is this true??9.1 compared to 11.8cr pistons..same brand, same bore why would the tolerances/clearances be tighter on the high cr pistons?can someone explain??or is it just some marketing ploy to get me to buy the oversize pistons they have in stock(which aint gonna happen but maybe they figure it will)

 

1) they are likely made from different alloys.
2) f/i and n/a pistons will require different clearances

 

The clearances may be tighter to reduce the amount of air that slips past the piston to the top piston ring, which means more air in a smaller area, which means more compression.

 

Cast pistons are run with tighter tolerances than forged pistons. It has something to do with different expansion rates of cast versus forged. I have never heard of compressoin being a factor in tolerances.

 

also, FI pistons run looser tolerances, because they are expected to run hotter, thus expanding more

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">also, FI pistons run looser tolerances, because they are expected to run hotter, thus expanding more</TD></TR></TABLE>

exactly

 

would the loosness be detrimental in a n/a setup?

here are the spec from jeff

0033 for turbo and .0028 for all motor.

.0033 is within tolerance for all motor, its just a little loose.

.0035 is the limit for all motor.

.004 is the limit for turbo.

whatchall think?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">also, FI pistons run looser tolerances, because they are expected to run hotter, thus expanding more</TD></TR></TABLE>

you took my words. this is why they have different piston to wall cleara nce's