Well I want more compression in my B18C5 and I wanted to know what size pistons to get. I have a brand new block from aruca and it has 0 miles on it but the USDM pistons are already installed. SO if I want to change my pistons do I get the standard size or do I get .25 over? I was thinking standard because there are no miles on it. OR do I have to get is honed out again for new pistons. I want the Spoon balanced JDM pistons.

thanks for any help in advance.

Chris


[Modified by underrated99si, 1:22 AM 2/19/2002]

 

I dont think that the diamater of the piston has to do with compression, on actual displacement, however I could be wrong

 

wouldnt 81.25mm bore pistons be an increase of the 81.0 mm stock bore?

 

Yes, a larger bore piston does have an affect on compression ratio. But only slightly. Check this out: http://www.bojangz.com/calculator/

 

I guess my post was miss understood. I want to put the balanced 11.1 Spoon JDM pistons in my B18C5 but I need to know If I have to get the cylinderwall honed again or can I just pull out the Stock pistons out and install the Spoon ones that are standard sized or do I need to hone out the bore and put in .25 over. The motor is brand new and has 0 miles on it so cylnder walls are cherry.

 

just slap them in. make sure you get the standard size. you'll be okay.
just make sure you check ring end gap and end gap placement.

 

I did the exact set up you are talking about, I bought my block from Mike k at Naples and put in a set of spoon jdm itr pistons right when I got it, stock bore. Honestly don't waste your time, if you have the chance now since it's apart and a since it's a easy uprade, drop some forged 11.5.1 or higher pistons in. Trust me when you start to want more power you will be kicking yourself in thre @$$ for going with the spoons.

 

if you go 81.25mm bore, you'll get a slight increase in compression, but nothing special. i'd drop in standard bore CTR or B16 pistons.

 

Wouldn't .25 over be over 81.5mm? I have some JE's for boost and they are .20 over and are considered 81.5 mm. .25 over would be .25 on the radius, not the diameter.

 

How much did you buy your block from Mike K? I'm interested in getting a block

 

get the std bore CTR pistons and use the same rings in there. Need to rebalance beacuse the ctr pistons are about 30grams more than type R integ.

0.25 over means in millimeters, so it would be 81mm stock bore plus 0.25mm over = total 81.25 ... just to put these terms into perspective, the american guys use the term ".010" over which is in inches, so 0.010 x 24.8mm = 0.25mm

Greg

 

Get standard bore pistons...

You would not need a re-hone because you already have a factory cross-hatch pattern, etc...

if you wanted to machine a block, you shoulda bought a used one

Suprdave