Saturn 5th Gear Swap Online ...
 

Hello -

I finally was able to do the 5th gear swap. It was based on this saturnfans.com thread :

MAD!! gear swap - 04-27-2006
https://www.saturnfans.com/forums/showthread.php?t=76116

My mechanic didn't want to do it at first because he normally farms out transmission work, but thanks to all the information I got at saturnfans, I described the process to him and he was able to do it, no problemo. He did have to pop the cover again to make an adjustment, but I just drove home and was super happy with it. Here are some pix :


Transmission Cover :
Attachment 892
As skewbe and others have said, you don't have to remove the transmission to do the mod. The 5th gear is under the transmission cover seen above.


OLD MP3 5th gear in place :
Attachment 893
This is my original "performance" 5th gear in place after my mechanic took off the cover.


NEW MP2 5th gear being installed :
Attachment 894
Here is the MP2 5th gear during installation. Fits like a bug in a rug.


Gear Ratios for 91-02
https://www.differentracing.com/tech_...gearratio.html
Attachment 895
It turns out that the 1998-2002 years had the best economy 5th gears for the MP2 transmission.


Some number crunching -

MP3 5th gears : 37*27 teeth => 27/37 = 0.7297 => 0.730 = The MP3 5th gear ratio seen above.

MP2 5th gears : 43*26 teeth => 26/43 = 0.6046 => 0.605 = The MP2 5th gear ratio seen above.

Dividing ratios : 0.730 / 0.605 = 1.2066 => ~21% reduction in RPMs => 21% gain in MPG.

Driving home today at close to steady-state 50 MPH, on a stretch of freeway that I am used to seeing ~40 MPG, I was seeing about ~50 MPG, so this fits the 20% increase predicted above.

There is an associated power loss, but it runs fine at 35 MPH on the flat in the new 5th gear. I have to be slightly lighter on the throttle, but I'm already "GasSaver trained" in the respect anyway, so no biggee. With the old gear, on the flat, I would say that the absolute bottom of the gear would have been about 20 MPH. Today, I think that is now closer to 25 MPH.

Right close to home, I always spend time "lugging it" uphill for about the last 3/4 mile. With my old 5th gear, I could just hold my own at 30 MPH going up the hill in cruise control. Today, I could feel the loss in power. But, since that is such a small component of my drive, I don't really care.

Just like skewbe and others have said, I did lose my cruise control. The ECU/PCM is none too pleased at this state of affairs, BUT I DON'T CARE!!!!!!!!!!!!!!!!!!!!!!

CarloSW2

That's great, makes the Saturn even more appealing to me! Is the "performance" transmission the one in the s*2 models? I was researching and saw that those models had a bit more horsepower but didn't think about the gear ratios.

How much did your mechanic charge you for this job?

Fourthbean -

Yes. The MP2 transmissions are in the S*1 models and the MP3 transmissions are in the S*2 models. Go here to see the transmission gear ratios :
https://www.differentracing.com/tech_...gearratio.html

He's my friend so he gave me a discount price, so it's not representative. I provided the gears, replacement bolts, and new gasket, so it was about 2 hours max labor and tranny oil.

CarloSW2

theclencher -

Thanks. If you could program this, I would call it an "exploit". I can't help but think of my car as a 1:1 slot car now, because up until this point, the only gears I have ever swapped have been in slot cars :

Attachment 896

CarloSW2

Hey Ya!

I just bought a Saturn SL2 a couple of months back whats the RPM change in 5th after the swap. I think I am about 2500rpm at 65 mph right now.

I wish I could go 80 at that rpm. Geez these saturn's are close.

Bump
 

Thanks to Geonerd for pointing out this thread, in another thread.

cfg83 (the original poster) hoped for a 21% increase in FE, and he did not get it but he definitely got an increase. I pasted his messy gaslog into Excel and averaged approximately 100 entries after the gear swap, as well as approximately 100 entries before the gear swap.
After: 9/4/2007 -> 6/20/2008 -- 18461 miles, 441 gallons, 41.8mpg.
Before: 8/11/2006 -> 8/25/2007 -- 22276 miles, 577 gallons, 38.6mpg.

That's about 5% difference. It sounds well worthwhile considering the small cost/effort involved in doing the job.

yea, you're doing 21% more miles for the same rpm. NOT necessarily 21% increase in FE because the engine IS working harder slightly and may not be at as efficient of an rpm for combustion... or more so.

I've been hoping to do something similar with my spare transmission, seeing if it's like some of the honda trannies that can change a 2nd for 5th and get a better ratio.