Metro taller transmission swap thread: +5% efficiency gain (taller final drive)

[MetroMPG]

More good news:

MORE>SETUP>SPEED
Both speed and distance can be adjusted to compensate for changes in tire size, gears, tire wear, etc..

That's from the ScanGauge 1 manual. So that's good - my OEM odo/speedo will go wonky if I do the swap, but I can compensate with the SG adjustment and continue to get accurate instant/trip readings.

Just do the swap already.

Tell you what - I'll go pick up the transaxle from Ivan's garage tomorrow. Maybe I'll do it this weekend. I have all the research done & bases covered.

[MetroMPG]

July 8 / 2006:

---

Started working on the swap this morning.

I'm basically at the point I had hoped to be at last night, but ended up wasting time troubleshooting the vacuum leak.

And I'm going to a friend's cottage for the afternoon, so I won't get much more done until tomorrow.

at this point...

1) degreased taller tranny
2) trans fluid drained
3) lower ball joints separated
4) axles removed
5) clutch cable disconnected
6) reverse switch wire disconnected
7) speedo cable disconnected
8) shifter linkage & support disconnected
9) most supporting / connecting nuts & bolts loosened and/or WD40'd

I was hoping not to have to drain the coolant, but looks like I'll also have to disconnect the lower rad hose steel tube that runs over top of stuff.

[MetroMPG]

July 9/2006:

Lunch time break. So far, only 2 minor snags:

- had to disconnect exhaust downpipe (thought I would get away with leaving it on, but couldn't get to rear tranny mount bolt)

- broke an engine mount bolt trying to remove it. This is the only bolt I've had *any* trouble with. I almost enjoy working on a car with low kms and no rust to speak of!

Also it's nice working with small, light parts.

Anyway, the broken bolt didn't really matter - the shorty transmission is OUT! I wiggled it off the motor with a minimum of fuss. Mounts are already swapped over to the tall one.

After lunch the process goes into reverse and I start putting it all back together. I'm taking my sweet time, chilling with the wrenches, and if all goes well, I'll be going for a drive by the end o' the day. If not, then sometime tomorrow.

[MetroMPG]

Another food break ...

I worked on the car most of this afternoon, with a couple of breaks for family stuff.

The hardest part was maneuvering the tall tranny in line with the motor - getting the splines on the input shaft to mate with the crank/flywheel. I spent quite a bit of time messing around with that before I noticed all my jigglin' and wigglin' had compressed the motor mounts over to one side of the engine bay, so the tranny was bumping against stuff it wouldnt' normally hit. Once I jiggled the motor back to its normal position, the tranny slipped right on.

So it's all in now. Just have to refill fluids, attach the clutch cable, torque the axle nuts and maybe one or 2 other things I forget at the moment. And then I can try it out!

But now... barbeque

[MetroMPG]

Originally Posted by SVOboy

Rather exciting, good sir, rather exciting indeed. I hope you had the tranny in neutral while trying to put it on!

NOW YOU TELL ME!

Actually I realized it should be in neutral after I started wiggling and jiggling. I have no idea what gear it was in. So I just turned the crank a tiny bit between each attempt and it slotted in eventually. And as mentioned, once I got the engine properly located that helped too.

SO!

I just got back from my test drive. First impressions = I love it. I have turned my car into a long-legged beauty. First gear isn't at all unmanageable. And based on 5 km or so, this gearing appears to suit my driving style perfectly. Very happy.

The speedo is clearly under-reporting. So, going out again to do a short Google Earth route, adjust the odo & speedo in the SG and get some preliminary MPG numeros.

[MetroMPG]

According to the numbers I have for this new final drive, my speed / distance should be underreporting by 19.8 % compared to the stock unit.

So I'm going to adjust the speed/odo in the SG now, and do some Google Earthing. I saved my route distances from last time, so I should be able to see what's going on as I'm driving and if my correction is right.

Back in a while...

[MetroMPG]

Strangeness.

According to Google Earth, my odo (and speed I assume also) is under-reporting by about 5.7%. Definitely not the 19.8% I was expecting.

I'm not sure what that means.

Either I calculated the differential difference wrong, or maybe I've been working with wrong numbers all along.

Anyway, I still really like the way it drives now. The car feels much more laid back.

[MetroMPG]

Figured out the odo/speedo difference. Man, I'm not very swift sometimes (actually I'm part Swift now, but... bad pun, never mind)...

The 5.7% difference has nothing to do with the final drive. Since the speedo cable runs off the FD, it *should* show the same vehicle speed on the gauge regardless of FD because the axles/wheels/tires are going to turn the same number of revolutions for a given distance. Only the engine speed changes.

BUT... the Swift the 3.52 FD came from had slightly different sized tires on the end of its axles: 165/65/13's if I remember right. Since I'm running the stock 155/80/13's that came with my original 4.39 FD, I've reduced the RPM of the axles.

As it turns out, the outside diameter difference between the 2 tire sizes results in a calculated 5.8% axle RPM difference. Pretty darned close to the 5.7% difference I saw last night. That's where my odo/speedo error is coming from.

Mystery solved!

Bonus: since my stock tires have a slightly bigger outside diameter than the tires that were spec'd for the 3.52 final drive from the Swift, that means is I'm actually adding to the gearing difference even more than the FD swap alone. Cool!

[MetroMPG]

OK Ben: since you can't wait to find out (neither could I)

65 km/h: W - 73.2 mpg (US) / E - 86.6 mpg (US) / avg 79.9
75 km/h: W - 63.0 mpg (US) / E - 77.6 mpg (US) / avg 70.3
85 km/h: W - 56.4 mpg (US) / E - 69.3 mpg (US) / avg 62.85

Last time I did this with the original transmission:

65 km/h: avg - 72.9 mpg (US)
75 km/h: avg - 64.95 mpg (US)
85 km/h: avg - 57.9 mpg (US)

Differences between the 2 tests... on THIS run:

- missing grille block
- there was a 10 kt breeze this time coming from the s/w
- new tranny

For an average FE improvement of 8.8% across those 3 speeds. (9.6/8.2/8.5)

Feeeeee!

[MetroMPG]

Originally Posted by SVOboy

RPM difference!?!?

Anyway, what's the lowest speed you can go in 5th with the new transmission?

RPM difference @ 65 km/h

Gear ... Old FD 4.39 ... New FD 3.52

5......2080....1650
4......2500....2003
3......3495....2783
2......5175....4118

new lowest speed in 5th: 60-65 km/h