Discussing CR (Caution Math involved!)
Thread Starter
Safety Car
Joined: Feb 2006
Posts: 4,855
Likes: 2
From: Columbia South Carolina
Discussing CR (Caution Math involved!)
I am trying to choose a piston that will achieve 9.0:1 - 9.2:1;
Using 781 heads with 113CC chambers and a head gasket that we will assume is 10CC in volume (from Summit web site) the cyl is 4.28" bore and stroke is 4" when reading piston specs teh description reads something like '9.71:1 with 106.9cc chambers....so when doing the conversion (to actual chamber volume) do I factor in the head gasket volume as part of the Combustion Chamber volume, so effectively I have 123CCs of Chamber?
Thanks
Don
Using 781 heads with 113CC chambers and a head gasket that we will assume is 10CC in volume (from Summit web site) the cyl is 4.28" bore and stroke is 4" when reading piston specs teh description reads something like '9.71:1 with 106.9cc chambers....so when doing the conversion (to actual chamber volume) do I factor in the head gasket volume as part of the Combustion Chamber volume, so effectively I have 123CCs of Chamber?
Thanks
Don
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
take a look here, click on links, and also do a search for cr, compression ratio, etc., for other help . . .
http://forums.corvetteforum.com/show...5&postcount=12
http://forums.corvetteforum.com/show...5&postcount=12
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
and if you're too busy to do the math ... this scr calculator from Federal Mogul aka sealed Power aka TRW is rather accurate & super handy.
http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx
it'll probably be even closer if you add about 1.7cc to the comb chamber volume to account for the crevice volume.
when at TDC, most pistons rest about 0.025" below a stock OE uncut deck ... aka deck clearance aka down in hole.
-edit- look at speedpro hyper p/n H426CP30 0.025" DC, +10.5cc DV and
sp forged p/n L2399F30 0.020" DC, +13.8cc DV
if you have uncut OE decks, 113cc heads & 10cc gasket ... you're gonna need a piston w/ advertised DV of about +11 to +15cc to yield 9-9.2:1 scr range.
seems 336781 chambers can be all over the place as much as 128cc ...unless you know your cc ... suggest you have em cc'd before you pick a piston.
http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx
it'll probably be even closer if you add about 1.7cc to the comb chamber volume to account for the crevice volume.
when at TDC, most pistons rest about 0.025" below a stock OE uncut deck ... aka deck clearance aka down in hole.
-edit- look at speedpro hyper p/n H426CP30 0.025" DC, +10.5cc DV and
sp forged p/n L2399F30 0.020" DC, +13.8cc DV
if you have uncut OE decks, 113cc heads & 10cc gasket ... you're gonna need a piston w/ advertised DV of about +11 to +15cc to yield 9-9.2:1 scr range.
seems 336781 chambers can be all over the place as much as 128cc ...unless you know your cc ... suggest you have em cc'd before you pick a piston.
Last edited by jackson; Jan 3, 2008 at 02:13 PM.
Thread Starter
Safety Car
Joined: Feb 2006
Posts: 4,855
Likes: 2
From: Columbia South Carolina
and if you're too busy to do the math ... this scr calculator from Federal Mogul aka sealed Power aka TRW is rather accurate & super handy.
http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx
it'll probably be even closer if you add about 1.7cc to the comb chamber volume to account for the crevice volume.
when at TDC, most pistons rest about 0.025" below a stock OE uncut deck ... aka deck clearance aka down in hole.
-edit- look at speedpro hyper p/n H426CP30 0.025" DC, +10.5cc DV and
sp forged p/n L2399F30 0.020" DC, +13.8cc DV
if you have uncut OE decks, 113cc heads & 10cc gasket ... you're gonna need a piston w/ advertised DV of about +11 to +15cc to yield 9-9.2:1 scr range.
seems 336781 chambers can be all over the place as much as 128cc ...unless you know your cc ... suggest you have em cc'd before you pick a piston.
http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx
it'll probably be even closer if you add about 1.7cc to the comb chamber volume to account for the crevice volume.
when at TDC, most pistons rest about 0.025" below a stock OE uncut deck ... aka deck clearance aka down in hole.
-edit- look at speedpro hyper p/n H426CP30 0.025" DC, +10.5cc DV and
sp forged p/n L2399F30 0.020" DC, +13.8cc DV
if you have uncut OE decks, 113cc heads & 10cc gasket ... you're gonna need a piston w/ advertised DV of about +11 to +15cc to yield 9-9.2:1 scr range.
seems 336781 chambers can be all over the place as much as 128cc ...unless you know your cc ... suggest you have em cc'd before you pick a piston.
Thanks for that last tidbit I was going on another sites info, I will check them for sure.
