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68Formula
05-21-2005, 04:06 AM
First let me define my terms to clarify:
Initial timing = initial timing with advance plugged
Centrifugal = mechanical advance only
Total = inital + mechanical without vacuum

Engine Specs: (purchased as used long block)
Displacement = 455
Compression = 8:1
Cam (approx. measured) = 223° and .460" at .050" lift (intake)
Ignition = HEI with Proform rebuild kit
Intake = Performer
Carb = Holley 750 vacuum sec.
Headers = 3 tube (center two ports paired) full length
Centrifugal allows additional 20° by 2800 rpm
Vacuum advance set to 9° at 15"
Compression check showed 135psi nominal with one cylinder at 130psi and one at 140psi (rest were all 135psi).

Running with 16 - 20° Initial
Required high idle set screw which necessitated opening up the secondaries to avoid exposing the primaries idle transfer slots. Car had poor power and aweful fuel economy (even for it's displacement). Ran extremely hot. All the symptoms of retarded ignition. Also, manifold vacuum was reading just under 15".

Running with 30° Inital
Engine idle smoothed. Was able to lower idle screw setting such that it takes 250 rpm more before the transfer slots in the primaries are exposed. Engine ran cooler and fuel economy improved significantly. Full and part throttle acceleration improved significantly (even with my Total being 50°), and no pinging. Vacuum increased to just over 16" (almost a 1.5" increase from before)

What is bothing me, is I don't believe this engine is running with this much timing, so something is wrong.

Here's what I've done so far:

Using calipers in the #1 spark plug hole, I moved the balancer first clockwise measuring until TDC, then from counter clockwise. Doing this three times in each direction showed the relationship between the balancer and timing marks for TDC are accurate.

With the rotor cap off, moved the crank back and forth with no visible play to the rotor, indicating no slop in the timing chain.

Borrowed second timing light and both were within 1° (although both Craftsman dial back lights).

What else could be causing this?

Tom Welch
05-22-2005, 09:21 AM
is the distributor clocked properly, or is it maybe 180 degrees out?

68Formula
05-22-2005, 12:31 PM
I would think it woudn't run at all with 180 out.

Railing68
06-27-2005, 05:58 PM
I would call Dave Ray, http://www.davessmallbodyheis.com/, he setup my distributor and helped me disassemble over the phone later on as well, when I changed the application. He knows HEIs inside out and Pontiacs. He will steer you in the right direction. SS