys to think I was crazy....

http://www.1stgen.org/viewtopic.php?t=3103&postdays=0&postorder=asc&highlight=spring&start=15
http://www.1stgen.org/viewtopic.php?t=3308&highlight=spring
http://www.1stgen.org/viewtopic.php?t=3220&highlight=spring
http://www.1stgen.org/viewtopic.php?t=4986&highlight=spring

On a side note to what BC847 said, I am gathering parts for a three stage valet switch. I will run a three position switch and two solenoids. I will run boost through one unregulated and regulate the other to try to get about half travel out of the fuel pin. With the switch in the off position I will have no boost to the afc. Don't know if it will work very well, but it seems like a good idea to me. I may have to borrow the boost controller idea when I get the big injectors and twins.

[Remps]

My 90 had a silver spring,but I switched it for the red/green out of the 93 5 spd. IDK if they are original IP's,but they were both virgins till I got em. The silver one is a fair bit stiffer.

[unixcowboy]

I think what a lot of people don't realize - myself included until I got to thinking it through - is that you cannot move the pin any further once the spring is compressed to where the coils touch.
I measured this height and is 0.300 with my pink/grn spring which has 0.068 dia wire.

If you raise the starwheel so that the well in the wheel where the spring sits is less than 0.300 ( in my case ) from the top of the center tube where the pin slides you are not getting full pin travel. The spring will bind and prevent the pin from going further - no matter how much boost you apply.

I set mine so the pin would get full travel then applied some black moly axle grease to the face of the pin, then drove it limiting the boost to 15 psi and then checked the track on the fuel pin. The track showed the pin moved ~ 1/3 of it's total travel.
I had also made a new spring using 0.125 music wire. That was a job getting it to be the correct dia. The wire is larger than stock so the ID had to be smaller to allow the OD to be correct and then....and then.....
Well, 4 springs later I got one that's almost the same as the stock one.
I must have done something right because now when I limit the boost to 15 psi the pin only travels ~ 1/4 or less of it full travel. Also, running around town feels about the same. The smoke when I pull away from a light is less.

I'll be able to test it better tonight when I go bowling 'cause I've got a stretch of road that has a 60 mph limit and I'll time it so I get caught on one of the lights. Than when I take off I'll give it ~1/2 throttle and watch the smoke...If it's less than it has been then I'll know I'm on the right track.
I'm sure there'll be more mods to come.

[Begle1]

How much is there to gain by swapping springs? It's gotta be one of the most minor tweaks that you could do...

[Richie O]

How much is there to gain by swapping springs? It's gotta be one of the most minor tweaks that you could do...

With a stock fuel cone afc settings are a joke. When you step up to a M+H or a Denny T pin you can feel major differences with afc tuning.

[RSWORDS]

Yeah my DennyT over fuels way to much at low boost, even with teh whell all teh way up. Its to teh point it hurts acceleration. If I could make it stay up longer I would be better off.