venolia piston big bore

[snap124]

I happened to come across a big bore top end. I have an extra motor that I had plans on rebuilding.
I got a nice set of heads ported and polished with o/s valves
cylinders with 80 mm over bore
Here is the problem, the pistons I have are a set of venolia 12.5:1 pistons with a 22mm wrist pin.The cam I got in this deal is a megacycle 250 30 -34 tooth.
The motor I have to rebuild is a 447 motor .I can run the pistons if I swap out my rods for 256 rods, not rocket surgery .I can press off my cam pulley and swap it out.
I work in a cnc machine shop as a set up tec., so I can shave these slugs down.
How much wall thickness do I need on the crowns. I have some drawings that are of a venolia 10:1 cr piston . I used my calipers and they are the same dim. as the 10:1 piston save for the crown. I think the drawing has a crown that is .325 have to look. The cam on the other hand is pretty rowdy .I am thinking this would be a little much for the street.
I need some input on what you guys think. rebuilding a stock motor is paint buy numbers, building a motor is picaso shit.

 

[TwoManyXS1Bs]

There's a 256/447 interchangeability minefield when considering cylinders and camchain tensioners.
Are your cylinders the early 4-hole, or 6-hole with narrow tunnel, that use the type "A" or "B" tensioners?

Some background on this:

http://www.xs650.com/forum/showthread.php?t=32147
http://www.xs650.com/forum/showthread.php?t=38674
http://www.xs650.com/forum/showthread.php?t=38840
http://www.xs650.com/forum/showthread.php?t=1204

 

[Jack]

You want a minimum of .180 dome thickness for any piston and for 10 to 1 compression you want 43 to 45 CC combustion chamber with piston dome height of at least.400 minimum to play with. The normal combustion chamber volume CCs runs between 62 to 63Ccs with the piston dome height bringing the C/C ccs down to 43CCs. Craig Weeks(650 performance) is more familiar with venolia pistons.

 

[snap124]

thx. guys, I am gonna do some research and give this some more thought .I did decide to keep the heads . They will work out for me if nothing else. I think cutting these pistons would be a bad move. the cam, I think it is a little much. The jugs are 6 hole, not sure on which style but ,I have a running motor and time to sort it all out .