Hi, Asif, [MENTION=24513]riddl3r[/MENTION].
For the clarification, in this thread, I will use the wording the 'Upgraded ABS', 'one body ABS', Bosch style ABS' referring to the ABS introduced from the 00 models.
Please note that the definition of the Year model is different depending on the market area, local regulation, country spec, etc.
For the classic ABS (91 - 99, the one with the ABS pump making that famous squeaking noise) excluding the Type-R and before the one body upgraded ABS was introduced for our NSX, there were 3 different ABS modulator spec.
They were;
The original '1st generation (1st gen)' with the famous leaky/stuck solenoid issue (91 - 92).
The '2nd generation (2nd gen)' with improved solenoids package but still not free from the leaky/stuck issue (92-96).
The '2nd alpha generation (2nd-α gen)' with the same improved solenoid package as the 2nd gen but with different ABS setup, especially for shifting the brake balance towards the rear (97 - 99).
The spring at the rear ABS piston is different.
From the software control point of view, there were 2 versions of ABS controllers (91 - 96 and 97 - 99).
The ABS light circuit was changed over the years but biggest change was introduced in 97.
Regardless of the NA1 or NA2, all 97+ models were equipped with the latest design of the front and rear brake caliper/disc set.
While the master cyl diameter was kept the same, the brake balance was massively shifted towards the rear side from 97+ models and hence, the changes in ABS as well.
As a side note, many owners refer to the later spec caliper/disc setup as the 'NA2 brake' even the same parts were used on the 97+ NA1 models.
You could be reminded from the strict owners that the NA1/NA2 are the engine code and not related to chassis/parts spec but I think many of us are now getting used to this '
NA2 brake' naming as it was introduced at the same time when the 3.2L NA2 model showed up to the market.
Back to your question.
I only have experience with the RHD ABS installation but I believe it would be the same for the LHD as well.
You can install the 97+ modulator (2nd-α gen) on NSX originally fitted with either the 91 - 92 1st gen or 92 - 96 2nd gen ones.
Obviously, the 97+ 2nd-α gen was designed for the 97+ chassis setup and strictly speaking, you won't get the full 97+ spec software control without the 97+ ABS controller (be careful with the reversed ABS light logic) but in my view, any classic ABS control is vague, slow and not sophisticated enough that it doesn't really matter.
Still,
on the public road, you are better off having at least some sort of operational ABS than having faulty ABS or nothing.
On track, that's a different story.
I won't trust
any classic ABS based on the actual testing carried out.
Until you get to the certain skill level, you want the one body upgraded ABS even on track.
So, in summary, based on only the RHD model experience, you '
can' install the 97+ ABS modulator on your 91 model.
You can keep your original ABS controller inside the cabin if you want to leave the ABS light logic as it is.
Strictly speaking, this combination (97+ modulator + 91 controller) setup is not optimised for your 91 model but any classic ABS control is vague (On/Off, slow reaction time, etc) that it doesn't really matter but far better than having nothing for the public road.
If you have modified the chassis setup such as the brake, tyre/wheel, suspension, rideheight, etc, you are already way off the OEM setup so OEM ABS setting doesn't matter.
Regarding the upgraded ABS using the non-NSX modulator, it doesn’t have to be using the S2000 one.
Before it was introduced here on Prime, it was already done by many NSX owners in Japan ages ago using S2000, etc (several models only sold in Japan) modulators.
If using AP1 S2000 modulator, please note that you will lose TCS (thank you to britlude for the detailed test;
http://www.nsxcb.co.uk/showthread.php?14147-collecting-parts-for-winter-project) but again, if you have 91 - 94 model (and 95 Type-R), it's non-DBW and in my view, it's not worth keeping TCS on non-DBW model as the control is so poor.
Kaz
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