NSX Health Check Service

[Kaz-kzukNA1]

Hi, all.
Recently, I installed the header designed by KSP Engineering Japan and I hope following info will assist some of the owners here on NSXCB.

Please note that these are purely based on my long term study and experience. I have no commercial relationship with any of the aftermarket parts companies and thus, these are just my personal view and I have no intension to say negative comments on your products that you may have on your NSX. I will appreciate your understanding on this and I just hope that you won't misunderstand my view or feel offended by my comments.

Also, the data presented here is based on JDM spec ECU which has different setup than non-JDM NSX so please keep this in mind.

A. Background
Until recently, I couldn’t decide what to do with my dreadful NA1 OEM header, or I should use the word ‘manifold’ instead, as on our NA1, it’s not a header but just a cast iron manifold.

There are lots of manufactures showing the dyno result of their products on the website.
Almost any aftermarket headers will produce more power/torque than the OEM NA1 manifold and thus, the peak absolute power figure on aftermarket headers is not important for me.

The position of the engine exhaust ports and the location of mating surface at each CATs are the same for any designer of headers for NA1 NSX so the input/output geometry is fixed.

The available space for the layout of headers surrounded by other parts is also the same for everyone and thus, the main difference would be the material, know-how, the length of primary/collector tubes and the diameter.

Our engine is NA and the rev limit is only around 8,000rpm and once again, the absolute peak power using aftermarket header is not important for me. You will get similar layout using the CAD simulation to design the header and the power curve will shift depending on the length and the diameter.

You can get lots of feedback from the owners on the specific headers through other car forum as well.

After installing the headers for many owners, looking at the actual products installed on the NSXs, listening to the feedback from other owners with many years of experience with the specific headers and even testing some of the products on the dyno, I came to a conclusion that for me, the following points would be the most important criteria for the selection of headers.

1. Ease of serviceability after the installation
With some of the headers, it is so difficult to work on the Gbox, clutch and engine after the header installation. Especially, when tilting the engine, part of the headers will hit other part of the chassis. Also, with some of the headers, you won’t be able to remove some of the bolts from the chassis without taking off the headers.
As I work on my NSX regularly, I need a header with these points addressed.

2. Ease of installation
If you installed several headers in the past, you will know what I mean… Some of them required trimming of other parts to get enough clearance, others couldn’t let you use torque wrench to tighten the fixing nuts and so on.
Some of them required extra hours to fit on AT models.
Once the rear O2 sensor was installed, there was no way accessing some of the bolts/nuts without removing the O2 sensor again…
Some of them even had their own heatshield attached to the headers but melted the timing belt cover as well.
Some of them showed no consideration on the routing of O2 sensor wire especially for the extended Front bank one.

3. Balance between the design, material, performance
Most of the aftermarket headers will use SUS304 for the tube and collector. For the flange, it will be SS41, SUS430 and so on.
SUS304 has quite big expansion rate so it is important to take this into the consideration for the design and layout.
Especially, this is important on the Rear bank because the drivetrain will generate rotational (twist) force between the header and CAT while the vibration on the two (header and CAT/exhaust) of which have different weight will create different inertia resulting in bending force at different phase/frequency.

From the durability point of view, it is best to use single tube structure than welding multiple short tubes.
However, this means that you need a certain length and bent radius to use single tube design without disturbing the exhaust flow at the Rear bank.

Front is easy.

Therefore, if you look at the design/structure/material of Rear header, you will know how much effort were put into the R&D of its header.

On some of the headers, the owners reported that they cracked after several years especially at the rear bank. Most of them had the structure of multiple short tubes welded together.

This is not a big issue as you can weld it but you need to remove the header and time is precious for me.

I don’t want to loose low-mid torque so for the header/exhaust performance, you just need the minimum diameter to achieve the free flow of exhaust gas with reasonable length of primary tube.

The internal wall of tubes where they meet at the flange as well as the collector must be polished to maximise the free flow.

I have used Inconel and Titanium on different projects but they were very pricey and not sure about the durability of the welded section. Also, may be it was just my ears but they sounded different compared to the headers made from SUS304 and for me, I preferred the tone/note of 304 than these expensive materials.

The area I live has lots of speed hump and thus, the three primary tubes passing across the oil pan at the Front bank must sit parallel to the ground to maximise the road clearance. Some of the headers showed one tube sitting lower than the other two… Not good for my application.

Addition to these, there were lots of other testings carried out.

For example, on standard NA1 engine, removing the CAT won’t improve the output power. It was measured on several different NA1 NSX back to back on the same day. Without the CAT, the throttle response showed big difference but not on the power curve. Only the peak power showed 2 – 3PS higher/lower figure depending on the NSX measured and different measurement timing. As the results were higher as well as lower, it was not consistent and too small to distinguish from measurement deviation.

Similar thing was found on the air box and air filter combination.

Several different aftermarket headers and exhausts were installed on the JDM NA1 NSX with standard engine and the power curve was compared between OEM NA1 airbox/airfilter against aftermarket airbox and airfilters.
Again, no big difference was monitored on the power curve apart from the intake sound/noise. Some of them even lost the low-mid range power against the OEM ones.

Further studies were carried out and there were noticeable increase in power for the modified (high lift profile Vtec camshaft etc) NA1 NA2 engine by using the aftermarket airbox/airfilter.
But, unless the engine modification reaches the certain level, there is no benefit for NA1 NA2 power by replacing the OEM airbox and filter.

Based on these, I decided to keep my OEM CATs and airbox/airfilter as my engine is standard NA1 with no modification. I haven’t decided what to do with the exhaust (silencer) yet but I’ll spend some time again as I know the OEM one is partially restricting the free flow and it is important to consider the entire intake/engine/header/exhaust as a package.

After many years of searching, finally, I decided to go for the headers from KSP Engineering.

Although I was allowed to use the dyno data and photos from KSP engineering, I don’t have access to the CAD/CATIA data so I measured the primary tube using the tape measure.
As you can easily imagine, this is not accurate enough as the headers are hand bent with complex curve and due to the diameter of the tube, the bent portion of the tube length would be different depending on where/how you measure that section unless you can measure the virtual centre line inside the tube.

This is why we normally use CAD/CATIA data for the ‘length’ of primary tube.

The measurement I got for the Front primary tube was about 710mm and for the Rear, it was about 715mm.

At the Front, the length of the collector was about 130mm followed by about 105mm for the O2 sensor mounting tube with ball socket joint before connecting to the CAT.

At the Rear, the length of the collector was about 135mm followed by about total of 160mm for the O2 sensor mounting tube with ball socket joint plus another very short tube with another ball joint before connecting to the CAT.

For IP reason, I can’t tell the detail but the OEM NA1 header was on purposely designed in that dreadful shape and material resulting in huge obstruction for the exhaust flow especially at the rear bank.

Also, if you cut them, you will see they are twin tube structure so the actual diameter of the tube is even smaller than what you can see from outside.