Super tuning car runs good shooting for great

AJ/FormS said
rmchgr
With a stock type teener I do see what you are saying. They have little to no reversion,so the manifold vacuum will be very high at idle and will hang there for a few hundred rpm before beginning to decrease,gently but continuously.
-But with performance cams, I find that the low idle-vacuum increases as rpm rises to the point where the reversion (due to the late closing intake valve),ends. For streeters(all I know), this is usually somewhere in the 1800 to 2200 area. Then,with no load on the engine,it will hang there, a good long way. I gear my car to run hiway at just above the no-load vacuum peak.
My 367 with a 230 cam,for instance, idles around 11inches, and with no load, the vacuum increases to around 22inches at 2200(24*timing), and IIRC it hangs there for at least 1000 rpm.
Now this data is subject to change somewhat with changes in timing, but it is not drastic. I think the cid/cr and chamber seal have the biggest effects on the size of this Vacuum number, and the ICA probably determines where it peaks,rpm wise. That's me thinking tho.

He said he has 3.91 gears so the RPMs will climb pretty quick if he is into the throttle, even with lighter acceleration. That's what gears are supposed to accomplish, right?

He didn't say what his vacuum is at idle but if I had to guess, it's probably between 13-17". At least you would hope a closed-chamber, aluminum headed 360 with a decent performance cam would be around there.

The stock, lo-po 400 in my truck with the silly long duration cam and high rise intake idles at 15" of vacuum which is actually pretty good. My initial timing is 18 degrees though which is almost double the factory setting. With a heavy vehicle, low geared trans. and 3.23 gears, it's likely why I run into issues with the V.A..

Again, if I changed the springs in the distributor to slow the advance curve it might help to dial in the V.A. but the cam is too big and it will be more of a dog than it is now. Frankly, life is too short to mess with it that much. I have a smaller cam for it but there's other projects to finish before I put it in.

One of these days I will get my Sun distributor tester up and running again and it will be easier to do but until then, no V.A.. But I digress...

I'm interested to hear about what happens when he backs off the initial. If I am right, he will have more room for the V.A. to work and the negative effects will be minimized. I would also like to hear if he tries to tune it without V.A. to see if things improve. It's a balancing act with a street car, there are no hard-fast rules to apply.