Overdrive Options

[Revhendo]

The bottom picture of post 119 is of my car. The fab guy that did that has told me that he has done a few cars with the t-bar triangulated back into the sub-frame connectors with no troubles yet. In my case one way or the other, either with Dillinger parts or a HemiDeny k-frame I will be losing the t-bars. As to the amount of power you lose, from what little I know, that is very variable. The 4l80 is is a bit of a pig...using factory stuff. Largely because the oem t/c weighs as much as a boat anchor. But at the same time with the right parts it can easily with stand 1500 hp. I think that you just have to pick your poison. None of the od transmissions are perfect. Take a GV unit behind any dinosaur 3 speed. If you have a loose convertor you may end up running around with the convertor slipping. Maybe not the case with a low powered dd but very possible with a high powered street car, spoke with Lenny at Ultimate Convertor a while back and he was fighting that very problem with a customer and his HEMI Dart. When the convertor was loose enough to perform at the strip it would slip on the street while the od was engaged. When it was tight enough to not slip on the street it was to tight to allow the car to launch well at the strip. Solution, a lock up convertor. Which opens up the need to do some cutting on the car. Just like most things in life, there is no one "right" answer. No matter which way you go you will always run into the nay sayers. Such is life.

True words my friend.

For the moment I am sticking with my trusty 727. Mainly because I'm tired of tripping over it in the garage and just had it resealed. 727s are power hogs, though, (explains why my Jeep gets such outstanding fuel economy). Which is why racers like to use 904s. I'm running 3.55 gears and don't do a bunch of long distances, so I'm good for now.

Got a 700 in the garage for the ol beater truck that will get put in one of these days, too.

Come to think of it, everything I own is a project.....

 

[rednesss]

Welding that 1/4" plate to the tunnel floor is where most of the strength comes in because it is being supported by the floor. The thickness of the material does very little and is mostly extra weight. It is also difficult to get good weld penetration when you weld dramatically different thicknesses together. In my opinion, you should just use the upper tunnel floor itself and box in a 1/2 - 5/8" tall channel with a more reasonable 1/8" plate. That would likely be stronger without all the unnecessary weight.

I used structural panel bond adhesive in between the 1/4" plate and the transmission tunnel, much stronger than MIG welding.

 

[BigBlockMopar]

I recently installed an A518 behind the 318 in my '73 Dart.
The 8-3/4" rear end has 2.93 gears in it, which I'm still using today.

Going from a 904 to the 518, I noticed the heavier drivetrain in the car, but I'm used to it now.

The motor is, of course, still way undergeared. On highway hills the car's speed drops back easily when in OD.
Only when doing 75-80 mph, the engine starts to get into it's powerband and the cars starts to move.

My mileage has dropped from an average 15mpg to 13mpg currently, but in the car's defence, the weather has become a lot colder aswell since I measured the 15mpg.

I would like to swap over to 3.23 gears and see what that does for mileage and highway driving. Next step up is a 3.9:1 gearunit I've got, but I think that will kill the mileage again.
I have a 5.7 Hemi in the works for the car, so I'm sure the Hemi will be able to handle the 3.23 gears or even the 2.93 gears much better than the lo-po 318.

 

[Revhendo]

I recently installed an A518 behind the 318 in my '73 Dart.
The 8-3/4" rear end has 2.93 gears in it, which I'm still using today.

Going from a 904 to the 518, I noticed the heavier drivetrain in the car, but I'm used to it now.

The motor is, of course, still way undergeared. On highway hills the car's speed drops back easily when in OD.
Only when doing 75-80 mph, the engine starts to get into it's powerband and the cars starts to move.

My mileage has dropped from an average 15mpg to 13mpg currently, but in the car's defence, the weather has become a lot colder aswell since I measured the 15mpg.

I would like to swap over to 3.23 gears and see what that does for mileage and highway driving. Next step up is a 3.9:1 gearunit I've got, but I think that will kill the mileage again.
I have a 5.7 Hemi in the works for the car, so I'm sure the Hemi will be able to handle the 3.23 gears or even the 2.93 gears much better than the lo-po 318.

More gear will definately help. Think 3.55 or better unless your hitting the autobahn.

 

[LJS30]

Guys I am totally obsessed with an overdrive unit in my Dart. So much so I might shoot for teaching, I'm a high school teacher, summer school just for an overdrive option. For instance just right now on the highway all I could think about was "lower rpm's...lower rpm's..lower rpm's..".

 

[Revhendo]

Guys I am totally obsessed with an overdrive unit in my Dart. So much so I might shoot for teaching, I'm a high school teacher, summer school just for an overdrive option. For instance just right now on the highway all I could think about was "lower rpm's...lower rpm's..lower rpm's..".

Pretty bad when the exhaust drone starts to sound like it's saying that.

 

[inkjunkie]

Guys I am totally obsessed with an overdrive unit in my Dart. So much so I might shoot for teaching, I'm a high school teacher, summer school just for an overdrive option. For instance just right now on the highway all I could think about was "lower rpm's...lower rpm's..lower rpm's..".

First time I drove the Fairlane with the t-5 in it I was hooked. When I was driving it on a somewhat daily basis every now & then I would leave it in 4th on the freeway, for what seemed to be the entire 15 or so miles home. In reality it was tenths of a mile. You will see a lot of folks saying that you will never recoup the money it takes to put an od in your car because your mileage will only go up x.x miles per gallon. While this may be true the car will be a lot more enjoyable to drive......what is that worth?

 

[LJS30]

Pretty bad when the exhaust drone starts to sound like it's saying that.

Oh the obsession is running deep now. I am leaning towards a Gear Vendors setup since it looks the least intrusive.

 

[LJS30]

First time I drove the Fairlane with the t-5 in it I was hooked. When I was driving it on a somewhat daily basis every now & then I would leave it in 4th on the freeway, for what seemed to be the entire 15 or so miles home. In reality it was tenths of a mile. You will see a lot of folks saying that you will never recoup the money it takes to put an od in your car because your mileage will only go up x.x miles per gallon. While this may be true the car will be a lot more enjoyable to drive......what is that worth?

Well that's what I've been weighing out in my mind. This is pretty much going to be my daily driver for the next two years and as stated earlier, I do a forty mile round trip commute three times a week. I think an overdrive/gear splitter would really make this old machine a legitimate and practical daily driver.

 

[Powerflite]

I recently installed an A518 behind the 318 in my '73 Dart.
The 8-3/4" rear end has 2.93 gears in it, which I'm still using today.

Going from a 904 to the 518, I noticed the heavier drivetrain in the car, but I'm used to it now.

The motor is, of course, still way undergeared. On highway hills the car's speed drops back easily when in OD.
Only when doing 75-80 mph, the engine starts to get into it's powerband and the cars starts to move.

My mileage has dropped from an average 15mpg to 13mpg currently, but in the car's defence, the weather has become a lot colder aswell since I measured the 15mpg....

Is the mileage change that you are quoting from the highway/freeway or stop and go driving? An overdrive will not help stop and go, in fact, it might make it a little worse. But it should improve your freeway mileage even if you are geared too high. Example: I saw a nice improvement when I swapped from 2.71 gears with a 904 trans in a '70 Satellite wagon to 2.94 gears with a 700R4 overdrive, even though it was way under-geared. But that was all highway miles.

 

[BigBlockMopar]

My daily usage contains mostly relatively short highway-trips and some city stop&go-driving. I think it's about 70% highway & 30% city.
Most of the highway trips are usually during rushhours though.

What I noticed during longer highway-trips, when doing around 60-65 in OD, was that I had to give it a tad more throttle than with the 904, to just maintain that speed. Intake vacuum is between 18-15, while normally it was around 18-22 during these speeds.
Slight changes in road-slope sometimes cause the car to slow back down to 50-55, which causes lower engine vacuum because of the wider throttle-opening and increased engine-load.
The stock (8.6:1cr) motor just doesn't make enough torque in those low rpm's. (I'm running on LPG/Propane aswell though)