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Hello,

In engine rebuilt i let my "worn" pistons coated by a company. I specified the coating thickness but they built up more than i specified.

They say to buff down the coating. That can easily be done by sanding with a fine grade paper.

But my question is what's the piston taper on diameter?
So if the skirt is ,at 90 degree from the piston pin and at 12mm from the skirt bottem, 93mm, what has it to be on the skirt top just below the rings on diameter?

Is some aditional clearance a good thing with supercharging?

Can't help you with the taper but usually in turbocharged engines they use more clearance all together to allow for more expansion . Bigger piston ring gaps are a good idea for instance.

I DRive at 0.75 bar boost. Don't know the clearance of the 1.8tb and boost level. Maybe ring gap settings and wall clearance is an good indicator.

Anyone knows clearance and standard boost of the 751.8tb.

Liner/piston clearance: .03-.05mm
Max std boost:0.65bar

In my engine, I have std pistons/liners/rings, 8.2:1 CR and I run 1.7bar with the GT2871R turbo, without any problems -of course bigger injectors and different ignition/fuel mapping.
Jim K.

Thanks guys. Can you tell me something about the taper?

I think Greg Gordon is the best person to ask. He used stock pistons for a few of the SC builds. I have not heard of any taper in the discussion. Maybe his Venolia pistons have taper? But if he can run stock pistons, why are you so worried about taper at 0.75 PSI with intercooling? I think Greg's early 2.5 SC ran 5 psi with no intercooling.

0.75 bar (11psi) with high lift cams and normal overlap so a little more air then the stock cams. Normal CR .Stock pistons have also got a little taper i tought. Jutst want it correct.

Sorry 0.75 bar, not 0.75 psi .