ok. talking about 400 sbc here.... i've been told that with flat top pistons, on standard bore, on 64 cc heads, i would get about a 10.84:1 compression..

now.. i'm wondering, if i went to .60 over, would the compression go down? if so. could i put domed pistons in, and hype back up the compression to about the same 10.84, or would it just make it go to like.. 13:1 like i have been told it would(but i duno what bore that was, i think it was standard). I think where i read it, it was talking about standard with everything.

thanks.

 

The compression ratio will go up as piston diameter goes up.

Enter all the needed information here and see fo' yo' seff.

http://members.uia.net/pkelley2/crc.htm

 

wtfs... getting like... 1. something :1 scr's. wt... what about the dynamic?... are #'s like that right?

 

i used another calculator too,... also getting 1.something's.. and same w/ dynamic....

make sure i have this right...
# of cylinders = 8
bore diameter inches = 4.155 (400 block .30 over)
stroke length inches = 3.750
combustion chamber voluem cc = 64
head gasket compressed thickness inches = 9.025
head gasket bore diameter inches = 4.155(i guessed it'd be same as bore?... i doubt tho)..
piston to deck clearance inches = .025

domed pistons
dome volume cc = .200

displacement ci = 406.77
displacement litres = 6.6658
scr = 1.4016:1

that was w/ domed pistons w/ .200 dome, i also did for flat top, and got around the same. i must be really missing out on something here....

but. i got these #'s from the specs on the pistons. cept for the gasket bore.... which i'm lost with. and the gasket thickness, that's what everyone uses... so i just threw that in there.

thanks.

 

Unless the head gasket thickness is a typo 9.25 is about 9 inchs to high.

 

You have to remember that deck height affects the CR if the pistons are zero decked then it is different than if they are .030 down in the hole.

 

Hes got that right thou. Its his deck clearance.

 

That would make it 1:1 compression.....

 

The compressed thickness is just that; how thick is the gasket when it's compressed? They can range anywhere from .015" to some as thick as .050" You need to find out which one you'll be using.

Quote:

head gasket bore diameter inches = 4.155(i guessed it'd be same as bore?... i doubt tho)..

You're correct, it's usually bigger. 4.166" should work for your calculations.

Quote:

dome volume cc = .200

That's the dome height, not the volume of area the dome takes up. You need to find that from the piston manufacture.

Take that FWIW.

If you really want an optimum engine you have to get the deck height measured, mill it if needed, buy the pistons, measure the volume of the piston in the cylinder, add that to the cc's the gasket will convert to, then add the combustion chamber.

There's more to it than that, but that's the basics. I'm not going to give you the forumla on how to calculate it all out yet because it's obvious you got confused just from the simple calculator I gave you to use.

You have a lot of reading to do. Go to the book store and buy books, primarily ones written by David Vizard.