Are NB8A headers cast iron or tubular?

[JINBA ITTAI]

I'm seeking confirmation on this -- are the headers on our Aus-delivered NB8A's cast iron (the one on the right) or tubular (the one on the left)?

I vaguely recall it was only the US NB8A models that got the crappy cast iron manifold, and then their NB8Bs eventually got tubular ones. In contrast, the rest of the civilised world got the nice tubular ones from NB8A onwards but I'm not totally sure if that's correct or just fake news.

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[rascal]

We got the tubular ones.
It was only the yanks for some reason that got the horrible cast things, which is why they are so keen to suggest diff headers as the first step in any performance gains

[hks_kansei]

Yep, tubes on aussie ones.

From memory the reason the Yanks got the cast ones was that California had some rules requiring there to be 2 catalytic converters, and the "new" converter was attached to the end of the cast manifolds.

And yeah, even though it was a one state rule I guess Mazda figured they'd just make them all like that for the USA.




Worth noting, the tubular ones in your pic are not NB8A ones, they appear to be NA ones.
The NB8A ones had the 4 pipes join into pairs at a strange trapezoid shaped flange,from which that pair of pipes then joined into a single pipe before the midpipe/cat flange.






garbage quality image I found, but the NB8A ones are on the bottom.
Just in case you're looking to buy some, helps to visually make sure you're getting the right part.

[rascal]

heres a better quality picture, of my actual headers off my NB8A..

[JINBA ITTAI]

Thanks gents, this has been really helpful.

Since the Aus NB8A headers go from 4 into 2 into that trapezoidal flange, I conclude they do not benefit from the usual scavenging effect that a 4 into 1 header set up offers.

I'm looking into swapping in some NB8B headers into my 10AE and just want to confirm -- are the 8B headers 4 into 1 (pre-flange) like the silver one in my photo? and will the 8A heat shield and EGR pipe bolt straight on?

[rascal]

I think you'll find that the NB8B still splits 4 into 2 for the first section and then 2 into 1 for the second section.

If you genuinely want 4 into 1 then I think you'll need to get aftermarket headers which will replace both first and second sections.
Though imo, unless you are running a reasonably modified motor then you'll see minimal gain from 4-1 and a 4-2-1 set would be quicker virtually everywhere.

fwiw, I run 4-2-1 aftermarket headers on my track car, as the 5kw gains at 4-5K (over a 4-1 set) were of more benefit than the <1kw gain at 7k.

[hks_kansei]

Since the Aus NB8A headers go from 4 into 2 into that trapezoidal flange, I conclude they do not benefit from the usual scavenging effect that a 4 into 1 header set up offers.

Scavenging is a little more complex than that.

Essentially scavenging works by precise timing of the exhaust pulses so that within a certain RPM range the slight vaccum of one pulse leaving the exhaust happens just as the next pulse is starting, helping to suck it out of the engine.

My understanding is that a 4-2-1 design, by nature of the added length of each runner, and the 1-4 and 2-3 pairing, can help with scavenging at lower rev ranges than a 4-1 design.

In saying that, it's all also affected by pipe size, angle, shape, length, etc, so it's not really as simple as "this one good, this one bad"





My understanding is that the Aussie spec NB8A and NB8B headers were basically the same.
I haven't had them side by side to confirm however.

[hks_kansei]

As far as options for your car.

you can also fit NA8 aftermarket headers to an NB without too much hassle.

The EGR will be removed, which is as simple as putting a blocking plate on the EGR port at the manifold.

And at the bottom end the flange where the exhaust joins the cat will be cut off and a roughly 15cm extension welded in, with a new flange to line up with the existing cat.

That's what i've had on my NB8A for a couple of years now.
factory ECU doesnt seem to care about the lack of EGR, drives fine, and the AFRs have not changed (I have a separate wideband o2 sensor in mine, leftover from a failed attempt at a standalone ECU)

[NitroDann]

No one has yet posted the NB8b header so here is a pic. It performs as well as a typical aftermarket header, however it has internal welds which need to be removed to optimise it.

[hks_kansei]

ahh, there we go.

same design, but with much smoother transitions on the 1-4 and 2-3 runners.

[JINBA ITTAI]

Thanks for all the insights.

I'm after more mid range performance (so 4-2-1 is ok) and a bolt on solution so I've just signed up for one of Nitro Dann's headers

[hks_kansei]

Probably the most cost effective option.

Just don't expect a night and day difference.


of the 3 dyno days my car has done, with differing setups, there's very little power in botl on mods.


run 2 was on a mainline Dynolog roller.
car from memory was an MX5 mania stlye firewall intake and a bolt on RSR Exmag muffler (fart can)
Power 76.7kw @ 6750rpm
Torque 123nm @ 5085rpm
ambient ~17c


Run after that was on a Dynapack hub dyno (which due to not taking wheels/tyres into account always reads higher than a roller dyno)
NA8 HKS 4-2-1 headers with EGR delete, 50cel high flow cat, OEM midpipe, SE muffler, 3inch coldside CAI, AFM delete, Adaptronic Select ECU
Power 85.8kw @ 6289rpm
Torque 142.87nm @ 4739rpm
Ambient ~28c


So all those mods gained about 9kw, and 20nm of torque.
BUT, since it's a roller dyno vs a hub dyno I would assume that much of those changes were within the margin of error.



(I will also add that I did have some issues with the tuner for my Adaptronic, he seemed fine for flat throttle power tuning, but the rest was where I had issues with the tune, even after multiple visits)

[rascal]

Not sure you can put much worth in a comparison on a roller dyno on a 17C day vs a hub dyno on a 28C day.There's prob 5kw difference just from the temp delta.

Also you have a handfull of changes that should make it breathe better, yet it makes max power 500rpm lower..!!
This would point to the tune being less than ideal, or at the least extra conservative.