View Full Version : How much would this increase compression?


Ryan 79
08-07-2006, 08:52:40 PM
How many points would a 100 CC head on a stock compression 76 454 raise compression versus a stock set of 781's?

theflash
08-07-2006, 09:45:06 PM
Depends on how many cc's the 781's are. I have 100cc heads on my 454 with a 10cc dome piston, and I'm making about 10-1

Ryan 79
08-07-2006, 10:10:11 PM
IIRC, I think the 781s are 119 cc

pdq67
08-07-2006, 10:17:58 PM
Probably from their terribly low CR that's like 7.9 to maybe 8 to 1 even tho they are supposed to be 8.5 to like 9.75 or so?

Using a cast-iron head like an old -206 and .020" steel shim headgaskets, imho....

pdq67

ZS10
08-08-2006, 03:09:22 AM
Look at a piston application chart.
You won't quite get a full point increase, maybe .7
A +.03 454 goes from 8.2 to 8.9 with a 12cc smaller chamber 124cc to 112cc.

You may drop 8-10cc with that swap.

rustbucket79
08-08-2006, 03:25:29 AM
Your static compression will end up at about 8.25:1 with composite gaskets, more with steel shims. (a common choice from the factory in the early 80's, 70's, etc) Not a bad swap with the correct cam, intake and headers.

As a side note, I did that swap using 366 truck heads on my 81 1 ton 4x4, including going up to the 2.06/1.725 valves, bowl work, etc. Still a slug due to the small propane system on the truck and stock exhaust manifolds, and my 04 extra cab long box with the 6L will KILL it while getting considerably better mileage. (and comfort) ;)