Vacuum advance distributor and big cams

[thrustnut]

I just installed a larger cam in my Z and my manifold vacuum at idle is down in the 7-8 in hg. range now. I was wondering if this will affect the vacuum advance in the distributor. I'm not sure what the vacuum is when driving, or what the difference is between a stock cam and the larger one while at cruse. I have a 77 280 with the stock dizzy running into a Crane Cams hi-6R with TRC (TRC not hooked up at this time). I am thinking about mega-jolt or a mechanical advance dizzy, so any one out there with experience in this issue let me know.

Chris

[JMortensen]

Vacuum advance is for mileage. I'd disconnect it and set total advance for somewhere in the mid 30's total advance after all the mechanical is in, which is probably 2500, so if you set it in the mid 30's at 3000 that should be it. The 280Z distributor has a lot of mechanical advance which is not good for low end power. You could get a 280ZX distributor and use it because they have less mech adv, or you could go to some sort of crankfire setup like megajolt.

 

I think crankfire is the way to go if you're going to spend money on ignition. No point in spending hundreds of dollars on a Mallory distributor when it is still a distributor and has the slop in the gears at the crank and the potential for failure in the cap and rotor and wires. If you're going to spend a lot of money get rid of of the dizzy and go crankfire.

[thrustnut]

So when you set your 30 deg. advance at 3000, do you just measure off the increments on your timing plate and fab a new one that extends positive? Would you just leave the vacuum advance disconnected? On the new ignition note, I would rather go with the MS system, I think it's 75.00 for the kit vs 300ish for the distributor. I will check my all in timing tomorrow and see where I'm at.