i have a question about piston size choice for my YB block my block is still on its standard bore and i know a std bore is 90.82mm but it's in for a rebuild so i want to give it the lightest overbore i can so a .25 i hope will do me so my question is in the link below there a wossner pistons for sale and all sizes available am i right in thinking a 90mm piston is std size and the 90.25 is the size im after but i was also told that high performance pistons has a tighter clearance than standard so what size do i need

http://www.ebay.co.uk/itm/WOSSNER-FO...item20b69dd86a

 

i not sure high performance pistons have a tighter clearance, why would you? Friction would increase...it could be to reduce blowby, but your choice of rings and breather system on a high performance option would cover this...

 

I've bought a spare bottom End for my yb lump. It's been rebored but the pistons are std.I asked the question, what is the maximum bored size for std pistons. I still need an answer in that so I'm interested in this thread.

 

im no engine builder but i heard that higher grade alloy in high performance pistons that handles the heat better by not expanding as much as a standard piston so a tighter clearance can be achieved that could be bullocks but i did read that somewhere

 

dont buy wosner,buy geniune cosworth pistons!!!

 

The Wossner forged have bigger clearance than standard as i've had these in my Cosworth
The Wossner have piston slap and when the engine is cold it sounds like a tractor on a hot engine it's ok and my bores were fine after 30000km.
Now changed to Cosworth forged and they're are very quiet and very little oil consumption
Best to meassure the bores, my largest bore was 90,95mm so +0,13 over standard and i used the +0,50 Cosworth forged pistons

 

Wiseco do 91mm 91.5mm & 92mm sizes