differences in headers between production years

[darock]

Hello

I read here on the forum that the euro cars differ from the US spec cars in some ways even in the same production year. Especially regarding OBD1 or 2 and all that comes with it.

I thought euro and us spec were the same so I searched for a 97-99 spec header as they are often used as a direct bolt in replacement (with adapters) for the awful log style headers of the 3.0 engine. At least that's what I found after searching nsxprime for at two days.

I found a set of 99 headers in Europe which made me happy because shipping will be cheaper than from US but now I am a little confused if it will fit.

According to prime the headers are as follows:

90-96 awful log style "boat anchor"
97-99 perfect direct bolt in with the adapters.
00+ same as 97-99 but rear header 2cm short (will tilt exhaust a little)

Is that also true for Euro spec cars?

Cheers,
Bernhard

[Hagasan]

Hi Bernard,

The adaptors are essentially for mating aftermarket rear exhausts to the later style cats. Upto to 96 cars have cats with a three bolt flange so no adaptor is necessary. 97-99 and 00+ converters have a two bolts flange. As most aftermarket exhausts are made in the three bolt design the adaptors mate the two bolt cat to the three bolt exhaust.

The headers are different between the 97-99 and 00+. They look very similar as do the cats but there are slightly different offset entry and exit pipes. As a consequence you get two different adaptors sets too.

If you change to OEM headers you'll need to change the cats as well or get by-pass pipes..then the appropriate adaptor..

Science of Speed sell the adaptors. Should you go this far and need OEM cats then I have a pair of 97-99 ones if you are interested.

I think I'm accurate in what I say for the UK and European OEM system? You'll also need longer O2 sensor wires.. If your car is pre 97 then you'll just use the pre-cat sensors then block off the post-cat O2 sensor holes with "bungs"

[darock]

My car is a 91 built car. Early model without power steering.

The plan is to use the 97-99 headers with 97-99 highflow cats and the needed adaptors you mentioned to bolt up to the 91-94 style exhaust.

Changing the length of the O2 sensor wires should be easy. I got both O2 sensors new anyway due to milage of the car.

It just confused me because I read about the OBD differences and I thought this may also effect the headers and cats ...

Bernhard

[Kaz-kzukNA1]

Hi, Bernhard.

As we are talking about the OEM header, followings are only applicable for the NA2 model as NA1 stayed with the exh manifold.

The spec of the header (F & R) is the same between US and UK model (and possibly other European models).
The Primary O2 sensor spec is also the same between the two countries.
However, the CAT spec is different between the two countries for both the 97-99 and 00-05 models.
The introduction of the Secondary O2 sensor is different. US NSX model already had it from 95 whereas in UK, it was only introduced around 99 model but not full OBD2 spec yet. It only became OBD2 from around 00 model.
While the spec of the Secondary O2 sensor is the same between the two countires for 99 model, it is not the case for 00-05 models.


I wrote the following for one member on NSX Prime so here is the cut and paste. It may help during the installation.
Please note that I don't know the spec of your aftermarket high flow CAT that #2 below may not be the case for your application.
Also, as your ECU doesn't have input for the secondary O2 sensors, I left the comment out of the followings.
You seemed to have already bought new O2 sensor so possibly too late for some of the points made below....


1. Front header heatshield
The heatshield at the front header will hit the A/C compressor bracket so you will need to trim off tiny potion of it.
The heatshield at the rear bank will fit without trimming it but you are going to have fun installing it with
lots of head scratching moments due to the limited space.

2. Rear sway/anti-roll bar (This section may not be the case as you are going to use aftermarket high flow CAT.)
Depending on your suspension setup and if you are using the OEM anti-roll bar that came on your NA1 model, the bottom half of the heatshield at the rear CAT may hit the anti-roll bar at full droop.
Once the car is on the ground, there will be enough clearance.
You can either replace the anti-roll bar to NA2 style, replace it with aftermarket NA2 style or simply not install the bottom half of the rear CAT heatshield.
If you have aftermarket coilover kit or suspension setup, you may not need to do anything.

3. O2 sensor cable
As others mentioned, you will need to extend the O2 sensor cable.
However, you can install the existing front one at the rear header without extending it and just extend the existing rear one when installing it at the front header.
If you are buying the sensor extension cable, normally it will come as a set of two so not much saving.....
Also, as mentioned in #6 later, if you are replacing the O2 sensor, you better calculate the cost of new O2 sensors with the cable length designed for NA2 layout (no extension required) against the new O2 sensor with NA1 cable length + the cost for the extension loom.
[Edit: you will need to be creative for the O2 sensor cable layout for the front bank if re-using the existing sump protection cover. NA2 spec will have extra fixing points on the sump guard, cross beam and firewall cover.]

4. Exh port gasket
Although the work shop manual states to replace this, you can re-use the NA1 gasket if it is not damaged.
However, while in there, I recommend replacing it to the NA2 one.
The port diameter of the NA2 gasket is slightly larger than the one on the NA1 type.
I have touched on this in my post #295 in the following link to NSXCB site; Header Installation (http://www.nsxcb.co.uk/showthread.php?p=72512#post72512)

5. Exh port nut
There are 7 nuts used at each bank when fixing the header to the engine.
While you can re-use your existing ones, you may want to use the one for NA2 model.
It has better treatment than NA1 model and will prevent corrosion for longer period.

6. O2 sensor
While you can re-use your existing ones, you may want to consider replacing them if you have covered about 60K miles even they were not faulty.
While it is easy to replace the one at the front bank, you could experience big time replacing the rear one later.
If replacing the sensors, please note the comment on the cost described in #3 above.

Good luck.

Kaz

[darock]

Thanks Kaz,

If you PM me your address I will send you a box full of chocolate for all your effort and information sharing with us. :D

Right now its freezing cold here in Austria and I definitely will not do the header swap without access to a lift.

I know the old style header nuts from the b16a1 engines and their tendency to destroy the thread where they are slotted. Will definitely replace them. I reused the Honda Metal header gaskets numerous times and never had issues with dem. Good to know that NSX is the same.

My car despite high milage seems it has not much corrosion so I hope everything will work out nice.

I ordered the denso o2 sensors and already read the trick to swap front and back and just extend the front. I don't buy the extensions, easy task to do it DIY.

Suspension is stock beside bilsteins on lower perch.

Cheers
Bernhard

[cadrega]

Very interesting post as I found myself in your same shoes, darock.

From what I understand the 95+ headers are better as there is no flexi-joint which is present instead on the 91-94. This joint tends to break.

My setup on my 1991 should be:

OBX Headers +95-01 -> Daliracing.com adapters ( http://www.daliracing.com/v666-5/catalog/index_browse_part.cfm?focus=2457 ) -> OEM 91 catalytic converters -> Taitec GTLW 91-94.

Hopefully it will work!

[darock]

Your setup should work. I read the OBX are the same as the Top Speed headers. They may require some grinding on the subframe as stated in some threads on prime.

That flexi joints do not seem to be a real issue. Mine are 230tkm old and still ok.

Bernhard