Manifold Vacuum Experiment
Following along. I am trying the same thing, although my happy place for idle is 25*. I would think that the trickiest part would be the mechanical advance curve. Getting enough in, while manifold is falling off under light acceleration......Keep us posted Rob :thumbsup:
It's pretty strange. All of them in the past I've done like this stopped idling up at what I would call a "reasonable" amount of initial timing. This one does not. It idles up right up to 44 degrees initial.
Admittedly, it takes several degrees before it begins to idle back down when pulling timing out. I also fully admit I never measured static compression, because I knew it was going to be low. I didn't care and I still don't. I haven't measured cylinder pressure with a compression gauge, either, although now that I am doing this with the timing, I'll get the gauge out tomorrow and see.
The factory "rated" compression for these engines was 8.4:1. Although where they blueprint is anyone's guess. Again, I didn't care then and I still don't. I knew unless I started whackin off .100" or more from the heads, I'd be ok. I said whackin off. I had the heads milled .060" originally when I had machine work done.
Also, these engines were known to be a bastion of a detonation problem, because of the negative deck clearance and long stroke. That was the reason for wanting a camshaft with some duration and a late IVCE (intake Valve Closing Event). So far, I've run as much as about 28 initial with the vacuum canister on ported vacuum and heard narry a peep of detonation all the while running on 87. ......which was my goal. A cool, lumpy idling truck engine that will pull the snot out of something on the bottom end and so far, that goal has been met the heck out of. This experiment is just to see if there's something to be gained from full manifold vacuum at the vacuum canister. We'll see. lol
