Turbosmart IWG75 Bypass Valve Fully Recirculating MotoIQ Project GR STi

turbosmart BPV subaru STi impreza

Project Gen 3 STi - Impressions of the Turbosmart IWG75 and BPV

By Wes Dumalski 

(for this installment should be DumbASSki)


"Hey Bro, do you want to test some Turbosmart stuff?" The quoted text is from none other than Martin G from MotoIQ headquarters asking me if I would like to play with any Turbosmart products on our GR STi project. With this project still in the early and mild stages I first scratched my head wondering what I would be able to use and test. When I think of Turbosmart I envision huge external wastegates on race cars and e-boost setups. Initially I wondered exactly what I could even use on the STi... Not wanting to miss an opportunity I perused their site and used their vehicle specific search feature to see what they had available.

Of course I found the normal external wastegates and other race inspired items but what jumped out at me was their internal wastegate replacement actuator. The IWG75 is a replacement actuator for internally wastegated turbos and Turbosmart offers this wastegate in application specific as well as universal applications and their claim is that it improves turbo response by providing superior control of the wastegate flapper. In short the theory is that with their spring design it will hold the flapper closed longer thereby reaching the desired boost target more quickly and anything we can do to improve response and power in the area under the curve is what we here at MotoIQ are all about. In addition to the IWG75 I also found their STi application specific BPV. The goal here was to upgrade these components with the goal of improving low end power/torque as well as improving overall drivability. 

turbosmart IWG75 Subaru STi
The IWG75 is available for both application specific and universal applications. 

After collaborating with Martin and the brains at Turbosmart our order was placed and these juicy bits were soon on their way to the land of cheese where our GR STi project resides. To be honest I was very curious as to what, if anything, these items would actually do to this project. I mean the car already has an OEM wastegate and BPV, how much better could these be? I sold myself on the idea that even if they offered very little in measurable/quantifiable performance they would LOOK cool in the engine bay and I eagerly awaited their arrival. After a particularly stressful  day at my "real employ" I arrived at the homestead to find a box on the counter. It was in fine shape and the brown army must have known that some serious quality parts lied within. Rather than change out of my work clothes or start making dinner I snatched up the box and headed downstairs for some alone time with my new parts. It is clear Turbosmart takes pride in their products as the packaging is as first rate as the components themselves.

Turbosmart fully recirculating BPV BOV
We opted for the fully recirculating STi application specific BPV. If you want the best performance coupled with a QUIET bypass valve this is the option for you. Turbosmart offers 4 models of this BOV/BPV for your WRX or STi. 

Included with both the IWG75 and the BPV were CD ROM's containing installation instructions for all Turbosmart products as well as some stickers. I always like to play arbiter on packaging and in this case it was first rate! Printed glossy color boxes, perfectly cut foam protecting the delicate bits, yup real stuff here! After reviewing the instructions I packed them back up to await installation day.

Turbosmart IWG75 Subaru WRX STi universal
The STi specific kit (TS-0605-1072) has everything you need for a bolt in installation. Minor mechanical aptitude is required and not included! 


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Thursday, March 21, 2013 8:34 AM
It seems that you now have more boost overshoot, which isn't a good thing.
Wes Dumalski
Wes Dumalskilink
Thursday, March 21, 2013 9:39 AM
The tension is adjustable. In this case I used the Turbosmart recommended setting. The STi uses an OEM boost control solenoid so rather than messing with actuator tension the car will be getting a tune with the new fuel system and we will be documenting the curve once again. This was simply to measure what was happening without a tune on THIS PARTICULAR application WITHOUT a tune.
Wes Dumalski
Wes Dumalskilink
Friday, March 22, 2013 9:47 AM
Something I did not mention in detail in the article is the positive impact this had on drivability. The car just idles and runs smoother overall. The OEM BPV was not leaking under vacuum on the bench but I can say without a doubt I noticed less idle hunting after the Turbosmart BPV install.
Marty Staggs
Marty Staggslink
Friday, March 22, 2013 5:26 PM
The boost overshoot is a direct result of having a higher base spring pressure than the stock unit.
Friday, March 22, 2013 7:48 PM
Would this IWG reduce/eliminate the need for noisy EWG? I planned on running an EWG with stock turbo on my GD STi to reduce a possible boost spike in the cooler months, but this seems like much less hassle and cheaper too.
Friday, March 29, 2013 5:55 PM
Show some transient pulls if you think it improved driveability, specifically time to boost and boost response with various tip-ins.

Also the idle improvement sounds like there was a vacuum leak at the bypass valve, and was fixed with the new CBV install. Otherwise take some data before/after and that will tell the truth.
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