Quenching

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Scamper

Scamper

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I have to ask what this means?
I have been reading on how to rebuild my 440
I keep reading versions of this statement:
engine has been built with quench technology so it will run great on pump gas
Any help would be appreciated and is this process necessary:read2:
 
Quench is achieved when the piston comes within very close proximity (I believe within .040") of the combustion chamber surface at TDC. It is usually done by using flat-top zero-deck pistons and "closed chamber" heads. This causes the compressing intake charge in the cylinder to be squeezed violently into one part of the chamber, imparting a huge amount of turbulence to the intake charge; this greatly reduces the chances of detonation during compression and allows you to run a higher static compression ratio with lower octane pump gas. There are a few members on here running around 10.5:1 compression with iron closed-chamber heads on 87 octane pump gas! Of course, you already know the more compression you have the more efficient your engine will be (more power and better gas mileage).
 
CO-incidence or???

I spent three hours last night researching the same question!

MopeKid - pretty close - but what you describe here -

This causes the compressing intake charge in the cylinder to be squeezed violently into one part of the chamber, imparting a huge amount of turbulence to the intake charge; this greatly reduces the chances of detonation during compression and allows you to run a higher static compression ratio with lower octane pump gas.
Click to expand...

is actually SQUISH.

Quench is the "dampening effect" created by the surface area of the squish pads after detonation.

Here's what I found....I highly recommend this article - easy to read and provides a great summary..not completely but close (they actually get the terms wrong as well!!)....:-D

..and in the interests of learning I also recommend getting over the fact its a Cheb magazine..... :read2:

http://www.chevyhiperformance.com/tech/engines_drivetrain/shortblock/94138_piston_head_clearance_guide/index.html

Theres also this - simulating the difference between a broad squish area and a compact one

tapersquicz2.jpg



and lastly :
 
here is an excerpt from a post on "Hotrodders.com" - credit where its due to "Old Bogie"

It describes perfectly the difference between "squish" and "quench", and how the whole thing comes together.


Remember I mentioned squish and quench, these are functions of that flat side of the combustion chamber. Both of these functions are aided by as close a closure of the piston's deck to the head's deck as is possible to achieve within mechanical limitations.

First in the compression cycle squish happens as these two sections close on each other. This drives the mixture in this area back into the chamber by the spark plug with great force. The resulting turbulence and high density makes for a fast and complete burn when the plug ignites it. This reduces the amount of timing lead which reduces early forces in the combustion process that want to drive the piston back the way it came, which results in power lost. It also delays peak cylinder pressure and temperature to a moment when the piston is headed down the bore in the proper direction. This effect is to reduce the tendency to detonate.

The second event after ignition is that the close proximity of the piston and head decks perform what's called "quench". This is where the hot end-burn gases that like to detonate are trapped between two relatively cool surfaces with a lot of area compared to the volume. This sucks a lot of heat out and prevents detonation.

A third feature of modern heads is the beak that protrudes from the squish/quench deck between the valves. This helps prevent incoming mixture from being sucked thru the exhaust during the cam's overlap phase. The result is a denser mixture upon compression and more power and efficiency. Of course this dampens out the rough idle of a big cam. But it trades the rumpty rump idle for more power, better fuel economy and lower emissions.

Now if you have a flat top piston with a .040 inch clearance on the squish/quench side, the effects of squish and quench are maximized by how close the piston and head deck close with each other. The effect is the same with a "D" dish piston where the dish is all under the valve pocket. However, a piston with a circular dish cannot close any more than the raised rim of the piston crown. So even if this crown is .040 inch away from the head's squish/quench deck the floor of the dish is a considerable distance away and it cannot and does not expel the mixture toward the plug with sufficient force upon compression to throughly agitate the mixture for the most effective burn. At the post ignition point, it does not provide the high surface area to volume ratio of a flat top so that the late burn's excessively high temps are not damped. Both of these conditions lead to reduced power as on the squish phase the burn is slower and weaker requiring more timing lead which has the effect of first trying to drive the piston backwards and second increases cylinder pressure and temperature too early which combined with inadequate quench leads to detonation and preignition.
Click to expand...
 
If I understand correctly, when I put 915 casting heads on my late 70's 440 to up the compression, I actually may lose power because the squish will not be correct?
 
No, you will have a net gain in power, but not gain from squish or quench. The magic distance is .050. If you have more than that, it gets less effective very fast. At .060 virtually nothing is gained. I aim for .035 on any bore size smaller than 4.325, no more, sometimes less depending.

edit... _ great answers guys.
 
I was tooling around with a stroker combo the other day - I arrived at 10.2 static comp with the flat top marine piston (1.65 CH) and gasket choice, which was near perfect for my needs - BUT -

the squish/quench is .116th!!!! :-(

Would this cause a huge amount of problems with detonation etc or is it "liveable with"? IOW a small sacrifice?
 
Moparmal said:
CO-incidence or???

I spent three hours last night researching the same question!

MopeKid - pretty close - but what you describe here -



is actually SQUISH.

Quench is the "dampening effect" created by the surface area of the squish pads after detonation.

Here's what I found....I highly recommend this article - easy to read and provides a great summary..not completely but close (they actually get the terms wrong as well!!)....:-D

..and in the interests of learning I also recommend getting over the fact its a Cheb magazine..... :read2:

http://www.chevyhiperformance.com/t.../94138_piston_head_clearance_guide/index.html

Theres also this - simulating the difference between a broad squish area and a compact one

tapersquicz2.jpg



and lastly :
Click to expand...

Yeah, sorry about that, I always think that they're the same thing.
 
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