Reply With QuoteI'll take a wild guess that it's 8.5 to 1the only way to find out what you really have is to measure it all up!..
i need to know the compression ratio on my genv 454 i got this number off the bottom of the piston when i changed oil pans TRW14097021 i believe this is a stock part, the motor came from mercruiser as the 385hp at the prop.thanks
I'll take a wild guess that it's 8.5 to 1
ok thats what i was guessing also, but let me ask ya this, i want to run a solid roller cam and the spec. on the cam say at least 9.5:1 seems i need to change pistons huh?
Maybe maybe not, if the pistons are down in the hole you can have the block decked to .000 and use a thinner head gasket, that will raise compression but everything will have to be measured up for clearances. Also it depends how much lift you have in the cam, the pistons you have now may or may not accomodate a lot of lift?????...
Yep, I've got TRW's that are .025 in the hole, I'm ditching the Fel-pro .043's and going with GM .022 stainless steel shim gaskets from the LS-6 BBC, these can be had for about $8 each from your local GMPP dealer. My compression is already over 12:1 but I was interested in bringing the piston to head quench area down to a more reasonable .047, but these will add nearly .5 more compression.
Maybe maybe not, if the pistons are down in the hole you can have the block decked to .000 and use a thinner head gasket, that will raise compression but everything will have to be measured up for clearances. Also it depends how much lift you have in the cam, the pistons you have now may or may not accomodate a lot of lift?????...
easier to change pistons,no?
easier to change pistons,no?
Not necessarily, if you change pistons that means rebalancing the motor, the thing to do is measure everything up first, you may be able to get away with what you have!..
Yep, I've got TRW's that are .025 in the hole, I'm ditching the Fel-pro .043's and going with GM .022 stainless steel shim gaskets from the LS-6 BBC, these can be had for about $8 each from your local GMPP dealer. My compression is already over 12:1 but I was interested in bringing the piston to head quench area down to a more reasonable .047, but these will add nearly .5 more compression.
Wow .025 down is a long ways, instead of changing gaskets I'd deck the block to .000 that would give you a better quench area rather than by just moving the head down!..
Jet City...You could do both...cut your block, and use the thinner shim gasket, pick up near a full point, and get your quench down in the low .030"s. BUT...don't forget to recheck your VP clearance.
Just as a note. I have Cosworth pistons that I run .005 out of the hole with a Felpro gasket. With the heads at 118cc, and a 44cc dome, I get 12.4:1 when I do an actual pour in the cyl to measure my dome vol, which is really the only way to know your true CR. The TRW's with the advertised 12.5:1 dome are typically a 40cc dome, and are hard pressed to get an actual 12:01. I did my friend's 467 (454 + .06), zero deck, 119 on the chambers and it calc'd out to 11.8:1. No where near the 12.5 to one they advertise. My point is that unless you're talking about a big inch motor, and if you have off the shelf pistons and stock style heads (no Big Chiefs or Olds style), and are .025 in the hole, I'm thinking you might not actually have 12:1+ compression. Just a thought. Closed chamber might be different, as I haven't messed with them too much...don't know. :coffeycup
Not necessarily, if you change pistons that means rebalancing the motor, the thing to do is measure everything up first, you may be able to get away with what you have!..
i hear ya.thanks alot!! :idea:
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