Reply to "Closed-chamber heads"

JWR,

milling material off the head does nothing to close the gap between the head and the top of the piston at TDC, it only reduces the volume of the combustion chamber and raises the comression ratio.

For "squish" to work effectively on a street motor, the clearance between the squish areas of the head and the top of the piston, at TDC, must be 0.045" +/- 0.010", ideally the thickness of the head gasket (piston dome flush with the deck of the block).

As I wrote in another post, the cc heads aid in controlling the timing of the occurence of peak combustion pressure at the right time during the piston's stroke. This improved control over the peak combustion pressure results in less of a tendency for detonation to occur (aka knock or pinging). In other words, with a decked block & cc heads, you can run higher compression than you can with open chamber heads, or with cc heads and a "non-decked" block.

The compression ratio of a standard displacement 351C with flat top pistons, zero decked block and cc 4V heads is about 10.0:1. With this set up you can run a typical street performance cam on pump gas.

Keep in mind, the compression ratio is determined by the camshaft, cylinder heads and type of fuel. The camshaft grinder should tell you what compression ratio to set the motor at.

After making any significant changes to a motor, such as heads and cam, the calibration of the ignition and carburetion must be checked and adjusted on a dyno.

Your friend on the DTBB, George