Timing on Pontiac 400 - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 02-24-2011, 11:20 PM Thread Starter
 
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Timing on Pontiac 400

Ok i have looked everywhere and cannot find a correct solution or question to this so here goes. I have a Pontiac 400 bored .60 over ported and polished 6x-4 heads, edelbrock performer rpm intake and cam, 1.65 roller rockers, edelbrock 800 cfm carb, and hei distributor. The only way to get it to start is if I set the timing at roughly 35 degrees what I believe is before top dead center timing mark on crank is under timing marks on engine. it idles around 700 or so with a little bit of a lope. I have heard that a 400 running 6x-4 heads is going to have higher compression and the cc's in the heads are around 90 or so, and the only way to get the engine to compesate for the higher amounts is to have the timing off by quite a bit. Do this seem right? Is there any ill affect to having it set this way if it is running good?
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post #2 of 4 (permalink) Old 02-24-2011, 11:31 PM
 
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you will need to run high octane in it to ward off detonation....96+ if you can get it.
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post #3 of 4 (permalink) Old 02-25-2011, 08:24 AM Thread Starter
 
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I know of a station about 20 miles away that sells 102 or 103 octane is that all I should worry about with the timing being where its at
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post #4 of 4 (permalink) Old 02-25-2011, 08:39 AM
 
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"Higher compression" is a relative term. Yes, -4s yield a little higher than -8s.

At 90 CCs, a 400 .060 over at "zero" deck (here that means .005 in the hole) will yield right at 8.8:1. No need for any "compensation" for 93 octane, should actually run well on 89.

If you have an aftermarket cam and intake, timing is a "hunt and peck" kind of thing. That is, you ned to find "the happy spot". each engine is different. Set intial at 10 BTDC and "total" at 32. Drive the car. Bump it up 2 degrees. See if it responds "better" (it should, but maybe same).

We genearlly try to keep "total" timing under 35, as Pontiac chambers a bit "too efficient" (yes, that IS possible) and are "timing sensitive". Beyond 36, we see head gaskets deteriorate rapidly. 670 heads are the "exception to the rule", as they have a "closed" chamber.

Jim
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