Piston To Bore Clearance, Forged Pistons

[Sky-Engineering]

I am wonder what people run for piston to bore clearances. I am looking for people with a lot of experience and or a very long time running engine.

HKS 87mm step 2 (molybdenum coated) (or Tomei/Trust/Greddy, all have similar material/size spec)

+-1.6 bar max street =

+-1.6 bar max track/drag =

+-2.0 bar max street =

+-2.0 bar max track/drag =

+2.0 bar street =

+2.0 bar track/drag =

CP 87mm (or JE/Wiseco, all have similar material/size spec)

+-1.6 bar max street =

+-1.6 bar max track/drag =

+-2.0 bar max street =

+-2.0 bar max track/drag =

+2.0 bar street =

+2.0 bar track/drag =

I run most engine's we build with HKS/Tomei/Trust pistons at:

1.6 bar = 1.9" thou STREET

2.0 bar = 2.2" thou STREET

+2.0bar = 2.4" thou STREET

1.6 bar = 3.0" thou RACE/DRAG

2.0 bar = 3.2" thou RACE/DRAG

+2.0bar = 3.5" thou RACE/DRAG

and CP/JE/Wiseco's at:

1.6 bar = 2.7" thou STREET

2.0 bar = 3.0" thou STREET

+2.0bar = 3.3" thou STREET

1.6 bar = 3.8" thou RACE/DRAG

2.0 bar = 4.0" thou RACE/DRAG

+2.0bar = 4.5" thou RACE/DRAG

Edited February 25, 2009 by Sky-Engineering

[The Dan]

Read the piston manufacturers instructions. I always use their figure plus half a thou on top. You can go 1 - 1.5 thou if there is nitrous involved but other than that, stay close to their instructions. Never make up your own clearances because they seem right. HKS run some fairly tight tolerances on some of their stuff but others are loose.

IT ALL COMES DOWN TO THE MATERIAL THE PISTON IS MADE OUT OF.

[The Dan]

And just to add to that, different manufacturers use different clearances measured at different areas on the piston. Some measure clearance from the centre, some from the crown, some from the bottom of the skirt etc. That is why it's important to read their instructions

[R31Nismoid]

Imagine using something as per the specs from the actual maker... What is the world coming too

[proengines]

Imagine using something as per the specs from the actual maker... What is the world coming too

Yeah, what would the manufacturer know about piston clearances?

I run pistons at nominal size, that is, if they are made to suit an 86.5 bore, I run an 86.5 bore. For something with nitrous or really high boost I may run .0005" more. One area worth a look though is ring gaps, damage can be huge if they are too tight. I don't use Venolia pistons though as I just can't cope with the huge clearances they run and the noise when they're cold.