Over Drive

Buster-I have wondered about this also. At 65 mph my Cobra Malibu 37' with a 460 and C6 is turning 3600 RPM. Way to high in my opinion. Furthermore, when I kick it into neutral running 60 mph it will coast forever. it seems as if the motor is working against itself. I've also considered changing the rear axle ratio. I think I read where mine has around a 5.00:1 ratio. As far as "if it would have been better to have an overdrive don't you think the factory would have done it?" yes, the next year the factory put an overdrive behind the 460 as did GM somewhere in that time frame. RPM's went way down and fuel mileage went up.

Maybe, maybe not, depending on where your gearing puts you on the torque curve for the speeds you run, and whether HP is adequate at the OD rpm and highway speed. It might even take a gearing change to optimize for the OD ratio.

The idea is right, have more gears to work with, but new cars with 6-8 speeds also have a fly by wire and a computer optimizing gears and throttle to your demands at the accelerator. With a TH and add on UD/OD you might have 5-6 gears to work with, some of them very close to each other, but you'd still lack the information needed to pick the right gear.

Will it pay? Maybe if you get it right and can run 500,000 to a couple million miles to save enough on fuel to pay for it.

Just remember Matt Colie, beside every good engineer there stands a great mechanic

Since you ar e located out West, I assume that you will be driving where there are hills/mountains. Chances are you will not be using the OD that much, except on flat level roads, especially if you are towing.
As mentioned, I doubt if you will save enough money in fuel to pay for the unit and the installation.

I always wondered about the over/under drives. I keep getting ads wanting me to buy them. Yes, I do know that you can have to high of a gear that will lug down a motor and cause it to use more fuel. This could be good for smaller rigs like the 25 to 28 footers. I just couldn't find anyone talking about it that wasn't someone wanting to sell them. And we all know that they will not tell you the downside of it. I would like to have heard from someone who has it and how it worked out. Thank for answering my question.

I would pass. The real question would be how many miles of traveling would it take and potential fuel savings before the unit is paid for. Myself as a weekend/summer vacation camper racking up may be 6K miles a year I'm not sure if I would ever see the savings.

so hows driving the brick going. happy-camping

I would like you to temper my response with the fact that I was a multi-decade driveline engineer. There is way too little information provided to even do more than scrug. There are so many variables that even if you told me everything you do know, I could not provide a more definitive answer. So, as the consensus has said,

No.

Matt

If it was helpful, don't you think the manufacturer would have added it??? Just asking.

Buster52 wrote:
Would it be worth having it done?

no