Short Gear Review

[Honcho]

Well, I picked up my NSX from LarryB yesterday after an extensive service, the major component of which was installation of the JDM gear stack, or "short gears," in my 1991 transmission. Unlike most who do this mod, I elected to keep my stock 4.06 final drive gear, although we pre-loaded the differential to NSX-R spec. Prior to the shim it unlocked at 54 lb/ft. It now unlocks at 115 lb/ft.

Since my transmission only has 83,000 miles, I chose to replace only the 2,3 and 4 gears and to keep my existing 1 and 5 gears. It turned out to be a good decision, as my gears and synchros measured close to the brand-new spec.

The verdict? Quite simply, these gears transform the NSX. This is the gear stack that should have shipped with the car in the first place and, in fact, it did in Japan and Europe after 1992. The 1-2 shift the first time you do it is stunning. I found the 2-3 and 3-4 shifts to be imperceptibly different from the US gears in terms of RPM, but the car felt much more lively and torquey in those gears. The lug, if any, is now on the 4-5 shift where it should be, as 5th gear is an overdrive gear.

I would enthusiastically recommend the short gears to all 5-speed NSX owners. If you are lucky enough to have LarryB nearby, I suggest having him do the swap. He was patient, methodical and went out of his way to make sure the job was done right.

 

[goldNSX]

I'm glad you like it. I felt the same back in 2005 and never lost a tear about the Indianapolis-long gears which are completely useless here up in our mountains. But even for overtaking...why having to do it in a gear which goes up to 81 while there's only 50 mph allowed? Even our interstate roads have a 75 mph limit. Did you notice that you've three instead of only two usable gears now? The third gear is also nice to play with. Have fun with it. It's not a cheap mod but one you'll never regret.

 

[dablackgoku1234]

we pre-loaded the differential to NSX-R spec. Prior to the shim it unlocked at 54 lb/ft. It now unlocks at 115 lb/ft.

Can you elaborate on this for the non-mechanical folks? What exactly does this do?

 

[Larry Bastanza]

Can you elaborate on this for the non-mechanical folks? What exactly does this do?

This is also known as "breakaway" torque. The NSX 1991-94 is a limited slip dif. that means the rear wheels are locked together into the torque setting is reached then the two rear wheels will "slip" with respect to each other. The 54 ft.lbs. spec is common for a stock rear end. The NSX-R spec is 110+ depending on the dif. this is done by shimming the dif clutched to "tighten up" the rear end.

Very nice on the track when coming off the corner.

HTH,
LarryB

 

[DutchBlackNsx]

Larry is tha man for nsx work.

The short gears are very good, but if you do a lot off highway driving, i found the long gears much better. Especially the long 2nd gear can dust a lot of higher powered other cars.
What i did was install the short gears, and then added the daliracing chip with a higher revlimmit, so i dont loose much top speed at red line in the shorter gears.

I really should have shimmed the diff when i was at it.

 

[goldNSX]

I really should have shimmed the diff when i was at it.

Not your fault. Stiffening up the diff means installing three parts. But only two (in our case) were delivered. I may be wrong but SOS doesn't sell the diff parts anymore. Not sure about that.
Larry, where did you get them?
I had one guy who had the stiffer diff installed but he didn't felt anything.

 

[Honcho]

Gold-

Having driven both gearsets I could not agree more. The US gears are simply not suited to the stock engine. The only instance I could see them being advantageous is if you live in a place like Montana with long straight roads and no daytime speed limit and/or you have a 400whp turbo or SC NSX. I also have you to credit for deciding to order a new snap ring and countershaft bearing ahead of time. Turns out we needed it.

dablackgoku1234-

To add to Larry's comment, the stiffer Type-R setting keeps the rear wheels locked together longer. This results in more understeer (push) through a turn. Having tested this feature @ 75 mph coming home from Larry's, I can vouch for its effectiveness. The rear end is more planted on throttle in the turns.

 

[Ty B]

Honcho,

Thanks for the write up, you are killing me! Is envy a bad thing? This is on my wish list, but the list had a delay installed this year. Maybe it will happen next year.

Gold,

Sure glad you post up all your insights as well, they have helped immensly. Sure wish your KWv3's were installed right now. Sigh, again, maybe next year.

Larry,

Are the diff shims still available and should everyone doing this think about having an new bearing and snap ring replacement on hand, just in case?

 

[pgilliam1]

Thanks to the PO I have the shorties too, but have no idea if the PO opted for the locked/stiffened diff. shim. My car has a lot of understeer but I blamed it on my tire sizing (215/17 front and 275/18 rear). Any way to tell for sure if it's locked??
Happy Motoring!

 

[Ty B]

In the manual is a procedure for checking. If I remember correctly, jack up one rear tire. Take tire off. Place Torque wrench on axle bolt and turn. Check torque required to turn axle, torque used is break-away torque.

But I'm sure someone will chime in if I am wrong.

 

[nsxtasy]

I found the 2-3 and 3-4 shifts to be imperceptibly different from the US gears in terms of RPM

The 2-3 shift is virtually identical with either set of gears. The "short gears" shortens the gap between first and second, and widens the gaps between third and fourth, and between fourth and fifth.

The only instance I could see them being advantageous is if you live in a place like Montana

Or if you drive your NSX on the track. Having driven both sets of gears on the track, I prefer the stock gears for track use. With the stock gears, the gears used on the track (second through fifth) are spaced closer together, providing a gearing advantage resulting in faster acceleration at the speeds typically used on the track (70 mph and faster). The stock gears are particularly beneficial by offering quicker acceleration in the 70-80 mph range, where you spend much of the time on so-called "rhythm tracks" (e.g. Mid-Ohio). If I were driving only on the street and interested in acceleration off the line (such as in the "stoplight grand prix"), then I would prefer the short gears for their better acceleration below 70 mph.

You can see where each set of gears is superior in these acceleration numbers:

0-70 mph (stock gears): 6.59 seconds
0-70 mph (short gears): 6.27 seconds
70-150 mph (stock gears): 31.19 seconds
70-150 mph (short gears): 34.79 seconds

As you can see, different gearsets do different things well, one of those "different strokes for different folks" type things. Glad you're enjoying yours.

 

[LJSB]

Later, add the 4.23R&P and a CTSC and you'll really feel a difference.:biggrin:

 

[goldNSX]

The 2-3 shift is virtually identical with either set of gears. The "short gears" shortens the gap between first and second, and widens the gaps between third and fourth, and between fourth and fifth.

I'd like to add that between 3rd and 4th there's a gap maybe on paper but with no practical relevance. The only gap I now feel is between 4th and 5th making the 5th one feel like an overdrive. I like it this way as it keeps noise on the highway down. If I would drive daily on the German Autobahn it may be annoying. But I'm only once a year there and the gap between 1st and 2nd of the long gears is 100 times more annoying than between 4th and 5th for my driving area. If anybody likes to have all gaps sorted out he can go for the expensive 6 speed. For me the 6 speed was worth the money.

Later, add the 4.23R&P and a CTSC and you'll really feel a difference.:biggrin:

I'm still waiting. I guess I would not have installed the FD 4.23 if I went the forced induction route as there's plenty of torque throughout the rpm-band. But now as it's already installed...:wink:

I also have you to credit for deciding to order a new snap ring and countershaft bearing ahead of time. Turns out we needed it.

That's an interesting info, thanks. All credits go to MikeW from Germany here on the board. Isn't nsxprime and the NSX community a great thing? :wink:

 

[ChopsJazz]

If I were driving only on the street and interested in acceleration off the line (such as in the "stoplight grand prix"), then I would prefer the short gears for their better acceleration below 70 mph.

The "stoplight grand prix". I like the sound of that. :biggrin:

BTW, i have had the short gears for about ten years and I like them a lot. I'm glad, however, that I took the vendor's advice and changed to the 4.23 R&P at the same time. They're pretty exciting when coupled with the CTSC.

 

[Honcho]

In the manual is a procedure for checking. If I remember correctly, jack up one rear tire. Take tire off. Place Torque wrench on axle bolt and turn. Check torque required to turn axle, torque used is break-away torque.

But I'm sure someone will chime in if I am wrong.

This is exactly how you do it while still on the car, but you can leave the tire on. Service manual page 15-4.

1. Jack up right rear wheel;
2. Rotate wheel clockwise with a torque wrench on the axle nut. The wheel will not rotate until you reach the break-away torque.
3. Record torque required to break wheel loose.

We had my diff on the bench, so we tested it outside the car.

 

[Hksdrager7]

The shift differentail only works when you have tcs on right? I know I spelled that wrong lol. So when exiting the turn you leave it on right?

 

[Rusted_nailz]

I'm glad to hear this. I am building my transmission due to snap ring and possibly worn syncros. I'll be adding the short gears and the 4.23 final drive.

 

[Honcho]

The shift differentail only works when you have tcs on right? I know I spelled that wrong lol. So when exiting the turn you leave it on right?

No, the differential is not related to the TCS system. TCS is an electronic throttle control system that turns on and off the throttle rapidly to provide traction on slippery surfaces. Kind of like how ABS works with the brakes.

The differential, really a just a spring-actuated clutch, can also provide better traction by diverting power to the wheel with better grip, but it is entirely mechanical and is not part of the TCS system. Therefore, it is always working no matter if the TCS is on or off.

 

[pgilliam1]

This is exactly how you do it while still on the car, but you can leave the tire on. Service manual page 15-4.

1. Jack up right rear wheel;
2. Rotate wheel clockwise with a torque wrench on the axle nut. The wheel will not rotate until you reach the break-away torque.
3. Record torque required to break wheel loose.

We had my diff on the bench, so we tested it outside the car.

I can't wait to try this. RM Racing did the tranny work, but the PO didn't keep any of the receipts .
Thanks and Happy Motoring!

 

[stuntman]

Thanks to the PO I have the shorties too, but have no idea if the PO opted for the locked/stiffened diff. shim. My car has a lot of understeer but I blamed it on my tire sizing (215/17 front and 275/18 rear). Any way to tell for sure if it's locked??
Happy Motoring!

Whats your suspension/spring rates & sway bar, tire, tire pressure, and alignment?


Has anyone ever found a legitimate reason why Japan changed the gear ratio for the US market? There are many ideas or theories but anything concrete? You'd think Honda would have a 'more ideal' gear ratio for their own market and not solely for an overseas market...

 

[Honcho]

The only official Honda explanation I found was "different driving conditions." I believe this is intentionally ambiguous on Honda's part. Given that the JDM gears are available through the US dealer network, this tells me that the US gear change was implemented very late in the design process. This suggests to me that:

1. Honda originally intended the US cars to have the short gears;
2. Honda changed the US gear stack at the last minute; and
2. The change was marketing, not performance-based because, for some reason, Honda believed that American drivers would not like the short gears.

Honda's change to the shorter US 2nd gear in 1995 and change to the full short gears for Euro cars starting in 1993 demonstrates that they knew they had screwed up. Eventually, everyone got the 6-speed, which corrected the problem permanently, as the 6MT ratios are very close to the short gears (until you get to 5 and 6).

But you are right, Billy. This is just an educated guess. The reason for the US gears seems to be one of the most closely guarded secrets about the NSX. Honda won't say why, which only reinforces my belief that it was a mistake.

Has anyone ever found a legitimate reason why Japan changed the gear ratio for the US market? There are many ideas or theories but anything concrete? You'd think Honda would have a 'more ideal' gear ratio for their own market and not solely for an overseas market...

 

[tbromley]

This is great reading guys but now i wonder if simply changing out second gear wouldn't achieve everything needed? If 2 -3 and 3 -4 is imperceptable - why do them? I know I must be missing something here. I'd like to do the shorties but I doubt there would be much savings just doing 2nd or if it would make sense but my tranny only has 47k miles on it.

 

[Honcho]

Just changing to the short 2nd would really screw with your ratios. Also, from a cost standpoint, changing 2nd is most of the cost of the full short gear upgrade anyway because second gear is integrated into the mainshaft, meaning you still have to buy a new mainshaft.

By "imperceptible", I meant in the RPM drop. 3rd and 4th are much more torquey than the US gears.

 

[usafdarkhorse]

Nice insights! Glad you're happy with the purchase and install. :biggrin:

I'm considering it myself when I finally get another.

 

[goldNSX]

1. Honda originally intended the US cars to have the short gears;
2. Honda changed the US gear stack at the last minute; and
2. The change was marketing, not performance-based because, for some reason, Honda believed that American drivers would not like the short gears.

Maybe Honda liked to keep the best things - like the Type R - for themself. Well, just guessing but the gearing decision of Honda remains a mystery to me. Why did they change it for Europe car but not for US ones back in 93? I also guess there was a compromise within Europe. German cars are better off with the long gears, Swiss cars should have gotten the shorter ones because of the speed limit and their mountains.