Theoretical header selection mathematics

[JIM THEO]

So what are your gains ONLY from the manifold, have you dynoed before and after your car (without remapping) to prove your theory?
Or did you logged it before and after just to show us the remarkable difference in fuel trims etc caused from the much better manifold design only?

The discussion is about header selection and you say the new manifold is so good and that's why you bought it, I say you bought it cause it was the only legal way to improve your car in Germany and you DID the right think, in your case it was the best compromise, that's it, this doesn't mean it is a better design from aftermarket headers for various reasons, just to stop a long discussion so many owners prove it again and again.


PS: Is not my logic that say where the gains come from, is what the factory pdf mention, read it please:

...THE INTAKE AIR CHANNEL OPTIMIZED TO REDUCE AIR FLOW RESISTANCE COMPARED TO 16MY (APROXIMATELLY -30%). COMBINED WITH CHANGES MADE TO THE EXHAUST SYSTEM, ENGINE POWER OUTPUT IS UP TO 205hp.

Regarding intake manifold that you say doesn't make a difference:

The material and shape of the intake manifold shape have been changed to maximize intake pulse resonance.
-Optimized branch length and increased cross-sectional area.

Is not a case my toy is better than yours...

[86MLR]

Originally Posted by tehShirt

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.

Killer B headers are a sweet bit of kit, pity they really only develop for WRX and STI.

That market probably keeps them busy enough with all the shiny things available, 86 market is tiny compared to the WRX and STI.

It would be good if they started racing a 86, the end result would be a sweet header made of top material and probably under the $1400 they ask for the holy header.

[tehShirt]

Originally Posted by 86MLR

Killer B headers are a sweet bit of kit, pity they really only develop for WRX and STI.

That market probably keeps them busy enough with all the shiny things available, 86 market is tiny compared to the WRX and STI.

It would be good if they started racing a 86, the end result would be a sweet header made of top material and probably under the $1400 they ask for the holy header.

I think that's the main issue. AFAIK they never had one of the twins. If they did make a header though, they would be far behind on the tuning support other options have.

[Lantanafrs2]

I'm starting to think that my next header will be connected to turbo piping.

[nikitopo]

Originally Posted by JIM THEO

So what are your gains ONLY from the manifold, have you dynoed before and after your car (without remapping) to prove your theory?
Or did you logged it before and after just to show us the remarkable difference in fuel trims etc caused from the much better manifold design only?

I don't have any measurements of the exhaust manifold alone, but there are measurements of the pre-'17 cars with certain aftermarket catbacks and no remapping that were giving a 4whp gain. This without changes on the intake which means that there was something left on the table just on the exhaust side. After the revision the same and newer catback designs of the same manufacturer were giving less than 1whp gain which is close to zero. So, I would say that the gain of the new exhaust manifold without any remapping is in the range of 3-4 whp. The specific manufacturer is quite reliable and the previous results are pretty accurate, but I don't want to give the name. Only hint I can give is that the same manufacturer designed the exhaust of the NBR 24h STI car.

[JIM THEO]

No pre/post dyno plus the catback exhaust, no pre/post dyno with the complete new intake only and so on, there are thousand of reasons this could be true or not especially from different cars, dynos, climate condition etc.

We could have unlimited discussions but to end up tell me please, agree or not when the factory says the reduced per 30% air flow resistance on intake (that makes no difference according to you) combined with the changes to the exhaust system lead to the 205hp engine power?

Agree or not with the factory when says the new red manifold has optimized branch length and increased cross-sectional area (compared with the old that you say has no difference)?

PS: By the way factory maps are based on this type EL exhaust manifold that's probably why they give better results.
If you remap a <MY16 car with only mod Tomei UEL headers and one with OEM MY17 headers Tomei car will be clear winner not because they know more than what Subaru knows but because in factory headers there are many limitations I described above!

[Lantanafrs2]

5 horsepower

[SuperTom]

u cant discuss headers without a proper tune

[nikitopo]

Originally Posted by JIM THEO

No pre/post dyno plus the catback exhaust, no pre/post dyno with the complete new intake only and so on, there are thousand of reasons this could be true or not especially from different cars, dynos, climate condition etc.

We could have unlimited discussions but to end up tell me please, agree or not when the factory says the reduced per 30% air flow resistance on intake (that makes no difference according to you) combined with the changes to the exhaust system lead to the 205hp engine power?

Agree or not with the factory when says the new red manifold has optimized branch length and increased cross-sectional area (compared with the old that you say has no difference)?

I am a bit bored to have this kind of discussions in a forum. Not specifically with you, but in general it is the same thing over and over again. When you provide evidence the others will say that there are too many variables without giving any importance to common sense. Same happened on the tire width discussions related to lap times and in the end people admitted that skinnier tires have an importance:
http://www.ft86club.com/forums/showp...8&postcount=19
I provided you dyno result numbers and you simply just want to ignore them.

And by the way it is not the same saying about specific power increases and the same about saying a 30% air flow resistance improvement. You never know if the latter will have any difference at all in the power result. This is not only for intakes. Same holds for exhausts that provide let's say 20% less back-pressure, but the manufacturer never provides specific power figure results. I never buy such arguments.

[nikitopo]

Originally Posted by SuperTom

u cant discuss headers without a proper tune

It depends the design. If it is catless or with lengthy runners then yes you need a proper tune. If it is catted, has similar EL design and similar lengths then it is not mandatory. If the fuel trims are fine you should be good. You might get an additional horsepower with a custom tune, but who cares. It is a very small difference.

[JIM THEO]

Understood, you answered me with no answer!
You agree with the factory when you want and disagree when you want, and you provided me evidence for the 5hp with no evidence (in other topic YOU say the power increase is much more than 5hp, where it comes from when the new headers give only 3-4hp?)!
Anyway there is no reason to continue the argument, keep your opinion and I'll keep mine based on what Subaru says.
Have a nice day!

[Lantanafrs2]

These cars will show a 5hp difference if more cows are laying down then standing up.

[Lantanafrs2]

Other than buy a different car, my only option is to boost it and leave the anecdotal na improvements behind.