FA24 OEM header on FA20

[BishamontenZC6]

Hi all,

By any chance, did anyone here already try installing a gen 2 OEM header on a pre-2017 gen 1 FRS/BRZ ?

I know there's Stratified's video on Youtube comparing those headers and combinations and their potential gains. I'm more interested on the actual fitting of FA24's header with the FA20 OEM overpipe, as the flange is apparently clocked with a slightly different angle and forces you to twist the overpipe a bit to connect, which can lead to it touching the subframe and rattling.

In Stratified's video, when they install the FA24 header on the FA20, we can see that they use an aftermarket overpipe, so hard to know with an OEM one.

If anyone tried, your input would be much welcome, thanks !

[gpvecchi]

You can fit the ZN8 header with ZN6 overpipe, but it will be a little restricted, as the ZN8 overpipe is bigger.

[BishamontenZC6]

Hi all and (belated) thanks gpvecchi for the information. I finally went for the installation of a GR86 header + overpipe on my car and I thought I should share the results with you all. Here's the basic info on my car :

2014 AT6 BRZ (EU market)
153'000km

Relevant mods :

• Cosworth air filter
• GTSpec catback (similar to Q300 and CircuitSport)
• Gutted 2014 OEM header
• Custom made stage 2 tune (via OFT)
• Everything else (engine & exhaust) is stock

So, first the installation is plug&play, as long as you have the GR86 overpipe (the old and new flanges are clocked slightly differently). The results you see below are without any other modification than simply swapping the headers + OP. The tune is still the one made especially for the 2014 header, so there's probably some headroom for optimisation there.

Made on Virtual Dyno 1.9 for visualization, based on the OFT datalogs. Made on the same stretch of road, on the same day, with the same conditions, on my usual pump SP98 gas :



Blue line is my "baseline", that I've been running for 18 months now. Red line is with the GR86 header. I'm pretty impressed, the torque dip is just gone. We can see a crossover around 4100rpm where the 2014 headers would make a little bit more torque than GR's. The absolute numbers aren't really relevant as there are too many variable, but the difference between the 2 setups is impressive, and you can really feel it, especially on an automatic where you spend quite some time in that powerband. The power delivery is much more linear.

Top end isn't bad at all, with an estimated 180whp at 6'750rpm. Max torque comes now at 3300rpm. It's funny how close it now is to the stock GR86 torque and power curve. I think it's now clear how they softened the torque dip on the FA24, it's mostly the design of the header, not because of the bigger displacement.

Based on my experience with the catted/gutted OEM 2014 header, the torque curve keeps mostly the same shape before and after gutting, it only gets higher torque and HP values. So it should probably be the same with the GR86 headers, which means that it also should fill the torque dip without gutting the cat, providing there's a proper tune to support it. This confirms the results explained by Stratified on their YT channel.

Of course this will not come useful for anybody who live in a country where mods are legal and where you can throw a Tomei or JDL, but if you're in one where anything other than stock is strictly forbidden, then you have a pretty nice solution there. It also retains the heatshields and prevent the tinny sound of some aftermarket UEL or EL headers, which is nice. The hardest thing in the end is to find a used GR86 OEM header. I got mine directly in Japan for cheap and the OP from the US.

[Compelica]

Thanks for the details! Any information you can share on your end regarding the install as well?

Hopefully the time comes which you have the tune sorted out.

[BishamontenZC6]

Installation was absolutely straightforward, everything fits perfectly as you would expect from OEM parts. I only struggled with the usual header/overpipe and overpipe/frontpipe leaks as I don’t have a lift and had to crawl under to car to work, which made the alignment difficult. I eventually threw in Remflex gaskets and got it totally sorted.

I’m also looking forward to have the tune refined. It’s so great now even like that, but it might be even better.