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


After double checking our work we started the car and took it for a spin. The IWG75 uses a 7 PSI spring and our initial thought was that we would not need to completely re-tune the car based on the spring rating and using the OEM boost control solenoid. We drove the car for a few short trips staying out of boost to make sure all of our values looked good on the access port. When we were sure everything was in line we data logged a pull in sport mode to see what the results were. The AP was used to watch boost in real time as we rolled in to the car at 2800 rpms and I watched as the boost gauge shot to about 19PSI. I backed out of the throttle to make sure it was in sport mode and not in sport sharp based on the high boost reading. Sure enough the car was making nearly 3 PSI more boost than it was before.

I put the car in sport# to do a quick pull and sure enough it made nearly 23 PSI and I immediately backed out of the throttle. What we noticed immediately was how much faster the car seemed to come up on boost. We had not even data logged the boost curve after the install but our asses clearly felt the large difference in low end power. In the interests of engine preservation we kept the car out of boost until we could get some time to data log. The reality is that we drove the car around for over a week largely staying out of boost and at most boosting to less than 10 PSI on firm throttle tip in. This is what offered us the best insight in to exactly WHAT the benefits of the IWG75 are.

TUrbosmart IWG75 installed

Yes, you can go balls to the wall and compare a 3,000 RPM pull before and after the gate and analyze the boost curve or dyno. chart, however that does NOT tell you the entire story. The reality is that the car is completely transformed. I do not mean it is now a fire breathing GTR eating monster. Nope it is just a MUCH better car to drive around on a daily basis. The STi does not suffer from a lack of low end power however when you add the IWG 75 it wakes the eff up! You can stay in a higher gear without the need to downshift when cruising or negotiating traffic and when you roll in the car scoots. You will spend less time rowing the boat with the IWG75 and more time texting your friends bout how kickass this mod is. OK fine so the latter is not condoned nor endorsed and our attorneys ask that I add this disclaimer that you NOT do that while operating a motor vehicle… We also noticed that the car seemed to idle smoother and had less hesitation under tip in than before. if you are familiar with the 08+ STi fuel supply system you know that the in line damper is the cause of a lot of problems with hesitation and despite the fact that some of that was still present, the car operated more smoothly over all under all driving conditions.  

Turbosmart IWG75 COBB heat shield installed STi Impreza WX
Here is how the IWG 75 fits when installed. We chose to zip tie a few of the OEM lines together to keep them from rubbing on the larger Cap of the IWG75. Sano install with superior fit and finish! 

Before we installed the IWG we took the time to data log the RPM and boost curve so that we could overlay the after installation data to see where the car was making more boost and at what RPM. We had hopes of being able to share data for both sport and sport sharp modes for all 6 gears however our fuel system had a different idea. When data logging our sport mode pulls we were getting Injector Duty Cycle readings of 100% and as such there was no way we were going to press our weak wristed ring land luck with pushing 23 PSI on the same tune. As such what we have are the overlays for sport mode. 

 Here are the overlays of the boost curve before and after the IWG75 install. We will be re-graphing this once the fuel system is upgraded and the car is re-tuned. Do not attempt to run the IWG75 without a retune! 

As you can see the IWG75 makes a marked improvement in boost response. My personal opinion after living with the car for a 2 months with this installed is that the above chart means a lot less to me than what I FEEL when I drive the car. It is a joy to drive around town regardless of if you are picking up groceries and teh childrenz or hitting the back roads for spirited driving without the aforementioned precious cargo. Aside from that the BPV works perfectly and is quite quiet which we LOVE! Turbosmart also offers a dual port valve if you prefer that setup and “sound” however we opted for the full recirc and are quite happy with both its function as well as fit and finish. As you would expect from Turbosmart their stuff is first rate, no corners are cut from design to packaging! Until we used the IWG 75 the thought of “upgrading” the internal wastegate had never crossed our mind; after spending time with the car it really is quite a change and we recommend that whatever internally gated turbo you are using you consider the IWG75 as a necessary upgrade. Of course our other mods. made HUGE power but the little IWG75 made such a large difference in how we use and drive the car we suggest it as one of your first modifications! 

In the coming installments of Project GR STi we will be upgrading the fuel system and eliminating the TGV's with the help of Motive, Injector Dynamics, and Cobb tuning. We will also be addressing suspension with our friends from M7 and with any luck wheels and tires, none of this necessarily in that order!


Without these people Project GR STi would suck! 

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