I am looking at installing a high compression piston for my DS650. The stock compression ratio is 9.6:1. There are two pistons available, one has an 11:1 compression ratio and the other has a 12:1 compression ratio. Is 12:1 too high for 92 octane street gas? If so, what fuel do you use and how much does it cost? Are there jetting changes needed if use non-street fuel?

 

I was told for my 440EX, an 11:1 piston required race gas.

 

I'd stick with the 11:1. My built 400cc (bored, stroked, cammed, ported, valved) runs a 10.25:1 and will ping on 89 reg unleaded but is fine on 92 or more octane. Trick race fuel can get pricey at $5 a gallon.

Another thing I've noticed is the Warrior electric starter has trouble sometimes turning the high compression and tight new motor over.
Starting may become an issue with a 12:1.