Nov 182016

About a year ago I got the bug to do something really different for the new 2015+ WRX. With the FRS/BRZ being well established in the aftermarket world, some really well thought out supercharger kits had started emerging. This got me thinking about adding a supercharger on my WRX! Its the same motor right? It should just bolt right on right? I contacted two companies to see about getting a supercharger to test fit to really see what is involved. There were two really high quality kits that I thought would be perfect for my project. Cosworth’s kit was kind of the primo kit out there, it was the most expensive and had really good charge coolers mounted inside the intake manifold. The problem is cost. Cosworth/RallySport Direct (Cosworth USA) wasn’t able to give us much of a discount as their kit was new, in super high demand and not available for a month or more. They were a little leary as the project wouldn’t have benefited them in selling more kits. We were in the same boat as this was going to cost us a lot of money and a lot of time/money and it may be for nothing. Then I found the Harrop TVS1320 kit one day. I fell in love as it just looks sexy under the hood on the BRZ. At the time Harrop was interested to help us out with the project but there was a huge delay on when we could get one. While both Cosworth and Harrop were willing to help, the delay in getting kits really killed the momentum with this crazy project.


Fast forward to this year (2016) and the bug bit me in the ass again. There were plenty of people with bigger turbos and lots of power, but still nothing as unique as a twincharged WRX. I hit up the same two companies to see about helping with the project. This time around Cosworth/RallySport Direct had taken this idea and started down the path of installing it on their SEMA WRX. I thought great, we can do this together… except that once again, the kit was out of stock for a couple of  months. Harrop came to the rescue and was able to ship us a kit within a few days! Perfect and not to knock the Cosworth kit or RSD for not having one, but the Harrop kit was actually my first choice because it looks sooooo good. My only hold ups with their kit was the fact that I had never seen one in person, and the fact very few BRZ guys had them. What makes up for that is their willingness to help us out, their killer water to air intercooler system, and completeness of their kit.


Why even do this? The one thing I have come to love about modding cars is the response you gain from the turbo/engine. Anytime you do something you gain some response or something that makes the car better. This is great for a while until you get used to it and you want more. Well I wanted more! Adding the instant response (boost response) of the SC, along with the midrange power of the turbo, this would make for a killer setup as long as it all worked. Secondly the stock WRX turbo doesn’t hold boost past 5000 RPM and having the SC and turbo working together, this should allow for higher boost at redline. In theory, this had the potential to do great things if it all worked. And if it didn’t work, at least it would look really awesome!

With parts on the way, my excitement grew and was compiling a few things needed to make it work. Since RSD had already been installing the Cosworth kit on their WRX, they gave a few things to have to look out for. In return we offered to help them with the front mounted intercooler needed, the tuning aspect and overall setup. I still had reservations with a few things like fitment, tuning, and would this all be worth some kind of gains we couldn’t get from a turbo. I was confident enough that I didn’t care, and I would make it work one way or another.


What was needed to make it fit? Lots of grinding, and also lots of grinding. I would have made really tall spacers to clear a few of the obstacles, but the kit nearly fits perfect without that. I ended up making spacers that reduce some of the grinding, and added space for the bypass valve, but mainly they were made to create the transition from the BRZ sized ports to the WRX heads. You would think that these engines are exactly the same, but their heads have different port sizes and bolt patterns.


I started out building it in stages working up to the final install. Like installing the WTA (Water to Air) intercooler plumbing and pump. It fit amazingly well behind the PERRIN FMIC and bump beam. Even the custom molded hoses that Harrop includes for the BRZ work pretty well. The pump and harness they include worked very well. As you can see the pump mounted perfectly behind the intercooler pipe, I just had to extend the wires to it.


Once that was all done, the next hurdle was the grinding aspect. The AC bracket required a lot of material to be removed. This was to clear the throttle body and also to make room for the dual port bypass valve. It took about 4 times to get it right and also make it look nice. The throttle body needed some massaging too. Grinding all this down with a proper die grind bit is easy compared to what was next. The clutch slave cylinder was about 3/8″ in the way. The easiest way to remove all the material was to do this on the car, but imagine removing a 1″ x 1″ x 3/8″ block of steel with a die grind tool. Not only is it time consuming, it is soooo messy.

The rest of the install nuts and bolts things. Playing with belts and pulleys to get the best wrap and belt tension was the big hurdle.  As you can see it looks very OEM like.


I was able to utilized 95% of our 15+ WRX FMIC kit to make this all work. That was important as there could be a day that enough people start do this and I didn’t want to create something that is over the top custom. The one custom part of the intercooler was the last charge pipe before the supercharger. With that said, it is setup so that the WRX turbo system is all in place just like it was, but it is feeding boost to the supercharger. The heated and compressed air from the turbo is being cooled by our front mounted intercooler, then compressed again from the supercharger, and cooled one more time by the built in water to air intercooler within the intake manifold. You could call this twincharged and twin intercooled!

The moment I took off for the maiden voyage, it was very obvious (even with the lowest boost pulley) that this would need some taming of the throttle as the SC adds a huge amount of response! I drove on the car with the 95mm pulley at first to understand how this whole system would work. Being that this pulley should create a boost curve of 4.5psi at 2500 ramping up to 7.5psi at 7000, I was hoping to see boost to run about 15psi ramping to 18psi at redline. I was WAYYYY  off!

There are a few factors to why I was wrong. One being that the supercharger is compressing air at a ratio (pressure ratio). The supercharger is taking ambient air pressure and compressing it at a ratio to make boost. Compressing the boost from the turbo at this same ratio ends up multiplying the actual boost pressure instead of adding it up. This means, it should be running more than (turbo boost plus SC boost). The thing is this still didn’t really show what I was seeing, especially at lower RPM.

The other factor (the bigger one) is even with the turbo running off the wastegate pressure only (10-ish PSI), the added energy from the superchargers boost spools the turbo even faster. This created a rising boost curve out of the turbo (18psi verus 10psi), which added to the natural rising boost curve of the SC. I would see 25psi at 4500, and it was still going up! Obviously this is a bit much for pump gas and stock motor. My goal was to be able to a minimum boost level that would  allow the stock ECU safety parameters to function. That way if the ECU sees too much knock or has a legit CEL, it would drop boost to a safe level. So obviously this crazy boost was not ok.

Fast forward to today and after about 4 or 5 versions of control systems, I finally got it dialed.  It is so good that I took it one step further and installed a 10mm smaller pulley to make even more boost down low.  This would not  have been possible without the dual port bypass valve Harrop includes and our EBCS Pro to control it. I can run at little as about 12psi or as much as probably 35psi, all fully controlled by the ECU.




As you can see by the pictures, I have a water meth injection system installed into each runner. I ended up doing this as injecting the mixture into the SC inlet would destroy the coating on the compressor. I have been using the Aquamist HFS-4 for a long time now, and it was a must to integrate this into a high power WRX that can’t run on E85 or run high quality fuel. With the carbon build up issues, blow by from the crappy PCV valve, EGR stuff, and also being able to make power on pump fuel, every 2015+ WRX customer should consider running a water/meth injection kit.


Why did it take so long to show this off? Its actually been running on the car for the last two weeks but there were many things that had to be worked out. Mainly was boost control but other things like oil cooler setup, routing of things, visual appearance, and most important was tuning/drive-ability. I didn’t want to show it off in its testing state with hoses and wires everywhere. Nor did I want to fail at answering peoples questions that I am sure would be asked.  As of two days ago all of this came together to a point where I was willing to show it off, and it turned out WAY better than I expected!


Does it work and was it worth all the effort are two really important questions. Absolutely! The response is amazing at all RPM’s, and the best part is there is virtually no turbo lag. If you are cruising at any RPM there is an instant 6psi of boost on tap. The higher the RPM the most instant boost you have. Even at 2300 RPM, if you go from 0% throttle to 100% throttle, it instantly hits 6.5PSI, and in .6seconds, I am seeing 17psi. At 3500 its even better. And it is even MORE responsive if you are at part throttle then smash the gas (because the boost tubes have some boost in them). So yes… it works and yes, this whole thing was worth

There is only one question that I can’t answer at this time, which is “How much power does this make?”. Dyno time will follow very soon. Every day, I am tweaking the setup dialing it in, working out bugs in order to get it on the dyno. I can say for sure that it absolutely makes power, and it a blast to drive! I will post up some good data with boost curves and things showing where the SC blows the turbo out of the water in the next few days.






 Posted by on November 18, 2016 Project Builds Tagged with: , , ,

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