A heads - why such big chambers?

I've been reading up on A heads lately and wondered why they have such big chambers.

Also, what are the typical depths of the valve reliefs in an A head flat top piston?

one reason is the valve angle.

In general terms I have always heard a flat top piston and a large chamber worked better in a lower compression engine. Not saying that this is necessarlly the case with the A heads, just in general theory. It is also harder to keep compression down in large displacement engines, so dished pistons, and larger chambers, are a combination of both are required.

One other possiabilty, also, If the valve is raised with the chamber you will gain more piston to valve clearance, to run a larger lift cam, which is good with a large CID engine.

Chamber size and configuration on A heads has evolved over time. The 3x chamber in the TFS A460's I got through Lem Evans in 2011 are visibly different, smaller, than the V1set I used starting in '06. At 588" 4.56"x4.5 the piston still needed a small spherical dish to hit 11.86:1 for the pump gas. New 598" is right at 12:1 with the same chamber and dish, still pump gas, fingers crossed. Tad more cam.

wowzers, 12:1 with pump gas.   Gotta love EFI and big cams.

Comparitively, the cam isn't that big, 282/294 @ .050, gross lift .830. That was the 588" deal. For the 598" I'm looking at an evolution of the same lobe at .903" or .927", same duration within one degree. Hopefully the same rpm range, just more torque with the limited fuel.

"and wondered why they have such big chambers."


All the better to eat Chevy's with.


Sorry. It slipped out.   

Thats about the size of it most of the time. A fellow with the nick name Hop Along in Houston, had a Blue 69 BBF Stang, like yours, and thats what he liked to do also. He told me a clutch came though the floor board once, hence the nickname. He also warned about the big valve CJ heads clipping valves when the SVO heads came up, many years back. No body seemed to want any of his action either.