You can put any engine in it that you want. Will it give you better mileage? It might and then again it might not. My '71 Riviera with me in it and some misc. stuff in the trunk rolled across the scale at 5100 lbs. It takes a certain amount of energy to move a car that size regardless of what engine is pushing it. There are several ways of improving mileage that I would address before trying to change engines. Small engines would also make this car not nearly as fun to drive. The obvious things to check and improve on would be the condition of the engine and it's state of tune. Excellent ring seal and free flowing exhaust and high energy ignition system would be of help. Tire pressure is important. Synthetic lubricants in the rearend can help. But usually the real key to fuel mileage is to slow the cycling rate of the engine. The easiest way to do that is to install an overdrive transmission. Many people underestimate the difference that a few hundred RPM can make. I believe that the '71 came with a 3.23 ratio in the rearend. An overdrive tranny like a 200 4R can drop your cruise RPM by quite a bit. Probably 800 RPM or so. This by itself would add considerably to your mileage. Another thing would be to add a modern fuel injection set up. I think it would be entirely possible to adapt a throttle body set up off of a 454 Chevy big block. There are several aftermarket companies that could assist you with that project. There are many benefits to computer controlled fuel systems. The last point I will bring up that is often overlooked is driving style or habits. The way you drive or where you drive can have a huge effect on your mileage. A lot of city driving will hurt, jackrabbit starts and high speed driving will hurt. A combination of an overdrive tranny swap, crack tuning on a tight engine and improved driving habits will be probably and realistically your best bet at getting closest to your goal. Just dropping in a 350 engine with no changes to the final drive ratio would likely be disappointing from a mileage standpoint. Not to mention from a performance standpoint. 20 mpg is probably doable but remember everything is a trade off. To gain in one area you will have to give up something in another area.
Bookmarks