been looking at pistons for the turbo unit.
the standard turbo pistons are 9.5:1 compression ratio
it would appear that the standard head volume and piston bowl area at 9.5:1 = about
on a 172 at 11:1 it is about
so, apx 9 cc is in the piston bowl.
it would appear the standard turbo pistons can be used to obtain about 9:1 by removing 4 cc from the piston bowl (lathe n polish).. or by increasing the head volume by 4ccs - might be difficult......
to get 8.75:1 would need another 5.5 ccs removing from somewhere..
I might decide to chop a turbo piston in half to examin the thickness of the areas that I intend to remove metal from.
hopefully a picture later of half a piston
so, bottom line, might be able to get away with standard renault parts.
will probably go this way for the first engine and only consider forged pistons after I see the results.
from an engine remanufacturer, these pistons will probably be very inexpensive.
Other breaking news
the inlet and exhault valves on the turbo head are exactly the same as a 172 !.. the porting on the 172 is marginal and in the are of the intake port (head inlet) only.
an interesting theoreticall hybrind would use the 172 inlet cam with vvt and the turbo exhaust cam with its greater duration.