CJG

ok. Putting a 455 .030 over, J heads with 3 angle valve job and new stainless valves, high comp Pistons, comp 278 cam, hooker comp headers, torker intake with Holley 850 double pumper carb, and a stage 2 built TH350 with a 2800 stall converter. The car will be driven 80% on 2 lane highway about 12 miles each way and the occasional longer road trip of 30-60 miles to a car show and maybe once or twice a year to the 1/8 mike drag strip just for fun. What rear ratio do you think we should go without? It has stock rear as far as I know now, 71 cutlass 10 bolt, maybe .278's? We will be putting a posi unit in it as well.

don71

My vote 3.23 might also consider 3.42

CJG

I was thinking 3.42 but wasn't sure how much gas mileage may increase with the 3.23. If it's only a mike or two per gallon of stock with 3.42 just for the added fun factor.

Fun71

What rear tires do you have? The tire diameter will have a HUGE impact on overall gear ratio.

CJG

Honestly I'm not sure....I think 255-70r15 or very similar.

CJG

Nope, way off lol. 275-60r15

don71

Like Kenneth said, tire sizes are important. Consider your expectations carefully. Mileage is going to fall somewhere in between. Don't let compromises get in the way of enjoying the car..like the price of gas getting in the way of having fun. Just saying...

CJG

I'm thinking 3.08 or 3.23 is where we probably need to be.

Fun71

OK, that's a 28" tall tire. Check the web for RPM calculators and see what your engine speed would be with various gear ratios, then select the ratio that you are comfortable with.

My car has 3.23 rear gears and for a long time I had short 245-60-14 tires (~25" tall) I was OK with turning 3200 RPM on the highway. This was an effective 3.73 ratio with 28" tall tires. Some folks are very uncomfortable with that RPM and others are OK with it. It all comes down to your comfort level.

CJG

Ok will check it out. I would rather be in the neighborhood of 2500-2800 rpm at 60ish mph. Thanks!