hey guys i dropped a b18c1 into my 99 si,got basic bolt ons,stock compression is 10 i think,if i wanna do a good all motor job,whats a good compression,i dunno if a 12.5 is to high or what, thanks alot,looking to make a beast of a na

 

you will barley be able to make on pump gas and with all motor higher comp is better but unless its gunna be a race gas motor stay between 11.1-12.3

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fezzie &raquo;</TD></TR><TR><TD CLASS="quote">you will barley be able to make on pump gas and with all motor higher comp is better but unless its gunna be a race gas motor stay between 11.1-12.3</TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mikes2000civicsi &raquo;</TD></TR><TR><TD CLASS="quote">hey guys i dropped a b18c1 into my 99 si,got basic bolt ons,stock compression is 10 i think,if i wanna do a good all motor job,whats a good compression,i dunno if a 12.5 is to high or what, thanks alot,looking to make a beast of a na </TD></TR></TABLE>

It really depends on if you want this car to maintain its daily drivability as well as what your plans are for bore size. You can run a little bit higher compression with larger bore sizes because you can effectively reduce the compression height while maintaining the same static CR. The subsequent effect on having a lower dome is being able to achieve better volumetric efficiency and reducing hot spots by having a flatter dome, which in turn allows you to run a bit higher CR, safely. There's a few more things going on there, but they're probably beyond the scope of this thread and your blossoming honda knowledge.
Also, builds utilizing a P72 GSR head can run a bit higher compression due to it's quench pads.

For a daily driven 87.2x81mm build (what you have now) I'd say about 11.5:1 would be safe with 91 octane on a good tune and some BKR7E spark plugs.
If you go with an 84mm bore, you can probably push that to about 12.0:1 on 91 octane using the same spark plugs. If you can get yourself some 93 octane, then you can raise those limits about .3-.4.

Honestly, all you really need is about 11.5:1 compression though. That's sufficient to meet pretty much any expectation you may have for power. The real key is in how you build the head. The power is in the HEAD.

 

wait so 83 mm means i need to bore it?

 

84mm means getting it sleeved.