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G3GM 1973 to 1977 A-bodys. Chevelles, Monte Carlos, El Caminos, Laguna, 442, Cutlass, Malibu, GTO, LeMans, Century, Regal, Grand Am, Grand Prix, Sprint, Gran Sport, Can Am, Hurst-olds, and other 73-77 A-bodies


Running 10:1 compression

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G3GM :: G3 Tech :: Engine & Driveline

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Running 10:1 compression Empty Running 10:1 compression

Post by Sinister Fri Apr 13, 2012 8:29 am

What are my options for running a compression ratio this high.
I know everyone recommends 9:1 for the street.
My actual math from my engine calculations = 9.78:1

Chevy 396
Bore 4.124
Stroke 3.766
cylinder head volume 118cc
Pistons TRW L2242f30
Dome height .335
dome volume -38.30
deck clearance .025 ???
Gasket thickness .040
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Post by Joe73 Fri Apr 13, 2012 9:15 am

I dont see a problem with 10:1 at all. Yes, you will have to retard the timing a bit but it wont be a problem. All my buddies all shoot for 10:1 when building their motors.
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Post by The Dude Fri Apr 13, 2012 1:06 pm

Your camshaft will play an important role if you plan to run that kind of compression on pump gas. You are looking at "static" compression. As long as your "dynamic" compression is around 7.5:1 or no more than about 8:1 you will be fine. I could go on for a while about the subject, but google is your friend. Also check some earlier posts about cam selection on this site. I want to say I went into detail about dynamic vs static on a couple of threads.
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Post by Sinister Fri Apr 13, 2012 9:12 pm

I do mix my own racing fuel...110 octane mixed with pump gas,but I don't want to rebuild this motor again.
Any cam recommendations would be great.
I'll probably go hydraulic with rhoads lifters,or maybe even solid cam.
No thanks to the roller crowd,I'd rather buy hard parts for $1000.
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Post by pila Sat Apr 14, 2012 12:49 am

Had a 406 in my '77 Elco, which calculated to 9.8:1, and it sure didn't like anything except premium gas. Ran real good on 100 low-lead avgas. That same engine, 408 now, is now in the Malibu, but with less CR, because of pistons with 4 valve notches instead of 2 on the pistons. It runs OK on mid-grade now. Same 280 cam on both rebuilds.

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