Give me some help here guys, I just got my 9.5:1 pistons through GQ626, what are some +s to having them coated? and about what is the cost?

 

There's a couple of differt types you can do. The main ones are coating the piston skirt which helps stop cylinder wall scarring and scratching. The Evo actually uses this from the factory. You can also coat the tops of the pistons with a ceramic type film that helps to contain heat to the combustion chamber and helps to stop it from being transfered to the piston. I think they also have some coating for the underside that helps to disapate (sp?) heat. Hope that helps!

 

AEBS uses Ross pistons, and thats who I have used in the past for my S2000 turbo blocks. They have a coating which is called "bannodizing" which is a hard annodizing used for very high cylinder pressures. This makes the piston extremely durable. They use this coating for top fuel dragsters and "they say it won't run with out it!".

Anyways, if you get your pistons coated, then you need to account for the thickness of the coating when you size everything out. Ross does this when they engineer their pistons. I think it takes up 1 or 2 thousandths.

If you go with a coating, this is what I would do! (rather, this IS what I do)

Chris

 

Just as a side note, it's not just the Evo's 4G63. The stock pistons in the VQ35DE also have moly-coated skirts.

 

Yes and a side note: the typicall Poly-Moly skirt coating actually allows the machinist to "reduce" the bore diameter, contrary to what it might seem at first look. The reason for this is that the typical extra clearance to used to avoid possible seizing and scarring of the skirt in the bore during cold start up and rapid piston to bore thermal expansion. The PM coating is mostly absorbed into to the molecular surface of the skirt and reduces friction during this critical expansion cycleing. So, this allows the machinist to reduce bore diameter ~.001" - .002 ".

 

What non-issues would coating help solve. I'm not aware of any significant wear problem with the skirts and it sure isn't going to be any protection from detonation.

 

Since the PM coating on the skirts allows the bores to be tightened a little, it reduce noise (slap) and wear. The OEM does this to improve emissions (tighter squish volume) and again to protect from cylinder scuffing over the long haul by abusive owners. Some owners start their car , and romp on it regularly way before complete warm up. On these engines , scuffing can defnatley reduce the lifspan of the engine and lead to pre-mature ring leakage.