Guys ive done a fair bit of searching both on here and on google regarding calculating the compression ratio of an engine with a given comp height of a piston. All i could find was a CR calculator on google where i need to know the deck height (???), rod length (152.5mm / 6.0039") & the piston deck height (32.512mm /1.280") The reason for this question is that ive been looking at a set of arias forged pistons and the only detail to CR is the labelled piston comp height of 1.280" Can someone please help me figure out the CR these pistons will give in an RB30ET? Thank You. ---------- Post added 27-02-13 at 18:39 ---------- Anybody?

bump. someone should turn this into a useful thread and place it in the technical section. I for one would like some more info on accurately calculating compression ratio's, setting up quench, working out cc of head etc.

its block deck height mitzsi..as the machinist will surface(deck) the block for a true/clean face, this changes you comp ratio, so you need head gasket thickness,block deck height, piston crown cc, combustion chamber cc's, thinks thats about it..lol Between decking your block and head, you can change the comp a fair bit cheers darren

Quote: Originally Posted by Jet R31 [View Post] its block deck height mitzsi..as the machinist will surface(deck) the block for a true/clean face, this changes you comp ratio, so you need head gasket thickness,block deck height, piston crown cc, combustion chamber cc's, thinks thats about it..lol Between decking your block and head, you can change the comp a fair bit cheers darren How do you measure the combustion chamber cc's? I need to work out the comp ratio of a rebuilt na rb30, .50 thou over, decked, standard r33 rb25det head and using a standard thickness headgasket.

Put something over combustion chamber(clear perspex or something, drill a little hole in it, and fill the chamber with liquid(obviously measuring it) or google it lol http://www.youtube.com/watch?v=8QJKkCFFTEI cheers darren

Quote: Originally Posted by Jet R31 [View Post] its block deck height mitzsi..as the machinist will surface(deck) the block for a true/clean face, this changes you comp ratio, so you need head gasket thickness,block deck height, piston crown cc, combustion chamber cc's, thinks thats about it..lol Between decking your block and head, you can change the comp a fair bit cheers darren Thanks for the reply darren, the following attachment is the details of the piston Arias can supply, however it seems it is the only listing in their catalog that doesnt specify the given comp ratio lol :S (typical for an rb30)

Daaren everything you stated in your first post is on the catalog..... Yet i cant seem to figure out the CR... :S

Google (compression ratio calculator) and type in all the your measured cc's, there is a couple of decent calculators that will help you.

Quote: Originally Posted by RB2530 [View Post] Google (compression ratio calculator) and type in all the your measured cc's, there is a couple of decent calculators that will help you. I did this and it gave me some random number...:S I shall give it another go.. When im looking for piston that will give me a CR of 8.5:1, are we talking static or dynamic compression?

Just buy the pistons, smash it together and don't worry about it..lol, you won't be able to tell the difference between 8.00 and 8.5..haha cheers darren

You're looking for 'static' ratio

Thanks for the help boys.. Some original photos have not been recovered yet.

What about changing your camshaft??