Rear gear change

[Tweek]

I'm looking for some imput on changing the ring and pinion in my 80 C3. I'm thinking the 3.54, or 3.73, but I would hate to change to the 3.73's and find it is geared to low for my turbo 350 tranny! Anyone make the change? Whats your likes and dislikes on any of the combo's. How about RPM's, what could I expect from the change. Whats a good price on a ring and pinion, and any vendors I could look at?

thanks Ron

 

[GerryLP]

Ron,

This calculator could give you an idea: http://www.quiknet.com/~ke6vut/rpmcalc.html

I paid $302.00 (shipping included) for a 3.31 DANA ring and pinions (and bearings, seals, and minor hardware) from Drivetrain Specialists 1-800-216-1632 (Las Vegas, Nevada). At the time, they were the best price I had found (June 2001), and they were prompt. The rear end specialist I took the pumpkin to had no problems with its quality.

I am not sure if the 1980 and 1981 third members are identical, but the 1981 pumkin requires a spreader tool which I could not get nor rent, so I had a specialist do it for me. Since I had removed the entire rear end components, I was able to just drop-off the pumkin for the gear swap. Expect to pay between $100 - $150 dollars if you do it the same way I did. He even magna fluxed the housing and inspected it for cracks and the like.

Because of the higher RPM on the engine, I noticed the engine noise, but that was because I was used to hearing a stock L81 at about 2,000 RPM. The motor in used today has more horsepower capacity and the headders make it sound louder (seemingly). Nevertheless, it helps me take advantage of the horsepower band more efficiently driving around town. This coming May will be my first long trip on the car since the gear swap, and I don't know if will mind or notice the higher sound levels.

I could be wrong, but as far as I know, it won't cause problems with the tranny shift-points. In my experience, shift-point changes are required for high-stall converters and to match the engine's RPM powerband more efficiently.

Don't worry though. If one likes quietness (and besides, everyone appreciates better milage), then the answer is to swap-in a 2004r tranny (4 speed auto) or 700r4. Many here in this forum can share with you information about it whenever you are ready.

 

[Glensgages]

How about RPM's, what could I expect from the change?

Assuming a non-lock/up THM350 and a 27" tire (typical of 255/60R15), at 65 MPH, you'd be turning 3150 RPMs w/ 3.54s, and 3330 RPMs w/ 3.73s.

Whats a good price on a ring and pinion, and any vendors I could look at?

I got a set of 3.73:1 gears (PRECISION GEARS) in August of '03 from:
'Ronnie' @ "Powertrain", on Long Island (N.Y.C.) {1-631-589-7020}, for $125 less S&H. He had several sets of our (Dana-44) gear-sets, and can get more, in several ring/pinion ratios.

I had a long-time buddy, with over 30 years of experience with Corvettes, do the install/set-up. My cost, including miscellaneous parts, and the parts ($75) & his labor to recalibrate the speedo, was $425.

My stock Cross-Fire previously ran 15-seventies @ 86 MPH with a 700R4 & 2.87:1 gears, and the only time I checked mileage, it got 23+ MPG on a 230+ mile trip.
After the gear-swap, I got 17+ MPG (with-out even TRYING!!!) on a 430+ mile trip over back-roads & two-lanes, and ran a best of 15.004 @ 90.89 MPH, and I now 'trap' @ 4300 RPM in 3rd Gear.

My '82 is not a daily-driver, and is used for 'nights-out' and 'weekend-rides', as-well-as the ocassional trip to the strip.
If mileage is not a concern of yours, or a vast-majority of your driving is in-town, consider the 3.73s; otherwise, the 3.54s are the way to go...

Just my $.02 worth...

 

[Tweek]

Thanks for the info guys, I'm still in a toss up over the 3.54, or 3.73's though. I guess I will just have to pick one and try it.

 

[WayneLBurnham]

I put in the 3.73 rear from Tom's Differentials about a year ago. I did this primarily because I only bought the heap to build and put in a monster super deck stroker big block that would shred the standard 10 bolt, and intended to immediately put in a Gear Vendors OD. 3.73 was the highest ratio TD offers, so I was stuck with those.

The car would hit 155 according to the speedometer at about 6K (people here believe that was actually 137-142, according to my tire size). Now, with an accurately set Nordskog electronic speedometer (calibrated on measured miles, rather than computation of driveline components) I am doing 4kRPM at 82 MPH, and have not exceeded 125 since, which was just over 6K. My gas mileage decreased slightly, but has never been above 10-11MPG, despite the weak little baby small block - but I have an oversized AFB carb, excellent big exhausts and drive like an idiot.

I would have preferred a 3.54 - even with a coming overdrive. The change from 3.08's to 3.73's DID give the car an enormous boost in take off, but an equally enormous penalty in top speed, engine wear and heating stress (mine heats up over 4200 sustained, which is where it often lives).

The acceleration is nice, but if I had no OD, I would hesitate on the 3.73's unless I didn't do a lot of highway driving.