Two different possible combonations to reach same goal, which route would you take?
Engine will be naturaly aspirated, pump gas.

Option A. 64cc chamber + 22 cc d shape dish piston

option B. 76cc chamber + flat top 4 valve relief


Both combos equal within .1:1 of each other.

 

That's to vague... you would need to know.. what else is going on in the motor combo... if it's a completely stock motor.. I would do best option "C" 64cc with 2 valve relief... or option "D" 64cc 4 valve relief...

 

small chamber + dishes

 

Obviously it's not a stock motor or I would not have the option of piston and chamber selection.
What else do you want to know? Both. Combos deliver 10.3:1-10.4:1.
It will be a street car with a voodoo roller cam, 185-200cc intake ports.
Typically builders want a flat top piston with as small a chamber as possible. Most say smaller chambers are better, but in this case the smallest I can go with a flat top is 76cc, a big chamber. The other option is a dish piston which is generally regarded as less desirable bug combined with the popular 64cc chamber.
So given both result in the same static compression ratio, which design would offer a more effecient cumbustion process?

 

sorry Mr. blaze
we cant assume what you have... re-planning the 409 or another build... how do we know. what cam you selected that could require. 11:1 up leaving you a lack of compression...
so if your only option is what you mentioned then option A

 

Thanks, I understand needing derails if I was asking for a compression ratio recomendation. But let's sag regardless of ratio, as both options give me the same ratio, what set up would you prefer?
Dish with small chamber or flat top with big chamber?

 

Really depends on the application and type of heads...There is a good thread talking about this on speedtalk.

A small chamber + reverse dome piston (like a dish) will make most power on most natural aspirated applications but the dome in the piston has to mirror the head chamber...so it really depends on the piston design. Same piston wont work to its full potential with 2 different chamber heads.

The spark flame front travel is shorter in the small chamber + dish piston setup. This produces the lowest burn angle and the highest combustion chamber pressure. Smaller surface area in the smaller head chamber quenches the flame less as well.

Now for a turbo/boosted car, the thought I've learned from some top head guys is that you want to put the combustion charge into the head chamber...so this would be more like a flat top with big cc head chamber. You want zero quench in the head so the chamber quench pads are eliminated where possible. This is for a serious higher boost setup..a flat top would have more piston material and make for a stronger piston in super high power setups. Probably well over 1000hp Maybe 2000hp type stuff.

The quench pads produce mixture motion which accelerates burn rate...this can be bad in a boosted application at higher boost levels because you can have too much pressure rise in the chamber too quickly and this will cause detonation...not good stuff.

So thats 2 different approaches for 2 different applications. Heavy nitrous use can be entirely different as well.

 

Thanks for the info, that's the kind of stuff I'm talking about. As stated in the first post it will be naturally aspirated, so small chambers if likely will be.

 

Wouldn't the bigger chambers breathe better? Could be less likely to shroud the valves?

 

Sometimes it unshrouds the valves more and get abit more flow but then again, the decrease in flame travel speed and burn angle could offset those gains. Its all in the design of the head too.

 

What is the "quench pad"?

 

the quench pads the area between the flat surface of the head and the matching flat surface on the piston
BOTH the piston and cylinder head must have MATCHED quench areas for quench to work


heres a cylinder head with a groove cut in the flat quench pad area to speed the quench gasses -trapped f/a mix jet forced into the cylinder to speed the cylinder burn time
read links
http://forum.grumpysperformance.com/...1&hilit=quench

http://forum.grumpysperformance.com/...t=quench#p9291

 

Thanks, but I think my head exploded. Interesting stuff.

 

related info

btw what your trying to accomplish is maintaining the highest pressure after tdc that you can and the lowest pressure btdc without getting into detonation with the available octane fuel
thus maximizing the pressure curve where you can effectively use that pressure

http://forum.grumpysperformance.com/...hp?f=70&t=4683

http://forum.grumpysperformance.com/...on+burn#p15129

http://forum.grumpysperformance.com/...me+front#p7854

http://forum.grumpysperformance.com/...onation#p16848