Having addressed most of our cooling concerns in part 1 we continue with the transmission upgrade for our Infiniti G37S. Ten years ago it would have been a fringe case to perform an automatic transmission upgrade for a project car. These days many manufacturers don’t even offer a manual for their high-performance models. Even enthusiast cars like the new BMW M5 use a standard torque converter automatic like our car instead of a DSG gearbox. We understand this isn’t the sort of upgrade for everyone, but the purpose of this car has shifted from daily driver to weekend project and we’ve invested a lot of time and money in the car already. The thought was then, what can we do to get rid of the laziness our car had due to slow shifts and slipping between gear changes to continue to upgrade our sports sedan.
Reading through the Nissan press releases on the G37 forums a term was used frequently for this gear change slipping called rev-flaring. Specifically on the early 7-speed automatic transmissions. This at least made us feel better that the slipping we were experiencing was normal but as an enthusiast it was still unwanted behavior. We were also less confident to proceed with any more power upgrades until the transmission was addressed. Those who have gone down the forced induction route state that any power over 400 lb/ft destroys the automatic transmission when boosting at low RPM’s in 5th, 6th or 7th gear. While it was great that Nissan wanted to provide driveability along with the performance and efficiency achieved with full lockup torque converter, the execution at times resulted in sluggish and worn out lockup torque converter clutch. Our UpRev tune did help firm up the shifts a bit by increasing the line pressure in the transmission, but at times the rev-flare slippage would creep in between shifts and sometimes acceleration just felt soggy due to the transmission.
We found a few upgrade options out there for our transmission, but to be honest rebuilding an automatic transmission isn’t something we’ve really done at MotoIQ and there weren’t a lot of references to call for upgrades. We did remember way back when there was a turbo FWD SR20 guy out there who had an automatic transmission modified by Level 10 for his B14 Sentra. With some quick internet searching, it turns out Level 10 is still around and they have an upgrade for our 7AT transmission (Part#INFIN-G1800-RE7). They offer the rebuild parts separately as components where you can have a local expert install them or they can send a complete transmission upgraded and ready for install. The individual components consist of:
- The rebuild kit, that includes all the clutches, gaskets seals, O rings, and upgraded clutch friction material to hold more power and provide improved gear engagement. Some of the clutch baskets are modified to take more discs to give more clutch friction area and torque capacity.
- An upgraded valve body which decreases shift times and improves the overall shifting quality of the transmission.
- An upgraded torque converter. The original torque converter was designed for the stock power levels of the car but we’d argue that ours wasn’t that great in handling the basic bolt-on increased power in our car. The Level-10 torque converter is stronger and has a higher stall speed. This is the speed that it engages, equate this to increasing the rpm that you let the clutch out at. The torque converter lock-up clutch material is changed from something like cardboard (no kidding) to a semi-metallic material that is stronger and grips harder.
6 comments
Surprised there is no love for this. I totaled my G37S at a track day and it still bums me out. But the transmission was a very weak link. I imagine this upgrade would really wake it up. How is the transmission for daily driving?
Daily driving is almost like stock. There’s definitely a difference when the transmission is cold versus warm; best described as a small stumble that happens between gear changes. Once warm though this completely goes away. When decelerating and the car downshifts the engine braking is definitely more pronounced. Not to repeat what was already put in the article but gear changes now really shove the car forward where before shifts really felt soggy. None of this takes away from the car it only adds to the grins and this upgrade appears to be a must for forced induction.
I’m sorry to read about your car. Hopefully your replacement is just as fun or you took it as an opportunity to try something different. There are a lot of cool cars out there I’d like to try. If I had to do it over again maybe I’d try a Golf R or a Q50 Redsport or a 335. Price was the deterrent to all those cars 4 years ago when I bought the G37S so bang for the buck it’s hard to beat the Z or G37 as a GT car. I don’t need to daily drive the car anymore so something a little more extreme like a used Camaro ZL1 or a Corvette come to mind as does a Cayman or Boxter or BMW M car but the price-point is obviously higher and so are the repair costs which is why I’m still very into what I have.
Hi Aaron, I have a g37s sedan that I have turned into a time attack track car. I definetly feel the transmission is the weak link. I really love the paddle shifters over a manual. Would you recommend this upgrade for the track? Does it make the car faster or just feel faster?
@Tom,
Sorry I don’t have timed verification for you on the quicker shifting. I didn’t take the car to the track before to see how the car performed to then have a measurement after. My main concern was removing the weak link in the powertrain when we add more power. I would definitely recommend this transmission for the track with the note that you should add both an oil cooler and a transmission cooler. Stay tuned and you might see an article on that soon ;). The 370Z and the G37 both seem to do a pretty good job of running the fluids hot.
I really do wish you could experience the Level10 transmission yourself beforehand to see how much better it is.
Ah man, I wonder how the good Dr. is doing. I loved watching the progress of his SE-R build with the transmission and turbo kit.
@Khiem, well I feel the same way about your S2k. This one has been fun as it has gone from daily driver to weekend toy. Hopefully, like you we’ll get to add a lot more power.