2005 Dodge Magnum SXT - Auto>Manual Conversion- 10.3% decrease in fuel consumption

[ALS]

I did the same swap in my old Volvo turbo wagon for better mileage.The automatic a non locker, had a .69 OD and 3.90 rear gears. The manual had a .80 OD and I also swapped in 3.31 rear gears.

Highway mileage the best I could get with the automatic was around 340 miles per tank, 15.8 gallons. After the swap including lowering the vehicle I jumped the mileage to 425-440 miles per tank.

Almost always the best bang for the buck mod for better mileage is swapping out the automatic for a manual and higher rear gears.

[ksa8907]

Originally Posted by oldtamiyaphile

I feel like it's been left out than an Auto on it's last legs may have had issues that caused poor economy. I had a 1.3 Suzuki with dead trans that struggled to get 25mpg.

A manual swap+ EOC would have sent that into the 60's.

I would vote no on that theory. The 42rle same as the 42le and 41te, were also known as chryslers "ultradrive" transmissions. They would automatically adjust themselves to operate as close to factory spec as possible no matter how worn the transmission got. Which is one reason why chrysler transmissions had the bad reputation for suddenly dieing with no warning, they were designed that way.

[t vago]

Originally Posted by ksa8907

I would vote no on that theory. The 42rle same as the 42le and 41te, were also known as chryslers "ultradrive" transmissions. They would automatically adjust themselves to operate as close to factory spec as possible no matter how worn the transmission got. Which is one reason why chrysler transmissions had the bad reputation for suddenly dieing with no warning, they were designed that way.

Yah, that, too.

[Xist]

Chryslers were designed to die without warning?! That explains so much!

What rear end came stock with the manual transmission. It looks like we have yet another automatic geared for fuel efficiency, while the manual was designed for acceleration.

What kind of mileage would the automatic have had with the new rear end?

[t vago]

Originally Posted by Xist

Chryslers were designed to die without warning?! That explains so much!

I am a lifelong Chrysler fan, and I approve of this message!

Originally Posted by Xist

What rear end came stock with the manual transmission. It looks like we have yet another automatic geared for fuel efficiency, while the manual was designed for acceleration.

Well, the Dodge Magnum was never offered with a manual transmission.

However, the later model Challenger, which is based off an update to the platform that the Magnum was built on, was offered with a 6-speed Tremec manual. It could have either a 3.73 rear end, or a 3.92 rear end.

Originally Posted by Xist

What kind of mileage would the automatic have had with the new rear end?

That's a 21.1% reduction in gearing from 3.636 to 2.87, so I would estimate a 10.5% reduction in fuel usage. I would also estimate that my Magnum would have gone from an average of 21.3 MPG (last winter 4-fillup average) to an average of 23.8 MPG. Performance would have suffered, though.

[Xist]

What performance? You would have been at 1,460 RPM on the freeway!

[t vago]

Originally Posted by Xist

What performance? You would have been at 1,460 RPM on the freeway!

Yes, but it would also become a LensCrafters car. You know...

"0 to 60... in about an hour!"

[RoadRaceJosh]

The old overall high gear ratio was 2.51:1 (3.636*.69). The new overall high gear ratio 2.87*.84 is 2.41. So the engine spins 96% as fast as it used to assuming no slippage. That's darn close.

What I'm curious to see is how you took a 4x4 trans and put a tail housing on it.

[t vago]

Originally Posted by RoadRaceJosh

The old overall high gear ratio was 2.51:1 (3.636*.69). The new overall high gear ratio 2.87*.84 is 2.41. So the engine spins 96% as fast as it used to assuming no slippage. That's darn close.

What I'm curious to see is how you took a 4x4 trans and put a tail housing on it.

Yah, that was the fun part - In the end, I basically made a franken-tranny.

In May 2015, I was scratching my head at making the rear of the Jeep transmission work in the Magnum. After several days of brainstorming, I came up with the remarkably bright idea of swapping transmission parts with a Chrysler Crossfire manual transmission (which was supposedly also an NSG370). Of course, I wasn't completely sure. Using Chrysler parts manuals for both the Jeep and the Crossfire, I performed a parts comparison between the Jeep transmission I had and the Crossfire transmission, and found out that they share 95% of the same parts.

So, I bought a Crossfire manual transmission, and inspected both transmissions. It turned out that I needed a sleeve bearing. Apart from that, I could mix and match the Jeep and Crossfire transmissions. Also made installing a shifter much easier.

Here are some pictures:

Comparison of front case internals for JK NSG370 and ZH NSG370


Comparison of rear case internals for JK NSG370 and ZH NSG370


3.8L V6 case, with a new shift shaft sleeve bearing installed


Original shift shaft sleeve bearing, pulled with blind hole bearing puller


Should someone want to power their JK Wrangler with a Mercedes engine, they can use the below transmission. Obviously, not going to happen - will probably keep this transmission for spare parts.

JK/ZH Franken-tranny


The item that will make it possible for a V6 Magnum to have a manual transmission...

LX Franken-tranny



Modified transmission mount, showing two drilled and tapped holes


Transmission mount, installed


RH, looking forward


LH, looking forward, with clutch slave cylinder


Close-up of clutch slave cylinder and clutch hose


Rear view, showing transmission crossmember in "NAG1" configuration

[RoadRaceJosh]

That's impressive! I used to want to put a RWD transmission behind a 3.5 V6, but buying 2 transmissions to build 1 is more of an undertaking than I desire.