Good question. I'm guessing your header I.D. after the collectors is around 63mm or 2.5in or so. Same as your front pipe. Those two are connected by a 50mm I.D. pipe. So that is your main restriction in your exhaust setup. Would be interesting to see what others say.

I'll question that with my tuning shop, see what they did on their racing 86 ... but shouldn't be much of a problem to make something !! ...

But yes indeed everything else is 2.5" so, as small as this part is, it is "in the way".

Let us know what they tell you. Thanks.

HKS don't have an overpipe
 

Heya. I got pretty much the same setup as you(cept my front pipe is catless - due to be installed in exactly 5-6 hours). Changing the overpipe *does* make a difference! Car noticeably revs alot free-er.

The overpipe is the curvy pipe that goes past the steering rack. You can see part of the pic here on the underside of my car.(its the pipe near that white square sticker)
http://i46.tinypic.com/2lt0tab.jpg

Here is a comparison pic between the STOCK overpipe and another overpipe(MOTIV Concepts) and you can quite easily see the difference in diameter of the two..
http://blog.perrinperformance.com/wp...o2-550x366.jpg

I myself purchase the MOTIV Concepts overpipe mainly because HKS strangely DO NOT have one yet on the market. Plus, the quality of the MOTIV is I dare say, better than what HKS could make imho.

Check out the quality of those welds!
http://i39.tinypic.com/2rxjj88.jpg
http://i44.tinypic.com/353az4y.jpg

You absolutely need to change that stock overpipe to match with the rest of your HKS exhaust.

Right now this part is restricting the entire system.

Just came back from a drive with my new FULL exhaust system(Frontpipe installed this morning)
Change the overpipe ASAP!! You will LOVE the sound!!

When free revving @ 4-5krpm its got a nice raspy bark. Almost sounds similar to the TRD Griffon exhaust(cept for NOT being Ti)
[ame="http://www.youtube.com/watch?v=ZFIksPFOJL8"]ã�Šã‚�らサーã‚*ット　モータースãƒ�ーム„フェス　86 TRD Griffon Concept - YouTube[/ame]

Hitting the gas at WOT, the car sounds damn angry, just a light touch on the throttle(while NOT under load) and it will rev to 3krpm easy.

hey stevo i heard an exhaust clip here:[ame="http://www.youtube.com/watch?v=Q2dhQgYaMtg"]HKS EL Header with T1R Catback on Scion FR-S and Subaru BRZ - YouTube[/ame]

and i like the sound but i like yours a lot better. is the exhaust not on the one in the video soft because of the hks header or is it cuz the front pipe or cuz the T1R cat back? I would imagine it would be louder or raspier than your setup cuz this one is a single exit but it isn't.
What made yours so raspy and loud? was it mainly the header? the over pipe? the front pipe?

stevo_12v exhaust(no tune yet)
 

Hahaha that video above on the race track is NOT my car. I WISH!! That's the TRD Griffon with prototype TRD Ti Race headers and straight pipes. Oh man, I wish I could have that setup!!

I managed to get a buddy to film me doing a driveby.. the video is a bit blurred, but that's not the stuff that really matters, the thing that matters is the SOUND. Here is my startup > driveby.

Note: The car has NOT had a tune yet. It is running ridiculously rich(I am getting 130km/200miles to HALF a tank). I believe a tune will change the exhaust note of it.
[ame]http://youtu.be/qFftuRByyPk[/ame]

EDIT: @ 35seconds, you can hear me feather the throttle a bit under load, I personally prefer that sound. Sounds more angry. ^_^

UPDATE(25th July):
Had someone interested in my exhaust setup and wanted a close up video of my car revving. I decided to rev it at its loudest(between 3.8krpm and 4.8krpm).
[ame]http://youtu.be/etZWcQ2eaBs[/ame]

Ordering the MOTIV *CATTED* front pipe to replace the HKS front pipe. Reason being I'm not too fond of the smell or the soot coming from such a straight through system. The sound of the exhaust sounds good to me so far. Maybe hoping the tone of the exhaust will be a little bit lower pitched with the catted MOTIV pipe, but still as loud :D

Here is a litle test i did this afternoon to give you a better feel of the sound ;) too bad you are missing 50% of the experience, the sound pressure, real life loudness, but its just awesome really.

[ame="https://www.youtube.com/watch?v=LXs7YZ6atfY"]VID1 - YouTube[/ame]

For those with the HKS header and front pipe catless setup, do you have a check engine light on?

Why did operator stop dyno at 6300 rpm on OEM setup when that car make max power at 7000 rpm in oem setup?

Very good question, answer is very simple too, in Japan cars are limited to 180km /h from factory ... wich is when it hitted 6300 rpm on the dyno ;)

After the ECUtek tune the speed limiter had been removed of course ! :)

And for previous question, no of course not any cells or codes showing up ;)

I didn't get any with mine. But, I believe every market has different spec cars depending on emission regulations

You don't have a CEL because you have a catted front pipe and relocated the second sensor after that cat.

I'm curious for those that has a full HKS header setup + test pipe with no cats if their car is throwing a CEL. I read on the HKS website that with their system without the cat setup will potentially throw a CEL which they said it's ok. For those that has that setup, is that happening like they said?