Real cost of the Retrofit Overdrive

by jerry46765 Fri Jun 21, 2013 1:17 pm

Everyone keeps talking about putting an overdrive transmission into an old car.
I just ran the numbers, and I don't think it makes any sense to do this type of retrofit.

Here is the cost analysis of retrofitting of an overdrive transmission in a vintage car.

For sake of argument, let’s say the cost of the gearbox and install is $1500.

The driving habits of a vintage car is either a daily driver or weekend cruiser.
For a daily driver, let’s say you put 15,000 miles on the car per year.
And 40% of your driving is highway driving, (15000x.40) or 6000 miles per year.
An overdrive will reduce engine speed by 30% (from 1 to .70).
Let’s say highway driving is 17 mpg currently and will improve to 22 mpg with the overdrive.
You will use (6000/17) 353 gallons of gas with the standard transmission, (6000/22) 273 gallons with overdrive, and save 80 gallons per year with new transmission.
At $3.65 per gallon, that is a savings of $292 per year (80x3.65).

It will take you (1500/292) 5.14 years to payoff the transmission before you begin see any real savings from the overdrive.

If you have a casual weekend driver and you drive 6000 miles per year, and drive the same 40% on highway (6000x.40) will be 2400 miles per year.
At 17mpg (2400/17) 141 gallons and at 22 mpg (2400/22) 109 gallons, so it will yield a savings of 32 gallons per year.
At $3.65 /gallon (3.65x32) will be a $116.80 savings per year.

To pay off the gearbox, (1500/116.80) will take 12.8 years….

So does this make any sense?
It will take nearly 13 years to pay off the transmission retrofit with the fuel savings benefit gained from the overdrive.
By the 13th year, you will have added (13x6000) 78,000 miles on the car, most of us will be due for a complete driveline rebuild.

Let your engine rev on the freeway, and enjoy the old car for what it is, an old car.

Thanks –

Jerry

by driveit Fri Jun 21, 2013 1:21 pm

hmm. I just posted a question about peoples opinion on this subject as I just found a 700R4 for 450$. Seems like I am getting about 12 mpg right now may be a little better, not sure!

...

by jerry46765 Fri Jun 21, 2013 2:26 pm

This topic comes up every summer when people have to buy gas for their car.

If you are having transmission issues, sure spend some more money and upgrade to overdrive. Aren't the TH350 and 400s bulletproof?

And aren't there a million other things to spend that $475 on with an old car?

by thatfnthing Fri Jun 21, 2013 2:44 pm

Some other reasons for doing it are reducing wear and tear on the engine, fewer oil changes, lower emissions, etc.

If you're going to go all cost-benefit-analysis on it, you can prove that essentially any modification is not worth the money/time/effort.

Not to mention sucking all the fun out of it.

by thatfnthing Fri Jun 21, 2013 2:59 pm

jerry46765 wrote:For a daily driver, let’s say you put 15,000 miles on the car per year.
And 40% of your driving is highway driving, (15000x.40) or 6000 miles per year.
An overdrive will reduce engine speed by 30% (from 1 to .70).
Let’s say highway driving is 17 mpg currently and will improve to 22 mpg with the overdrive.
You will use (6000/17) 353 gallons of gas with the standard transmission, (6000/22) 273 gallons with overdrive, and save 80 gallons per year with new transmission.
At $3.65 per gallon, that is a savings of $292 per year (80x3.65).

And you have a couple faulty assumptions here.

First, some people pay a lot more than $3.65 per gallon.

Second, overdrive is in play by 40 mph, so it's not just highway driving -- it's most of your driving.

Third, savings is a percent of what you're getting now, and as such has greater impact if you're getting driveit's 12 mpg now versus your example of 17 mpg. You went from 17 to 22, which is a 30% increase. So using your math above a 30% improvement over driveit's current 12 mpg gets him to 15.6 mpg, which yields him a savings then of 115 gallons per year.

by driveit Fri Jun 21, 2013 3:27 pm

Mind blown... I need more gears and a diet!!! The second is for me and my car! lol.

I guess if I lost weight the car would too. Motivation!

by jerry46765 Fri Jun 21, 2013 4:24 pm

Modifying your car, such as rebuilding an engine or doing body work is different than retrofitting an overdrive. You don't install an overdrive to get more top speed, or because chicks dig overdrives. You install it because you have the 'preceived notion' of saving money on gas by getting better mileage.

But in reality the cost doesn't outweigh the benifit.

So you are going to spend $5 to save a nickel...

by jerry46765 Fri Jun 21, 2013 4:33 pm

thatfnthing wrote:
jerry46765 wrote:For a daily driver, let’s say you put 15,000 miles on the car per year.
And 40% of your driving is highway driving, (15000x.40) or 6000 miles per year.
An overdrive will reduce engine speed by 30% (from 1 to .70).
Let’s say highway driving is 17 mpg currently and will improve to 22 mpg with the overdrive.
You will use (6000/17) 353 gallons of gas with the standard transmission, (6000/22) 273 gallons with overdrive, and save 80 gallons per year with new transmission.
At $3.65 per gallon, that is a savings of $292 per year (80x3.65).

And you have a couple faulty assumptions here.

First, some people pay a lot more than $3.65 per gallon.

Second, overdrive is in play by 40 mph, so it's not just highway driving -- it's most of your driving.

Third, savings is a percent of what you're getting now, and as such has greater impact if you're getting driveit's 12 mpg now versus your example of 17 mpg. You went from 17 to 22, which is a 30% increase. So using your math above a 30% improvement over driveit's current 12 mpg gets him to 15.6 mpg, which yields him a savings then of 115 gallons per year.

These are purely examples. Your experience may vary based on your market conditions.

But the math is sound, so you can input any values to suit your application.

And if you can mathmatically make it work, post it up.

Thanks -

by thatfnthing Fri Jun 21, 2013 5:19 pm

jerry46765 wrote:Modifying your car, such as rebuilding an engine or doing body work is different than retrofitting an overdrive. You don't install an overdrive to get more top speed, or because chicks dig overdrives. You install it because you have the 'preceived notion' of saving money on gas by getting better mileage.

But in reality the cost doesn't outweigh the benifit.

So you are going to spend $5 to save a nickel...

I got mine to have larger rear gears and the attendant acceleration boost without having a 3000 RPM screamer on the highway.

While I can't speak for everyone, I would expect that this is the primary reason most people retrofit them. Certainly if any of the car rags are to be believed.

Overall better mileage was just a bonus. Smile

by dynchel Fri Jun 21, 2013 7:45 pm

The "best of both worlds" always appealed to me. Steep gears with low engine rpm's. But I had my th350 performance rebuilt back when I had money (before wife and kids) so no new (different) trans for me. Sad

by JB2wheeler Fri Jun 21, 2013 8:45 pm

thatfnthing wrote:
jerry46765 wrote:
So you are going to spend $5 to save a nickel...
I got mine to have larger rear gears and the attendant acceleration boost without having a 3000 RPM screamer on the highway.

While I can't speak for everyone, I would expect that this is the primary reason most people retrofit them. Certainly if any of the car rags are to be believed.

Overall better mileage was just a bonus. ---I agree 100%. JB

by ant7377 Fri Jun 21, 2013 11:44 pm

I think a good alternative is build a huge motor go all out with what ever you are building,huge cubes using after market block Motown or Big M block but with reasonable compression.Then run like a 3.08 rear and you wont need overdrive just keep your th 350 or 400.

by 77mali Sat Jun 22, 2013 7:07 am

I can see where the math (in terms of monetary savings) makes little sense if it's purely a good weather driver, cruise nights, etc.

12 mpg sucks so if you drive alot, that's a big chunk of cash that I'm sure you'd rather spend elsewhere if possible.

Another thought would be to get a Muncie 4 speed manual & swap the rear end to the appropriate gears.

by pila Sat Jun 22, 2013 7:14 am

Of course, the ideal scenario is to have a daily driver that gets decent mileage, and a week-end toy that eats rear tires & gas, and is a blast to drive ! Very Happy

(my Malibu gets 9 MPG ,while my Chevy pickup gets 18 )

If we were really concerned about the cost of what we do with these older cars, we would be driving ricers ! Very Happy

by 77mali Sat Jun 22, 2013 7:59 am

Like this?????
Real cost of the Retrofit Overdrive 38978310

Silly Ricers, useless wings are for penguins!

by ant7377 Sat Jun 22, 2013 11:24 pm

Paul,you mean you want that ^^^^^ for a weekend car? Why the hell would you want that? Maybe for a winter car or something,I thought you liked American cars,something wrong with you now?! .

by 77mali Sat Jun 22, 2013 11:38 pm

You been hitting the sauce again Anthony? Drinking Party

I detest Asian cars.

"""Like this?????
Real cost of the Retrofit Overdrive 38978310

Silly Ricers, useless wings are for penguins!"""

by ant7377 Sun Jun 23, 2013 8:10 am

Ha! I think that photo is from Limerock Park . Its got CT plates on it. CT isnt far from MA where Paul lives--must be his!

by 77mali Sun Jun 23, 2013 8:17 am

Oh YES! My secret 1.5L 102 hp front wheel drive, giant "whale-tale" winged Honda.
Thank you Anthony for exposing the truth.

There's nothing like stomping on the gas and hearing the pur of a retarded kitty-cat.
BTW, Lime Rock is WWWWWWWAY closer to NY than Boston. Suspect

by bigredlaguna Mon Jun 24, 2013 1:04 am

When did car guys ever do anything with a car that made financial sense?

by Bruisr Mon Jun 24, 2013 5:14 pm

According to my wife NEVER! " Its all just a big waste of money", she says, but I like it so I keep doing it.

by 77mali Mon Jun 24, 2013 5:53 pm

Bruisr wrote:According to my wife NEVER! " Its all just a big waste of money", she says, but I like it so I keep doing it.

I stopped listening to that argument too.

The fairer sex always thinks that they know what's up but the truth of the matter is, they really want to keep an eye on us so they deal with it. If we're always home & under a car in our spare time & they can keep an eye on us...they're good.
jocolor

by driveit Tue Jun 25, 2013 8:36 am

My goal is to make this car a daily driver. I am shooting for as close to 20 mpg as I can get.

I want to remove as much weight as I can get another gear and tighten up the suspension. I want the car low and mean sounding whether it really is or not. As long as its got enough hp to get itself out of the way I will be happy.

Wants:
- Lite
- Nimble
- Thunderous
- Gas sipping

Oh the things that dreams are made of!!!

by dynchel Tue Jun 25, 2013 9:14 am

There is a sticky on reducing the weight if you haven't seen it. Its pretty easy to lighten a '74 chevelle, it just depends how far you are willing to go. I gutted the front bumper, hole sawed the header panel supports, have aluminum wheels (including the spare) and intake and removed the sound deadener from under the carpet. My car factory had no a/c or power brakes, and the battery relocated to the trunk.

by driveit Tue Jun 25, 2013 9:34 am

I have saw that and have been studying it. I plan to start working on the Chevelle's diet soon. I hope to start with lightening the bumpers. I am looking for plastic fender-wells for the front. I like the hole saw technique. Gotta get one of those. I am nervous about messing with the bars in the doors, but that is a lot of weight! I would also like to add modern seats to make it bit lighter as well.

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