Changing individual gear ratios?

[CrankyOldMan]

I've looked over the threads on final drive (FD) swap and the much more substantial 5->6 speed swap, but I haven't found any info on changing individual gear ratios.

A co-worker gave me a spreadsheet that helps calculate RPM drops between gears and by looking at some dyno charts it seems that the gap between 1-2 is too far, and the gap between 3-4 and 4-5 are less than ideal. I've also tried to find some coherent info on "shift points" but it still isn't making sense. My basic understanding at this point is: the torque doesn't really kick in until about 4k, and the redline is between 6k and 6.5k, meaning that you want to shift at redline but have the next gear pick up right around 4k to keep yourself in the power band.

All that said, is it possible/practical to alter the individual ratios to optimize them? I haven't dismantled a manual transmission before, but I built a LEGO model with a 3-speed gearbox once, so I understand that there are some important clearance issues with gear diameters.

Assuming that it is possible, it would of course make sense to have this done at the same time as a FD/clutch/flywheel/LSD mod. Your thoughts?

[Jason@SportsCar]

You can pave the way and figure out what other cars internals fit. Seems like a big headache to me, for a very minimal change. What is it you want to do with the car?

With the xB FD we don't use 1st gear for anything but getting the car moving (about 10'), and when we still ran the 15" wheel/tire combo we rarely used 2nd gear, so that big split was a non issue.

If you want to make the car quicker put in the xB FD. If you want to cut your shift spacing, put in the 6spd. If you need a project that will burn a lot of spare time and money, buy a bunch of Toyota transmissions from a wrecking yard and try building something custom.

Here is the speed difference between the two FDs: http://www.fatboyraceworks.com/gears...raph&Compare=1

[CrankyOldMan]

Originally Posted by Jason@SportsCar

You can pave the way and figure out what other cars internals fit. Seems like a big headache to me, for a very minimal change. What is it you want to do with the car?

It's currently my DD, but I would love to get into autoX, possibly even road courses with SCCA. In the mean time, I drive it like I stole it.

With the xB FD we don't use 1st gear for anything but getting the car moving (about 10'), and when we still ran the 15" wheel/tire combo we rarely used 2nd gear, so that big split was a non issue.

There are multiple stops between home and work/school, so using 1st/2nd regularly is inevitable. I've fantasized about doing the xB FD swap, but it would likely not be until after I've finished my degree in 3-ish years. Yes, this would also likely include a flywheel/clutch/lsd swap to save on labor.

If you want to make the car quicker put in the xB FD. If you want to cut your shift spacing, put in the 6spd. If you need a project that will burn a lot of spare time and money, buy a bunch of Toyota transmissions from a wrecking yard and try building something custom.

I actually LOL'd here. I'm assuming from the xB FD swap thread that when you replace the output shaft, you have to remove all the gears from the original output shaft and re-install them on the xB one. My first impression was that you just plonk the whole xB shaft (gears and all) into the old gearbox. After reading the repair manual, that doesn't seem to be the case.

My big concern about the 6-speed is the whole frame cutting bit. Not really a bolt-on solution, which is primarily what I'm interested in/capable of, even if I pay a shop to do it. Even then, I can't see a shop putting a warranty on that kind of work.

If I had access to those kinds of resources I would gladly devote them to it, but being a full time student, father of 4, and husband, niether time nor money are readily available for these kinds of projects.

Here is the speed difference between the two FDs: http://www.fatboyraceworks.com/gears...raph&Compare=1

I'm not entirely sure what benefit the chart is showing. I get that changing the FD alters the mechanical advantage (less RPM, more torque), but I don't understand how to estimate the improvement in acceleration from the given info.

[Jason@SportsCar]

Originally Posted by CrankyOldMan

I actually LOL'd here. I'm assuming from the xB FD swap thread that when you replace the output shaft, you have to remove all the gears from the original output shaft and re-install them on the xB one. My first impression was that you just plonk the whole xB shaft (gears and all) into the old gearbox. After reading the repair manual, that doesn't seem to be the case.

If I had access to those kinds of resources I would gladly devote them to it, but being a full time student, father of 4, and husband, niether time nor money are readily available for these kinds of projects.

I'm not entirely sure what benefit the chart is showing. I get that changing the FD alters the mechanical advantage (less RPM, more torque), but I don't understand how to estimate the improvement in acceleration from the given info.

I know my limits... I pull the trans out, order the FD/output shaft, drop it off at the shop. Then I pick up a piece that is ready to install in the car. When I first saw the trans open I thought no big deal, then I noticed the bucket of parts on the floor, that still had to go back in. Some jobs are best left to the pros.

Resources... You have four kids, this sounds like a family bonding project. Kids have small hands, great for little parts. I can't wait till my 6yr old can reach the pedals, then she can replace the wife when its time to bleed the brakes.

The chart just shows the difference in speed VS RPM.

Here is a trans for $200. http://www.yarisworld.com/forums/sho...20&postcount=1 Even is the synchros are crap, all you want is the FD and output shaft. Hell, I would ask the seller to pull out those two parts and chuck the rest, saves on shipping.

[BEEF]

being an old truck guy, generally if you decrease the numerical rear end (ie 3.55 to 3.21) you get better mileage but worse acceleration and vice versa for increasing the number.

I know it is actually 1/3.55 and what not but to be simple I look at it backwards.

one of the best things I did for power was go from 3.55s to 4.10s. it was by far the best thing I did but it was very expensive and it was on a rear wheel drive vehicle. not sure how it would be on a front wheel drive vehicle.

given the final drive gear ratios, I would think it would be a very noticeable difference.

[CrankyOldMan]

I'm not sure if this is a reposted link, but it seems at least partly relevant: http://www.wcengineering.com/articles/toyotatrans.html

[Lil Abner]

Well, my previous just was designing and engineering transmissions for small cars (like ours) for about 3 years. Can it be done? Yes. Will it be cheap? Heck no!! Custom helical cut gears are not cheap, even if you stick with stock gear cutter sizes. And you'll have to do the engineering on your own unless you can get the drawings for the current transmission, or have access to someone with some really good measuring tools. A caliper just won't cut it. If you have the time and cash, it would be a fun project!

[CrankyOldMan]

I've got access to a huge (30"?) optical comparator at work, so getting precise measurements wouldn't be too much of an issue for me. My biggest obstacle would be the metallurgy: I don't know enough about heat treating to even be able to guess what kind of hardening/annealing processes to use. Perhaps you have some insight here LilAbner?

All of the fantasy custom fabrication aside, the simple answer here would be: rev high enough in each gear to be able to drop close to the low end of the power band. Yes?

[Lil Abner]

Well, the only spec I can remember right now is:
Material: UNS G86200 (Rc 31-37)
Heat Treat: Carb Nitride
Hardness: Rc 58-62
Heat Treat Depth: 0.5-0.75mm

We also used a different material, but I can't remember what it was since I haven't worked there in a few years.

[CrankyOldMan]

Ok, after a bit of perusing around the web, I found a nice list of (accurate?) gear ratios for the C family of transmissions on Wikipedia. There are a few variants of ratios for each gear, but not all of the transmissions include information on which vehicles they were attached to.

Bluevitz-RS was also involved in a thread on yarisfans.com that documented swapping some internals between a C56 and a C150. The work involved was pretty spectacular, but the end result was very much functional and narrowed the RPM drop between gears to stay in the power band when upshifting from redline.

All in all, this gives me some hope of it being possible. That said, the probablility of finding the right donor vehicles could be very low. I'm going to spend some time working with my gear ratio spreadsheet to see which ratios are good candidates, then see about tracking down their sources.

[CrankyOldMan]

So after a few hours of trying to cross reference the wikipedia information with the parts diagrams on toyotapartszone, I've come to a few conclusions:

1. The close ratio C56 would be ideal, but because it's set up for performance it's both highly sought after, and high priced. ($1200-1600 used).

2. The C52 is a close second because it has the 1st, 2nd and 5th gear ratios of the C56 (the smaller diameter gear is integral to the input/output shaft) and the 3rd and 4th gears are close. The output shaft from the '84-'89 MR2 (crosschecks on toyodiy as being the same as the 1NZ xA/xB) has the 4.058 FD ratio, reinforcing the idea that shaft swapping is possible as long as you match the in/out by 1st and 5th gear, possibly 2nd too. These are also hard to come by for less than $1k.

3. The C59 is mathematically identical to the C52, but "stronger" so it may have better race/boosted performance and/or longevity. Broken ones can be found for under $500, but good ones will cost upwards of $1k.

So at this point, while I would love to get elbows deep in my wallet and a few salvaged gearboxes, I have to keep this on the back burner. If someone has a few different 5-speed gear sets lying around, I would love to hear if the in/out shafts can be dropped directly into a different C5# gearbox.

[CrankyOldMan]

More scrubbing and cross referencing:

* The 09 xD (C50) has the same gearbox case as the 09 Yaris, but a different bell housing. The 03 Matrix (C59) has the same output shaft and gear ring as the 09 xD. Therefore, the FD of the Matrix /should/ fit in the stock Yaris gearbox. The 03 Matrix and 08 xD are both listed as having a 3.941 FD.

* The 09 xD also has the same input shaft as the 09 Yaris, so the clutch should bolt up just fine.. All three vehicles have different part numbers for 1st gear, so I'm a bit fuzzy on how that sorts out. The Yaris and xD should have a 3.545:1 1st gear ratio, but the Matrix has the coveted 3.166 of the C52/C56.

Yes, I should just go take a few stacks of $20 bills to the scrap yard and have at it, but doing it this way only costs time. =)

[CrankyOldMan]

Time for an update, I suppose. I think I've covered this elsewhere, but here's what I'm looking at for a custom gearbox:

1st: 3.166:1 (C56)
2nd: 1.904:1 (C56)
3rd: 1.310:1 (C50)
4th: 0.969:1 (C50)
5th: 0.725:1 (C59)
Final: 4.312:1 (C56)

There are some tricky details about which year/model the parts come from, but most of them are eluding me at the moment. Perhaps I'll sort that out soon.

[CrankyOldMan]

It's a bit busy, but the intention here is to show how changing the gear ratios leads to improved spread. Stock C50 is in dotted red, C56 in blue, Custom in dark green. You can follow the gear shifts by starting on the lowest line and following the horizontal lines to the left once you reach 6k rpm. There really isn't much to be done about the gap between 1st and 2nd, but as Jason has indicated above, 1st becomes pretty irrelevant for racing applications.

[fnkngrv]

Perhaps if things play out right I can give you a better confirmation on the top speed with the stock rev limiter in place. Right now my 143 pretty much matches up to your graph.

[Jerkratt]

Hey cranky any news on the transaction gears I plan on hunting down the gears I need...

[CrankyOldMan]

I haven't had a chance to tinker with it this summer--too much AutoX! But this winter I will be at school pretty much full time, so I will have more frequent access to the shop where I'm working on it. Could you refresh my memory on what your plans were?

[Jerkratt]

Originally Posted by CrankyOldMan

I haven't had a chance to tinker with it this summer--too much AutoX! But this winter I will be at school pretty much full time, so I will have more frequent access to the shop where I'm working on it. Could you refresh my memory on what your plans were?

My stock trans is at my transmission guy. Any info on the gear ratios you posted a few posts up. If you found out what car/model/year Ect. Please and thank you. Personal chat might work better if so email me at Jerkratt@gmail.com