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Old 01-05-2012, 11:31 PM
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cobalt327 cobalt327 is offline
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Once you put the fresh set of plugs in, take a magic marker and put a reference line at 12 0'clock on each plug. That way you will know if any of the deposits that you might see are related to a particular valve.

The following was a question I received about the plugs, etc. I'm adding it here in hopes that it may be of some use to someone doing a similar search:
Originally Posted by cobalt
Originally Posted by 396chevelle
Cam lift is .510/.495 duration 287/304 degrees---lobe center 110 dgrees-----overlap 19.00 degrees. Air gap intake and the jets on the primarys are 78/78 secondaries are 86/86. The picture's in my post that you were looking at was the one on the left was at idle and the one on the right was at mid range. I haven't done a WOT yet. Due to the motor being new. I was trying to get a few miles on it first, but I guess since it was dynoed before I dropped it in the car it will be fine. I was also worried about the A/F being to out of wack before I jammed on it. I've got it set at highest vacuum at about 7 in. hg. 3/4 turns out on all 4 mixture screws.
The plug on the right looks fine. The plugs will color more evenly after the engine has some run time on it- that gives the rings a chance to fully seat and the blow-by that's present (to some extent) on any new build will be reduced. I see no reason by what you've shown to change the heat range.

Lean is fast. Too lean is detonation, and too rich is slow and soggy. Do not arbitrarily add jetting to the primary side. Why not? If the plug color is good, adding fuel will net you nada except it'll burn more fuel. Let the plugs and/or an air/fuel ratio meter tell you what the engine needs.

In another thread you mentioned you have a heavy smell and eye watering exhaust. This is caused by incomplete combustion and is an indication that the initial timing needs to be increased to then be able to close the primary throttle blades to get back out of the transition circuit more than you now are. The idle and transition circuits are active at idle, but you want to limit the transition circuit's contribution to the idle air/fuel mixture.

If you feel the timing is optimum for the engine, you can (instead of advancing the initial timing) open the secondary throttle blades a touch (to allow more idle air into the engine) to offset closing the primary blades down by using the curb idle speed screw. This can (in some cases- all engines are different) help the idle smell you're getting.

There may be a need to change to a smaller idle air bleed at some point, but for now try the things above first. If you see no improvement you can go from there.

The most important thing to have control of before running WFO is the total timing. There can be NO DETONATION while at WOT under load- like running at the strip. If you have 37 degrees total- and you're positive that there's no timing "creep" occurring at higher RPM, you'll be fine as long as you run good gas as insurance.

The timing creep I mentioned can be easily checked by winging the throttle while using the timing light. The idea is to verify there's no advance above the RPM that you believe the timing is all in by. If you give it a quick rev to see 5000 RPM and you see no added advance, you can be sure the mechanical is all in.

In cases where the carb is too small, there can be manifold vacuum at WOT that could in some cases cause a vacuum advance to start adding timing at WOT. Being as your carb is a 850, this shouldn't be a problem. But if you're using a vacuum advance, you don't want more than 10-12 degrees, and you'll want to tune the tip-in point to match the engine.

Last edited by cobalt327; 01-05-2012 at 11:40 PM.
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