I'm rebuilding my type r block with Wiseco 81.50 mm. ceramic coated pistons for a roadrace application.
The standard Wiseco's have a recommended piston to cylinder wall clearance of 0.0030-0.0033.
Should the ceramic coated pistons run tighter due to the less thermal expansion?


Modified by paulITR at 12:18 PM 3/27/2007

 

nope

 

Can you explain why?

 

basicly the ceramic coating on the tops of the pistons will burn off over time, so if you run it tighter it will be fine till the coating burns off, then its going to be too tight. we typically run the pistons a little looser than that, especially for a RR application where the stuff is going to see alot of abuse. the moly coating on the sides will wear off very quickly as well, so its best to build the motor as if those coatings arent there.

 

On a RR app, I would go with .0033 to .0035. If it were a drag race motor only, I would go with .0030. When RRing the pistons will see heat for longer periods of time and will expand more than anticipated some times...

 

so any wiseco pistons that are skirt coated will be fine running .0033 piston-wall clearence??

 

no. many times with the bigger the bore you will need a greater p to w clearance.

 

Now i'm confused about how much p/w clearance to set since the sheet which came with the pistons recommendes 0.0025 for the ceramic coated.

Is that a clearance that works until the coating burns off only?
And how long is the coating suppose to last?

 

just run on the loose side of the spec sheet if you are gonna road race, the more heat the more expansion...

 

so if the coatingon the sides of the pistons wear off then why do they put it there in the first place? waqt is that coating suppose to do?

 

The Wiseco spec sheet reports the .0025 clearance only without separate between a drag or different application.
It's very tight compared to the clearance suggested in this discussion but if i want to give credence to Wiseco it should be fine at least till the coating burns off.
But how many miles will it last?
I'm scratching my head.......

 

I'm in for the same dilema for road race too.

I got some wiseco 81mm for a friends B16A and spec sheet says the same 0.0025. But we are going for 0.003 min as this engine will be living in 7000-9500rpm most of the time.

I got another set wiseco 85mm that calls for 0.004 which is pretty loose to me. This set we are also deciding to go for wiseco spec at 0.004 or a loose 0.0045.

Anyone?

 

bigger pistons expand more..

but for most 84-85mm stuff we run 4 to 5 thou depending on how much power its gona be making.

 

Anyone?