Thread: The quest for quench

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In conversation with a member on another forum the subject of quench came up and a discussion ensued, of course more research was required on my part, and I found this article. Anyone not familiar with what quench is please read the article I linked to. But reading the article and getting a general idea of what qunech is does not end my quest...

It seems apparent that quench, or squish, is yet another variable to consider or manipulate when designing an engine build, but it is NOT related to any one specific compression ratio as much as it does to ONE specific dimension, the space above the flat surface of the piston and the roof of the cylinder head, if I understand it correctly.

Though higher compression ratios are more prone to detonation than lower under corresponding circumstances, the ability to reach an optimal quench will bring us to higher compression ratios. Obviously though, to achieve the optimal quench range of .040 - .050 the compression ratio will be quite close to 10:1, as my calculations have proven, but sometimes higher or lower depending on the piston profile, volume, etc.

A few thoughts and questions:
The obviously easy way to set your quench is to zero deck your block/pistons and use a .040" head gasket. But it seems to me you can have the optimal quench setup as well with your pistons in the hole a bit too; for example: with a deck height of .035" (pistons in the hole .030) you can use a .015" compressed thickness head gasket and get a .045" quench - yes?

In the real world, even a zero decked block may not guarantee ALL pistons at zero deck height, rod and piston variations may push a piston above the deck or allow it to sit below, not accounting for rod stretch during operation at higher RPM. So the next question is, when choosing a head gasket thickness to tune your quench, do you go by the deepest deck clearance value, the shallowest or the average deck height?

Here is a real-world example, my SBC 357ci. Deck heights when assembled were as follows:

Cyl 1 - .028
Cyl 2 - .032
Cyl 3 - .025
Cyl 4 - .027
Cyl 5 - .030
Cyl 6 - .030
Cyl 7 - .024
Cyl 8 - .025

Average deck height .027625"

Using my average DH of .027625 the deck volume of all 8 cylinders is only .354ci, but is an average value accurate enough?

Using a standard .040" (compressed thickness) head gasket, my quench distance, using my average deck height, would be .067625, not within the quench sweet spot, and my compression ratio is 9.354 SCR and 8.531 DCR. But switching to a .015" head gasket would net me a .042625" quench distance, well within the desired range, and my compression would jump to 9.904 SCR and 9.026 DCR.

Using the example of my chevy engine, which is not entirely ping resistant, am I better off with a lower DCR or an optimal quench - if I were looking to optimize combustion and power production and eliminate the possibility of detonation?

I have two more engine build projects in the works, one for my Scamp and one for my buddy's Mustang, so mastering this concept is of valuable significance to me. Looking forward to input and discussion on the subject.