Another Compression Question

[Bayrunner]

O.K. Guys. Here is my question.

I can achieve my optimal ( For My Build) compression by doing either of two things.

1. Use larger dish pistons and zero deck the block
or
2. Use smaller dish pistons and take of less of the block

Does one have an advantage over the other?

Thanks in Advance

 

[Thad]

Where is the difference in the dish volume, area or depth?
If area of dish is the same then the big volume dish /deck combination will give a tighter squinch. If the smaller volume dish has a smaller area then the small dish would have a larger squinch area.

Squinch is good but needs to be tight to work, the combination that gets closest to zero deck would be the better of the two possibilities.

 

[Bayrunner]

o.k. one piston has a 7 cc dish while the other has a 12 to 18 cc dish.

Please xplain.

 

[Thad]

Volume is area X depth. For the larger dish volume it could be same area but greater depth or same depth with a greater area.

 

[Bayrunner]

I will find out.

Thanks

 

[CZLN6]

Howdy Back:

To answer you question- Deck the block to zero and build the other variables to goal CR.

YOu do have another option to reach your goal CR. First, what is your goal CR?

A third option is to open the combustion chamber by relieving the shrouding around the intake valve. This option will not only reduce CR, but will also increase flow.

Just a thought.

 

[MustangSix]

Zero deck is close, but still not optimal for quench. If your piston-to-valve clearance allows with the head gasket you're using, you could bring the piston out of the hole by .005 to .010" then open the chamber to relieve the valves and get the CR where it needs to be. The extra quench will help promote less possibility of detonation, more swirl, and more power.

 

[Bayrunner]

before I go on a tangent and shave toooo much off my head, Does anyone know where to find a formula to calculate cc chamber in cylinder head prior to milling?


Help please.

 

[JackFish]

http://falconperformance.sundog.net/compcalculator.asp

 

[CZLN6]

Howdy :

Q- "Does anyone know where to find a formula to calculate cc chamber in cylinder head prior to milling?"

A- The formula we use in estimating a mill cut to reduce chamber cc is- a cut of .010" will reduce the chamber volume by 2.4 ccs. This holds true and is fairly accurate on all 200/250 engines. Cuts past about .075" will begin to lessen the cc amount as the chambers get smaller. This is the formula we use in estimating a cut, then we measure each chamber to verify and to equalizevolumes.

Jack added, "Zero deck is close, but still not optimal for quench." To elaborate, an ideal quench height would be more like .030" to .035". With a composite head gasket at .044" (Victor) to .050" (Felpro) compressed thickness, even decking to zero does not get our engines to an ideal quench height. That is why several block builders on this forum have decked their blocks past zero, to have the piston pop up above the block deck .005" to .010".

Adios, David

 

[Bayrunner]

Thanks guys. You are more helpful than anyone else I have come across.