Opinions on gearing please

[Stretch]

I never race my car. Ever! The nearest drag strip is 150 miles away. I have talked about going but It just isn't going to happen. All I ever do is cruise in it and just enjoy it. Lets face it, gas isn't going to get any cheeper. With that in mind I would like to hear what your thoughs are about gear changes for gas mileage with my combo.

Here is the info on what I have in it now.
'73 charger rallye
original stock 340 with factory t-quad
recurved stock electronic distributor
Stock 727 with home grown shift kit. I drilled the seperator plate, removed the accumulator spring and backed off the line pressure adjustment.
Exhaust is long tube headers with 3" collectors into 2 1/4 pipes with an x pipe and repo hemi mufflers.
Rear end is an 8 3/4 a 3.55 sure grip.
Rear tires are 295/50/15's

I have a 3.23 gear set a 2.76 set. Both set up in pigs.

Im asking this because I have had conversations with a really good friend who once worked for Ray Barton. His opnion is that the 2.76 set will pull the 340 out of it's "sweet spot" and get worse fuel mileage. I dont see that. At 65mph I'm turnning about 3400 RPM with the 3.55's Getting the R's down would have to better the gas mileage. He seams to think it will lug.  

As I side note. The nearest 4 lane Highway is about 70 miles south of here and I almost never go to Green Bay let alone with my charger. I'm going to swap gears out for mileage so what is your experance and opinion.

Thanks
Jason

[Troy]

I doubt you'll see much difference(?). You don't say what your converter stall speed is but you very well could drop the RPMs below that and your mileage AND performance will suck. I don't know enough about that year 340 to tell you if you'll drop out of the torque/hp band. You have relatively short tires so going to a highway type gear won't hurt as much as it does for some of us with tall tires. I'd say the 3.23 will be better all around - 2.76 if you spend a significant amount of time on the highway. I wouldn't go to with the 2.76 if you spend a lot of time below 50 mph or on city streets.

Troy

[Stretch]

The converter is stock aswell. I think the stall speed is 2400. It might be 2200. I don't recall. I had the 323's in it at one time. It runs about 200 rpm higher with the 355's

[daveco]

Just as a point of reference, I had a '69 Charger with a 318 2bbl, auto with 2.73 gears. Stock other than headers and dual exhaust.
It got around 16-18 mpg hwy.
My '69 R/T with a stout 440 and 3.23s got 12-14mpg hwy.
I think the gas money saved will not be huge, but it is no fun cruising a sluggish barge.

[Dino]

I went from 3.55 to 2.96 on my '69 with 440 and it's a huge improvement rpm wise but I don't see a real difference in gas mileage, it still sucks!  I hope to see an improvement when I switch to the tq.  Regardless it is much more fun to drive now it's no longer revving so high.  (I have short tires)

[charger_fan_4ever]

Without an overdive gear highway mileage is going to suck regardless of the gear.
maybe with a 275 60 tire an 2.76 might be a small improvement on the highway, but will kill stoplight to stoplight fun.A smallblock with ~260HP in a what (3800lbs with driver) 28inch tall tires is going to be no fun.

[DixieRestoParts]

  I'd say the 3.23 will be better all around 

For what you say you want to do, but really, as little as we drive these cars, what's an extra $10 in gas on a weekend?

[Scaregrabber]

A big torquey 440 would improve fuel mileage with the higher gears but the guy from Ray Barton is right, the 340 has a nice sweet spot that would be gone with higher gears. I think the 3.55's are fairly optimal for your tires and weight.

Sheldon

[Joshua]

Keep the 3.55's....those are a near perfect gear for screwing around with.....
If ya wanna pick up some mileage...ditch the auto or put a Gear Vendors behind it.....

[Stretch]

  I'd say the 3.23 will be better all around 

For what you say you want to do, but really, as little as we drive these cars, what's an extra $10 in gas on a weekend?

I live 25 miles from work and in the summer I drive it pretty much every day back and forth to work. As long as it's nice out.

[Stretch]

Keep the 3.55's....those are a near perfect gear for screwing around with.....
If ya wanna pick up some mileage...ditch the auto or put a Gear Vendors behind it.....

I don't want to cut this car. It's all original. Paint, vinyl top, decals, all of it. I don't mind making changes as long as it's bolt on stuff. I keep everything so it can go back on if I want to.

[cdr]

get an a518 trans from a dodge truck or van 1994 & back,you have a 340 so its pretty much a bolt in,rear crossmember mod & driveshaft,no big deal

[DixieRestoParts]

  I'd say the 3.23 will be better all around 

For what you say you want to do, but really, as little as we drive these cars, what's an extra $10 in gas on a weekend?

I live 25 miles from work and in the summer I drive it pretty much every day back and forth to work. As long as it's nice out.

Now that is cool !! 

So, let's say you get 12 mpg now. 250 miles round trip is around 21 gallons. 21 X 3.65/gal = $76.65. If you change the gears and get 14 mpg that works out to 250/14 = 18 gals x 3.65/gal = $65.70. These are rough numbers, but you get the idea. I don't see the increase in mileage worth it personally. I'd leave the 3.55's, but it's your call.

Let us know what you decide to do and the changes in mileage you get. 

[Stretch]

get an a518 trans from a dodge truck or van 1994 & back,you have a 340 so its pretty much a bolt in,rear crossmember mod & driveshaft,no big deal

I was going to do that but I thought you had to cut the car. I don't want to cut this one at all. If I have to cut or change a bolt on part (like a cross member) I'm ok with it.


My '65 valiant is going under the knife.

[rt green]

you could spend an afternoon and change cams. what cam do you have?

[Stretch]

you could spend an afternoon and change cams. what cam do you have?

Other than the headers, distributor curve kit, and 15 inch tires the car is as it left the Lynch Road plant. The car has 80,000 miles on it. The cam is the factory '73 340 cam. The deepest into the engine I have been is a new double roller timing set, intake gaskets, and a rebuild of the thermoquad.

[70charginglizard]

3:23 definately 3:23.

Thats what I have for cruising and I love it way better then the 2:76 I had in there previously

[Kern Dog]

You do NOT have to cut anything on your car to fit a Gear Vendors unit. I have one in my 70 and the only modifications that I made were converting the crossmember to a spool type, and two small dimples in the trans tunnel to clear bolts in the GV unit.

[elacruze]

You can't do anything whatsoever that will not more than offset the gas you save. A higher gear ratio will just make it a pig and cost more than the gas you save. An overdrive of any sort will cost a lot more than the gas you save.

I have 3.55's in my '68 pickup behind a 318 and it gets about 15mpg @ 70 and as good as 20 @ 60-65mph.

I had a 1986 Camaro with 305 and 700r4 trans which averaged about 24 @ 55 (the speed limit at the time) I drove it once from Ft. Wayne IN to Detroit, with an average overtheroad speed of 80-85mph-and got 27mpg doing it. After that, I tried holding it out of overdrive at 55, and the mileage was exactly the same. Point is, the motor has a sweet spot and you may be able to find it while you drive if you keep your average speed up/down from normal-then you could make a more educated decision about how to stay in it more often.

It appears to me, that the economics point towards leaving it as is. What you really need to decide is what you want the car to do. Burning rubber with a small-block automatic is pretty hard to do with any less gear than you already have.

Personally, I'd probably look for the later model overdrive trans at the yard and put an appropriate converter in front of it.

[Troy]

Both the A518 and Gear Vendor cost a fair chunk of money and do require some modifications to the car (even small ones). As I understand it, he already has the gears. Swapping gears is fairly easy and very cheap in this case. If you're only hunting mileage it will take many years for most people to break even on an OD conversion (or EFI install). If you're at low speed or in traffic you are not going to significantly improve the mileage (neither the A518 or GV will even shift into OD until you're near 45-50 mph). Gears can help - or hurt. If you drive 80 mph on the highway for nearly 50% of the miles you put on the car (like I do) then the gears and/or OD make a massive improvement.

Troy

[Stretch]

I do have the gears and they are all set up in center sections. I live in a small town so there is no "city" driving. The town I work in is about a 25 mile two lane highway drive (55). I do go to Kewaunee WI. a few times a year. That is about 120 miles 1 way. It is 4 lane interstate for about half of the trip. I have taken the charger a few times. At 65mph (the speed limit) I'm turning about 3500 RPM's I get about 15mpg on that trip. At 65 I'm NOT keeping up with the flow of traffic. I guess I more worry about the revs and 39 year old valve springs.

As for what I do with the car, I drive it as often as possable and have for the 16 or so years that I have had it. I never have been one to beat on it or burn the tires. I would rather have people notice the car for what it is, not for the car that gets the crap beat out of it. This is a very small area. There is only about 26,000 people in the county. The town I live in has 75 houses. Everyone knows everyone! 

With all of that in mind and the fuel mileage gain potential of only a mile or two, I think I'll just leave it alone. After all I only put about 1000 miles a year on it.

[Sublime/Sixpack]

Swapping out a Third member (dropout, pig, center section whatever you choose to call it) isn't a difficult job. If I were in your situation I'd just swap out the 3.55's for the 3.23's and slip in the correct speedometer gear then drive it to see how it feels.
All you'd be out is a gasket, some gear oil, speedo gear, and your time.

[Stretch]

Yah. It's easy work.

[firefighter3931]

At 65mph (the speed limit) I'm turning about 3500 RPM's

How accurate is your speedo ? How about the tach ? Is this the original gear ratio for the car ?

The reason i ask is because the numbers seem way off....with a 295/50 & 3.55 gears you should be at 3050 rpms @ 65mph, even calculating 5% for converter slippage.

here's a neat tool to play with : http://vexer.com/automotive-tools/speed-rpm-calculator


Ron

[Stretch]

You know I thought that too. I checked my speed with my hand held GPS and at 65mph on the speedo the gps says 63.5. The Tach may be suspect. It is the factory rallye cluster tach. I've been meaning to hook up my digatal timing light and see what it says the Rev's are at 65 mph. (my timing light is a snap-on digatal advance light. It has a tach feature).