Being 'foreign' I would have to nominate a foreign engine - BMC / BL's A-series engine - 803-1275cc. The one used in the class Mini Coopers, the MG Midget / AH Sprite and hundreds of other cars.
I had the 64 MPG car in this advert
back in the day - 998cc, 46 bhp, 82 mph and 0-60 officially in 18.2 seconds.
Needless to say it didn't manage 64 every day as I was 17 and stupid, but I did have the odd tank of 50+ mpg, which was very useful as it only had a small 5.5 gallon fuel tank. The developments that gave it the potential for 60+ were simple - high compression and a long (for the day) top gear of 18.6 mph/1000 rpm.
It also had the superbly economical single SU HIF carb - and I know that people who remember the unreliable setups of MGs of the 50s and 60s will be curing that statement - but this version did away with the side float chamber and actually remained in tune for more than the time it took to drive away from the garage.
The A-series was efficient enough to remain in production for a long long time - 1952 to 2000+ and whenever a replacement came along it was always just "good enough" to not be replaced even though it was a pushrod OHV design in the days of DOHC/16v units. Honda had been making VTECs for 2 decades by the time it was phased out.
It wasn't light (Iron block / head) and it had inefficient siamese ports but the combustion chamber design was very effective, plus being a long stroke unit it was good for low and mid range torque and made better use of the fuel it did burn. It also only had 3 main bearings so it didn't have a lot of friction lossed but at the expense of reliability at higher engine speeds - but then again did I mention the siamese ports ?
Later ones in the run-out classic Minis actually got port FI, ECUs and catalysts as well as electric cooling (for noise reasons) but with the low gearing of the Mini they weren't going to be especially good at FE.