carb licked...now timing

[XFlow_Fairlane]

so what is the cheap way to control timing (boost retard) on a turbo car? I know a msd 6btm would be best but I don't have money for that. should I just lock my timing and set my total advance? fancy vac line logic? dual port advance on teh dissy? whats the trick I need? or is there none? I have both a loadamatic and a dual advance points dizzy and should be picking up a duraspark soon. run them off ported vac or manifold?

 

[Fingers]

Some of the early factory carb/turbo vehicles (the example I am thinking is a Mitsubishi Sigma) used a Vacuum advance style setup on the distributor that actually retarded the timing rather than advancing it. It was a dual diaphragm unit that was vacuum = advance/ pressure = retard.

 

[Does10s]

This is what I did. BTW we've got a Duraspark distrib.

Disconnected the vac. line to the distrib. Threw it in the garbage.
Using a vac. line plug (cap) I put that on the vac. adv. canister on the distrib. I did this after some testing using my timing light. It slowed down the rate of adv. perfectly by adding some resistence to the mech. adv.
I know this sounds strange but I tested it over and over and it seems to work pretty good.
We've got our initial timing set at 8* BTDC.

That's it! I know it's not the best way to do it but it works and it's free!
If you play with that dual type vac. adv. canister that might work better. Maybe put a bleed off type valve in there so that you can control the amount of adv. under boost.
I need to do some more experimenting with Kelly's car. Might be able to pick up few tenths just with timing!
Will

 

[XFlow_Fairlane]

hmmm I got a hobbs switch so maybe I will get a duraspark and wire up the start retard on it too. so pretty much you just switched what side the "vac" line goes to? might have to find a dual port canister for mine

 

[MustangSix]

If you're doing a blow thru, another way might be to use a Duraspark with the dual vacuum advance. Hook up the advance as usual, leaving the inner retard port open.

When under no boost or light cruise you will be pulling a vacuum and the distributor will get vacuum advance. As the boost builds, the pressure will begin to retard the distributor.