im looking for a gas milage car, i want a crx HF but i cant find one at the price i want thats not butchered

im looking at an 89 CRX SI how much of a difference is the MPG between these cars

and can you make the SI get the HF's MPG if you change somethings?

 

Driving habits can put you damn near 40 with the SI on the highway but if you are really set on increasing it to closer to the HF you can swap out the transmissions.