best compression ratio street build?

For gearing, run 3.23s max. 2.74s would be fine with the small factory tires too. What kills mpg is two things... The rpm at which the engine runs most efficient and the combination of torque convertor and rear axle ratio. A good running 360, with a tight (factory stall) convertor, and 3.23s or higher gearing should get at least 16mpg mixed driving and if it was mine I'd bet I could get 20 out of it with careful tuning.