To overdrive or not to overdrive, that is the question.

[carrman]

Gentlemen, I am in the process of purchasing a rather nice '68 Newport convertible with a 383. The car has 2.76 rear gears, and rides on 235/75/15 rubber. I will be primarily using this for cruises and the occasional road trip for out of town car shows. I'm contemplating a Gearvendors O/D unit, but I was wondering, will I just be creating an over geared beast, or will it be worthwhile with the setup I'm getting? No, not dreaming here, I can do this is it's worth it for fuel mileage and driveability.

 

[300rag]

You are already running a slightly oversized tire, and a 2.76 rear. At 60mph you are only running at about 1800 RPM. I doubt you will see any significant gain, not enough to get payback in your lifetime unless you are planning on a huge amount of highway cruising. With a 3.23 it is probably still a wash. 3.55 would be worth it.

 

[carrman]

Any long distance cruise I take will involve climbing mountain passes, and our speed limit on the freeways here is 65-70, speeds of 70-75 receive a blind eye from state patrol.

 

[Big_John]

What is the cost versus the savings?

Just to toss some figures up... If you drove 5000 miles a year and got 20% greater fuel mileage. Let's say 15 MPG and $3 a gallon. That's exactly $1000 spent per year in gas. So... it's now 18 MPG and $833 spent in gas per year. You've saved $167 in gas.

So... now let's say your overdrive costs $2000. In 12 years, you would have saved enough gas money to make it worthwhile.

That's figuring high gas prices and 5000 miles annually is high for a collector car. I also think that 20% probably isn't a realistic number and neither is $2000 for cost. Maybe more like 10% and $3000 if you are lucky, but it gives you some food for thought.

Now... Let's take that $2000 and invest it. At 4% compounded annually, you'd make $1200 in 12 years.

 

[carrman]

I'm not so much worried about ROI, but wondering if it will make a difference in economy, driveability, and keeping the revs down so it's quieter. Even if it doesn't pay for itself I wonder if it will make it more pleasant to drive.

 

[CanCritter]

l think you have a pretty good setup as it stands...only way it gets better imo for gas would be a 318

 

[Big_John]

Economy is ROI.

As far as the rest, I'd say no. Quiet the car down with good mufflers/exhaust and sound deadening on the floor and doors. You are already running a tall tire and 2.76 gears. Chances are you would not be happy with the performance.

If you wanted to go to a 3.55 gear and the overdrive, then it might make some sense.

 

[carrman]

Excellent info gentlemen, you've saved me 4 grand...;-) I suspected it might make it an over-geared pig, but I wanted to be sure.

 

[Turboomni]

Who makes these overdrive units? I would think the main benefit is that you are able to have a low rear end ratio for off the line performance and the overdrive so you wouldn't be cursing while on the highway with 500 miles to go.

 

[carrman]

Gearvendors.

 

[Turboomni]

Thanks

 

[polara71]

I plan on going the gear vendors route in a few years.

 

[Turboomni]

I would think it would be very nice to 3.55 posi rear with overdrive. Best of both worlds.

 

[jct]

I would think it would be very nice to 3.55 suregrip rear with overdrive. Best of both worlds.

ftfy

 

[Turboomni]

Well I guess you said fixed this for you or ,,,,

 

[Slantsix]

I dont like Gearvendors, because no lock up converter.
My future plan is 3.91 or 4.1x rear end with A518 (46RH or 47RH) + ultrabell and 27-28" tall tires.

 

[cantflip]

Nice... seems like too much unless you are seriously going to put on miles. I don't mind a little hot rodding or modifying... but I wouldn't see that as the right way for the Twins, jury is out for the NYB, but that is way down the road before I go there.

 

[66/440]

Just my opinion but with the over drive unit I would think the 383 would be out of it's power band/ torque band and lug like crazy.
I would think that the 518 as mentioned above would be the way to go or A&A sells a low gear set for the 727. This set up makes the car think it has a higher numerical gear by a factor of 2 in first gear. So if you have 3.23's then first gear acts like you have 3.91's or your 2.76's become 3.23's. Once it shifts to second then everything is back to normal. I have this setup in a 5K lb. Ramcharger with a small block and it works great!

 

[carrman]

Well just got home from the road trip where I picked her up. As she sits, I turn 2600 RPM at 80 mph. Don't think I need an overdrive!

 

[commando1]

Umm, No you don't