This B210 was brought home from the local parts yard, missing the engine upper half and a few other pieces, but mostly there. After a couple years of tinkering, I have my coupe running. Needs rust repair here and there, and paint someday.
Found a new A12 short block on ebay, added a A14 mpg cylinder head (casting 990) and exhaust manifold, and 1200 intake manifold. decked the block for pistons 0.006 inch above deck. Milled the head for 24cc combustion chamber volume. Works out to 10.0:1 compression with quench clearance of 0.035 inch. Runs great on regular gas with point ignition.
Running Hitachi carb from 1972 A12 with all original jetting. 4 speed transmission and 3.89 axle ratio are original 1976 parts in great condition. Car has heavy US 5 mph bumpers. No weight removal program so far.
Average fuel economy for first run was 43 mpg running 175-70R13 tires at 41 psi. Speed was 60 mph for 110 miles with 1900 foot total vertical rise/fall from start to finish. Outside temp was -2 c with some wind.
Car could be driven across Australia tomorrow no problem. I would love to be there.
Future ideas include 5 speed trany, electronic ignition, and maybe taller axle ratio, but engine works pretty hard as it is to get the car going...so axle ratio change maybe poor idea. I'll post pics at some point. Cheers.

Yes, that sounds about right. With the higher compression and careful driving 43 mpg sounds spot on. After you add the 5-speed it should top 50 mpg.

43 mpg first time out. photos not coming thru.

US gallons?
neg deck heights and min piston to head are the go!
go for a killer ign system too

Yes, US gallons. And measured with Datsun Speedometer, which is typically 5-10% too high. So you may have gotten a real 40mpg... if tires are the correct size. And if the tank actually filled to the exact same level as before.

5-speed B210s -- when new -- got between 45-50 mph depending on year (not the California models) ... 4-speed models, just over 40.

what octane fuel r u running? I find with high compression a series 91 octane pings a lot, 95 ok and 98 smooth and sweet and easily pays for itself with better mpg.

also if u r going for best mpg I think your speeds a bit high, slow down to 50mph or 80kmh, assuming u r not holding up traffic...

if you run high comp then high octane fuel is more economical
if you dont its just expensive exhaust gas
compression= economy (if you can light it)
dazza

Yes, US gallons. I'm running cheap old regular gas, maybe 85 octane. I live at 5000 foot elevation so can get away with higher compression without ping. I set the piston to head quench clearance close to help avoid detonation, and it works. Lets you run higher compression on lower grade fuel.
Mileage run distance was measured off the road map, not the speedo. Tank was topped off to the cap using same pump at the station, so distance and fuel economy is accurate.
Slowing down probably a good idea, but everyone here is in a big hurry. I was lucky to get away with 60 mph. I should try slower as you suggest, and drop in the electronic ignition. Thanks. I'll keep you posted.