Reply to "351C cylinder heads, open chamber vs closed chamber"

Mike,

You've got it backwards, the open chamber heads produce less hydrocarbons (and less NOx too).

Closed chamber heads on a "non-decked" block create small pockets at TDC where fuel molecules are hidden from the flame front.

Decking the block, closing the gap between piston dome & head at TDC, reduces the amount of molecules that are hidden, it actually produces a "squeeze" on the gases in those "squish areas" that evacuates the gases from them very well.

So now you're wondering, since the oc heads combust all the fuel, why don't they make equivalent or more power than cc heads with a decked block? Because there's more to it than simply burning all the fuel. The cc heads focus more of the burn on the piston dome, the turbulence spreads the pressure of combustion more evenly across the piston dome, and the cc heads aid in controlling the timing of the occurence of peak combustion pressure at the right time during the piston's stroke.

Also, I am told by those who's profession is porting heads, that the cc heads actually flow better than oc heads, because as the fuel air mixture is flowing past the open intake valve, it hugs the wall of the cc heads and is therefore directed away from the valve head; the fuel air mixture separates from the wall of the oc heads and crashes into the valve head. This is why, on a professionally ported set of Cleveland heads, the combustion chamber around the intake valve is left pretty much as is, the intake valve is not "unshrowded".

The modern aftermarket heads for all brands, all race heads for the last 30 years, even the heads in modern production engines with over head cams, incorporate features of the Cleveland combustion chamber. It's a good one. It was the last cylinder head developed by Ford engineers during the total performance era, and combined everything they had learned (and borrowed from others) up to that point.

Your friend on the DTBB, George