Theoretical header selection mathematics

[22R]

Lotta math and smarter people than me here. I like the sound the coated Gruppe S header makes when I push the pedal down kinda far. It seems to make the car a bit quicker with the OFT but not dramatic from stock IMO

22R

[Lantanafrs2]

Same actual acceleration numbers as a 2013. 20 years ago this car wouldve been fast. Not now

[churchx]

Plenty fast on track.

[Lantanafrs2]

Unfortunately I don't commute on a track lol

[JIM THEO]

That's what the factory says nikitopo, one image - million words, who am I that try to convince you are wrong?

[Prodigalson]

Originally Posted by Lantanafrs2

Same actual acceleration numbers as a 2013. 20 years ago this car wouldve been fast. Not now

My Acura Integra GSR had way less hp than the FRS, but there were many forum members who were scrupulous about the technical aspect of mods and it was a much cheaper and slower car than the FRS.

Frankly, the cost of the car, how many (or how few) hp the car has is irrelevant. A person can throw money at a car and hope it makes it faster (or more enjoyable to you) or they can put some money into it after doing some reading, discussion and thought. Honestly, it makes a whole lot of sense to be thoughtful about everything in life, let alone car mods.

[Tcoat]

Originally Posted by Lantanafrs2

Same actual acceleration numbers as a 2013. 20 years ago this car wouldve been fast. Not now

It is still fast. Just not as fast as some others. That does not make it slow just slower than some.

[Tcoat]

Originally Posted by Prodigalson

My Acura Integra GSR had way less hp than the FRS, but there were many forum members who were scrupulous about the technical aspect of mods and it was a much cheaper and slower car than the FRS.

Frankly, the cost of the car, how many (or how few) hp the car has is irrelevant. A person can throw money at a car and hope it makes it faster (or more enjoyable to you) or they can put some money into it after doing some reading, discussion and thought. Honestly, it makes a whole lot of sense to be thoughtful about everything in life, let alone car mods.

You can also over think things. Nothing wrong with thinking it through but at some point you need to just stop thinking and do.

[gtengr]

Originally Posted by churchx

gtengr: well, IF toyota.co.uk site doesn't lie, then i am sure.
From technical specs found there "Euro class: EURO 6 AG".
Hence - most probable reason for EUDM to not get FD/header/intake upgrades.

The website isn't lying. An approved exemption to the standard is the same thing as compliance as far as registration is concerned.

[nikitopo]

Originally Posted by JIM THEO

That's what the factory says nikitopo, one image - million words, who am I that try to convince you are wrong?

Trust me. If the gains of the red intake manifold worth it, then I would have it already. Here is an old discussion with a user that order it from Japan:
https://www.ft86club.com/forums/show...8&postcount=11

There wasn't much from it even after the tune.

The rest of the intake changes were because factory couldn't go with the less filtration of an aftermarket filter. So, they had to revise the box, the filter and the front area.



Overall the specific "header selection" topic was quite interesting, but of very small importance since almost everyone goes catless. It would be interesting to see how well many of the aftermarket crap would perform if they were catted and if they had same converter specs like the one of factory ...

[JIM THEO]

The discussion is not comparison between catted aftermarket and MY17 headers!
We can't compare them cause the factory headers should meet some strict criteria, exhaust gases/noise/insulation/cost etc where the aftermarkets none.
In many cases the aftermarket headers are very well designed but they suffer elsewhere for example reliability, position of sensors, thermal insulation and so on.

But if I had to choose between both catted headers for performance clear winner would have been an aftermarket one.

Regarding the differences between pre/post 16 BRZ they come from both intake exhaust and mapping.
Probably more from the intake rather from the new exhaust manifold.
The intake differences are the red manifold which is bigger and favors torque (surface irregularities of aluminum cause turbulence), the bigger/better intake tube, the 4 times increased filtration area, and the 30% decreased pressure loss, while in headers the difference is the increased (less than 5%) pipe size and the slightly new design.
Why you believe the gains are from the headers, it is clear and the above Subaru docs prove it, they come from both exhaust AND intake!

[Lantanafrs2]

Because the manifold produces no gains on earlier cars. Surface finish turbulence is based on theory. Aluminum is good on a boosted car because it won't inflate like the plastic manifold.

[tehShirt]

Originally Posted by 86MLR

Due to the inherited metallurgy of 304 it tends to work harden from heat cycling.

321 is much better IRT coping with heat cycling, as is mild steel.

This is based on my experience with both turbo and NA cars with alot of track abuse.

There are other variables, poor welds or not correctly supported turbos, but, even with all these issues engineered out during fabrication you cannot get past how 304 work hardens through heat cycing.

From the header back 304 is good to go IMO, but for headers I won't use it.

Options may vary.

KillerB makes 321 headers for the turbo Subaru engines. I had one on my previous WRX, it was lovely. I've contacted them multiple times about any plans to develop an application for the twins. Most of the emails were not answered. I finally got a snarky response on Instagram about most twin owners liking "budget" priced products.


I guess they don't know people drop $1600 on the ACE header setup.

[nikitopo]

Originally Posted by JIM THEO

The discussion is not comparison between catted aftermarket and MY17 headers!
...
while in headers the difference is the increased (less than 5%) pipe size and the slightly new design.
Why you believe the gains are from the headers, it is clear and the above Subaru docs prove it, they come from both exhaust AND intake!

Ok, let's go back to mathematics!

A change in the branch diameter from φ42.5 -> 45 is not a 5% increase. It is a 12% increase of the pipe area:




Same in the geometry where it is entirely different with less angle bending and much closer to equal length:



You can see the re-design of the branch pipes in the red circles. Many manufacturers will say that their manifold is equal lenght, but in reality few of them are really equal.

I understand when you say that gains should come from both exhaust AND intake. This is what logic says, but this platform has been studied for more than 6 years. It is clear that the restriction on the pre-'17 cars was mainly on the exhaust manifold side and the program mapping with a rich AFR.


The only restriction is now the torque dip, but it is a general problem and you cannot solve it without going catless or maybe with a sports cat. The issue is that NONE of them are approved or legal here. Even manufacturers saying that their sports cats have a European certification is bs. Personally, even if all these were legal I wouldn't go with something that would add more pollution and more smell. We are in the 2010's and not in the 80's or the 90's ...

Originally Posted by Lantanafrs2

Because the manifold produces no gains on earlier cars. Surface finish turbulence is based on theory. Aluminum is good on a boosted car because it won't inflate like the plastic manifold.

Yes. This is what I am aware.