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It will run better on manifold advance.
#1 tuning change.
All factory settings back then had retarded advance, especially that one, it is at least 10-15* retarded at idle, from "ideal".
Early emissions tuning. Runs hotter, etc. Many of these hi-perf engines also had air injection into the exhaust manifolds, they had to run hot enough to use the exhaust as an early "convertor" to help burn off any leftover hydrocarbons. The extra oxygen and the heat did the trick. By 1974 they had to run them so hot to try to meet the ever tighter HC emissions, they began having exhaust valve seat erosion problems. And went to hardened stellite valve seats, and so on.
That retarded timing was pretty much standard procedure after 1964, which was the last time a factory SBC had an ideal "performance" timing curve. If you check a factory 327/365HP timing curve, and the "ideal" performance one in the Chevy Power Book, published by GM and mentioned for decades for Competition use "only", they are practically identical, and virtually identical to the curve we discussed earlier.
Here are several different ways to get the good 36 degree curve, depending on how much initial timing any particular engine "likes".
The bigger the cam duration, and overlap, the more initial timing the engine needs/likes, to run well. A cam like yours will probably like 14-16 initial. That cam is a pretty well known hot street cam, and so is the curve it needs. Columns 1-4.
Your original idle setting of 8*, with no vacuum at idle, will jump to the 26* range, on manifold vacuum. Yes that is 18* more, and it will like it! But the difference is only at idle. But yes you will need a 10* can, not the factory 15-18* can.
ok, will test again all this. I've doubt now to get 0° of vacuum at idle. will feed back. thks.
A fitting like that, on the bottom base plate, is "probably" full manifold vacuum.
But I would conform it, with a vacuum gauge, or even just put your thumb over it at idle.
A timed or ported fitting will yield zero vacuum at idle, but starts to work when you open the throttle.
A fitting like that, on the bottom base plate, is "probably" full manifold vacuum.
But I would conform it, with a vacuum gauge, or even just put your thumb over it at idle.
A timed or ported fitting will yield zero vacuum at idle, but starts to work when you open the throttle.
That is ported vacuum you need to tee of the one under the bowl.if you need pics I will send them
it will not idle properly on the fitting that is ported vacuum off idle . Hope this makes sense to you
I have been there.
That is ported vacuum you need to tee of the one under the bowl.if you need pics I will send them
it will not idle properly on the fitting that is ported vacuum off idle . Hope this makes sense to you
I have been there.
I "T"d mine from the choke pulloff hose. Next time I have the center carb off, I'm going to modify the base plate so the ported port becomes a manifold vacuum port.
05-12-2024, 04:44 PM
