[Schurkey]

Originally Posted by Tom Vaught

That being said, there is no Quench vs a pontiac engine.

Originally Posted by chiphead

Didn't some B mopars like the B400 have the pistons waay down in the hole to reduce compression? Basically right at the .100" mark at about 8.5:1 compression. So beyond the quench range and not enough compression to detonate on dishwater gas.

Any number of engine designs do not have a quench/squish area between piston and head. Without a place to create squish, head gasket thickness does little beyond adjusting compression ratio, and(within reason) allowing the intake manifold to fit properly.

Lots of Mopars had "open" chambers with no squish/quench. Buick 350s have no squish/quench. Lots of 4-valve heads have no squish/quench. An "open" chamber may or may not have "lazy" combustion--needing a lot of spark advance for max power.

The problem is when there's a squish/quench area that traps excessive end-gasses. The end-gasses are too enclosed for the flame-front to reach them, yet they still absorb combustion heat especially if the lazy combustion requires a long burn-time. The heated end-gasses spontaneously ignite...and there you have detonation.

Squeeze them out of the quench area with proper quench distance to minimize the volume, and you speed combustion and reduce the volume of end-gasses. Open the chamber so the flame front can get to them, and the end-gasses burn normally instead of detonating.

[dmac]

The SCE site has all their Pontiac gaskets listed but are hard to compare. I used the Summitracing.com site and selected by brand. Takes a few steps but you can select first under head gaskets, then select Pontiac, then select SCE under 'brand' and then you can select by bore or thickness. You can select multiple bores or thicknesses at the same time, and click on about 8 of those to compare. Once you get to the page with the comparisons, it is very easy to narrow it down, and then you can eliminate those that won't work, and go back and add more to compare. I selected all the gaskets with the 4.32 bore because it will clear and came up with 9 choices.


I decided on this- https://www.summitracing.com/parts/sce-s28328/overview/ because it needs no o-ring, and the other options either required or recommended o-rings. Even though expensive,
I will end up with 9.5:1 CR with KRE heads and be out of the quench danger zone by basically eliminating the quench area. I think that because this isn't an all out build that saving me from reworking a new short block will be worth the extra cost of the top line head gaskets.. I want to thank Shurkey and the others for their contribution regarding quench area. It helped me understand how I could help reduce detonation chances while also eliminating problems using an extra thin head gasket could cause.

I think that going this way will make my build longer lasting, even though it might not be the meanest pontiac around.

https://www.summitracing.com/compare

[tom s]

FYI,SCE makes a 21 thou copper gasket.They have a stainless wire around the bore.Give them a call.Had a good tech on the phone.Tom

[dmac]

Originally Posted by tom s

FYI,SCE makes a 21 thou copper gasket.They have a stainless wire around the bore.Give them a call.Had a good tech on the phone.Tom

I saw that they had a .021 thick gasket, but the one I saw recommended o-ringing. From the Summit site description-

"Not all solid copper gaskets are created equal. SCE uses premium 99% pure copper sheets that are precisely rolled to our specifications and tested for uniform flatness to assure precise cylinder head-to-block alignment and eliminate uneven loading. After processing, each gasket is annealed to ensure optimum mating and provide measurable gains in cylinder sealing, as evidenced by lower leak-down percentages. O-ringing is recommended. Pro Copper gaskets are available in many bore and thickness combinations to suit your performance needs."

I'm also considering what some have said about thin gaskets sealing, and using with dissimilar metals. Since I haven't purchased the heads yet, I can end up at just about any CR I want.

Eliminating potential issues is high on my list. My only real issues are the .030 deck height and cam selection. to safely use pump gas. The bottom end is new, as will the heads, lifters, rockers, pushrods, timing set, cooling system. I will never push it to the limits, and may never see 5000 rpms unless it takes that much to pass slow freeway traffic. The 2.73 gears will help keep rpms on the low end, further increasing engine life.

[dataway]

Schurkey ... great explanation.

I've worked mostly with hemi-head motorcycle engines, no squish at all.

[Tom Vaught]

Originally Posted by Schurkey

Any number of engine designs do not have a quench/squish area between piston and head. Without a place to create squish, head gasket thickness does little beyond adjusting compression ratio, and(within reason) allowing the intake manifold to fit properly.

Lots of Mopars had "open" chambers with no squish/quench. Buick 350s have no squish/quench. Lots of 4-valve heads have no squish/quench. An "open" chamber may or may not have "lazy" combustion--needing a lot of spark advance for max power.

The problem is when there's a squish/quench area that traps excessive end-gasses. The end-gasses are too enclosed for the flame-front to reach them, yet they still absorb combustion heat especially if the lazy combustion requires a long burn-time. The heated end-gasses spontaneously ignite...and there you have detonation.

Squeeze them out of the quench area with proper quench distance to minimize the volume, and you speed combustion and reduce the volume of end-gasses. Open the chamber so the flame front can get to them, and the end-gasses burn normally instead of detonating.

Can't explain it any better than that. Your post basically clears up the "Why does that quench distance make any difference at all" question. Thanks again.

This link will help some with more detailed info on the combustion processes.

http://www.masterenginetuner.com/pre...etonation.html

Tom V.

[dmac]

Just to see if this has any affect- With a longer stroke, the piston moves further in the bore with each degree of rotation.. It would take an engineer to look into where the piston would be compared to the flame front. I don't have a clue how fast the flame front moves, but with a longer stroke, might the piston be far enough down in the bore to negate some of the quench effect compared to a shorter stroke?

If so, then a bigger bore/shorter stroke motor with the same CR and same CI would be more efficient due to more of the positive potential quench effect.

[tom s]

The tech guy told me that with a N/A street compression there would be no need to Oring.He said the spray copper coat on both sides,let sit,install when dry.TQ,heat cycle and let cool over night and reTQ.He said they do a lot of biz with Butler so you might give them a call and get their opinion.Tom

[chiphead]

9.5 CR with a modern aluminum chamber should be OK at .110" total deck clearance. Just don't use a fast ramp or too small a cam. Still may need 93 octane depending on how moody it is. The steep rear gears won't help, because it will be heavily loaded at peak torque.

The issue is that you light the fire BTDC, so the piston is moving upward when the flame front starts. The idea is that the tight piston to head quench pushes the end gases into the flame front before they detonate.

With more than .100" clearance, I assume that the end gasses just burn normally, as they aren't trapped and set off by poor quench and heat reflected by the piston.