307 in '81 Century

[rhb1999]

I have a 1981 Buick Century w/the original 231 V6 coupled to an automatic (250?) & limited slip differential 7.5 ring gear? The engine went bad from lack of oil. I also have a 307 Olds roller engine, what would it take to put this engine in this car. The optional V8 ( according to the owners manual) would have been a 265 cu.in. Pontiac, I guess debored 301? Would the motor mount location on the frame have changed? I also would like to put an overdrive in, I understand this would present some crossmember problems? Finally would the differential be strong enough for a V8? Thanks in advance.

[joe_padavano]

You'll need the frame and motor mounts for the 307 in addition to the accessory brackets (which are all different). The frame and motor mounts from any 79-88 G-body with an Olds motor or any 77-90 B-body with an Olds motor will work. Here in Northern VA, the wrecking yards are full of B-body wagons with the Olds 307 and 200-4R OD trans combination. The 200-4R was a common trans in the G-body cars, so if your current crossmember won't work, a junkyard part will be easy to find.

A couple of other things to watch out for: The 307 originally came with a computer controlled carb and distributor. You'll either need to rewire your car and incorporate the ECM or you'll need to install a non-feedback carb and conventional distributor. If the distributor currently on the 307 does not have a vacuum advance canister, it won't work without the computer.

Your rear axle should be the wimpy 7.5" unit that originally came into the world under the Vega. This same axle was standard equipment under all G-body cars with 307s except for the 84-87 Hurst/Olds and 442s, which got the 8.5" axle. Either learn to live with your 7.5" axle or expect to pay big bucks for the rare 8.5" unit or an aftermarket axle. The 7.5 will live if you don't plan to regularly drag race the car.

If your 307 has 7A heads with the tiny exhaust ports, be aware that it uses special exhaust gaskets different from those used on every other Olds V8. Regular Olds exhaust gaskets won't seal and will leak. Don't ask me how I know this....

With the right parts, this is a drop-in. Good luck.