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2005 Dodge Magnum SXT - Auto>Manual Conversion- 10.3% decrease in fuel consumption
This past March, my Dodge Magnum decided to shred apart its 4-speed automatic transmission. Shortly afterward, I decided to swap the 4-speed out for a 6-speed NSG370 transmission. I placed the Magnum back on the road with the new transmission this past October, and start gathering fuel consumption data for it in November.
2015 (with 6-speed NSG370)
2014 (with 4-speed 42RLE)
Note: I also changed the rear end from 3.636 to 2.87, in order to compensate for the top gear change from 0.69 (42RLE, 4th) to 0.84 (NSG370, 6th). However, the resultant decrease in engine speed from this swap (about 3.9%) cannot account for the 10.1% decrease in fuel consumption. |
I read the title and thought you started using MORE fuel, glad i was wrong! contrats! I'm a bit jealous, i always wanted to drive a chrysler 3.5 with a manual trans.
what are the rpms at 60? |
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Here's a short vid, using Torque Pro and Track Recorder, shortly after I returned the Karen-mobile back to the road. [youtube]yrAfN-1irGE[/youtube] |
....so h0w do you know it WASNT the rear gear change that improved the mileage.....and why not include that info in the first post......
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Top gear on the dead 42RLE had a ratio of 0.69. Top gear on the replacement NSG370 has a ratio of 0.84. This represents about a 21.7% increase in propshaft rotation speed, for a given vehicle speed. If I were to have left the original 3.636 rear end in place, that should have resulted in a definite increase in fuel consumption. The FDR was 3.636, while it is now 2.87. This represents about a 21.1% decrease in required pinion input speed, for a given vehicle speed. These two changes almost cancel each other out, and the net decrease in engine speed (about 3.9%) does not account for the 10.1% decrease in fuel consumption. Put it another way - Engine speed at 60 MPH was about 1850. Now, it's about 1780. There is no way that this change in engine speed (~3.9%), by itself, would have resulted in the measured decrease in fuel consumption. Quote:
You do bring up an interesting idea - What if I had left the original 3.636 rear end in place? Engine speed would have been about 2250 RPM at 60 MPH, which would have resulted in a net increase in engine speed of... 21.7% from when the 4-speed was still installed. I would have expected a 10.9% increase in fuel consumption just from swapping in the NSG370, if I were to have treated the engine speed increase as a result of swapping in a (nonexistent) 4.43 rear end. |
Nice mod. I bet its a lot more fun to drive now too.
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Shortly after I placed the Karen-mobile back on the road, I accidentally gave too much gas when starting in 1st from a dead stop. I left a nice, pretty black tire stripe for about 20 feet on dry pavement. Obviously, not good for either tire life or fuel economy. I shudder to think what would have happened, had I left that 3.636 diff in. |
The lower weight of a manual transmission and the absence of the torque converter slip should be taken into account for the final results, but what about the gear spread of the 4-speed automatic and this 6-speed manual? Is it the same transmission used in the Wrangler and the Sprinter, right?
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The 42le and 42rle were really just a modern take on much older transmission design. The increase is probably a result of no converter slip when accelerating, no pumping fliud, etc. Plus now you're essentially doing mini pulse and glides whule shifting.
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42RLE gears
NSG370 gears
The gearing appears to be more closely spaced together on the 6-speed. That would help with fuel economy during acceleration, particularly with city driving. I think that the two largest power drains were torque converter slippage and pumping losses through the transmission oil pump. Not sure if transmission weight itself would have played much of a part. I lost maybe 50 lbs or so from the swap. Quote:
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If i remember correctly, the intrepid (42le) with 3.66 gears was 2000 rpm @ 60 and with 3.89 and 215's instead of 225's i was running about 2200@60. I still brushed 30mpg average with the 3.89's.
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The first gen intrepid came stock with a 3.3, same as 3.8 |
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Drag racers certainly would think it significant.
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I should quit driving around with my wife. She's 100 pounds. |
A navigator/commo/spotter that only costs 100 pounds is golden.
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Well, made a few discoveries since last posting -
I had flashed the Magnum with a DiabloSport canned performance 93 octane tune a few years ago, and left it in there for up until a few days ago. I found out that this canned tune had caused my cold idle speed to be about 3000 (three thousand) RPM, and warm idle to consume about .55 gallons per hour. I reverted the Magnum's tune back to stock, then played around with the stock tune with the limited tweaking capability built into the Predator. Basically, I advanced ignition timing by 8 degrees from 0-4000 RPM, and experimented with lowering the idle engine speeds (idle in P/N w/ no AC, idle in R/D/3/L w/ no AC, idle in P/N w/ AC on, idle in R/D/3/L w/ AC on). Turns out that advancing stock ignition timing does wonders with fuel economy, above and beyond with what the performance 93 canned tune did. I got 28 MPG on a mostly-highway 29 mile drive last night, then got 25 MPG on a 6.5 mile city drive about an hour later. Also learned that messing with the stock idle speeds is counterproductive, even with lowering the speeds by 50 RPM. When warm, the Magnum would attempt to idle at the lowered idle speed, then somehow the engine computer would experience some sort of underflow condition and cause idle speed to jump up to about 2000 RPM. I returned the idle speeds back to stock settings, and that solved the idle speed problem. I am also consuming about 0.35 gallons per hour in idle, now. Also, the performance 93 tune messed with DFCO. The Magnum is now more willing to enter DFCO when I let off the gas. |
Nice work!
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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. |
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Here's the part that failed. It's part of the rear carrier assembly, the part that transmits engine power through 2nd, 4th, and reverse. Part of this rear carrier assembly is still inside the transmission. In the background, you can see the rear annulus, front carrier assembly, and a couple of large snap rings. http://www.tom-viki.com/spgm/gal/Car...1509120004.jpg Here's a picture of a complete and unbroken rear carrier assembly. The part I'm holding in my hand is the bottom of the complete assembly. http://www.tom-viki.com/spgm/gal/Car...1509140000.jpg |
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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. |
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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. |
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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? :) |
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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. Quote:
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What performance? You would have been at 1,460 RPM on the freeway! :)
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"0 to 60... in about an hour!" |
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. |
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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 http://www.tom-viki.com/spgm/gal/Car...1505230000.jpg Comparison of rear case internals for JK NSG370 and ZH NSG370 http://www.tom-viki.com/spgm/gal/Car...1505230001.jpg 3.8L V6 case, with a new shift shaft sleeve bearing installed http://www.tom-viki.com/spgm/gal/Car...1506060000.jpg Original shift shaft sleeve bearing, pulled with blind hole bearing puller http://www.tom-viki.com/spgm/gal/Car...1506060001.jpg 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 http://www.tom-viki.com/spgm/gal/Car...1506070004.jpg The item that will make it possible for a V6 Magnum to have a manual transmission... LX Franken-tranny http://www.tom-viki.com/spgm/gal/Car...1506070005.jpg Modified transmission mount, showing two drilled and tapped holes http://www.tom-viki.com/spgm/gal/Car...1507260000.jpg Transmission mount, installed http://www.tom-viki.com/spgm/gal/Car...1507260001.jpg RH, looking forward http://www.tom-viki.com/spgm/gal/Car...1507260006.jpg LH, looking forward, with clutch slave cylinder http://www.tom-viki.com/spgm/gal/Car...1507260007.jpg Close-up of clutch slave cylinder and clutch hose http://www.tom-viki.com/spgm/gal/Car...1507260008.jpg Rear view, showing transmission crossmember in "NAG1" configuration http://www.tom-viki.com/spgm/gal/Car...1507260009.jpg |
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.
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impressive :thumbup:
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