TxTtopZ

So I am doing some research on a stroker motor in another thread (to get my mind off the fact the Cowboys lost due to a refs crap call).... and I am concerned about the 2 pistons offered by KB that do the same compression wise but they are different in design. One is a d-cup +10cc and the other is a circular dish at the same volume.

D-Cup (leave the titty jokes alone, we all know D-cups are better than reversed dome) PISTON.
http://www.summitracing.com/parts/ue...-std/overview/

DISHED w/ 2 valve reliefs
http://www.summitracing.com/parts/ue...-std/overview/

Granted the d-cup has more quench which will raise compression, and the other has what seems to be an open chamber design that will unshroud the valves even further, allowing for more flow. But what style chamber prefers which piston crown??

The fastburn and vortec style heads have a note that suggests you use those heads with a flat top piston. I am assuming thats the deal because the flame front travels faster so they will get a better burn if they don't have a piston formality fighting against the chamber??

The TFS 175 heads also have a closed chamber "heart" design but they dont mention which piston to use with them?

What are your thoughts on this?

AlkyIROC

There are so many factors which can determine which is best or not.

Having a large dome means the flame front has a longer distance to travel across the piston. Although the small bore of a SBC won't be very noticeable, every little bit helps.

A larger chamber in the head also allows for larger valves which won't be shrouded by the walls of the chamber. Increased compression is then adjusted by the size of the dome on the piston.

Dished pistons are to lower the compression especially when using a power adder such as a blower or turbo. Lower compression allows more boost. An 8:1 compression engine can take 10 psi of boost easier than a 12:1 compression engine.

The valve reliefs are just there to allow greater valve lift. The loss of area in the relief can be made up with a small dome to keep the same compression ratio.

My BBC has standard 119cc combustion chambers and huge intake valves. The pistons I use are the biggest dome possible for my combination and even with 0.800" lift, there's enough room in the reliefs that the valves don't make contact with the piston. I run alcohol as a fuel so 14:1 compression works perfectly.

TxTtopZ

Yeah, I am aware of all that, thats pretty basic. I am talking more of a design standpoint. Will D-cup crowns prefer a closed chamber design due to centered and angled spark plugs, thus having the force of combustion localized to a more specific point on the piston... more force in a smaller location increases psi...

As for the open chamber heads having an actual quench specific part of the crown if using the same d-cup... Were talking science of flame fronts etc.. Not basic info.

TxTtopZ

PS... alky motors can use that dome... I cant do that. lol

Orr89RocZ

iTrader: (20)

Links show same piston part?

TxTtopZ

Fixed.

TxTtopZ

I think this must be a typo on Summits part... but the question still remains.

Orr89RocZ

iTrader: (20)

I dont see a noteworthy difference other than one having two valve reliefs vs a trench cut into the piston. You lose some volume there so would expect to see less compression but the design accomplishes the same thing, allowing more valve clearance.

Ideal is a piston inverted dome that mirrors the combustion chamber if needing a dish. That along with a sparkplug angled towards exhaust valve will give the most complete burn and make most power.

Want the squish pads to line up and force the mixture towards that spark plug so flame front doesnt have to travel as far. Should need less timing

TxTtopZ

Yeah, I've read that too. Still would like a more in depth data set for them. Like why GM recommends a flat top with fast burn etc