jferg92

Can someone explain what the head cc is and how it relates to piston choice and compression ratio. Im guessing its the combustion chamber volume which means the more highly modified heads have less? What is the stock size on an unmodified head?

Edit: looks like the stock 4.6 head is 49.77cc so I wonder if the 5.4 is the same

ibd2328

iTrader: (2)

here you go at [MENTION=64669]jferg92[/MENTION]

Displacement = (Bore ÷ 2)2 x 3.14 x Stroke x 16.387
Head Gasket space = (Bore ÷ 2)2 x 3.14 x Gasket thickness x 16.387064
Deck Height space = (Bore ÷ 2)2 x 3.14 x Deck Height x 16.387064
Compressed Volume = Head Gasket space + Deck Height space +
Piston Top volume + Combustion chamber volume
Uncompressed Volume = Compressed Volume + Displacement
Compression Ratio = Uncompressed volume ÷ Compressed volume

ibd2328

iTrader: (2)

All pi heads have 42+ sd. of 1.5 cc combustion chambers. This is fairly small, so when put pi heads on a non PI factory block it greatly increases the ratio. The non pi's had around 51cc combusition chambers, nearly the same as the 5.4L DOCH heads.

I had factory PI heads 42cc and went with trick flow race heads with 38cc combustion chambers and my CR went up to 9.5

ibd2328

iTrader: (2)

Say for istance you run flat top pistons on a factory 5.4L with 44cc heads. Your ratio would be 10.65 static.

If you run dished pistons to give more volume, say a -11 cc, then you would have 9.34

This is all static compression ratios.

jferg92

Thanks for info. Really helpful calculations for the manufacturers don't have the conversion charts. What is an "ideal" compression for DD naturally aspirated moderate 2v build

ibd2328

iTrader: (2)

What kind of heads and power? Adding new cams?

ibd2328

iTrader: (2)

If you went with pistons it would def be worth it to get your block checked and bored.

jferg92

020 over, stock heads with some porting, 265ah cams, Manley rods, lightning crank.

ibd2328

iTrader: (2)

No need for a lightning crank.. Your factory forged is the same.

Don't see any reason for porting heads if you are going N/A and not looking for huge numbers.

I would go with a very slight dished piston -10 or -7 Compression would be great for a NA enginge with a good set of cams.

fordmotorsport

Dependent on the year for the forged crank right?