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Opinion: '91 NSX JDM 5spd w/ 4.23 vs JDM 5spd w/ supercharger w/ or w/o 4.23

7 May 2017
I recently bought a really nice, stock '91 NSX, and am planning out some modifications and would like input from you guys that have done it before. Normally, I'm not a "mod" guy; I've had a GT3 for a while, that I've only added a center muffler delete, and have no further plans. I had a 993 long ago that I made more and more into a dedicated track car, but then it became an awful street car. With the NSX, there are a few things I'd like to change with an eye on keeping it a great street car. I have driven 2 other NSX's with mods that I really like. The first is a '91 with 6spd conversion, 4.23 final drive, LWF, and headers. The second is a '91 with JDM 5spd, LWF, and a supercharger. I've searched and found old threads on these setups in different places, but would like to see what the current thought is. Either route I go, I will do headers/exhaust/LWF.

Driving the first car, I like the idea of staying NA. I definitely like the lower gear spread of the 6spd gears; my understanding is that the first 4 gears of the JDM 5 spd and 6 speed are very similar, with 5th (5spd) and 6th gears, respectively, being close too. I'm a little concerned of the higher cruising rpm's; right now 80 mph is about 3400 rpm for me, and I was told that the 4.23 raises that about 400rpm. Is this accurate? Is that extra obtrusive with headers/exhaust? So, option 1 for me is JDM short gears and 4.23.

After driving the second car, I was really impressed with the power. This car had the JDM short gears, and the stock 4.06 final drive, and a supercharger set up for 9psi boost. To me, the gearing felt really good, and I don't know if the 4.23 would be just right, or too much? From what I've seen, most supercharged cars fizzle out after a few laps on track, but I club race with a dedicated race car, so I really don't plan to track the NSX. I want a fun car for carving up twisty back roads.

The last change is suspension. I bought a set of Advan RSII's with Dunlop's, and that had more rub than I can live with at stock height, and that set off thinking about suspension changes. My original plan was to go to Bilstein shocks set to the lower height, and keep everything else stock. Now, I'm also considering a type S setup, and a KW variant 3 setup.

What do you guys think? Thanks in advance for your help!

Hi David depends on budget I run KW V3's and wouldn't recommend anything else 'if' they fit in your budget. As far as gearing goes remember different tire sizes can affect gearing too so it does depend on what your wheel/tire setup will be, for instance 235/275 on 17/18 with stock gearing is geared high but if you were to go with the 4.23 or even a 4.4 final that will only bring you back to where it was on the 15/16 OEM setup it does make that much difference.
I have stayed N/A because well that's me its just a whole lot less hassle and for my track work it just runs all day
I've ended up w/ 17/18 on 215/265, and in the short time I've had that I've been very pleased. I didn't notice much of a difference gearing wise from one to the other, but the grip level and composure was huge. I've heard nothing but good things on the KW's, except for getting them dialed in. I'm normally not a big fan of forced induction. I've driven 2 z06's on track, and both had heat problems. But, the NSX is a fun street car for me, and won't see the track much. I really liked the supercharged car I drove.
A nice and stock 91 is of special value to some people. Some others think that there are still enough of these virgin cars around and decide against modding it.

I've a 91 with CTSC (low-boost), shorties and 4.23 and can't imagine going back to completely stock.

In your case I'd drive the 91 for a while and give it a chance in its virgin stock form. If want to take it a step further here is my recommendation:

- CTSC but starting with low-boost first
- shorties, the gears 2, 3, 4 are shorter. 1st and 5th remain the same (considering noise at 80 mph)
- 4.23, I'm at 3.500 rpm at 80 mph with 255 fitted in the rear. No problem with the noise as I still have the stock exhaust (strict noise regulation over here)

CTSC with the long gears is ok but the charger unit likes revs too, so CTSC AND shorties are a good match. If money is no object I'd throw the 4.23 in as 4.1 % higher revs are not worth debating about. You won't be at 4000 rpm at 80 mph unless you use very small tires. Your choice of exhaust will influce that much more than anything else.

Suspension: Type S hard to get nowadays. KW v3 very good but maybe not as long living like Bilstein.
I do hesitate to change around such an original car, but I look at it as I was not driving when they were new, and couldn't afford one when they were cheaper. This car is as close as I can get to going back in time and getting a new one. I'm not saving it for anyone, and everything I would do would be reversible. I got to drive a car with short gears and SC, and loved it. I was worried about adding 4.23 from the perspective of it being too busy w/ SC, and too high rpm/noisy at hwy speed. But from what I've read, going to 17/18 wheels helps with that. I've read the 4.23 adds 160 rpm, and somewhere else said 400 rpm. From what you guys are saying it sounds closer to the 160 which shouldn't be bad.

I've read all good things about the KW's (except some complain of squeaks and reliability?) vs bilsteins. The lower perch ride height of the bilsteins would suit me fine, so it's a toss up. I'll read up more on them, but my current stock suspension isn't bad. I club race, so I won't be taking the nsx to the track except for rare occasion, but I do appreciate the small improvements a good coilover setup provides for road use and fun daybreak drives. The shocks are something I can do later after recovering from money spent on the other stuff, though.
235/275 on 17/18 with stock gearing is geared high


I don't understand how running a 275 is "geared high". Comparing to a 265, a 275, the 275 is only .28" larger in diameter. than the 265. Are you comparing the 275's to the OEM '91 - '93 225/50-16?
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. . . I've read all good things about the KW's (except some complain of squeaks and reliability?) . . .


The complaints regarding squeaks with the KW3 are largely related to users who reuse their old worn out top hats when installing the KW3's. If you go that route (KW3) then I would recommend getting new factory top hat assemblies.

Haven't heard anyone complain about reliability issues with the KW3's. But if you are concerned about reliability then I would recommend MCS dampers. Very pricey though and you will need to source the springs separately.

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. . . Driving the first car, I like the idea of staying NA . . .

Until you get taken out by a Civic Type R . . .

Think 450hp - either twin turbo or supercharged (I prefer twin turbo)

The NSX is a GREAT platform but it is also a 26 year old platform. Advanced at the time, but 270hp isn't pavement-ripping numbers anymore. Hell, my Audi Q5 goes 0-60 in 5.8 seconds, and that's with a 2.0 4 cylinder turbo! The NSX was clocked at 5.6 seconds. Not bashing the NSX (I LOVE mine), but it is what it is.

In the right (experienced) hands though it is as good a car as you can buy for the money (watch the YouTube video of Senna ripping around Suzuka Raceway in a Type R - in loafers of all things!). A couple of tweeks here and there and you have a supercar all over again.
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I don't understand how running a 275 is "geared high". Comparing to a 265, a 275, the 275 is only .28" larger in diameter. than the 265. Are you comparing the 275's to the OEM '91 - '93 225/50-16?
OK a lot will depend on what tire we are comparing, so to confirm what I know since I run both wheel combos at the track my 215/265 on Dunlop Z11's are quicker geared than my 235/275 Nitto NT01's and the dia is significantly different as we have to adjust the coilovers height every-time we change the setup. So my 265 rear is geared lower than my 275 and the power delivery is noticeable while the grip level is lower so I went to the OS Giken to get my gearing back down when using the 235/275 setup. My next set of Dunlops will be the same size as the Nitto's to try and help keep things similar or closer to each set.