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Old 09-19-2020, 10:43 PM   #1
user1029
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Join Date: Mar 2004
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2008 STi IAG built
HTA86 E85 Kel272s Cos IM

Default Easy 10% power gain: wastegate as exhaust bypass



Solid lines = hp and tq with cutout
Dotted lines = hp and tq before cutout

+80whp! XONA Rotor 8269S 0.82 AR @40psi both runs



Running IAG Stage 4 extreme with stock crank + IAG stage 5 heads with Kelford 272s

I chose the PTE 66mm wastegate over a traditional cutout because it is made of materials that can stand up to exhaust gas heat and offer optimum seal. No failing electric motors or metal valves that don***8217;t seal causing exhaust leaks. The wastegate opens at 15psi boost pressure

Everyone should definitely do this mod if you want a quiet exhaust without sacrificing power when you get on it
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Last edited by user1029; 09-20-2020 at 01:18 AM.
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Old 09-19-2020, 11:00 PM   #2
can250
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great results why the difference in spool though
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Old 09-19-2020, 11:34 PM   #3
user1029
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HTA86 E85 Kel272s Cos IM

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Less back pressure = quicker spool
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Old 09-20-2020, 12:36 AM   #4
GalaxyWide
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No, the graph shows no cutout = faster spool. Therefore more back pressure = quicker spool.
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Old 09-20-2020, 01:00 AM   #5
user1029
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HTA86 E85 Kel272s Cos IM

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Oops mislabeled by me

Dotted line is no cutout
Solid line is with cutout

I***8217;ll upload another graph
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Old 09-20-2020, 11:14 AM   #6
Bariga
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your turbo and exhaust housing is to small for your power goals
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Old 09-20-2020, 11:30 AM   #7
user1029
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HTA86 E85 Kel272s Cos IM

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Honestly my power goal was 700whp and then I said what the hell and added the cutout, here I am at 800whp
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Old 09-20-2020, 02:53 PM   #8
NighthawkSTI
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Quote:
Originally Posted by GalaxyWide View Post
No, the graph shows no cutout = faster spool. Therefore more back pressure = quicker spool.

??? there is more torque where the graph starts over approx. 800-1000 RPM ramp up from 3000 to 4000 WITH the cutout. Then they merge without the cutout and then with the cut out really takes off.
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Old 09-20-2020, 02:58 PM   #9
NighthawkSTI
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Quote:
Originally Posted by user1029 View Post
Honestly my power goal was 700whp and then I said what the hell and added the cutout, here I am at 800whp
and it is a much quicker less expensive power gain than choosing another turbo. Nice job.
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Old 09-20-2020, 03:31 PM   #10
user1029
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HTA86 E85 Kel272s Cos IM

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Quote:
Originally Posted by NighthawkSTI View Post
??? there is more torque where the graph starts over approx. 800-1000 RPM ramp up from 3000 to 4000 WITH the cutout. Then they merge without the cutout and then with the cut out really takes off.
My first dyno graph was labeled wrong lol
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Old 09-20-2020, 03:32 PM   #11
user1029
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HTA86 E85 Kel272s Cos IM

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Quote:
Originally Posted by NighthawkSTI View Post
and it is a much quicker less expensive power gain than choosing another turbo. Nice job.
Plus it sounds like a V8 when it opens
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Old 09-20-2020, 10:22 PM   #12
user1029
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You can get even earlier spool by running a wastegate spring that opens even earlier I didn***8217;t want to terrorize my local school zone just leisurely driving through it
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Old 09-21-2020, 02:42 PM   #13
NighthawkSTI
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Quote:
Originally Posted by user1029 View Post
Plus it sounds like a V8 when it opens
a win win!
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Old 09-21-2020, 03:19 PM   #14
Bariga
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Most important thing is pre-turbo back pressure if you doing 40 psi and your back pressure is 60psi then your motor wont be happy camper
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Old 09-21-2020, 03:32 PM   #15
Stretch18
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Quote:
Originally Posted by Bariga View Post
Most important thing is pre-turbo back pressure if you doing 40 psi and your back pressure is 60psi then your motor wont be happy camper
This should alleviate back pressure under boost. It might cause some turbulence at low boost, but even then can't be enough to even add as a footnote.

Honestly, I'm filing this in the 'great idea, but mad at OP that I didn't think about it myself' folder...
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Old 09-21-2020, 05:51 PM   #16
user1029
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HTA86 E85 Kel272s Cos IM

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Prior to doing this mod, I scoured every google result but nothing tangible. Hopefully I set a precedent with this solid test and hopefully nothing bad happens in the coming months
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Old 09-22-2020, 11:12 PM   #17
user1029
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HTA86 E85 Kel272s Cos IM

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Old 09-23-2020, 02:10 AM   #18
Gally316
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Is a tune required fore this mod?
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Old 09-23-2020, 06:26 AM   #19
user1029
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HTA86 E85 Kel272s Cos IM

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Yup definitely, you will instantly run lean otherwise
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Old 09-23-2020, 08:31 AM   #20
KillerBMotorsport
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No 2 ways about it, if your exhaust is a bottleneck you either need a cutout or a custom exhaust. This is the far more economical route as getting a larger diameter custom exhaust it big $... and it's still going to sap some power over a cut-out.

On a +700whp setup here's a 3" to 3.5" megaphone at the turbine outlet that transitions to 4" oval under the car, and back to 3.5" round at the muffler. VERY expensive. I don't recall what we lost over the dual side-pipe setup that was just deafening (even with a helmet on), I want to say ~30whp, but the full cat-back would allow you to hear a passenger without having to scream directly into their ear, lol.


Last edited by KillerBMotorsport; 09-23-2020 at 09:43 AM.
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Old 09-23-2020, 09:40 PM   #21
scotte30m3
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I have a cutout like this on my 15 WRX. Been running it for years. Itís boost activated but also on a switch so I can use it when I want to and keep it quit when I need to. Itís mounted as a 3Ē dump at the end of the y-pipe just before the stock mufflers.
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Old 09-24-2020, 09:47 AM   #22
TyranosaurusWRX
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Genius. So no vacuum lines or anything, just opens up on spring pressure? I have an old 38mm Tial I can use. Not as big but even little is better than none I'd imagine.
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Old 09-24-2020, 04:53 PM   #23
user1029
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2008 STi IAG built
HTA86 E85 Kel272s Cos IM

Default

Give it 15psi of boost and it***8217;ll open or whatever spring you choose. No need for any fancy solenoids
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Old 09-28-2020, 12:58 PM   #24
subbi7
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the spring pressure without any boost hose to the wastegate will keep 15psi pressure in youre exhoust system...
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Old 10-04-2020, 08:49 PM   #25
Xerxeys
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Nice!
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