427 FE heads 68cc vs 72cc chamber size

Mike Chase · #1 (**permalink**) 10-01-2001, 02:16 PM

Is bigger always better? can stock fe 68 cc heads be reworked to out perform stock fe 72cc heads ? Can you run medium riser valves with 68cc?

mickmate · #2 (**permalink**) 10-20-2001, 08:27 PM

Bigger is worse with combustion chambers. The smaller chambers give a higher compression ratio and more bang. They also require a higher octane fuel to stop pinking etc. The head rise you refer to are intake port related and valves don't change. The best combination for performance and fit under the bonnet is small chamber, big valves and medium riser. If you do a search there's a lot of head info available.
Cheers Nick

Steve Dickey · #3 (**permalink**) 10-20-2001, 10:37 PM

Mike,
You have to look at the big picture. Given your bore,stroke,deck height,compressed head gasket thickness, piston valve pocket volume,a 72cc chamber may result in the compression ratio your looking for. The only way to know is to do the math. If your looking to build an engine that will run on pump gas and a 68cc chamber results in a 12:1 compression ratio, smaller may not be better given your requirments.
Take care, Steve

Mike Chase · #4 (**permalink**) 10-23-2001, 07:49 PM

Fellow Club Cobra members, I did not post the
message you responded to - don't know what's
going on here - this has happened once before. I have reported it to the moderator. I'm a small block kind of guy but I appreciate the help fellow members are always willing to offer! Best regards, Mike