You'll use this area to make your spec.
From this flat too the deck....

 

You'll use this area to make your spec.
From this flat too the deck....

Shouldn't that be from that flat to the top of the compressed head gasket?

 

Yes you are right. I was thinking of deck height, only part of the equation.

 

OK, straighten me out. Which flat are we discussing, Dome flat or the highlighted area of the piston.

 

Misread the post. I understand where to take the measurements. Highlighted area to top of compressed head gasket.

 

Check.



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This looks like a really good place to bring up piston compression height, the distance from the centerline of the wrist pin to the crown of the piston. Zooma has bought pistons that have a 1.560" compression height, which is stock for a 350 Chevy. Some manufacturers produce their pistons with a taller compression height to help the engine builder reach a thinner squish/quench (0.035"-0.045") without taking so much material off the block decks to get there. Keith Black Pistons, for instance makes several of their pistons with an increased compression height. Skip White Performance has made a deal with Wiseco to manufacture pistons that are 0.015" taller than stock in the small block line (1.575") and 0.010" taller in the big block line of pistons (1.655"). Wiseco, by the way, is an old and respected name in the piston manufacturing business. I used to use Wiseco forged pistons in a racing go-kart that I raced in the late 50's.
https://skipwhiteperformance.com
https://uempistons.com


When building a motor, it's smart to know all the dimensions of all the parts before you begin planning the build. Knowing the block deck height will allow you to design the "stack" of parts you will use ahead of time, which will allow you to cut the block decks to the exact height they need to be to set the squish/quench where it needs to be without jacking around with this piston and that piston and this gasket and that gasket and wondering how much you will have to take off the decks to get where you want to be without having to disassemble the motor to cut the decks when you should have done that in the first place, before you ever began putting the motor together.
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A well stated man up there. Have a plan on paper first so you know where your going and where your coming from.

 

The quench area of a combustion chamber is between the flat part of the pistons to the flat part of the combustion chamber. SB Chevrolet heads have what is known as “wedge” heads.

The Chevrolet 396, 427 and 454 heads that have a “open chamber” has no quench area. BB Chevrolet Open combustion chamber heads has no quench area compared to a SB Chevrolet wedge combustion chamber with a quench area. The Chevrolet 348 and 409 engines have no combustion chamber quench area. The combustion chamber of the 348 and 409 engines is in the cylinders and there is no quench area.

A Chrysler “Hemi” is another engine that has no quench area.

 

…….The Chevrolet 396, 427 and 454 heads that have a “open chamber” has no quench area...…..

Wrong again....

The closed chamber BBC head has double quench pads, on either side of the combustion chamber. The open chamber BBC heads have just one quench pad....the other that would match the closed chamber head is now the "opened" part of the chamber.
4V ford Cleveland is very similar, has a multi sided quench area on the head.

If you want a prime example of a truly no quench open chamber head, look at the 2V Cleveland/341M/400 Ford heads....they are awful.

Some of the Mopar "wedge" engines are full open chambers too, so calling something "wedge" doesn't denote "quench pad". Prime example is later 383/440 and 400 Big Block Chrysler, and the 318/360 LA small blocks after about 1971 or so.

 

Listen to Techinspector. There are way too many factors to know for sure. You can get close if you know the piston compression height and you assume stock deck height (which could be off rather significantly)

Without measuring exact piston depth below (or above) the deck it will be tough, but you can get close.

 

Basically dome pistons are all quench area with little to no squish. Quench being the result of a small volume trapped within a large surface area, such the heat is sunk out of the volume quickly by the area. The big problem you have to check out carefully is valves missing pistons. Especially given that this style piston is usually run with big cams. Squish is a function of a zone of the chamber having a small volume such that as the piston approaches TDC mixture in the tight closing zone is ejected toward the spark plug. With a dome that's an up hill battle, pun intended.

The race with these type piston is one of power gained through compression against power lost to a convoluted burn taking place over and around the dome, and temperature being surrendred to the added surface area. Obviously well all know the compression builds power faster than the negatives take it way, you just have to appreciate that it isn't a free lunch.

You want a head that places the spark plug high to the chamber roof as that's where the mixture action is.

Certainly domed pistons have their place, but a tighter chamber, within reason, and a flat top piston is a better choice if it can be worked into the equation.

Bogie

 

Basically dome pistons are all quench area with little to no squish. ......................

You want a head that places the spark plug high to the chamber roof as that's where the mixture action is.

Certainly domed pistons have their place, but a tighter chamber, within reason, and a flat top piston is a better choice if it can be worked into the equation.

Bogie

Bogie, question, is the spark plug tip position as critical in a flat top piston as it is in a dome piston? And does the spark advance affect this too? Thank you

 

Open vs closed chambers example:

Pontiac 400 engines changed from 72 cc closed chamber heads to 72 cc open chamber heads in 1968. That permitted the engine to operate with more initial timing advance for more complete combustion chamber burn and less pollution.

I put 1969 #48 open chamber Firebird 400 heads on my 1966 GTO and dropped the ET one second.

 

To add....A big dome does indeed block the flame travel however if kept small such as the 1/8 or so, the increase in compression is a bigger factor to power than the the minor impeded flame.
That said, a flat top with a small chamber, or even a flat chamber and a dished piston, will make more power.
Domes are cheaper to make.

John Kaase I think, won the Engine Master Competition a number of years ago while back using tiny chambers and piston with the crown machined to the mimic the chamber. Basically the piston became the chamber and the head was only big enough to hold the valves.