Wedge verses Poly - understanding combustion chambers a little bit

A Wedge Combustion Chamber has the cross sectional shape of a wedge, due to the angle of the valves
This combustion chamber does not control how the flame front impacts the piston dome very well
It creates an area of "dead space" shielded from the flame front, below the large squish surface
This area is a source of detonation and reduces volumetric efficiency. This is why the small squish
clearance is so important in these motors



The Chrysler poly spherical head didn't have a "dead space" and had no squish area. The valve angles
are smaller, the chamber is relatively shallow. The chamber cross-section is not wedge shaped. The raised
areas surrounding the valves adjust chamber volume, allowing the motor to utilize flat top pistons rather
than domed pistons which were required by their hemi motor. Like a hemi the shape of the combustion chamber
is designed to focus the flame front on the center of the piston dome



The 351C chamber is very shallow, the valve angles are merely 9-1/2 degrees. There is no dead space. The
chamber cross-section is not wedge shaped. This shape evenly distributes the flame front over the entire
surface of the piston dome.

Engine designers realize the combustion chamber is the heart of an internal combustion engine. The best
designed intake port in the world cannot produce superior torque and horsepower if it is supplying fuel
and air to a cylinder with a poor or average combustion chamber. The 351C had the highest volumetric
efficiency of any mass produced push-rod (OHV) V8 not solely because it had well designed ports and large
valves, but also because it had a well designed combustion chamber. Although it may not be intuitive, what
you are looking at in the picture below is one of the best performing combustion chambers of any mass
produced push-rod V8.



The 351C quench chamber is nothing more than the open chamber with raised areas on either side of the
valves primarily there to adjust chamber volume, although the turbulence this creates also improves low
rpm torque. Since the smaller chamber is very well centered in the cylinder, the flame front is focused
upon the center of the piston dome.



Chevy LS7 combustion chamber, even though the head still uses in-line valves, this is not a wedge combustion
chamber, valve angles are only 12-1/2 degrees, the chamber is very shallow and it does not have a wedge shaped
cross-section. There's no dead space. The small amount of squish is for adjusting chamber volume, possibly for
creating turbulence, but not for preventing detonation.



-G
____________________________________________________________

Pantera Photos | 351C Historic Information | 351C Technical Information

If you use a 351C 4V powered vehicle for a grocery getter ... the eggs aren't going to make it home!