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Metro taller transmission swap thread: +5% efficiency gain (taller final drive)
(Originally written: 05-29-2006)
--- Motivated by SVOBoy's transmission swap... Exactly when I would make the time to do this, I don't know. I already have too many projects stacked up in a holding pattern over the airport. But, I figure: start this thread and maybe it'll motivate me or someone else. There it is - transmission from a 4-cylinder (non-GT) Suzukiclone. Same housing and gear ratios as the 3-cylinder version, just a taller final drive: 1998 Metro/Firefly 1.0 L: 1st = 3.416 2nd = 1.894 3rd = 1.280 4th = 0.914 5th = 0.757 Final = 4.39 1989-1994 Swift 1.3L SOHC 5-speed: 1st = 3.416 2nd = 1.894 3rd = 1.280 4th = 0.914 5th = 0.757 final = 3.523 gear ... mph ... ratio ... rpm @ 4.39 calculated (observed) ... rpm @ 3.523 2 ... 40.4 ... 1.894 ... 4959 (5175) ... 4157 3 ... 40.4 ... 1.280 ... 3351 (3495) ... 2809 4 ... 40.4 ... 0.914 ... 2393 (2500) ... 2006 5 ... 40.4 ... 0.757 ... 1982 (2080) ... 1591 Engine RPM figures are calculated from this site: http://wildcatent.freeyellow.com/zookmods/calc.htm using outside tire diameter of 22.764 inches, calculated here: http://www.net-comber.com/tirecalc.html (Observed RPM) may not be reliable because it's hard to get a figure off the ScanGauge - digital tachs suck, especially when the numbers move around. Works out to a caculated 391 rpm drop going from the stock 4.39 final drive to 3.523 in 5th gear at 40.4 mph There was an observed 420 rpm drop on the stock 4.39 when shifting from 4th to 5th @ 40.4 mph. The mini experiment showed a 8.9 mpg/18.9% improvement in FE from that 420 rpm drop at that speed. Something to think about anyway. |
Some more to think about: this car's 0-60 time in stock form is about 15 seconds. This swap will make it ... much worse! One teamswift member found this swap intolerable.
Then there's the issue of the speedometer/odometer being off. Can compensate for that in the ScanGauge though. |
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A straight swap should theoretically only take a couple of hours: - remove starter - detatch steel lower rad tube bolted on top - disconnect clutch cable, reverse switch wires, speedo cable - remove axles - support engine - unbolt & remove tranny |
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Yes it would force you to shift more (in and out of top gear) depending on terrain, speed, cargo/passenger load. But if you're willing to tick the nerd gear box on the option sheet, I'd bet you'd also be willing to shift more for the FE advantage if it's right for your situation. |
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As for the gear ratios, everything I've learned about those trannies, I learned at TeamSwift. If I recall rightly, all the 3-cyl cars had the same ratios, but used different final drives depending on: XFi/12 in rims/13 in rims/convertable (heavier). Some bedtime reading... http://www.teamswift.net/viewtopic.php?t=14845 http://www.teamswift.net/viewtopic.php?p=163307 http://www.teamswift.net/viewtopic.php?t=23748 |
Increasing wheel/tire size would have the same effect. And truth be told, if I knew someone with a big honking set of 14 or 15 inch wheels that would fit our odd-ball bolt pattern, I would like to try them first and do some calculations to see whether or not I'd be happy with the transmission swap.
I probably wouldn't be doing any of this if I didn't have the transmission. It was essentially free. |
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Assuming I was OK with the driveability, I would still switch back to the smaller wheels and tires and do the swap because of the aero, LRR, and rotating mass advantages of the OEM tires/wheels setup (assuming the bigger wheels/tires combo is heavier). Quote:
http://www.my330i.com/mod19.php - So reducing rotational mass will particularly help if your driving is not primarily steady speed. |
Weak synchros are the biggest problem with these cars. I've driven 7 different versions of these cars, and four of them had crunchy 2nd gears or balky 3rd gears. Even in my 98, which is essentially "brand new" (just passed 8000 km yesterday), I have to be careful changing up to 2nd: I can crunch it if I switch too quickly (ie. "normal" speed in any other car), especially when cold.
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However, one concern of going with a too-high final drive is clutch wear. Starting from a stop will require more slip. One of the TeamSwift posters said starting on a hill with the 13 in tires and diff from the 4-cyl car would not be good news at all. We'll see. Perhaps. |
Some more thinking out loud... (have a highway trip coming up in the next couple of weeks, which gets me thinking about aerodynamics and gear ratios)
If I had a hypothetical 1st gear ratio of 3.0 and a final drive of 4.0, that means my engine turns 12 times (3.0 x 4.0) for each turn of the axle, correct? If that's the case, then the taller diff on the 4-cyl tranny isn't horribly different than the 3-cyl car. From a few comments I've read, it sounded like starting out in first gear would be made much harder - like the equivalent of starting in second gear all the time with the stock tranny. But if I compare the 1st and 2nd gears of the stock tranny to the 1st gear of the taller one, I get: 3-cyl tranny: gear 1 (3.416) x final drive (4.39) = 15.0 wheel revolutions per engine revolution 3-cyl tranny: gear 2 (1.894) x final drive (4.39) = 8.3 wheel revolutions per engine revolution 4-cyl tranny: gear 1 (3.416) x final drive (3.52) = 12.0 wheel revolutions per engine revolution By that math, it's not quite like starting in my current 2nd gear. It's roughly in the middle of my existing gears 1 & 2 (slightly closer to 1). |
Where ERPWR = "engine revs per wheel rev" (gear ratio * final drive ratio)
gear ... gear ratio ... ERPWR, stock tranny ... ERPWR, 3.52 final (4 cyl) tranny 1 ... 3.416 ... 14.99624 ... 12.02432 2 ... 1.894 ... 8.31466 ... 6.66688 3 ... 1.28 ... 5.6192 ... 4.5056 4 ... 0.914 ... 4.01246 ... 3.21728 5 ... 0.757 ... 3.32323 ... 2.66464 So I'm kind of "gaining" another gear. The stock tranny 5th gear/diff product is actually slightly shorter than the product of the 4-cyl tranny's 4th gear/diff. |
More good news:
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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. |
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. |
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 |
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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. |
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... |
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. |
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! |
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! :) |
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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 |
Theoretically, the lower RPM should help with the moderate load/low RPM accel technique during P&G.
I definitely have to shift later now. Up by approximately 7-10 km/h per gear. (e.g. 1-2 @ 25k, 2-3 @ 35-40 k, 3-4 @ 45-50 k, etc.) |
I effectively gained another gear. I did this mainly as a way to boost highway FE. I don't think it's going to have a big impact on city mpg. In fact, a case could be made that this could hurt city FE (at least that's what someone at teamswift said who did it. He said he stood on the gas much more to get the car moving, which negated the gains from different gearing... then again, I'm not likely to do adopt that driving style...)
Haven't decided what I'm going to do with the short legs. I could easily sell it - some of the teamswift speed enthusiasts like do do the exact opposite of what I just did: put the 1.0 trannys in the 4-cyl GT cars. http://www.gassavers.org/images/smilies/biggrin.gif I'm tempted to just hang on to it because: I'll have a back-up in case I have trouble with the taller one (it's got about 180,000 km on it); or if I ever want to revert the car back to "stock" for some reason. |
July 12/2006...
Update: I've noticed one mechanical issue with the 3.52. Sometimes when engine-off coasting, I can't easily get back into gear to do my next clutch start. Meaning: I'm coasting with the engine off, depress the clutch and try to select a gear. And... no go - the shifter resists slotting into gear. If I force the shifter under these circumstances, I crunch into the gear I'm trying to get. I've tried double clutching, and tried to select other gears than the one I want, but it doesn't seem to work. The transmission itself seems to shift nicely when the engine's running though. I don't think it's synchro related. One other thing I noticed that may be related to this: yesterday I popped the car into neutral to roll out of a parking spot (hadn't yet started the engine), and it wouldn't really roll easily, like something was hanging up a little bit. I pressed and released the clutch once, and that fixed it - something seemed to unhitch and the car rolled normally. Mechanical gurus: all this seems to suggest what? That the clutch is not fully releasing sometimes? Is that the clutch release bearing (which I know nothing about... I'm just throwing that term out there)? It's not a massive problem, as it only happens once in a while. Edit: the "new" tranny also has a very quiet mechanical "whine" when the car is stopped (engine running), the shifter in neutral, and the clutch pedal released. Don't remember the original tranny making that sound. Adding this in case it's related. |
PROBLEM SOLVED!
Adjusted my clutch cable this afternoon - I believe it was engaging too close to the floor (in terms of pedal travel). That would have caused problems re-engaging any gear coasting with the engine stopped if there was even the smallest amount of clutch drag. I ran errands this evening, and the transmission didn't balk / hang up once. In fact, it also seems to shift smoother (though that could just be placebo effect). |
July 26/06 ...
Update: since the clutch cable adjustment, I've had absolutely NO problems with the 'new' long-legged transmission in any way. I've almost unlearned my old shifting-based-on-engine-rpm habit developed with the original gearbox (I have to stretch the RPM just a little more when accelerating since the gaps between gears are larger). Hill starts require noticeably more clutch slippage, as my "new" 1st gear is equivalent to somewhere between gears 1 & 2 on the original gearbox. But it's not unmanageable. If I were driving around with 2 or 3 people in the car on a regular basis and lived in a hilly place, it would perhaps be an issue. I also do believe it shifts nicer than the original unit, but that's pretty darned subjective, isn't it. My satisfaction, however isn't. I'm still very glad I did the swap. |
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http://images6.theimagehosting.com/108mpg-m.th.jpg edit: Round trip - 7.9 mi. My normal sub/ex/urban "loop". Very good, but not optimal traffic/light conditions. |
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Edit: which, now that I think of it, is actually an improvement since my previous best of 101 was without the belt. |
August 10/06:
The only other hot-weather bi-directional runs I did in warm weather before changing transmisisons was the alternator/no alternator test. Unfortunately, it's a little complicated by the fact that I tested at 70 km/h, which was the one speed on the speed vs. mpg graph where the data seemed to get a little out of line (literally): http://images6.theimagehosting.com/m...art.371.th.gif (should be an image above this line) I'm inclined to think that 71.0 jump at 70 km/h was testing error, since in the alternator vs. no alternator test, the control runs (5 bi-directional) at 70 km/h in 71F temps (vs 58F for the speed runs) averaged 70.8 (i.e. same results, at higher temps, which you wouldn't expect to see). http://images6.theimagehosting.com/m...chart-z.th.gif (should be an image above this line -) All of this is a long-winded way of saying that the FE improvement from the transmisison is likely closer to 5% (5.6%, based on the single 70 km/h point comparison) than 8.8% I claimed before. |
August 21/06:
Collected a bit more info: http://metrompg.com/offsite/mpg-vs-s...t-z-b4-aft.gif I find that "bump" at 70 curious, as well as the narrowing of the difference between the 2 as speed increases. |
The taller transmission lowered RPM by 19.8%. It was lowered a further 5.8% because the OEM tires on the Blackfly are taller than the tires originally spec'd on the taller transmission car. For a total effecive gearing change of 25.6%.
With the extra information posted in the above chart, the average difference between the measured speeds vs mpg's for the 2 transmissions is 7.9% from original. That's the most reliable baseline difference yet, since there's more speeds to compare. But that figure also includes the effect of ambient temperature difference. |
Feeding the aero/rr web tool my car's stats, and varying just the ambient temperature, I get the following:
Temp: ... 15C/59F ... 25C/77F ... mpg change (from lower temp) 45 MPH ... 74.48 mpg ... 76.28 ... 2.36% 50 MPH ... 63.9 mpg ... 65.54 ... 2.57% 55 MPH ... 55.22 mpg ... 56.71 ... 2.63% Avg difference: 2.52% |
thanks for thw work you've done!
I too have been toying with the idea of a trans swap, but it may be too much. I love the look of my new wheels, but they are a bit too tall and def wider. going from the factory 145R12 to 175/65R14 I figure my gearing from a stock 4.1(91 metro) to be a 3.78. At home I have 2 trannies because I want to get another metro and have one for fun(this one now is for fun and econo, so i'm stuck in a cross-hair). I have a 3.52 and a 3.79. If I'm right, the 3.79 would give me a 3.49, and the 3.52 would give me an overall 3.24....which could be unbearable with such big wide tires on. Oh, what to do...... Just filled up yesterday, so I'll see what my mpg is and go from there. Maybe I'll wear down these tires for the next 2yrs, then go thinner again and to 13" with steelies before I do a swap. putting rear disc on and front vented rotors probably added weigth, along with a neon center console, so maybe this will be the fun car then, since I still have sway bars I want to install. |
Without the XFi cam (more low end torque), I'd be reluctant to go with the 3.52 final drive with taller tires on the car. But with it, I'd probably do it. Then you'd have bragging rights for the tallest effective gearing in a Metro that I know of.
That help? :D |
Metro-I thought you remembered-I do have that cam :D
I can't seem to get my distributor to go past 5* though..... Tranny would be nice, but do have atleast one big hill home in either 3 directions.....I may get the urge to atleast throw in the 3.79 to start. |
xfi vs custom 181 cam test
I getting ready to test these 3.52's in a '96. I am starting out with a rebuilt engine (.020 over, around 10.25-1 compression,1.3 flywheel). There is a new cam out from Crower that has a 181 duration (very high torque/low rpm cam that works better then the xfi cam. I can't post links yet but you can see the test for yourself. Go to youtube and you can find it under ... Geo Metro XFi Camshaft vs Custom Grind.
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Only reading the original post, I'd assume the discrepancy would be speedometer calibration, possibly from incorrectly using loaded tire radius rather than correctly using unloaded. But that will save you from speeding tickets, using loaded.
Anyway, the solution for taller gearing hurting acceleration is a turbo, plus turbos like tall gearing to pull against. |
What discrepancy are you referring to?
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