What compression would .25 over CTR pistons make in a B18c5 block with the ITR head milled .15?

 

Compression ratio: Volume of the cylinder, piston dish and head dish and
headgasket from top to bottom of the stroke, divided by the head, piston,
and headgasket volume or:

bore(in.) x bore(in.) =__ x .7854 =__ x stroke (in.) =__/ .061=__cc of
cylinder + (head cc +piston cc + headgasket cc) / (head cc+ piston
cc+headgasket cc) = compression ratio

do the math

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vtecvoodoo &raquo;</TD></TR><TR><TD CLASS="quote">

do the math
</TD></TR></TABLE>

God Damn
I knew thier would be math involved.
Anyone want to take a stab?

 

little over 12-1

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by soakit &raquo;</TD></TR><TR><TD CLASS="quote">little over 12-1</TD></TR></TABLE>

wrong, more like 12.5-12.9

 

I'll say about 12.65-13.1:1. Normal setup would be about 12.1-12.3:1 with head milling it will put you close to 13:1

 

http://www.c-speedracing.com/h...c.php

with itr head/block/piston to deck height and .014 for head gasket thickness (to compensate for the .015 mill with stock head gasket)....

compression ratio would be around 12.2-12.4

 

C-speed is off by .3- remember that....

 

the question is which .3 higher or lower....but still not quite 13:1.

that can be the difference between pinging or not with 92-93 octane pump gas.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by advanracing62 &raquo;</TD></TR><TR><TD CLASS="quote">C-speed is off by .3- remember that....</TD></TR></TABLE>

I put a stock USDM GSR through it and got 10:1, a USDM LS and got 9.2:1.

I would think it's pretty accurate, but maybe custom combos throw it off?

 

it's only off on the PCT pistons. I think it's .3 low

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by advanracing62 &raquo;</TD></TR><TR><TD CLASS="quote">it's only off on the PCT pistons. I think it's .3 low</TD></TR></TABLE>

So your saying CTR pistons in a b18c with a b16 head or itr head dont yield 11.77 compression and more like 12.1 ? with a 3 layer oem head gasket? how do u know its .3 low?

 

lots of testing, and time.<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by igotyofire &raquo;</TD></TR><TR><TD CLASS="quote">

So your saying CTR pistons in a b18c with a b16 head or itr head dont yield 11.77 compression and more like 12.1 ? with a 3 layer oem head gasket? how do u know its .3 low?</TD></TR></TABLE>

 

so is 12.1 correct? i want to know

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by igotyofire &raquo;</TD></TR><TR><TD CLASS="quote">so is 12.1 correct? i want to know</TD></TR></TABLE>

its higher than that. SGT on the board knows around what it should be. I trust him more than c-speed racing. He knows more about b series engines than i know about myself

 

How about with JDM ITR pistons and the Mugen head gasket? About 11.5 or so?

 

yeah, that sounds right, and thats without milling the head of course

 

Now here is a stupid question:

I think Im going to go with JDM ITR pistons with mugen/spoon headgasket. Can I get by with just ordering them in the standard size or do I need to get .25 over and rebore/hone the block? Also do I have to change the bearings? The motor is pretty new :2001 USDM B18C5 w/ ~30k

 

it depends on if your cylinder walls have been scratched or not. either way youll probably need to hone the walls, but ill let someone that knows more than i do answer your question

 

If you're going to pull the bottom end apart, might as well throw in new bearings....add a lil comfort and security to the build