Quench area and HHead Milling

[msgdsrf]

So it seems the general understanding that milling of heads does not effect quench. Yet my understanding of the benefit of tight quench is the distance of valve to piston and the turbulence it creates. So milling of heads does move the valves closer and so shouldn't this be considered. It would maybe even seem that the chamber size as whole could be considered as a factor in Quench.

Any reason why my thinking is off?

[suville]

curious myself

[T Smith]

Quench is the distance from the piston head at top dead center to the cylinder head surface and includes the head gasket compressed thickness. Milling the head does not change this distance. Decking the block, piston pin height, and head gasket thickness are the things to play with to get the quench like you want it.

[msgdsrf]

Understood. But the effect sought by good quench distance, that is what I'm thinking about. If the goal of quench distance is about getting the piston closer to the valves then it seem reasonable that moving the valves closer the piston would have some positive benefits seen with decking the block. Not as good as, because the chamber can have a better shape than the cylinder, but in similar fashion.

[T Smith]

Originally Posted by msgdsrf

Understood. But the effect sought by good quench distance, that is what I'm thinking about. If the goal of quench distance is about getting the piston closer to the valves then it seem reasonable that moving the valves closer the piston would have some positive benefits seen with decking the block. Not as good as, because the chamber can have a better shape than the cylinder, but in similar fashion.

The "goal of quench distance" has nothing to do with the location of the valves. The "effect sought by good quench distance" it to create turbulence in the combustion chamber to promote a better burn and help eliminate hot spots and even out combustion chamber temps. When the piston comes up it "squishes" the mixture between its top and the flat part of the head next to the combustion chamber, this is the quench. The mixture gets squished from this tight area over into the combustion chamber creating the turbulence. Proper quench will allow you to run a bit more compression, too much quench will be prone to detonation regardless of the compression.

[msgdsrf]

Originally Posted by T Smith

The "goal of quench distance" has nothing to do with the location of the valves. The "effect sought by good quench distance" it to create turbulence in the combustion chamber to promote a better burn and help eliminate hot spots and even out combustion chamber temps. When the piston comes up it "squishes" the mixture between its top and the flat part of the head next to the combustion chamber, this is the quench. The mixture gets squished from this tight area over into the combustion chamber creating the turbulence. Proper quench will allow you to run a bit more compression, too much quench will be prone to detonation regardless of the compression.

Yet from my research it's largely the valve piston interaction that creates the turbulance that we're looking for... And we agree the turbulance allows for gas movement and lower temps to put off detonation.

I mean think about it. Is there more turblance simply because the area is smaller? Or maybe because of the movement (of the valves) in a smaller area..

Anyways, I guess it's just food for thought. My thought at least, as I'm building my engine right now. Plan to drop it in in 3-4 wks. My quench is .050

[T Smith]

I don't see the valves having anything to do with it, they're closed when all this quenching is going on, the piston is coming to tdc to fire. The turbulence comes from the piston/head squishing together and causing the mixture to cross into the combustion chamber.

I'm mocking one up right now, 1.560 pin height flat tops w 2 valve reliefs, gonna cut it zero deck, .041 head gasket, 64cc heads. It'll be 10.6ish to 1 but with good quench and aluminum heads it should be fine on pump premium

[Marv D]

Ditto
As the gasses leave the quench at near supersomic speeds it is almost impossible for them to ignite. Chamber 'shape' can be detonation resistant (i.e. the kidney shaped chamber) ,, but my thoughts is because it offers even more 'quench' surface and again creating turbulences.

[msgdsrf]

Good point. My heads were milled for an earlier build plan. Plans changed now I'm figuring how it will effect things.

I'm at 11:1 on a 383 Roller, cam and volumetric efficiency will tell me what gas I can run. Plugged in a Comp Cam XR282.

[Super73]

Some more food for thought.

Tighter quench (to a point) generally increases effiency. Tighten the quench and more times then not, you can run less advance (not talking 10* less, it is marginal and often times not even noticeable). But is that always a good thing? Short answer, no.

Think of a dedicated N20 motor. Tighter quench in a sense reduces your tuning window. 1* of timing in a tight quench set up will make bigger changes than 2* of timing with more quench. If you are putting things on the edge and need some room for a little fudge factor, super tight quench is not always the best idea. You can get your effiency back up with a slightly bigger N20 jet.
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