MP2 5th Gear Swap into MP3 Online ...

[cfg83]

Hello -

I'm one of those crazy MPG whackos from gassavers.org.

I finally was able to do the 5th gear swap. It was based on this thread that 1993 started (THANKS 1993!!!!) :

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

I also relied on Different Racing for the transmission dissasembly instructions :

Disassembling the Saturn Manual Transaxle
http://www.differentracing.com/tech_...sassembly.html

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 from you guys, 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 drove home just now and was super happy with it. Here are some pix :


Transmission Cover :
01_cover.jpg
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 :
02_mp3_5th_gear.jpg
This is my original "performance" 5th gear in place after my mechanic took off the cover.


NEW MP2 5th gear being installed :
03_mp2_5th_gear.jpg
Here is the MP2 5th gear during installation. Fits like a bug in a rug.


Gear Ratios for 91-02
http://www.differentracing.com/tech_...gearratio.html
10_gear_ratios.jpg
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

[amazinghl]

21% reduction does not mean 21% gain in gasmilage.

[plastic torpedo]

That's pretty cool, I didn't know you could do that!

[cfg83]

amazinghl -

Originally Posted by amazinghl

21% reduction does not mean 21% gain in gasmilage.

Yeah, you're right, I am being too enthusiastic. But, I spend a lot of time in 5th gear, so I will be getting a nice gain. I'll post a more representative update later when I do one of my normal "drive to work" runs.

plastic torpedo -

I learned it here!

CarloSW2

[quiksc2]

This is awesome! I want to do this. I mean, it's fun when ricers drop gear to try to pass you, and you floor it in 5th and they're gone, but I need the mileage. Thanks for the write up.

Wait, cruise control doesn't work? I don't use it much, but the long trips that I want the higher 5th gear for is when I want cruise control. If this is true, any way around it? Such as SOHC cruise control? 5th is pretty much the only gear I use cruise control in.

[tarsun]

Yeah I heard of people doing this. They have all the performance of the MP2 tranny and the economy of the MP3 tranny. Or there abouts. Its like a little overdrive. Pretty neat if you ask me…

[amazinghl]

By the way, lugging the engine is one of the worst thing you can do to the bearings.

[tarsun]

what'ing the engine?

[cfg83]

tarsun -

Originally Posted by tarsun

what'ing the engine?

DICTIONARY OF AUTOMOTIVE TERMS
http://www.motorera.com/dictionary/LU.HTM

Lug:
1. To cause the engine to labor by failing to shift to a lower gear when necessary. The British term is "labour."
2. A protrusion on an object.
3. A sleeve into which bicycle frame tubes are inserted to form a joint.
Also See:
dog
4. An external metal sleeve that holds two or more tubes together at the joints of a frame.
5. A device mounted on a rotating shaft or component that engages in a recess of a component to be driven.
6. A solid block of tread on a tire.


Lugging the engine:
Letting the rpms fall below the engine's powerband

I don't actually lug the engine all the time, but I know that the taller gear effects the "lug line", so to speak, so I tried to be observant of that after the gear change.

amazinghl -

... Oh, I see. My expression in the first post implies that I am "in" the lug zone going uphill. I try to be above the "lug line", but I am close to it. I used to go uphill in 5th@30 MPH. From now on I will try to be in 5th@40 MPH, which is the actual speed limit going up that hill. If it doesn't work, I'll just have to use 4th, which I have to use anyway when the slope changes near my home.

CarloSW2

[tarsun]

O ok.

[sl2clone]

In 5th gear at 30 going uphill? WHat are you babbling about? My old SL2 wouldn't go any slower than 35 in 5th on flat ground without lugging , let alone 5th gear uphill at 30. I DO NOT belive that one bit. Uphill at 40 in 5th now with the MP2 5th gear , I still find that hard to believe. WHat grade are you talking about? 2% grade? Or a real hill. I keep reading some VERY hard to believe posts from the "gas saver" people. Stuff I can not believe unless I see proof. It all seems way too far fetched.0
It's better to be in a lower gear giving it less gas than a higher gear giving it more gas. That made a big improvement in my MPG right there. There is NO way you are not lugging the engine from what you have posted.
The only thing you have posted that I find believeable is how easy the 5th gear swap is. I find 50mpg from a saturn AWFULLY hard to believe. Best run was 43 with a SOHC , highway , AC off and manual steering.
I am not trying to attack here. This is just VERY hard to believe.

[cfg83]

sl2clone -

Originally Posted by sl2clone

In 5th gear at 30 going uphill? WHat are you babbling about? My old SL2 wouldn't go any slower than 35 in 5th on flat ground without lugging , let alone 5th gear uphill at 30.

In my 1999 SW2, before the swap, the ECU/PCM would allow me to engage cruise control on the flat in 5th gear at 25 MPH.

I DO NOT belive that one bit. Uphill at 40 in 5th now with the MP2 5th gear , I still find that hard to believe. WHat grade are you talking about? 2% grade? Or a real hill. I keep reading some VERY hard to believe posts from the "gas saver" people. Stuff I can not believe unless I see proof. It all seems way too far fetched.0
It's better to be in a lower gear giving it less gas than a higher gear giving it more gas. That made a big improvement in my MPG right there. There is NO way you are not lugging the engine from what you have posted.
The only thing you have posted that I find believeable is how easy the 5th gear swap is. I find 50mpg from a saturn AWFULLY hard to believe. Best run was 43 with a SOHC , highway , AC off and manual steering.
I am not trying to attack here. This is just VERY hard to believe.

That's ok, you don't have to believe me. I shouldn't have published the observed MPG because it was NOT part of my normal test runs (aka going to work ). It was a rough guesstimate. I will publish a comparison to a normal run later on.

The hill I'm talking about is a "gentle grade" for the first chunk. I can't tell you the % because I don't know what it is. If I GPS it, I will post it. Later on the grade is too steep for 5th.

Question : Do you define lugging to occur at a point *before* the car starts to shake and buck?

CarloSW2

[plastic torpedo]

I don't see why cruise control wouldn't work? I swapped a 95 MP3 manual in an automatic 2000 SL2 and it works just fine with the automatic PCM still in it

[alleninpa]

looking at the gearing chart, I see why my sl1 sucks so bad going from 2ed to 3rd gear.
I wish I had a 3rd gear from a sx2.

Al

[cfg83]

plastic torpedo -

Originally Posted by plastic torpedo

I don't see why cruise control wouldn't work? I swapped a 95 MP3 manual in an automatic 2000 SL2 and it works just fine with the automatic PCM still in it

Hrmmmm. Interesting. I need to look at the electrical schematics. I do know that the CC is different between 1st and 2nd gen S-Series, but I don't know if it changed again for 3rd gen.

I don't know why it stops working either. In the past, I couldn't engage it below 25 MPH in 5th. My theory is that some kind of "threshold equation" using MPH and RPM is used for deciding when to allow CC to engage in my 1999 PCM for manual tranny. Since my new RPMs in 5th are much lower, the equation is never evaluating to "true", so the CC won't engage.

CarloSW2

[fetchitfido]

If you can do 30 mph in 5th uphill, you don't know what a hill is.

[BarnOwl]

Originally Posted by plastic torpedo

I don't see why cruise control wouldn't work? I swapped a 95 MP3 manual in an automatic 2000 SL2 and it works just fine with the automatic PCM still in it

There's no physical reason the cruise control can't work. However, on a 5-speed the PCM infers that you have hit the clutch when it detects a gear ratio it's not used to and kills the cruise. The dealer can only program the PCM for options that actually came on the car. There was never a DOHC with an MP2 5th gear. So, you can't get it programmed in.

It would be interesting to see whether your cruise control still works if you ever get the proper PCM in there. What does it do if you hit the clutch with the cruise control on now?

[RalliArt16]

eh, my clutch switch is bypassed so its like the clutch pedal is always pressed, cruise works fine...

[quiksc2]

Originally Posted by RalliArt16

eh, my clutch switch is bypassed so its like the clutch pedal is always pressed, cruise works fine...

Odd... If I have the cruise control on, and push in the clutch, it turns off the cuise control...

[cfg83]

RalliArt16 -

Originally Posted by RalliArt16

eh, my clutch switch is bypassed so its like the clutch pedal is always pressed, cruise works fine...

I never heard of that mod. Is this what you did? :

Start engine w/o clutch
http://www.saturnfans.com/forums/showthread.php?t=65142

If yes, then I'll give it a try.

CarloSW2