4.23 final drive ratio and your 6-spd

[ScienceofSpeed]

We've received quite a few inquiries from customers with 6-speed NSXes since the arrival of the new Japanese 6-speed equipped NSX-R as to if the R spec 4.23 final drive will work with their cars.

The answer is yes, and no.

In 1995, Honda changed the differential to a torque reactive style. This included changing the inner gear surface of the ring gear to tapered teeth. This prevented 95-96 5-speed NSXes from enjoying the performance offered from the 4.23 final drive of the NSX-R since a 4.23 ring gear was not available that was compatible with the 4.23 countershaft. Honda continued to employ the torque reactive differential until model year 2001. For 2002, the transmission was reverted back to the torque control differential. Now that a 6-speed counter shaft is available with the correct number of teeth and 4.23 ratio, the 4.23 final drive can be installed in a 6-speed transmission. Unfortunately, it is only compatible on 2002 and later cars.

Interestingly, Honda has discontinued the old 6-speed transmission (part no. 20011-PR8-E61) and replaced the part with the new 2002 transmission (part no. 20011-PR8-A61). If you were to place an order for a 6-speed transmission from your Acura dealer (or ScienceofSpeed) for 1997-2003 you would receive a A61 since the E61's are depleted from inventory. If you have the A61 transmission, you can use the 4.23 NA2 NSX-R final drive.

You can find both the 5-spd and 6-spd NSX-R final drive gear kits here (along with recently lowered prices). We stock both:
http://www.scienceofspeed.com/products/drivetrain_performance_products/NSX/Honda/NSX-R_RP

Thanks,
-- Chris

 

[Eric5273]

Can you please explain what exactly this does to the car. If there is a performance increase, obviously it must also be some disadvantage also or else all NSX's would come this way. Thanks.

 

[AJKS]

I ordered the R gears for my 2002. SOS just got them in today and I hope to have them installed in 2-3 weeks. The only real down side should be fuel economy. You will have a higher RPM for a given speed. The NSX R's, for 2002, come factory with the 423.5 ratio. They have a 0-60 time of 4.4sec .5 better than a factory NSX. The only other advantage for the R is weight reduction. Top end may be a bit less 2-3mph but as far as I know the slower top end is not proven.

 

[nsxtasy]

Can you please explain what exactly this does to the car. If there is a performance increase, obviously it must also be some disadvantage also or else all NSX's would come this way.

Basically, having a higher number R&P makes the gearing shorter in all gears.

Advantage: the acceleration is better within any gear; perceived advantage of faster acceleration (perceived more than actual)

Disadvantages: the gas mileage is worse, and the shift points are lowered; acceleration is worse at some speeds (where the different setups would be in different gears); purchase cost (of course); installation labor (1-2 days) although this is minimal if you are doing other tranny work anyway; "bang for the buck" is less than some other mods

Basically, all of the acceleration advantage comes in first gear before the first upshift with the shorter R&P; after that, you would have a disadvantage overall because part of the time you would be forced into a higher gear with the shorter R&P, making acceleration worse. In general, most gearing changes only help at some speeds, and hurt at others.

How much of an actual difference in acceleration are we talking about? Because the 4.235 R&P is a new product for the six-speed, we don't have calculations for it in the article by our friend, Lt. Col. Butler USAF. But he has calculated that the 4.235 R&P in the five-speed reduces 0-60 times by 0.13 second and 1/4 mile times by 0.10 second. Gains would likely be similar in the six-speed. (I say that because Bob has calculated gains for the even shorter 4.55 R&P in the six-speed as 0.18 second and 0.20 second, respectively, over stock.)

 

[Lud]

Chris, thanks for researching that. Very good info that I haven't seen anywhere else.

 

[nsx1]

We've received quite a few inquiries from customers with 6-speed NSXes since the arrival of the new Japanese 6-speed equipped NSX-R as to if the R spec 4.23 final drive will work with their cars.

The answer is yes, and no.

In 1995, Honda changed the differential to a torque reactive style. This included changing the inner gear surface of the ring gear to tapered teeth. This prevented 95-96 5-speed NSXes from enjoying the performance offered from the 4.23 final drive of the NSX-R since a 4.23 ring gear was not available that was compatible with the 4.23 countershaft. Honda continued to employ the torque reactive differential until model year 2001. For 2002, the transmission was reverted back to the torque control differential. Now that a 6-speed counter shaft is available with the correct number of teeth and 4.23 ratio, the 4.23 final drive can be installed in a 6-speed transmission. Unfortunately, it is only compatible on 2002 and later cars.

Interestingly, Honda has discontinued the old 6-speed transmission (part no. 20011-PR8-E61) and replaced the part with the new 2002 transmission (part no. 20011-PR8-A61). If you were to place an order for a 6-speed transmission from your Acura dealer (or ScienceofSpeed) for 1997-2003 you would receive a A61 since the E61's are depleted from inventory. If you have the A61 transmission, you can use the 4.23 NA2 NSX-R final drive.

You can find both the 5-spd and 6-spd NSX-R final drive gear kits here (along with recently lowered prices). We stock both:
http://www.scienceofspeed.com/products/drivetrain_performance_products/NSX/Honda/NSX-R_RP

Thanks,
-- Chris

Just to set the record straight, Chris, and others, have found this not to be the case. Apparently, the 2002 manual still has the torque-reactive differential. (see this thread.) I'm trying to get to the bottom of the fitment issue here. In the 2nd post, Chris explains. Obviously, I need the help from guys like Chris.