>I have a choice between dished and flat-top pistons for my 1592 engine,
>providing compression ratios of 8.5:1 and 9:1 respectively. I also plan
>to mill my head 050. Around here I can get gas with 96-98 octane
>("Premium").
>
> - Is that high enough?
There are actually 3 piston sets to fit the 1592.
Large dish = low compression export alpine ~(8.0/1)
small dish = high compression alpine ~(9.1/1) MOST COMMON.
Flat top = normal compression (hillman head) ~(8.5/1) or (10.5+/1) using the lower volume alpine alloy head.
The flat tops would seem attractive, but the high compression is very tough on the engine with available fuels. In US speak, a 10/1 engine will need better than 96 octane (R+M)/2.
You will also likely need to do some work on the distributor advance to keep from pinging.
If you mill your head, that will allmost totally disqualify the flat tops, as the above compression figures are at sts bore, and with virgin heads.
Jarrid Gross