Pistons, Clearances, Compression Ratios and Fuel

[apardal]

Hi again!

Sorry for the bunch of topics regarding similar subjects, but each one has new different questions...

I've just bought a set of wiseco pistons and I'll be receiving them next week, I hope. Ready to come is also some ARP bolts and studs for conrod, crank and flywheel. Going to use new OEM head bolts.

Crankshaft is going to be balanced along with the flywheel, pressure plate and crank pulley.

Block will be bored to fit the 81.5mm wiseco forged pistons.

OEM pistons broke after some 100k miles and this is how they looked like.





Engine setup was HKS 264/264 8.1mm lift cams, tsudo header and complete exhaust with 2.25", stock intake manifold with monsterflow air filter, ported head with polished exhaust, bronze valve guides, 3 angle valve job, 0.6mm decked head, 0.1mm decked block and 0.5mm TRD head gasket. Tuned ECU to raise rev limit at around ~8400rpm. I also have a piggy back (Apexi SAFC) ready to assemble if my wideband O2 sensor starts reading lean AFR's.

With this in mind, I googled a compression ratio calculator and found this one:

http://www.csgnetwork.com/compcalc.html

I measured my cylinder chamber volume and it is around 34cc's (not to precise, but helps to have an idea.

With 5.9 cc piston dome volume and 0.76mm deck clearance from Wiseco product sheet, I calculated 11.9:1 CR with a 1mm (minus 0.1mm for block skim) HKS metal head gasket that has 82mm of bore.

I really don't know if this will bring me piston to head clearance problems, might have to check on that when pistons arrive but hoping it will all be ok, I'm a little worried that 11.9 might be a little too much compression.

What do you guys think, and what fuel will cope with this new compression? In Portugal, we have available 95, 98 and 100 octane at almost all gas stations. Or would you just put a higher head gasket (1.6mm for example) and shave the head 0.1-0.3mm?

Best regards