Compression ratio help

[Rubths]

I just had a 454 rebuilt and bought some merlin heads that were cc'd to 123 and I went with a very slight dome piston, I dont have the engine specs to share with you but I was hoping that someone could give me a rough estimate of my compression ratio from the motor compression. Each cylender is at 185 what do you think? :confused:

[1BIGJIM]

YOU BETTER BE RUNNING PREMIUM FUEL!

[565edge]

to get the right comp ratio we need to know if the block was decked,or how far the piston is in the hole,what pistons and how thick your head gaskets were.I had a 565 inch chevy built that was supposed to be 14 to 1 comp,after i had it rebuilt i found the block not being decked,the heads were supposed to be 118 they were 123cc and the thickness of the head gasket put it at 12.9 to 1.the new motor after decking the block,cutting the heads to 114cc makes 14.8 to 1,my pistons were .035 in the hole until we zero decked it.it sound like you have big cc heads and with a small dome your probally around 9.5 to 10.5 comp ratio.

[Rubths]

1BIGJIM:
YOU BETTER BE RUNNING PREMIUM FUEL!Is 185 considered high compression? When you say premium fuel do you mean 91-92 octain or 100+ octain?

[Rubths]

Where are all you gear heads when I need your input?
:confused:

[Hotcrusader76]

I am sitting at 128psi all the way around + or - 1-2 psi. I know I am around 9.5. But I concurr with the later response. You need to know deck height, piston specs, head gasket thickness, amount of head cc's, etc. Otherwise its just a guessing game.
Keep the Premium fuel in your boat. 91-92 octane with maybe a 10:1 mix of VP or Trick to be on the safe side. I run that in mine (probably overkill, but better than being killed) all the time.
Good luck bro!
Ty

[Infomaniac]

Rubths:
Where are all you gear heads when I need your input?
:confused: Your Avatar should answer that

[058]

Cranking compresson does not have anything to do with Compresson ratio. Camshaft profile is the biggest influence to cranking compresson. An 8.5 to 1 c/r engine can have 180 lbs. of cranking comp. and a 12.5 to 1 could have 125 lbs of crank. comp. It mostly depends on the cam profile.

[Jordy]

If you know what pistons were put in the motor, as far as dome cc and bore size, ie. 4.25 for a stock 454, 4.310" is .060 over, 4.35" would be .100 over, along with your heads that were cc'ed at 123, you should be able to find out from any speed shop, or even online at the piston builder's web site. They have it figured based on bore for just about every common cc chamber head from 103cc on up. This would at least put you in the ball park. If I had to guess based on the information you gave though, with a 123cc head and small domed piston, I wouldn't think much more than 10:1, if even that. Probably closer to 9:1.
Jordan

[Liberator TJ1984]

I agree with Jordy..I put TRW .095 dome pistons in my 454 w/119cc heads, fel pro gaskets.039 compressed..comes out to 8 3/4:1 w/pistons .010 in hole...try to get some more info if ya can... :confused:

[Jordy]

I am in the process of building a motor right now so I will elaborate a little more while it is still fresh in my mind. I have a set of SRP pistons .070 over with a 14cc dome. In a motor running a 4" stroke with a 6.135 rod (std 454) and 118cc open chamber heads with a 4.320" bore SRP says these pistons will be 9.5:1 compression. However, I am running 105cc closed chamber race ported heads, which bumps the compression up to a little better than 10.5:1 according to their charts. The deciding factors will be your dome cc, head cc and if you can approximate your bore and stroke. I still think you are somewhere in the neighborhood of 9:1 compression though, in which case 92 octane is all you need to run.
Jordy
[ July 26, 2002, 11:14 AM: Message edited by: jordanpaulk ]

[Rubths]

Thanks for the good info, I wanted to be no more than 9.5 compression.

[Hotcrusader76]

Rubths:
Thanks for the good info, I wanted to be no more than 9.5 compression.Yeah its easier on the wallet when it comes to gas mileage figures like....3 gallons to the mile...LOL

[Jordy]

Ty, if anyone here was worried about gas mileage that much, we would all be on the Sailboat Forums at Hot Sailboat.com
Jordy :D

[JEThro]

Rubths,Find someone that has Mondellos Olds Tech Manual. The formula for comp. ratio is in it. Jethro

[Hotcrusader76]

jordanpaulk:
Ty, if anyone here was worried about gas mileage that much, we would all be on the Sailboat Forums at Hot Sailboat.com
Jordy :D Ask my Julie aka "GTJewels"(girlfriend)....LOL>....There was times that setting sail with the Coors light beach towel was in order....
:::Flickering fuel pressure::: ::::sound of sputtering carbs:::: Oh shit! Sounds like we are out of gas......again!
Life story for me at the river! LMAO

[Hotcrusader76]

jordanpaulk:
Ty, if anyone here was worried about gas mileage that much, we would all be on the Sailboat Forums at Hot Sailboat.com
Jordy :D If things don't cool off soon overseas (sand country) then we might all be hanging out at Hotsailboat.com....LOL... We might have to switch to diesel fuel or Vodka...something! Prices will soon rise again...
[ July 28, 2002, 06:45 PM: Message edited by: Hotcrusader76 ]