[screamingchief]

Originally Posted by tr709

Someone previously asked about the plugs. They are NGK6945, probably not what I would have picked. But if that is an issue, even I can change spark plus

Those are too hot a plug for a high performance engine IMHO,they are an NGK 4 heat range.

Only plug hotter from NGK is a 2,and those typically are for lawn mowers and such.

And they're an extended tip plug to boot (makes them act a bit hotter for the given heat range).

Not to mention an extended gap (.060") plug.

Originally Posted by amcmike

Friend of mine had problems similar to yours. Turns out the plugs he used were incorrect for the head, and didn't seat deep enough (way up from the combustion chamber) Changed them, and it really woke up the engine. Something else to look at.

This is the opposite problem here.

What he has is a tapered seat plug,this in heads ('71 #96) that are meant for use with a gasketed seat plug.

That is a deal breaker,and here's why.

Understand that the plug reach on the tapered seat plugs is all wrong for those #96 heads as well.

NGK 6945 plug reach is 11mm (7/16" or .437"),and the early ('67-'71) gasketed seat plug reach is 3/8" reach (thus .375"),so you likely have the end of the plug hanging out into the chamber some with those NGK plugs in there.

That is not a good thing!

So those are way,way wrong plugs for those heads.

Most guys use a heat range up around 6 or 7 for an NGK plug in a healthy performance oriented pontiac engine,as the NGK heat range the higher numbers are the cooler plugs,opposite of brands like A-C or Autolite where the higher numbers are the hotter plugs.

And I see absolutely no reason to run the bigger gaps,never have.

I use .045" gap as the max for the most part,often .035" works just fine,usually I just split the difference and use .040".

Plugs I would use for something like this:
(all are extended tip/resistor plugs except as noted)
Autolite #85
Denso #W20PR-U
A-C #R43S
NGK racing #R5670-6 (non-resistor)

Gap @ .035" to .040".

So that would be a good place to start IMO,you can put the right plugs in there when you go ahead and do the compression testing.

HTH

Bret P.