I run 9.8:1 comp and was wondering if I could get away with useing 95?

Probably not for too long.
By retarding the spark some, you can overcome most of the detonation problems, but you loose so much power that it negates the reason you have high comp pistons in the first place.

I run 11:1 compression on a 1287cc A series. 15 years on 96 Leaded then 95 Unleaded plus Lead replacement Additive (usually Red line or BP Valvemaster) with no problems.

Cam timing/overlap will come into it.

I run a GX engine with standard compression (10-1) on 91 premium unleaded with no problems but I'm also still using the GX cam. Don't know if US numbers for octane are differant then elsewhere.

Tom

I think it would be fine. 9.8:1 is less than the GX engine's 10:1 compression ratio.

USA 91 octane "Premium" is probably equivalent to:
AUS 96 octane "Super"

Which is equivalent to:
pre-1973 - 96 octane
1973 - 92 octane

It depends on the rating method (MON, RON or (R+M)/2) used at the time and country.

Details: club article: Fuel Requirements

Lead Replacement Additive is not required for Datsun 1200 stock valves and valve seats. They are already engineered for lead-free fuel.


Btw, many of the new 2008 models have 11:1 compression ratio. The 2008 Corvette is 505 HP, yet gets 24 mpg. None of these cars need racing gas or any additives, just the "Premium" fuel available at every Gas Station.