[steve25]

Good quench or adequate quench depends on what factory head you’re talking about.

The heads up to 66 and the B body heads up to mid 67 had the most quench area.

These where not the greatest in terms of unburned fuel emissions, but they had better tolerance for octane level for a given compression ratio.

The 1967 670 and RA997 casting gave up some of that quench area.

The 061 casting of late 67 I call the mule head because it was used by the factory to see how far they could go with an open chamber and still not have a head that was prone to detonating.

The good thing about these 061 castings and there shallow chambers is they have about .040” more short turn height to them so when porting them to flow intake flow levels above 260 cfm it’s easier to keep them from breaking into a tumble condition and going into flow regression.

The 68 and up chambers with there increased quench are over the 061 casting shows that they found out which direction they needed to go to have control of emissions, a good burn rate and a unshrouded chamber.

Where talking non RAII ( 1968 1/2 ) D port heads only.

[PAUL K]

Originally Posted by steve25

Good quench or adequate quench depends on what factory head you’re talking about.

The heads up to 66 and the B body heads up to mid 67 had the most quench area.

These where not the greatest in terms of unburned fuel emissions, but they had better tolerance for octane level for a given compression ratio.

The 1967 670 and RA997 casting gave up some of that quench area.

The 061 casting of late 67 I call the mule head because it was used by the factory to see how far they could go with an open chamber and still not have a head that was prone to detonating.

The good thing about these 061 castings and there shallow chambers is they have about .040” more short turn height to them so when porting them to flow intake flow levels above 260 cfm it’s easier to keep them from breaking into a tumble condition and going into flow regression.

The 68 and up chambers with there increased quench are over the 061 casting shows that they found out which direction they needed to go to have control of emissions, a good burn rate and a unshrouded chamber.

Where talking non RAII ( 1968 1/2 ) D port heads only.

Steve25 have you compared the 061 intake port to a 670? Any difference?

[65 Lamnas]

I don't know a lot about quench/squish other than what I've read.

My understanding is:

A relatively small (.032-.040") quench distance causes a turbulent "mixture motion" which in turn has a cooling effect to the combustion chamber. This deters/eliminates "hot spots" in the chamber and results in a more constant temperature. I think that's where the octane-tolerance comes from....no pre-ignition from said "hot spots". The turbulent motion also causes the fuel mixture to be more homogenous = more efficient burn.

Someone mentioned factory head gasket crushed thickness. Here's a photo of the old HO-Racing parts and specs book related to the gaskets.

I don't know if Royal Pontiac used the steel shim head gaskets as part of their Bobcat package to simply raise compression or if they actually knew about the benefits of a tight quench distance, but the gasket caused a positive effect for both.

I've taken apart MORE THAN 1 original '69 RA-IV engine that had the shim gaskets. Those engines appeared to have never been apart.

Don't forget how different fuel was back in the day. Benzene, Toluene, TEL were all a part of the old cocktail called fuel.