I'm aware this may be an ancient discussion, but since Im just now entertaining the idea of a 6 speed swap (I'm going to assume you've seen the Teaser Video) ...lets take a look at the numbers for a minute. A lot of modern sports cars have 6 speeds, so they must be better right? Maybe....or maybe not.
To learn the technical answer we need to first consider our engine, and additionally each of us may have a different idea of what's "best". So lets look at our 2ZRVIOS. We have a Toyota 2ZR-FE Dual VVTi engine making 139HP @ 6000rpm/131FTLBS @4100rpm. You can see here that our power band is from 4100rpm to 6000rpm, so we need our gearing to keep the engine speed in that range. Now if you can remember our ARtrackbox build, a Yaris C50 transaxle with the Cusco Type-RS LSD and a Scion 4.3 final drive. This transmission has awesome acceleration and provides flawless grip under all racing conditions. Aside from its limited 5th gear, the C50 ratios are a perfect match for the 2ZR-FE.
See how the 2nd to 3rd and the 3rd to 4th shift drops the engine speed directly onto that 4100rpm mark? That results in full use of the engines peak torque and horsepower. Then we shift to 5th gear, and we only get an extra 14mph before the car reaches its engine speed limit. We got very close to hitting the limiter in 5th gear on the front straight of Willow Springs Raceway, and there are still plenty of performance upgrades to do to the engine. So this is where you can see the C50 ratios are not designed for motorsports, but for daily use and economy. Now we could buy some close ratio gears for the C50 and give that a shot, but why do something thats already been done? Here at Armstrong Racing we love to take on challenges and try new parts, so why not go straight to a transmission we know has motorsports pedigree - The Toyota C60.
The C60 transmission may not strike a bell with you right away, unless you've had a vehicle with it. This close ratio 6 speed came coupled to the 189 horsepower, Yamaha designed 1.8L 2ZZGE in the Celica GTS, Corolla/Matrix XRS, and Pontiac Vibe GT. So we are taking this transmission from an engine with a very high 8600rpm redline, and mating it to a mass produced economy engine. Im pretty sure alarms are going off in everyones head night now saying "its not going to work". Hear me out though, how do you increase acceleration without increasing power substantially? Answer- Gear ratio tuning. We can't change our C50 final drive to anything higher, since were already nearly maxed out on top speed. Another option is to install a modified 5th gear, but that won't help acceleration. So lets take a look at the C60 ratios:
The C60 has a 4.5 final drive, so there's our acceleration increase. It also has a 6th gear top speed of 135mph with the 2ZR-FE rpm range, so there is both problems solved. Now another concern others have mentioned is how these ratios will keep the 2zr around peak rpm for longer, having a negative impact on longevity. If you study these charts long enough you will see that the C60 rpm drop after each shift is on average just 600rpm higher than that of the C50, the 2zr makes peak torque all the way to 5200rpm so were aren't losing or risking anything more really. Another concern may be extra shifting on the autocross courses, but again refer to the chart and you can see the C60 3rd gear is perfect. With a range of 45-68mph, I'll actually be shifting less than I was with the C50!
I'm not exactly sure what modifications installing a C60 into a Yaris chassis requires, or what additional parts I'll need to complete the swap. That's the fun part though right? Blazing a trail where no one has before, and challenging ourselves and constantly moving forward. We are fully committed and will make custom mounts if necessary, so stay tuned for the C60 swap writeup and videos.