tnwheelgunner

Hello everybody, im wanting to ditch the 2.73s in my 1977 cutlass. I has a 10 bolt and im pretty sure its a 8.5. its original to the car. my main questions are how do I know its just a 8.5 10 bolt because ive read somewhere that oldsmobiles had some inbred 12 bolt with a 10 bolt cover or something like that. Also whats a good gear for good eighth mile performance with limited street use? speed limit to the track varies between 45-55mph. Its a stock olds 350 with headers,2.5 inch duals, and a quadrajet with some tuning done on it and a th350 stock converter. thanks in advance.

2blu442

If you don't get a reply contact member named monzaz. He's one of the resident experts with rear differentials used in these cars.

John

Fun71

The O-Type 12 bolt rear would not fit into your era car without major modifications, so you likely have the corporate 8.5" 10 bolt rear.

monzaz

10 bolt 8.5 will be the better rear to have as it can have parts purchased the other 10 bolt cover 12 bolt gut HD rear that came in some of the A-bodies will not have any gears available.
Ok onto the 1/8 mile deal. You say LIMITED STREET... Meaning not much at all? You will need tire size d you want to use all of the 3 speeds of your trans in full? Your car is NO light weight and you will need some serious gears and slicks to get off the line to give you the best ETs

YOU really need to figure out what you want your car to do for you and where it will spend most of its time.

4.56 4.88 Will be great 1/8" gears BUT very limited for street driving... nasty amount of RPM when driving. YOU NEED A high stall converter to do proper track launches. 2500 at the very least if your cam is stock -

You will need a posi to get both wheel working for you on traction.

Again it is your call how far you want the car to be track bound compared to street bound. Jim

J D RAce