Dished vs flat top pistons at same CR

[Protech Racing]

I have some room in the rules to deck the block/head for compression . My 1.8 litre 8 Valve VW currently use a small dished piston with a narrow squish band . The Piston tp head is about 042 or so. Loose bore, gapless rings, gas ported top ring. This makes very good power and the car is very fast at this point .
The Euro VWs often use a dished piston with a flat head . The vavles are flush and pretty unshrouded. I can not duplicate the flat head, but I can mill the head another 080 and dish the pistons more to get the CR back to legal .

My in the brain simulation says that ; This would add round shapes for the inlet air to tumble more /.
Get the valves closer to the bore.
Improve the pressure vector acting on the piston.
Evacuate the chamber a tiny bit better with rounder shapes and closer valves.
Does this sound correct? I may add the dimples to the pistons also ..
Thanks for any input, MM

[PackardV8]

FWIW, we went through a time here spending big bucks having the combustion chamber mirrored in the piston top. A NASCAR builder proved to me a symmetrical dish in the piston made more power; go figure.

[F120]

do whatever you can to get the most squish area possible

[digger]

if you have same squish and CR, i cant see why a flatter shape chamber that results from flat top would be preferred except where you can't get enough mean into the crown of the piston ofc. In chamber mixture motion is a bit more complex than human logic though

[DCal]

FWIW, we went through a time here spending big bucks having the combustion chamber mirrored in the piston top. A NASCAR builder proved to me a symmetrical dish in the piston made more power; go figure.

.
Maybe not in all instances but in most anyway. For the with first time ever I needed to lose -17 cc, instead of a dome or flat top. So I already know some are going to disagree with me and I didn't do an A to B test but here's what I did and why. SBC 23 with 4.125 bore and a 3.700 dish diameter x .125 deep. We used a 2"radius from the edge of the dish to the floor of the dish, so it's essentially a spherical shape that's only .125 deep.
I try to envision what the piston to valve situation is like at or near TDC and this dish, in my mind, after making pistons for 42 years, allows the inlet charge to spread quickly and without obstruction. It may help the exhaust cycle too by making a smoother approach to the valve seat.

[mag2555]

Possibly at TDC and if a head has a shallow chamber, added power is made at the end of the intake cycle by a dish that helps with pressure recovery on the shallow side of the chamber.

[Walter R. Malik]

I have been told by some very astute engineers that a parabolic dish with about a half inch flat around it is the best for more than just power as it keeps the piston crown stresses within the cylinder the same, all the time.

[frnkeore]

1950's tractor tech

https://duckduckgo.com/?q=allis+chalmer ... 00x600.jpg

[289nate]

I have always wondered if a dish piston will potentially bring more air into the cylinder since there will be increased depth at the bottom of the cylinder even though the volume stays the same due to combustion chamber size difference? Someone told me this once. They were a part of some pretty nice builds so I had to take it kind of seriously though I cannot wrap my head around it.

[swampbuggy]

How about it Warpspeed, give us your input please . Mark H.