Midrange ping. Considering quench/squish

Larry, I seem to recall that u had a knock? If so, how did u overcome it? What do u run your squish at? stock?

Davel. If u run a copper gasket. u WILL need APE studs for sure.

Mark,

I put 1197cc 10.25:1 pistons in mine and there's no "audible" knock now.

As for squish, it depends on several factors. It starts with cc the combustion chambers and measure deck with a stock base gasket. Then work things out from there.

You know how it is....you have to work with what you have in front of you and more often than not with these old motors, things have been modified.

Heads get shaved, different valves get installed....it all adds up plus or minus....so you assemble, check and tweak as required.

larrycavan wrote:

You seem to like to experiment with things, www.rexresearch.com/singh/singh.htm

I've communicated with a guy that performed that modification to a truck engine he uses to tow his race car. He swears it works......

It's one of those deals that people argue about. Seems perfect for KZR......

Interesting read...He seems to have combined the squish theory with surface treatment of the CC - basically scratches and gouges in the head...It's tempting but I think I'll hold off on the scratches and gouges for now. Though this could be an unforseen benefit to dropping a valve. Maybe it's good I'm not running a rev limiter :woohoo:

No seriously, he makes some good points about engine performance, efficiency, cylinder turbulence and burn. And at this point, the effect of squish zones on efficency has been pretty well proven and documented. The CC surface treatment is definitely new to me.

Taking more material off the head surface is only going to raise cylinder pressure. I highly doubt it's going to help the knock situation.

I calculated a 0.30 point rise in compression with a 0.015" reduction in squish/gasket thickness. I'm not sure this is going to do much for me either way since there is a very small squish zone. I'm banking on the copper head gasket to dissipate considerably more heat into the block than the fiber.

Member Steell posted this article on squish a while ago. www.speedomotive.com/t-showbymodel.aspx
It's a good one

If you do take the head off, go in there with a die grinder and clean all the slag out of the air passages in the fin area. Sometimes those castings are really bad and the air passages are up to 40% blocked. Every bit helps.

If you can get it in NYC, try fueling up with Sunoco Ultra and see if that helps any.

Will look into these

I love that article, I read it at least once a month. The only thing is, while the concepts will work the numbers they post assume water cooling and RPM's below what our buzz boxes run.


A good book on everything motorcycle is kevin Cameron's Sport bike performance handbook...

Edit My bad, I just double checked the book to see what his input is, and he never mentions squish zone, quelch or whatnot. Forget I ever mentioned it :lol:

hardr0ck68 wrote:

A good book on everything motorcycle is kevin Cameron's Sport bike performance handbook...

This is the best book I've read on all aspects of motorcycle performance. Highly recommended. Kevin Camron is the man!

Edit My bad, I just double checked the book to see what his input is, and he never mentions squish zone, quelch or whatnot. Forget I ever mentioned it :lol:

It's in there on page 76 (2nd edition) under the heading "Compression Compromise"

I thought it would be in there, I must have been looking in the wrong chapter... It was before my first cup of coffee, so I will blame my error on lack of cafeine

Something about this discussion has been bothering me, so I have gone looking around. I don't think quench/squish applies to hemi style heads. My understanding is that this works with small block chevy heads whose design is very different from a hemi. If you have ever looked at a SBC head, you will notice that most of the piston crown is covered and off to the side is where the valves are located.

Squish refers to the squishing out of the air/fuel charge from the tight part of the head into the chamber area as the piston comes up on the power stroke. That leads to useful turbulence and better fuel mixture.

Here is a link to an article with pictures that might help:

www.chevyhiperformance.com/tech/engines_...nce_guide/index.html

The key here is the "wedge shaped head".

kpier998 wrote:

I don't think quench/squish applies to hemi style heads.

Normally you are right. I verified this with the solder squish test. But check out this link to Pop Yoshimura's 1978 GS1000. slcelectronics.com/GS1000_Build/Yoshimura-specs.pdf Mark1122 posted this last week.

Scroll down to page 7 and notice how his custom machined piston tops follow the countour of the hemi combustion chamber then flatten out. That's pro!

Quench zones and a compact combustion chambers are possible with a hemi head but it requires a lot of custom machine work. That's a good reason for modern performance engines use closed combustion chambers and flat top pistons. Much easier to adjust deck height to match a flat top piston.

Decided to just cut and paste the image though the article is definitely worth reading. The old 2 valve GS and KZ motors were pretty similar

i think the squish applies to most heads. the bigger the piston the farther the flame has to travel.The more stagnant the area around the edge is, the more likely u will have pre-ignition. The squish band provides movement to the otherwise, stagnant mixture at the edge, and moves it towards the spark.
the air cooled 2 valve heads had to have the valves at a steep angle,to fit in the small area provided by the cyl diam. this was part of the problem. With a water cooled 4 valve head , they could lay them flatter, and change the chamber shape to have a small chamber pocket that would ignite faster and have a large squish area.
When u add a 2nd plug the the 2 valve u will pick up a bit in the mid range.But likely, only when u have high enough dome to impede the flame.say in the 12:1 or higher, range.

I guess my point is that the effect of this in the CHP article was 3 horsepower. There is a whole lot of squishing :dry: going on in this case. In the case of the hemi head, there is not much area around the perimeter of the cylinder to be squished.

But in the case of the chevy small block head, over half of the head is involved in the squish.

Here are the images:

Here is the other picture for the Hemi KZ head. I couldn't get both in the same post:


As you point out, the quench area is a wee bit around the perimter...

But I am open to the idea if I am missing something. I love these kind of discussions.