You may want to measure a chamber, I'm pretty sure a +.140" deck height will be smashing the piston into the head. Most positive deck height I know of anyone getting away with was +.020", and the chambers had to be ground out for that.

With that much of the piston out of the deck you may be very close to popping the top ring out too.

Sounds feasible. I don't know if there is enough meat in a stock piston to cut that much dish and keep enough strength though.

Here's a different twist on the same idea... calculate and measure with stock rods and work with one of the custom piston manufacturers like Ross to design a custom quench pad piston. It could be a flat top plus quench pad. CR would be dialed in to target 9.5 by letting the flat part be a little below deck. Maybe target 9.2 or so to allow for cleanup milling of the head and block without exceeding 9.5. Leave the pad a little high like KB so the piston can be fitted to the engine by milling.

Ordered for one engine it would be a bit expensive but if you find some fellow "slanters" to go in with you and order several sets at once, I bet you could get a better deal.

ahy, interesting idea, but if 225 rods were used, it would call for a piston with a 1.921" CH, and that's just too much above the pin, for me anyway.

My understanding over at the Slant 6 site was that the combustion chamber floor sat an average of .200" above the flat face of the head (as would be seen from underneight). The floor then climbs up toward the valves and plug area. If true, then a piston top .147" out of the hole would not hit any part of the combustion chamber, particularly with a .020" head gasket between them.

Since the head simply cannot be milled enough to create a closed chamber, positive piston deck height is the only possible way to acheive real quench.

Yes, the KB 268 with 198 rods would be perfect if it had just a tad more CH. The 268's have 1.594" CH, but for usable quench with 225 rods, a piston with a CH of about 1.614" or more is needed.

Understand again that I have not measured any of this yet. I'm just speculating on how to approach it. Guess I'll do some piston research as well.

The chamber is not the same diameter as the piston. Look up an empty bore with a head on and you will see the chamber overhanging. The piston will hit it.

In the old days b 4 closed chamber heads were more avail guys (w 906's) welded up the OC recess then milled it flat & no reason it couldn't b done to a slant head if there's no piston that will get r done

Again, not sure about the six, but on a big block the piston is physically wider than the chamber on an open chamber head. Pretty sure the 225 chambers are smaller than the piston tops, so it wont fit inside... but i'm still guessing. Maybe if this is the case you could get tricky and carve out the edges ov the chambers to fit the piston inside...??? Seems like a helluva lot ov work to accomplish this quench goal though...

Or maybe i'm reading you wrong...???

what is the rpm range
that the slant six
needs to be 'optimized' for?

it is worth remembering the basics:

Quench is best at creating turbulence
in the air and fuel mixture
near top dead center
for faster burn
and better octane tolerance

Quench works best
up to a specific RPM range

Above that RPM range
the extra horsepower to 'squirt out' that mixture can take away power, rather than add it

Quench surfaces are like a high pressure pump that the piston has to run
... the more quench area
and the tighter the quench clearance,
the greater the horsepower need to
'run the quench fire hose nozzle'
becomes as the RPM goes up

As rpm rises
just the up and down motion of the piston
begins to provide a lot of turbulence
to the air and fuel mixture

in the 1500 to 3500 rpm range
you could also get more turbulence
inside the slant six's combustion chamber
by swirling
or tumbling
the air flow in the intake port

it is relatively easy to get more swirl:
just add to the intake port
some
welded in vanes
or spirals of little dimples
or a twist-able butterfly valve
or a more "shrouded" valve seat

a dish in a piston
will 'concentrate' and increase any swirl present
just like an ice skater
will spin faster
if she pulls her arms in close to her body

tumble is more tricky
but the right intake port mods can do that too

when you see
an oval dish cut into a piston crown
rather than a perfectly circular dish
the designers are trying to
concentrate tumble motion near top dead center
as well as swirl