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I have a carbureted 1986 Corvette L98 350 in my 83 El Camino SS that I am looking to upgrade in the near future. I am blueprinting the upgrades and I am trying to figure out the current compression ratio to see if I need to fit pistons into the budget. The pistons in the engine are flat top with 4 relief cuts for the valves that originally had 76'cc heads which equate to 9:1 compression ratio. I have 1987 58'cc Corvette Aluminum heads on it now with 4.125 bore, .039in. thick compressed head gasket size. I have found different compression ratio calculators on the web, but I need to know how many cc's the piston's valve relief cuts holds to finish the calculation. If anyone can help me figure out what my current Static Compression Ratio is I would appreciate it.
 

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with different brand pistons it will vary a little,,most are +6 to 7cc for all 4reliefs ..
heres a search> http://www.summitracing.com/search/Part-Type/Pistons/Quantity/Sold-as-a-set-of-8/Engine-Size/5-7L-350/Make/CHEVROLET/Engine-Family/Chevy-small-block-Gen-I/Piston-Style/Flat-top-with-four-valve-reliefs/?Ns=Rank%7cAsc

need to know the deck hight also,, .025 is normal,,they also vary from .015 to .032..:texas:
The '86 block has never been touched that I am aware of, so I assume that it has the stock deck height which I believe is .025. I have read somewhere that 7ccs is the stock size for the flat top piston in the L98 with 76cc iron heads. If I did the math right it comes to 10.11:1 Static Compression Ratio. Can you verify this?
 

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the chart that came with my probe piston said they were 10.49 with a 64 cc and they are factory replacement lt1 flat top w /4 valve relief. i am preety sure the early l98 used 624 casting head. and the ones i have seen were small chamber heads
 

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bore 4.0
stroke 3.48
head cc 58
vlv relief 7
gasket .039
deck .025 ===10.17cr

bore 4.0
stroke 3.48
head cc 58
vlv relief 6
gasket .039
deck .025 =====10.29cr

this one dosnt have the gasket diameter,,thats probly the difference..:dontknow:

heres a pile of calculaters http://www.wallaceracing.com/Calculators.htm :texas:

bore 4.0
stroke 3.48
head cc 64
vlv relief 7
gasket .039
deck .025====9.5cr ...............with a .015 gasket=10.04cr


bore 4.0
stroke 3.48
head cc 76
vlv relief 7
gasket .039
deck .025=====8.45cr...........with a .015 gasket=8.85cr
 
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