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So I don't work in the automotive industry but have built more than a few engines in the last 40+ years. The quench on these engines has been from 0.057" to 0.040" to unknown with my current dished piston blown engine. In my years on this forum I have seen so many individuals get hung up on getting the perfect quench. based on my experience, my opinion has been that quench is important just like many other items associated with building an engine like piston to cylinder clearance, ring end gap, bearing clearance, etc. but there are other factors that influence a tendency for an engine to ping or detonate. It's all about the total package.

The engine that had 0.057" quench was a 10.9:1 compression smallblock that cranked 215-230PSI on a cold compression check. I ran that car for years on 91 octane pump gas and there was never an indication of detonation. I believe what helped it was the 4.10 rear gear, 5K ish converter and 3,400 pound race weight. That same engine in a 4,000 pound car with a manual transmission and 3.07 rear gear would probably have issues with detonation on the same 91 octane pump gas.

So now lets move on to a dished piston engine on boost. My current setup has dished pistons. The pistons are zero decked and the tiny bit of quench that it does have is at 0.040". Most engines have the entire flat area of the head and piston for the quench area. A dished piston like the ones in my engine has a ring around the top that is only about 1/8" wide. The quench area is greatly reduced but this engine runs at 27 pounds of boost. So again, it begs the questions. How important is quench?

It would be great for people to contribute actual data to this thread not just opinion. Again, it would be great for people to contribute actual data to this thread not just opinion.
 

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Discussion Starter · #2 ·
Couple of interesting video's about removing the quench area from the cylinder head. One video is from MBE cylinder heads and the other is from Steve Morris.


 

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Interesting topic. First, I am not sure that you will find much real data about quench. There are so many variables on how quench will affect the efficiency of an engine that it all depends on the combination. You will note that the MBE video he keeps talking about NA combinations. Supercharged and Turbocharged applications are different. The boost seems to mix the air/fuel better and doesn't require quench to promote combustion. The tapered area discussed in the videos will still squish the mixture back toward the combustion chamber. I have been running 4.600" bore big blocks since the late 80s. The big bores flow better but take a lot of timing. I think shows the inefficiencies of burning the fuel. I have changed pistons to increase compression and decrease quench from 0.060" to 0.045" and seen a difference in total timing the engine liked by -4 degrees. That is on a highly inefficient conventional combustion chamber and domed piston. My latest motor is a twin turbocharged set up with a very small dome and 0.060 down in the hole. It would have been a reverse round/cylinder shape if I had been willing to go down from 9.0:1 compression.
 
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It IS all about the burn, and, the filling of these areas with fuel, to make a complete burn, and, mixture retention to both stop lean hot spots (pre-ignition areas), and place mixture down the side of the piston to cool the top ring.

Other than 5that, too tight, mixture is blown out of those areas, too loose, mix migrates out, leaning those areas, NOT good.

You guys have to start coming up with valid videos, not comedy shows, I wasted a whole Coke Zero Sugar, and unsalted popcorn watching all that hilarity above from Morris. .
 
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