Exhausts with good flow velocity

[Yoshoobaroo]

Greddy claims +7 hp with the Supreme SP catback, and that’s stock diameter.

[spcmafia]

Originally Posted by alphasaur

I think the spec L just sounds good down low so it feels faster. Spec L gang

I wonder if anyone has ever taken just about every exhaust option out there and tested on the dyno. As far as I could tell, the Spec L made the car "feel" faster, but nothing extraordinary. I've been thinking about going full HKS and see what the car would sound like. I love Spec L, just looks and sound so good.

[nikitopo]

Originally Posted by ZDan

In short, I don't believe those plots. NObody's *really* gaining real-world +20 hp with a catback and "more aggressive tune" vs. stock on any year FT86...

Regarding "good flow velocity", it's a bit of a myth... From what I've seen on 150rwhp 2.4 liter ITS 240Z dynos, bigger exhaust always helped but going from 2.5" to 3" was a small, almost negligible gain, point of diminishing returns.

You could run a 1" catback and get massive gains in "flow velocity" and if you measured at a static pressure port in that 1" section it would show low pressure due to Bernoulli. However you will have lost power due to increased pressure upstream...

Noone said to run a 1" catback. It is about keeping a balance between back pressure and flow velocity. Especially on this engine which doesn’t have much power after 6,500 rpm. But anyways, who cares ... some of the serious tuners are out of the platform nowadays and the next big thing for others will be the FA24 engine or different engine swaps ...

[DarkPira7e]

I am assuming that Nikitopo is referencing exhaust scavenging. This effect is list of the exhaust chamber cannot be filled because it is too open.



I think this effect is limited to the header and downpipe section of the exhaust. Changing the axleback really isn't going to do much except change noise on anything more recent than 2004

[ZDan]

Originally Posted by nikitopo

Noone said to run a 1" catback. It is about keeping a balance between back pressure and flow velocity.

There's no magic point of "balance" as far as catback exhaust diameter. From what i've seen, bigger is better but beyond probably ~3" you're just taking up more space and adding weight without much if any more to be gained. Wouldn't/shouldn't be hurting low/midrange torque though.

Especially on this engine which doesn’t have much power after 6,500 rpm.

Mine peaked at 7000 stock, and also with header/tune.

Anyway, nothing to particularly worry about here I don't think, overkill may be mostly pointless but it's not likely to be hurting power/torque.

[nikitopo]

Pfff.

[ayau]

money is better spent on a tune than an axleback/catback if your goal is more power.

i'd also put lighter wheels and higher grip tires before an exhaust. exhaust is for noise at nearly stock power levels IMO.

[ZDan]

Originally Posted by nikitopo

Pfff.

Pretty much!

[Dirty Harry]

I’ve got the regular STI axle back, but geez how good does the titanium version look.

[Dirty Harry]

Yeah I didn’t notice any difference after adding the axle back. I felt more of an improvement when I added lighter wheels.

I assume there would be some gains though, doubt there’d be none, maybe a few hp but not that noticeable.

[Ultramaroon]

Originally Posted by nikitopo

Pfff.

Sounds like my lg90

[nikitopo]

Originally Posted by Dirty Harry

Yeah I didn’t notice any difference after adding the axle back. I felt more of an improvement when I added lighter wheels.

I assume there would be some gains though, doubt there’d be none, maybe a few hp but not that noticeable.

Which one did you get? The STI sports muffler or the STI performance muffler? There were 2 versions. First version was just sound improvement and second version was changing the back pressure too. I got the performance muffler and at first there wasn't much of a difference. Then I logged accidentally the engine and noticed that the ECU was off and it was constantly trying to add more fuel in high rpm. This happened after the installation of the STI muffler. I had to talk to my tuner and he had to dial the MAF scaling. After the fix it was found that there was ~10g/sec of additional air and the change in performance was noticeable. The physics reasoning behind this is that the gas temperature falls in the last part of the exhaust and it is important to optimize this area, but as usual in the forum and internet world we "know" better ...

[Dirty Harry]

Originally Posted by nikitopo

Which one did you get? The STI sports muffler or the STI performance muffler? There were 2 versions. First version was just sound improvement and second version was changing the back pressure too. I got the performance muffler and at first there wasn't much of a difference. Then I logged accidentally the engine and noticed that the ECU was off and it was constantly trying to add more fuel in high rpm. This happened after the installation of the STI muffler. I had to talk to my tuner and he had to dial the MAF scaling. After the fix it was found that there was ~10g/sec of additional air and the change in performance was noticeable. The physics reasoning behind this is that the gas temperature falls in the last part of the exhaust and it is important to optimize this area, but as usual in the forum and internet world we "know" better ...

Interesting, yeah I just looked at the receipt, the part number is: ST44300AS000, which I am guessing is the sport muffler? As the others on the STI website end in either 010 or 020. But it does say on the STI website “*Part numbers differ depending on the country.” So not sure, I bought it through a Subaru dealer in 2018.

[nikitopo]

Yes. This part number is the STI sports muffler.