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Gear Recommendations for the Street

 

Gear Recommendations for the Street

Gearing is much less than an exact science. I definitely don't have any concrete answers for you here. I can only give my thoughts and assumptions, and the directions I'd consider. What you end up doing is up to you only, and either way you go, it should end up fast ('cuz it's an Olds, and that's inherent in the design, right?). The gearing and RPM range of the motor will just dictate when that fastness is most noticed.

What do you want? Good street performance or 1/8 or1/4 mile performance? If you want good street performance gear it so you keep the rpm's in the optimum power range of your motor at your typical cruise mph. If you want straight line performance gear it so that the motor is at the top of the power band at the end of the track. You also want to make sure that your tires can handle the extra torque that a steeper gear will create at the tires.

Running 3.23's, I think it's too steep for a BB and the highway. For racing, though, I'd go a bit steeper. 3.50's might be fine, or 3.73's might be where to shoot for. It will probably all boil down to your engine's redline. If your engine can stay at 8,000 RPM for a while without the mechanical rev limiter (aka rod) taking over, then the steeper gears will be great. The 455's usually don't get that high, though, (without BIG$$$) which should leave you topped before 6000, I'd assume. With 4.11's and that range, I'd guess you'd likely be topped out before the end of the quarter, I'm not sure. My GS with the 3.42's goes through at just over six, usually, but its RPM characteristics are markedly different than the Olds was for me. OTOH, with the really steep gears, you'll top out faster, but you'll have alot more speed keeping you going. You'll only go 100 MPH, but you'll be there alot sooner than the other guy, and he'll still have trouble keeping up, even if he goes through the traps at 120 MPH.

I guess in my eyes, it will depend on what RPM range your motor produces it's torque. If you'll have monster low end torque, but limited high end, then a lower (numerical) gear would probably be better. If you have a lot of power at lower RPM's, you may be happy with a 3.23 to 3.55 gear, and still maintain highway drivability.

If you have nothing but high end power, than the motor will need all the help it can get to get the sled moving, so the 3.73's and higher (numerically) would be a better choice. You need a 3.73 - 3.90 gear in order to get the RPM's up high fast. With 3.90's and 245R60/15's you are turning 3500 RPM at 60 MPH.

If you plan on streeting it, you'd want to modify those numbers a bit, too. I'd have a hard time recommending anything steeper than 3.73's for the street, unless you get an overdrive in there. It'll drive ya nuts on the highway. It looks like with the proper selection of tires, you'll have no problem locking them onto the pavement. The stall and gears will like that.

The rear end gears you pick depend on what you want the car to do. The Dart's 3.55's and high RPM HP isn't too practical for around town (35mph-45mph speed limits), because to enjoy it, it has to be wound out too much, which results in going too fast when really enjoying it. 3.73's or 3.90's would be better suited for this car for power, but it will kill all highway drivability.

I recommend 3.23's highly. I like the good combination of torque at lower rpms, and gas mileage that is acceptable.

If you're running a tall tire (30"+), then you need to take that into account in your gear selection. That 3.50 gear and a 27" tire might be the equivalent of a 3.00 gear with a much taller tire. Figure what RPMs you can live with at highway speed, and then figure out what gears will put you there with your tire and tranny selection (you might have to go with 4.56's to get you there with a tall tire).

Some examples:

1970 Buick GS Stage 1 with a 3:23 posi. Used for 3 years as a family car. The RPMs were not objectionable at all; my wife never complained. The car was always quiet & smooth. I believe that I was turning a little under 3000 RPM (27-2800?) at 70 MPH. Gas mileage was 14 MPG on the highway.

1973 Vista Cruiser w/455 & a 3.23 posi was always very quiet at 70 MPH & (after modifications) got 14 MPG on the highway. The Vista Cruiser was owned for 13 years with 130K miles on it. It was used often for trailering long distances.

1962 Jetfire with a 3.31 diff is just fine as far as highway engine noise. The 1968 442 has a 3.91 posi which is far too noisy at highway speeds. I am trying a 3.42 posi diff in my current 1970 GS, hoping that I will like it. It may be borderline though.

1964 Olds (330/4V) is a 3.36 diff and 215R70/14's: the 3.36's are a good mix of matching the 330's mid range torque and high RPM HP with a drivable car on the freeway. It turns 3,000 at 60 MPH; good passing, 40-70 MPH (kick down 2nd gear) acceleration is a lot of fun.

1969 Dart (built 318/4V) with a 3.55 diff and 225R70/14 tires. The engine is built for high RPM HP, it has nothing below 3000 RPM. The torque comes in at 3,000 RPM, and the the HP come in at 4,000. It turns 3,200 RPM at 60 MPH.

1974 Plymouth Satelitte (440/4V) with a 3.23 diff and 255R60/15 tires: tons of low end torque match the 3.23's at 35 MPH to 90 MPH (with 2 gear changes) quite nicely. The 3.23's allows a kick down to second at 50 MPH. This thing is a monster between 45 MPH and 70 MPH. (ex-cop car).

1970 4-4-2 with the standard 455 (mildly modified) and 3.23 diff. At 60 MPH, I could punch it and instantly pass anything I ever met. Yet the RPM's were comfortably in the 2500-3000 range.

Cutlass with 3.42's and 25 in. tall 235/60/14 tires. It turns about 2700 RPM @ 60 MPH. I like the 3.42's for all around performance and driving ease.

Additional Alternatives

Why compromise? Go with the overdrive transmission and keep the 3.73s! Alternatively, get a Ford 9" and two center sections, one with 3.91's and one with 3.08's. Switch gears for your upcoming driving needs.

I have 3:91's in my H/O and, while the engine tachs out on the freeway, I don't mind the noise (I'm on the far end of that tolerance scale).

Actually, have you really considered the cheapest way out? Get a set of tall rear tires for highway cruising. This will effectively give you a lower numerical rear end for improved highway mileage and reduced rpms. Just swap the shorter tires for strip terrorizing. The only problem is that your speedo will be wrong with at least one of these configurations!

BFG makes some T/As for street trucks which are pretty tall (up to 35" diameter, which obviously won't fit in your wheel well). These are not the off-road tires which most stores stock, so you may have to order them.

[ Thanks to Doug Ahern, Charley Buehner, Bill Culp, Joe Padavano, Dave Wyatt, Bob Barry, Daren for this information ]
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