Wben it comes to lowering the compression ratio, dished pistons are an alternative option versus using big chambered heads. With that being said, there are several options on the dish design. Here are some pics of various dished pistons for the Y. For an all out blown application, I lean heavily toward the reverse hemispherical design.

Lorena, Texas (South of Waco)

Thanks for the pics, Ted! Fascinating!

Wouldn't the "reverse hemi" design eliminate the quench, and the better mixing it's supposed to have?

I've been wondering about the compression issue for the Y blocks. With the amount of compression a lot of street blown cars are running now why can't a flat top piston Y run G heads and a McCullouch? Is it due to the age of the design in the castings or what? I ran G heads with my McCullouch before and didn't see any real problems. ? Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

G heads on a zero deck 292 will be about 8.6:1. When you consider that most Y blocks are no bigger than a 292, it looks like they should do a reasonable job. Most also will not be zero deck so the compression drops further. For 312s and strokers, the G's and flat tops probably are too much.

Modern turbocharged and supercharged cars do run higher compression but they are also entirely computer controlled and I imagine that is where a lot of that ability comes from. The computer can make adjustments much more effectively than a mechanical system can and keep the engine in the safe zone.


Lawrenceville, GA

Compression ratio is much more an issue with Rootes or positive displacement blowers than with centrifugal blowers like the McCullochs. Macs just just don't make much boost below 2500-3000 RPM so detonation is much less likely to occur.Some experienced people have told me the best way to build an engine with a centrifugal blower is to build it like a naturally aspirated engine and add the blower.
Frank RIce's engine does have the -471 heads on flat top pistons and runs very well but the blower is making more boost than a standard Mac or Paxton.
The amount of boost is probably of greater concern than the compression ratio or it does, at least, dictate the C/R. Adding boost increases the effective compression ratio because you are filling the cylinder to more than 100%. Assuming 100% V.E., 7.4 lbs of boost (1/2 atmosphere) will give you a theoretic 150% V.E.
Logic would indicate that a dish that mirror images the combustion chamber would be the best but the Rep at Race Tec pistons swears they made more power with a circular dish (reverse dome in custom piston parlance). I have never done any back to back testing so me opinion would be just an opinion.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Thanks John and Charlie for your response. I am running the 471 heads on my new motor so the blower shouldn't have a problem. I'm still planning to set up the 4-71 blower for next year but forgot about the hood issue. I may have a line on a fiberglass hood that I can cut for the air cleaner. Didn't think about it sticking out of the hood. I sure don't want to cut the louvered one. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

I am also running the 471 heads and flat top pistons in my new supercharged motor, but I relieved the block on the recommendation of Gord McMillen. I didn't have any detonation issues on the limited dyno test I had run, but I was also using an MSD 6BTM box which retards the spark under boost conditions.

Rono

  Ron Lane,  Meridian, ID

The idea behind the reverse hemispherical dome is to concentrate the combustion pressure on the center of the piston. This reduces the piston skirt friction that is normally induced when the combustion pressure is non-centered on the piston top with a combustion chamber specific or ‘D’ shaped dish.

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I did use the reverse hemi dish on the naturally aspirated EMC Y-Block engine which made 528 HP on the UNOH dyno while burning 86 octane fuel (MON method). Here at the shop that same engine made 540 HP when tuning for a peak horsepower number and not worrying as much about the low end torque values which were otherwise needed to help the EMC score. The EMC engine had a very long connecting rod (6.750”) which maximized dwell time at TDC and helped to defray any detonation issues that may have been present if using a 6.300” or shorter rod with the lower octane fuel. Because of the rod length and paying particular attention to the dynamic compression ratio numbers, I didn’t worry about maximizing the quench on that engine.

Lorena, Texas (South of Waco)

Most of turboharged engines are intercooled what cannot be done easily with roots-style chargers.


Hyvinkää, FI

I do have to run 30 degrees or less total and 110 octane to really make it work though, wish i could legally run a set of your heads!!.

Frank/Rebop

Bristol, In ( by Elkhart)