View Full Version : Little more compression on a 454


MartinD
02-17-2011, 04:10:11 PM
About to redo the 454 in my Chevy C-20 and need some tips. The current engine is around 8:1 compression and I would like to be around 9 or 9.5. Im assuming it has big chamber heads on it. What would be a decent set of factory heads to use to get the compression up? I will upgrading the cam some but nothing crazy. Thanks

mjoc
02-17-2011, 05:48:02 PM
Change the pistons to great the increase in compression.

Michael

5spd540
02-17-2011, 06:19:38 PM
Get a set of 100cc or 98cc heads from a early 396

rcb1970Z28
02-17-2011, 09:06:34 PM
Be careful that you don't actually lose more compression when you reassemble. If it came stock with a steel shim head gasket (.019") & you reassemble with a composition head gasket (.041"), then your compression is going to drop. This will also increase quench-area clearance, which you don't want to do. Most stock or shelf pistons I've seen on a bbc seem to end up around .020-.025 in the hole on a 9.800" deck, so decking the block to 9.780" & using a composition gasket works well (steel-rod motor). Of course, you have to check all this crap carefully &/or check with your machine shop (or someone who knows) to make sure these clearances end up ok.

If you're simply going to change the heads, and it had a steel shim head gasket, then I'd go back in with a steel-shim head gasket!

rustbucket79
02-17-2011, 09:36:28 PM
And if you're running typical open chamber heads and stock replacement cast flat top pistons, you're likely closer to 7.5:1 with composite head gaskets. I did the 366 head swap when I built the 454 in my previous truck, without any decking/etc, and with the 101 cc chambers I netted about 8.3:1 give or take a tenth. BBC's NEED a domed piston to get any decent compression ratio with factory style heads.

MartinD
02-21-2011, 02:18:49 PM
Thanks guys. this gives me alot to think about on the build. :)

Rich Schmidt
02-21-2011, 02:52:56 PM
N matter how you configure it,going from 118 cc to 100 cc on any low compression 454=1 full point in compression ( 7.5:1 to 8.5:1). In you rcase there are 2 different 454 pistons for trucks. The true flat top with 1 4cc valve notch yeilds 7.8:1 with 118cc heads and 8.8:1 with 100 cc heads. With the common 10 cc dish you get 7.5:1 with 118 and 8.6 with 100cc heads. This is all with a .040" thick composition gasket. Chevy hasnt used a steel shim gasket on a passenger car or truck since about 1972,and I dont think they ever used one on a truck 454. Either way,both calculations were with a composistion gasket.

Closed chamber small valve heads are typically between 96 and 101 cc while the larger valve version are the 106 or 108 cc heads(larger valve are rectangualr port perfromance heads). You could take a 96 cc head or a 100 cc head and flat mill it .050" and not have a gasket seal problem and get about another 3/4 point in compression. All the early heads are large oval port,and would be required if you have large oval ports now. If you have peanut port heads,and dont have any interest in an aftermarket manifold,you can look for a set of heads from a 366 truck engine. They typically have the same size ports and valves as other peanut port heads but are also avalable in small chambers. You need to look for the right castings,but they are probably more available from local rebuillders then a set of early heads. The early heads are still very cheap,but you will be daling with 45 year old castings with non hardened seats. Even a good stock rebuild with new budget valves/springs ect will set you back around $500.

Good luck.

MartinD
02-21-2011, 03:08:05 PM
Thanks for the great info. Ive always been a small block person and picked up this pretty nice 86 with the stock 454. I plan on and have started redoing it and would like a nice "punchy" 454 but streetable if i want to drive a pretty good distance as well. I am assuming that it being an 86 it has the peanut ports. If i can find a nice set of heads i would upgrade the intake manifold as well. :)

hhott71
02-21-2011, 05:46:21 PM
You can use the 11:1 closed chamber piston on Open chamber heads and get about 10:1 comp.

rcb1970Z28
02-21-2011, 06:25:42 PM
If you want to raise compression, and your pistons are .025" in the hole (and they probably are), then you want to be using a steel-shim gasket. Using .040" composition gasket would be throwing away free compression. Just be sure to confirm that total deck clearance is at least .035"-.040"