I'm in the process of piecing together my engine and need some advice.

I've got a 454 that is going to be bored out either 0.030 or 0.060 with 781 open chamber ovals with the bigger 2.19/1.88 valves.

Talking to a guy who will order my pistons, he recommended the pistons that will give me about 9.5:1 compression but the catalog refered to 109cc heads for that compression. Everywhere I check the 781s are around 118cc. How much compression would I lose if I got those pistons and my head chambers were 9cc bigger? Also, the cam calls for around 10:1 compression. Will that make a huge difference?

Also, what's the max compression you could run with iron heads on 93 octane?

Sorry for all the questions. Thanks for any info!

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1970 Camaro RS project

[This message has been edited by SML350 (edited October 28, 2005).]

Whatever you do cc them so you will know what size dome pistons to buy!!

-781's vary all over the map AND since these have been reworked, all the more important to cc them!

pdq67

Have them cc'd.

I've seen data from different sources that puts them anywhere from 110 to 120cc's.

<font face="Arial,Verdana" size="2">Originally posted by SML350:
[B] How much compression would I lose if I got those pistons and my head chambers were 9cc bigger? </font>

About 1/2 a point (ex 9.5 would be about 9). More than likely they are large chambers in the 118cc range. Only way to be sure is to CC them.

I cc'd 2 different chambers multiple times and came out with 123-124 cc's each time.

Is it more because of the larger valves possibly?

So I definatelly need different pistons then I guess.

Very well may be b/c of any plunge-cut unshrouding the Machinist did along with the big valve install.

pdq67

PS., Fwiw, SB big valve, -461 double hump heads are usually like 66 cc's vs about 62 for the little valves and 64 for the medium valves. You can see and feel the plunge-cut in the big valve chambers.

I know, not BB, but nonetheless.........