Project Infiniti G20 Racecar: Transmission Upgrades

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Improved OE transmission mount location on newer B15 and P11 chassis.

With our transmission mounted and happy in the car, we had one final bit of work to do to reduce the likelihood of shattering yet another gearstack.  One of the major improvements in the B15 and P11 cars that made these transmissions more reliable was moving the motor mount location.  With the RS5F32V transmissions, the transmission mount bolts to the front of the trans.  Our new unit had provisions to bolt the motor mount to the front, but the best location for the transmission mount is centered on top.  The reasons for this are twofold.  One, with the mount on the front of the transmission, and the other mount located on the back, the torque of the drivetrain will try to pull the transmission apart, likely causing unwanted gear spread.  Two, the centered mount gives a nice, beefy, external brace for the case to help keep the gearstacks better located.  Our solution was relatively simple if you’ve got some cutoff wheels, a welder, some 3/16″ mild steel plate, and some Cardboard Aided Design (CAD) skills.

Our bridge-like transmission brace emulated the stock motor mount bracket.  If your transmission came with the stock mount, you could probably grind off the motor mount brackets and leave the brace.  This should keep both sides of the transmission together, and will also help to spread out drivetrain torque over both sides of the transmission instead of just one.  To keep the gearcase and bellhousing located together, and just to add a little starch to our mount, we also connected it to the clutch release cable bracket.

So, was it worth it?  Absolutely!  Time will tell if the RS5F70A can withstand the abuse of a turbo SR20 in racing conditions, but there really is no downside to this upgrade that we can discern.  The longer gears have reduced the number of shifts needed on a track and are more forgiving of ham-fisted throttle applications.  The shift feel of the new unit is much improved, and the NISMO differential and JWT clutch perform flawlessly.  Corner exit speeds are definitely among the best in the series, thanks to the traction offered by the NISMO diff and the ample low-end power to push it.  The best part of all, obviously, is that the transmission lasted more than three race laps.  We’ve (ab)used this transmission for 2 race weekends and a couple hotlapping events so far, and it hasn’t hiccupped once.   With the upgrades performed, the transmission failures are now at the back of our mind where they should be.  Again, we can’t help but wonder how far the SE-R community could have taken this car had it not came with such a comically weak transmission.

Two race weekends and a couple hotlapping events have revealed no flaws in our new setup.  Project G20 even completed a couple MPTCC races this year and will be making a run at the entire 2013 season.

Sources:

Jim Wolf Technology

WPC

Cryoscience

Technosquare

ARP

GSpec Performance

Want more Project G20?  Check out the rest of the series:  MotoIQ Project Infiniti G20 Racecar