Hi, sorry for this basic question but I need to know. I have a 1999 b18b engine. My bore is 81mm right?. Well, this said, my piston (if I buy new one) should be 81mm as well.... so why is there some 81.25 mm piston ? How do they go into the sleeve... Do we absolutely need to rebore bigger or is there something I can do with ring asjutement etc...

Thanks for the help

 

Pistons that are .25 over are simply 81.25 mm in diameter. This is for any instances where cylinder walls are slightly damaged and need to be bored out slightly. Honda makes cylinders .25 over so that you can still use oem parts if this scenario should occur. No, you can't adjust the rings to use overbore pistons, you must bore out the sleeves. A good idea though in any situation in which you are replacing pistons.

 

.25 is the size in inches that the piston is in diameter larger than that of the original factory spec ones. They do this so that if you need to rebuild your engine you can still use fatory equipment if the wall of the cylinders need boring out to get rid of surface imperfections.

EDIT:
Well, Type R Bob beat me to it...I am a slow typer.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EKhatch &raquo;</TD></TR><TR><TD CLASS="quote">.25 is the size in inches that the piston is in diameter larger than that of the original factory spec ones. </TD></TR></TABLE>

Inches? That would be a hell of an overbore. It's millimeters .

 

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

Inches? That would be a hell of an overbore. It's millimeters .</TD></TR></TABLE>

Oh yeah. I don't know what the hell I typed inches for?

 

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

Oh yeah. I don't know what the hell I typed inches for? </TD></TR></TABLE>

Well his original thread title of .20 would be an overbore in inches.... honda doesn't make a .20mm over...

BTW, if you're going overbore... honda also makes the largest overbore of .50 on itr pistons... hell, if yer gonna bore...go for broke !

X2

 

so would using CTR oversized pistons in a LSVTEC produce more power then the standard bore? or is so close it does not matter? Also how would this affect rod ratio?