posted on December 10, 2012 00:00
Project Infiniti G20 Racecar: Transmission Upgrades
By Steve Rockwood
It seems that every time we try to do something to make Project G20 faster, we find a faster way to break something. This time around, we were certain that while the stock Nissan RS5F32V transmission was made of sugar glass, that our G20's modest turbo power levels, stock clutch, and not-so-abusive driving habits should make it last through a season. After three race laps, we were greeted with the all too familiar sound of a fork in a garbage disposal coming from the transmission. Someday, we'll learn a lesson the easy way.
|Three laps. Done.
To this day, we are still amazed that Nissan could pair such a ludicrously stout engine like the SR20 with the comically-weak RS5F32V transmission. This is even more of a slap in the face when you consider that they installed this poor excuse for power transmission over their extremely stout RS5F50 (which has a limited slip variant) found in the lower-power first generation Altima. Indeed, the path to a boosted SE-R is littered with the broken tears of SE-R transmission past: shattered cases, the dreaded fifth gear popout, bent shift forks, and, of course, the ubiquitous third gear failures. Past SE-R enthusiast Chris "Shaggy" Allen became so adept at bombardiering third gear sets that the community quickly termed this failure mode "Shagging the transmission". You'd be hard-pressed to find an SR20 boost junkie who doesn't know how to tear down his own transmission. Not many other enthusiast communities can claim this dubious distinction.
There are a number of ways in which Nissan screwed the pooch when it comes to the design of this transmission. For starters, unlike the block it's attached to, the transmission has very little in the way of bracing or support, and seems to exist only to hold fluid in and keep the gearstacks sort of near each other. Under wide open throttle, the case flexes enough to allow the input and countershaft to separate from each other, this problem is only exacerbated by the prodigious torque a boosted SR20 will belt out. This separation reduces gear tooth overlap and puts the onus of corralling power to the very tips of the gears. This problem is especially egregious in third gear, which is located at the center of the gearstack, and is the primary reason for failure under excessive power levels.
The case fails in its role of supporting the differential area as well, where a cutout we can only assume exists to drain fluid from a failed axle seal results in an unsupported section in the critical area between the diff and rear motor mount. The easiest way to remedy this was to fill the void with epoxy, but cracks in the case are still common here, especially in cars that experience excessive wheel hop
It's not all the case's fault, however. The SE-R transmission features an odd combination of stout gears (first and second) and high-wire-narrow gears (third and fourth) that will shatter as soon as you even think about putting your foot down.
So, what to do? We could tear the transmission apart, buy a new input shaft (gears one through four are integrated with the input shaft), treat them in every imaginable way, and pray they last a weekend, or we can send the whole thing to the scrapyard where it belongs and start over. We like starting over.
Luckily, we didn't have to go far to start over. Broken SE-R transmissions aren't exactly new to us, and two options sat, covered in dust, waiting for us to do something with them. Option one was Nissan's own attempt at salvation: an RS5F70A transmission yanked from a 2001 Infiniti G20. This transmission's case no longer lets it down, its gears are 15% wider, and the arrangement of the gearstack reduces the length of unsupported input and countershaft strung between mounting points on the case. A number of improvements in shift linkage support also help shift feel and prevent parts from failure as well. One must wonder how the SE-R community would compare to the Honda community had Nissan installed a real transmission in the B13 to start with.
|The RS5F70A we used has thicker gears with larger teeth, a beefier case with more support, and a much improved shifting mechanism.
Monday, December 10, 2012 7:20 AM
Now I know the proper order to treat parts: cryo, shotpeen, WPC!
Monday, December 10, 2012 2:15 PM
I've found it funny how Nissan can hit some drivetrains out of the park (the RB26, the SR20, the VQ and VR), and then completely miss on others (the QR, this transmission, the KA in the S13). It's like they're the bi-polar drivetrain builders. At least there are fixes out there for their oopses.
I'm surprised nobody makes a racing case for this transmission. It's a popular platform, so you would think someone would have done it by now to prevent this kind of failure.
Monday, December 10, 2012 2:26 PM
Car & Driver summed it up nicely recently when talking about the new Altima:
"What is Nissan? It can’t decide if it’s the samurai performance dojo that created the GT-R, the polar-bear rescue squad behind the Leaf, or Team Versa, which aims to clobber not just the Koreans but also the Chinese and Bulgarians on price. Likewise, the Altima is a confusion of aspirations and priorities, all of which fight each other to a stalemate."
PAR came out with a gearset, but it's $3k pricetag was way too high for Sentra owners and they sold but a handful. A whole gearbox would be prohibitive.
Monday, December 10, 2012 4:02 PM
We have enough broke RS5F50A's here (1st gear goes, I think it is?) and the 50A gearset is BETTER than the 32A? Oy. Man. Both are crap... o_0
Monday, December 10, 2012 5:16 PM
The 50 is supposed to be almost TWICE as strong.
RS6F51H is strong, but 4th is now a little weak, and the trans shifts like the shikaka. It also adds about 60 lbs up front.
70 is where it's at south of 300whp, IMO.
Monday, December 10, 2012 6:07 PM
SO..what your saying Brian is this. Get a RS5F50 trans and install a PAR gear set into it to hold 400+HP ?
Monday, December 10, 2012 7:01 PM
We've got enough broken 2nd gears in RS5F50A's here... I thought they were reliable til my friends got seriously into road racing.
I'd love to go PAR gearset myself, but for $3k, umm, I'm not making enough power to justify that! I can get an RS6F51H for pennies (well, maybe quarters) compared to that and I get a 6th gear for highway cruising? Sold! The later ones also get better synchros....
RFS6F52H ('08 Altima & '07 Sentra SE-R SpecV):
3rd gear double-cone synchronizer
1st & 2nd triple-cone synchronizer
RFS6F51H ('05 & '06 Maxima):
Same as above.
RFS6F51H ('04 Maxima):
2nd triple-cone synchronizer
1st double-cone synchronizer
RFS6F51H ('02 & '03 Maxima):
1st & 2nd double-cone synchronizer
Monday, December 10, 2012 7:18 PM
Great article. I haven't torn down my toasted transmission yet, it left me stranded last season but not until I'd put it through 1.5 seasons of track abuse. I was lucky. My garden shed is my transmission storage depot!
Monday, December 10, 2012 7:43 PM
PAR gearsets are officially MotoIQ Certified Garbage! ..and their customer service is crap. I got suckered into buying one of those early run dog gearsets for my SE-R many years ago and after it broke cuz of a lame design (the gear was so small they cut the teeth into the side of the dogs) they basically told me to piss off. I busted off a couple dogs with only 280whp. I went back and forth with those bozos for probably a year before finally giving up. RAAWRRR! venting complete :)
Monday, December 10, 2012 10:26 PM
the 50A/V transmission is supposedly pretty good (according to people in the FWD Nissan community I'm familiar with (Maxima). However there are some people who disagree stating that the 04A/V automatic is a stronger transmission (partially because the 2 fastest 1/4 mile known maximas run them). One guy in particular labels the 50A/V as "Borg Warner garbage". I'm not going to say that any of this forum babble is fact but just bringing it to light. Another thing about the 50A/V at least is that the input shaft bearing (ISB) tends to go bad in Maxima applications.
Tuesday, December 11, 2012 1:03 AM
Is shot peening really needed if one is going to do WPC?
WPC's web site sounds like the shot peening part should be skipped:
Tuesday, December 11, 2012 7:46 PM
mx5 actually has a really good question. Since WPC is shot at higher speeds and uses finer media than shot peening, wouldn't WPC do the same thing shot peening does, and then some? The only argument I can think of against that is that the larger shot peen particles have higher inertia and do a better job of initially compacting the metal's surface. Has anyone ever done a stress test between a shot peened vs. WPC vs. shot peened & WPC before?
Wednesday, December 12, 2012 10:25 AM
We felt that the shotpeening would be a good course treatment before WPC.
No data that we know of combining the two though.
Thursday, December 13, 2012 11:56 PM
RFS6F52H or 51H... These Trans. are they holding up to 400HP plus without breaking teeth?? And Jeff, apologize for bringing up those old hurtful feelings.... never knew you took it in the pooper with them....
Friday, December 14, 2012 9:49 AM
RS5R30A. That's the Z32 gearbox, why does it have open diff code when all z32 are v-lsd?
Friday, December 14, 2012 12:41 PM
@ Freak: 51H is holding big power right now, some guys over 500whp.
@ Tarik: Probably because the diff isn't part of the transmission?
Monday, December 17, 2012 3:44 PM
Maybe I missed it or something but you didn't seem to talk about the diff settings much. Did you run the NISMO diff with the factory settings? I am curious to see what they were and how they worked in your application.
Tuesday, December 18, 2012 3:18 PM
Cant wait to see more commentary on the 2013 season this car has. Nice work guys!
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