Warhead

The reason I asked the initial question on which is best is because I am having a hard time with my manifold vacuum. For me to maintain 10in or better I need and idle of @1000 rpm, any rpm lower and vacuum drops to 7in. I am using a Mallory dist, vacuum can doesnt start kicking in until 8 or 9 in (checked for movement using vacuum pump).

If I set idle to 1000 I get the vac advance, as soon as I put it in gear rpm drops, I loose manifold vac and vac advance. I do not have any vac leaks, capped all ports and sprayed carb cleaner around manifold, no idle change.

I welcome any sugjestions, engine specs are:
355, Edlbrock RPM heads(64cc, 195 runners), RPM manifold, and 750 carb.
Cam is 234/244, ls 112, lift at valve .488/.510, This is Edlbrocks top end package.

Kalway

You've gotta adjust your idle screws until you have the most vacuum you can get.

Boofers

My White 79 - you may want to double check that your tach is accurate, just a thought...

...Roger...

Providing you have no vacumn leaks and your valves are adjusted properly.Put your vacumn gauge on the "ported" vacumn port at idle -if you are reading vacumn your throttle plates are open far enough your coming out of the idle circuit.This alone will make your vacumn low at idle.If this is going on you need to get those plates closed until that vacumn goes down on that port.Now your idle is too low.Try to increase initial timing and readjust idle mixture.If too much initial makes it crank slow then try weaker advance springs so your getting a little cent. at idle.

lars

Change your vacuum advance control unit to a unit that pulls its full range in at the vacuum reading of your engine (or below). The VC1810 unit pulls its full range in at 6 to 8 inches of vacuum and starts pulling at between 3 and 5. Sounds liker a better match for your engine.

Use whichever one produces the best quality idle (not nessessarily fastest idle). Some engines like a lot of timing at idle (bigger cams), so manifold vacuum works well. I've seen other small-cammed applications that do not like that much timing at idle, so ported seems to work better for best quality idle (the engine in my 64 liked ported vacuum until I swapped out cams, and now I run manifold vacuum). Most engines will benefit from straight manifold vacuum for idle quality and lower engine temps, but use the option as a tuning vaiable for your application - I always try both sources on every car I tune on the Tuning for Beer Tours and use the one the engine wants.
Lars