Make your NA NSX faster

[sparky]

OK I admit, I'm pushing the concept behind NA forum boundary with this one, but hey I have good motives!

Have you noticed that SoS are finally offering a 4.4:1 differential? read about it here

Before going to the trouble of engineering the design of the 4.4:1 (in Japan) SoS tested the demand in prior thread and at least 10 of us responded. Now it's actually available only 2 or 3 of us have put our hands up again, and unless we get 10 it probably won't go ahead.

And why would you do this - well, after 10 seconds off the line a NSX equipped with 4.44 diff will be about 1.5 car lengths ahead of it's stock sibling .... now that's a real NA performance boost :smile:

 

[Hapa88]

Here's the benefit of the 4.235 ratio from the NSX-R.

Fast forward to 4:42 on this video.
<iframe width="420" height="315" src="http://www.youtube.com/embed/es1RKcW_tSA" frameborder="0" allowfullscreen></iframe>

 

[sparky]

great demo, after 13 secs with 4.235:1 the NSX-R did the NSX by about 1.5 car lengths.

A stock NSX fitted with a 4.4:1 diff will be about 2 car lengths ahead of a stock NSX after 13 seconds (i.e. about 1/2 car ahead of NSX-R)

 

[A.S. Motorsport]

IMHO, It isn't just about that quick get up and go.
Your seriously altering the gearing here and you will bring down top speed and bump cruising RPM this is definitely not for road tripping or cruising.

For a winding twisting back road it's going to be a lot of fun, but not that suited to high way driving.

 

[Hapa88]

IMHO, It isn't just about that quick get up and go.
Your seriously altering the gearing here and you will bring down top speed and bump cruising RPM this is definitely not for road tripping or cruising.

For a winding twisting back road it's going to be a lot of fun, but not that suited to high way driving.

I agree with this, but it doesn't seem to affect top speed or RPMs that much.
On the OEM 5spd, cruising at 70mph is around 3000 rpm.
Change the final drive to 4.4:1 and the 70mph rpm is around 3250 rpm.
Theoretical top speed drops from 186 mph to 173 mph.

I used this calculator to come up with those numbers (tire size 245/40/17 and 5th gear ratio of 0.771):
http://www.kabamus.com/garage/gears.html

 

[A.S. Motorsport]

Well the drive ability changes greatly, years ago I experimented with small motorcycles classics and modern engines, roughly same power and specs with 3,4,6 speed transmissions.
Having to shift all the time due to short ratios is fun for a while on a real drive it get's exhausting.

Personally I like having the time to listen to the engine hauling trough the rev range, not shifting every few seconds.
Answer to our issue here is TORQUE.

 

[sparky]

I agree with this, but it doesn't seem to affect top speed or RPMs that much.
On the OEM 5spd, cruising at 70mph is around 3000 rpm.
Change the final drive to 4.4:1 and the 70mph rpm is around 3250 rpm.
Theoretical top speed drops from 186 mph to 173 mph.

From my perspective 3250 vs 3000 rpm at 70mph is barely noticeable. I'm after performance, and if economy suffers a little, so be it. almost all performance increases come with an economy penalty

Top speed is reduced but no where near that much. What changes is the revs at which top speed is achieved. My (comprehensive) MATLAB NSX performance model predicts top speed only reduces by only about 3 kph to 267 kph (~166mph) BUT top speed rpm increases to about 7,725 rpm compared to 7,150 rpm for stock. The lower ratio is able to get enough torque to the rear wheels to fight the aero drag all the way to 7,725rpm. Although the stock higher diff ratio achieves the slightly higher speed it's torque transfer to the wheels to fight the aero runs out much earlier in the 7,000 - 8,000rpm band.

In practical terms how often does one get to top speed, even on race tracks? It takes about 3 miles / 5km of flat straight road to approach top speed. Apart from the autobahns there are few places to do this, and few race tracks have straights that long.

For my money the 5SP NSX gearing is too tall / widely spaced. eg. 120 kph (~75mph) in second gear and the 4.4:1 diff would be a huge improvement in this area, which is where we spend most time and get most enjoyment.

 

[A.S. Motorsport]

Driving styles, habits and location come in to play here.
In Europe we'd require a wide range for twisty back roads and alpine passes to long high speed run's on autobahns.

With my cars or at least with my Honda I drive a lot of highway and longer trips, for city use I've got a different daily.

 

[luigib]

I have the OS Giken 4.44 ring gear with the superlock diff and jdm short gears. The speed difference is obvious, however, not a great enough rpm difference to keep me off the highways. I daily this car through the winter and have no problems with it. It completely transforms the car and I hope this group buy pulls through because anyone who gets it will have no regrets.

 

[jond]

Interesting thread.
Anyone have guesses on how many hours it takes to install?

 

[funkynsx]

great demo, after 13 secs with 4.235:1 the NSX-R did the NSX by about 1.5 car lengths.

A stock NSX fitted with a 4.4:1 diff will be about 2 car lengths ahead of a stock NSX after 13 seconds (i.e. about 1/2 car ahead of NSX-R)

I'm not sure about your figures there sparky
Are you taking into account that the nsxr is alot lighter than the nsx?
A few years ago i swaped my nsx gearbox with a genuine nsxr box and found a definite increase in acceleration and it wouldnt drop out of v tech shifting from 1st to 2nd.
The nsxr advantage is a combination of better gear ratios and being lighter.

 

[sparky]

funky, I agree that part of the NSX-R advantage is reduced weight (I think it's only about 50kg less - must check) but the diff ratio is the major contributor to the 1/4 mile performance improvement. It comes down to some straight forward maths, specifically the increase in torque transferred to the rear wheels. My MATLAB NSX performance model takes this into account (including air drag etc) and that is shown in the charts I posted earlier. When I get a chance I'll run a 3 car comparison through the model, stock, NSX-R, stock+4:44. where the NSX-R has 4.235 diff and reduced weight.

But my entusisasm for this mod may be wasted, it doesn't look like we're going to get the required 10 buyers that SoS need to produce these. such a shame

 

[funkynsx]

Thats a pity.
I do like the concept.
I think the lightest version of the nsxr was 1230kg from memory.
I had my 94 corner weighted at 1350kg before i fitted the supercharger.
I hope sos gets some more interest in it.
Good luck

 

[GhettoRacer]

I didn't see any target MSRP mentioned. What was it going to be for the SOS 4.4 FD?

 

[NetViper]

I had 4.55 on a 5 speed and I hated it on the highway. Would never do that again.

 

[Rope]

I enjoy the 4.55 and don't have an issue on the highway. I think it may have to do with other mods on how comfortable it is cruising down the highway with the 4.55 final.

 

[docjohn]

I was a 4.55 guy also...80 mph in 5th was about 4100 rpm with 265/38/18 rear tires.

 

[jwmelvin]

Was?

 

[Rope]

Hmmm, my tach sits just below 4000, I would assume around 3900 at 80 and that is with 255/35R18

 

[docjohn]

Was?

I've since gone to the 4.23.......works better for watkins glen.