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Limited Edition OS Giken 4.642 gear ratio & LSD

Joined
6 February 2003
Messages
1,015
Location
Silicon Valley, CA
In doing some research on the best gear ratio / transmission combo for my NSX, I came across something that looks pretty interesting. The 4.642 gears are even more extreme than Comptech's 4.55's. Since I plan on keeping my NSX an NA, these are very interesting to me.

nsx-lsd-final-kit3.jpg


Click here for the OS Giken webpage and info

Here are the prices based on today's exchange rate:
6spd gears + lsd = $2368.91
5spd gears + lsd = $2415.73
5spd gears only = $1151.69
6spd gears only = $1198.50

I'm not sure if the "gears only" sets will fit with the stock LSD or only with the OS Giken LSD. It also looks as though there is a 20 set limitation on sales? Maybe an OS Giken retailer can comment (SOS?)?

This 4.642 gear ratio produces the following shift points for japanese gear sets (in mph):

......5spd. 6spd.
1 - 41.54 41.54
2 - 65.10 65.72
3 - 90.52 89.90
4 - 122.76 113.46
5 - 178.56 140.12
6 - ....... 178.56

Can someone (i.e. Bob Butler :wink:) do an acceleration calculation based on these numbers?
 
Last edited:
AutoVation said:
This 4.642 gear ratio produces the following shift points for japanese gear sets (in mph):

......5spd. 6spd.
1 - 41.54 41.54
2 - 65.10 65.72
3 - 90.52 89.90
4 - 122.76 113.46
5 - 178.56 140.12
6 - 178.56
There are a few small errors in those numbers. The gear ratio for first gear is not the same for the five-speed and the six-speed (it's close, but not exact - 3.071 and 3.066) and the speed at redline in fifth gear with the five speed should be less than the 166 mph that applies to the 4.55 R&P.

Incidentally, the way this board formats posts makes it appear that the speed shown for sixth gear applies to the 5-speed (because it doesn't display the full width for the twelve consecutive spaces), but it actually applies to the 6-speed.

AutoVation said:
Can someone (i.e. Bob Butler :wink:) do an acceleration calculation based on these numbers?
PM sent...
 
nsxtasy said:
There are a few small errors in those numbers. The gear ratio for first gear is not the same for the five-speed and the six-speed (it's close, but not exact - 3.071 and 3.066) and the speed at redline in fifth gear with the five speed should be less than the 166 mph that applies to the 4.55 R&P.

Incidentally, the way this board formats posts makes it appear that the speed shown for sixth gear applies to the 5-speed (because it doesn't display the full width for the twelve consecutive spaces), but it actually applies to the 6-speed.

PM sent...

I thought some of the numbers on the OS Giken website just didn't look right.

I also added some space holders to make the table read right. (I had done it for the 5spd 6spd line already but missed the one you caught)
 
looking at the quarter mile times of nsx's with short gear transmission, it seems as if this improvement makes a huge difference in acceleration. Is this why j-spec nsx's are faster than us spec nsx's?
 
WealthBuildR said:
looking at the quarter mile times of nsx's with short gear transmission, it seems as if this improvement makes a huge difference in acceleration. Is this why j-spec nsx's are faster than us spec nsx's?
The JDM '91 NSXs (aside from the Type R) have the same 4.062 R&P as the USM '91 NSXs, but they have the "short gears". According to Bob Butler's analysis, this improves 1/4 mile acceleration times by 0.11 second.

The JDM NSX Type R (first generation) has a 4.235 R&P and short gears, and a number of additional performance improvements (e.g. lighter weight). The gearing changes alone improve 1/4 mile acceleration times by 0.19 second over the USM NSX. You can read about the differences of the Type R model in the FAQ (General - Model Information). The Type R model is 265 pounds lighter, which improves acceleration far, far more than the gearing changes. (Reducing only 100 pounds improves 1/4 mile times by 0.16 second.)
 
So are you just saying that some people here need to lose weight if they want to go faster? :tongue:
 
AutoVation said:
Can someone (i.e. Bob Butler :wink:) do an acceleration calculation based on these numbers?

Sorry guys. I have been busy moving in and starting the new job. Wow, now I get paid to do vehicle and other computations I used to do for fun. I'll perform the requested calculations when I get a chance and post the results.

Bob
 
1BADNSX said:
Sorry guys. I have been busy moving in and starting the new job. Wow, now I get paid to do vehicle and other computations I used to do for fun. I'll perform the requested calculations when I get a chance and post the results.

Bob

How about the rpm's in 6th gear at 75mph also? :biggrin:
 
On a 5-speed with 4:642 gears/LSD would one really need the short gearset? Anyone know if just doing the 4:642 would keep the car in the powerband like short gears do?
 
AutoVation said:
How about the rpm's in 6th gear at 75mph also? :biggrin:
That's a straight multiplication. The FAQ shows that with the six-speed and the stock 4.062 R&P, sixth gear hits redline (8000 RPM) at 202 mph (or would, if aerodynamic drag weren't a problem). Therefore, with a 4.642 R&P, 75 mph would occur at
8000 RPM x (4.624 / 4.062) x (75 / 202) = 3381 RPM.

mackash said:
On a 5-speed with 4:642 gears/LSD would one really need the short gearset?
Need? One could easily argue that you don't really need any mods. But the short gears will still narrow the wide gap between first and second (while spreading the narrower gaps between the upper gears).

mackash said:
Anyone know if just doing the 4:642 would keep the car in the powerband like short gears do?
The short gears help, not because there is a "powerband" (in fact, the torque curve is remarkably flat, so there is no huge torque advantage in being at one rev point vs another), but rather, because of the gearing advantage of having the ratios fairly close together. Just doing the 4.642 (whose ratio is 4.642:1, not 4:642) doesn't change the ratios between adjacent gears; for example, the revs after upshifting from redline will be the same as with any other R&P gear.
 
Is it possible to get these in the U.S. ? That seems like a great gear ratio for autocross and street driving use.
 
Bob. Can you do calculations for 5-speed cars with a comtpech and BBSC assuming 330rwhp on a comptech and 380rhwp on a BBSC.
 
NetViper said:
Bob. Can you do calculations for 5-speed cars with a comtpech and BBSC assuming 330rwhp on a comptech and 380rhwp on a BBSC.
If you provide the dyno horsepower curve as a function or RPM. Curve fit the data using a multi-order polynomial and give me the equation HP = f(RPM).

Bob
 
W said:

You will be turning a lot of RPM cruising on the highway. It will be noisy and bad for fuel economy. In a daily driver, I don't think it is a great idea. Thats just my opinion.
 
NetViper said:
Bob. Can you do calculations for 5-speed cars with a comtpech and BBSC assuming 330rwhp on a comptech and 380rhwp on a BBSC.

I can do the calculations for this... $3000 wasted dollars and 3 weeks down time. Ask me how I know.
The Comptech 4:55 has failed on many FI cars, the teeth are just not thick enough at this ratio. The teeth on a higher ratio will be even thinner.I am just playing devil's advocate so you might save some money and tears.

Joe
 
jdnsx said:
I can do the calculations for this... $3000 wasted dollars and 3 weeks down time. Ask me how I know.
The Comptech 4:55 has failed on many FI cars, the teeth are just not thick enough at this ratio. The teeth on a higher ratio will be even thinner.I am just playing devil's advocate so you might save some money and tears.

Joe

FYI the teeth on the OS giken unit are as thick as the OEM gear. It comes with a new counter shaft coupled with the final gear to accomodate the change. Also the final gear is a bit bigger than the OEM one due to this.
 
Old thread BUT,

Are these 4.642 gear ratio available?
Have any of you guys ordered just the Ring+Pinion and installed it?
 
since thats my next mod i am very interested as well. could anyone verify if it is necessary to use OS lsd or is stock ok? i have a 6spd so i would have to change the lsd anyway.
 
has anyone installed their 4.44 setup that sos sells?

I did one for ak, who has commented above:). This version was a 1.5 dif IIRC(they come in different lock settings)

I was a nice change, the car was quite fun in the back roads out where I live. Ak and I discussed the different types of fluids to use in it, and he will have to comment about what he is running now. I recall us using redline when I installed it per the Giken recommendation, but they offered a special oil we could not get from Japan. Ak will comment I am sure:).

HTH,
LarryB
 
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