Which do you guys run on your holley's and why. Right now I have mine plugged into manifold vacuum, but I was going to try the ported vacuum port. Which do you guys run and why?

 

You're having a hell of a time with your ignition setup eh?

Alright, i'll let you in on my little secret, but hush hush, take it with you to your grave!

Ok, so your idle speed, and off idle characteristics are set by many things:

-throttle position (idle speed screw)
-idle mixture (mixture screws)
-timing
-other variables

So, we all know "most" SBC engines like to have ~36* at peak torque to make max power. We also know we can get away with ~46-50* at light load cruise. So from 36*->~50* we use our vacuum advance. The thing we can play with is initial. However, you'd need to weld up your advance slot to run gobs of initial if you still want 36* at WOT.

Ok, so here comes my secret To get a good idle-off idle transfer, you need to have your throttle position in the ballpark. If your throttle is too far open at idle, your mixture screws will have little (or no) effect, and you'll be running partially on your primaries at idle. Off idle may have a flat-spot or bog.
If you're too low on throttle angle, same deal. You have a ballpark where you show ~.040" of the transition slot. This is on a q-jet, I *THINK* it's the same on a holley.
So, you set your idle screw in the ballpark, fire up the car, then adjust the idle screw so it'll idle. With a big engine or lots of cam, you've gotta crank up the idle screw - count the turns you open it, you'll want to go back to your baseline later. Baseline however barely gave you a 500RPM idle right? Or it wouldn't idle at all.
So you need more timing at idle to keep the beast running. TIMING is how I adjust my idle speed. You also get more vacuum at idle (better for brakes) by using more timing.

Now, if you use a bunch of initial, and shorten your mechanical travel, well, that's what I do. Then I use ported advance.

Or, you can use manifold advance, get your gobs of base timing, but once you go WOT the vacuum advance goes away so you don't go over 36* at WOT.

Problems with either?
Manifold - Some people have reported hunting idle speed. Some people claim a drop in power when you go WOT because you lose too much timing at lower RPM.

Ported.... Not sure, i'm liking it. You can have situations where you've got a lightly loaded engine and it's got too much timing and it pings. Loading it in high gear sorta thing. It hasn't happened much, I just remember to downshift.

Do a search, I remember a debate about this. I think F-bird'88 and another member were arguing about it. The point is that a lot of useful info, tips, and points of view were brought up in that.

 

good info sonix.
remember that when "ported" came about the smog police were (and still are) nuts about lowering NOx. ported timing meant less timing at idle (lowering NOx at idle) and lots of timing at cruise (lower cruise emissions, smoother driveabiliy, and egr helping w/ NOx now that we're crusing) to a carmaker that had big v8s as their main line of vehicles back in the mid seventies, that was the greatest thing since sliced bread. so ported vacuum may be less oriented to performance, more to emissions control/driveability of mostly stock engines of that time.

different carb/cam/displacements need different timing characteristics. if you have a long duration cam 350 for example, you may need lots of advance just to idle at all. a shorter duration camshaft may only need 8 deg. or so i idle nice and go w/ ported vac. timing. carbs like different timing settings as well. engines respond to what they like by the way they perform

 

Well, my camshaft has a pretty decent amount of duration and I have my timing at around 22 degrees at idle w/ the vacuum advance plugged. What should I run? I have it on ported right now.

 

I'd run it locked out at full advance.
But if you can get it running ok, leave 'er be. No bog off idle? Then it's good.