Unlocking the hidden power and flow of your OEM turbo

***WARNING Altering your wastegate actuator spring rate will increase your system potential for higher boost. This means if a line pops off your boost controller or other failure could cause excessive boost pressure. Please make sure you take precautions and have your boost cut set properly.***

*Second warning: Buying a spring of X pressure does not insure you will achieve that pressure. Preloading of the wastegate actuator will ultimately dictate the pressure when the wastegate flapper opens. I suggest you run a line directly between the wastegate actuator and the pressure supply to confirm your spring opening pressure.*

There is massive amounts of information available on how to get more power out of your setup. Lots of debates decyphering numerous details. I personally strive to get the most bang out of your dollar. In my mind the ideal setup is utilizing the least amount of parts with the greatest amounts of gains. Now I have some solid data to back up my claims, and to show you what you actually need to make good power.

First I want to talk about a few topics that are overly covered and have endless opinions, yet don't entirely line up with my data. For discussion purposes I will be refering to my current setup (2011 WRX, VF52, stock top feed injectors, stock fuel pump) Which is not drastically different from say an 07 LGT with a VF52.

Restrictive Intake: I hear all too often that people are claiming the stock intake is restrictive or I couldnt break X whp with the stock intake. Now in a larger setup certainly you will max out the Maf by exceeding its range 1-5 volts. A larger MAF housing allows less signal at a given flow so there is some truth behind this yet, at VF52, VF39, etc flow rates its pretty unlikely you are maxxing out your MAF.

Limited by Injectors: Similar to intakes people are timid to run stock fueling with a VF52, due to it being on the edge and such. Is your VF52 really flowing that much? I will cover this in more detail.

(What gave me the idea was seeing one VF52 boost creep to 21 psi by redline, so I knew they could easily push over 14 psi up top)

What I want to share is essentially some boost curve testing I have done with the stock boost control solenoid, a grimmspeed boost control solenoid, a stock wastegate spring, and an upgraded wastegate spring. Power and torque are typically defined by how much boost we jam into our motors, but more important and often overlooked is how well is boost holding. Well the turbos in Subaru's come with a gentle 7-8psi wastegate spring. This keeps you from overboosting if a line comes off the boost controller but also limits your top end boost. So collected some data with the stock EBCS and spring first. You can in fact see some boost creep occuring in the orange and dark blue lines, they start at 8 or 10 psi and creep up abit to 11 or 12 psi. This is due to the wastegate port maxxing out and diverting exhaust back into the turbo. No worries because I want lots of boost up top and 12 psi is not much.

You may also notice that I can get more peak boost with the grimmspeed than the stock controller as seen in the light blue and dark red lines. Please also note that boost falls regardless of controller to about 14 psi by 6000-6200 rpms. This is due to the stock 7 lb spring, in theory you can only hit about 2x the spring pressure at redline, assuming your turbo can physically flow that. Well guess what a VF52 can flow more than 14 psi @ 6200 rpm on a EJ255.

Visible in the light green line, I'm now sitting happily above 16 psi at 6200 rpm or so. More boost means more flow! Previously I was pulling about 280g/s on the Maf at 14psi at 6000 rpm. The light green pull it pulled 296 g/s at 6200 rpm. I will post voltage instead to give a more accurate comparison and to show you my stock maf is not maxxed. I plan to add more preload and hold about 17 psi at redline.

Please also note the power starts at different times, this is just when I happen to start the run.

My conclusion is that you only need minimal mods: A high flow down pipe, upgraded wastegate actuator, and upgraded EBCS, and a quality tune.

Other information to keep in mind that may not be entirely obvious...

There is more to a wastegate than just it opening at the desired pressure. The other important detail is that a higher spring rate, will not also start to open at a higher pressure, but at say 18 psi, the valve will have less lift or opening than a stock spring would have a 18psi. So maybe it is half open instead of 100% open. So tuning of the spring pressure alters maximum theoretical boost pressure at redlline, and also the flow rate of the wastegate at various pressures.

I noticed something similar when I had my tune. Due to an EWG, EBCS, and a ported/polished VF52, I'm only tapering down to 17 psi at 6500RPM, with over 310g/sec. And that's with a grimmspeed TMIC, which sees a little pressure drop to boot. I didn't realize that the wastegate played such a huge part in it!

Yes, you would not hit that with the stock spring. Recent Sti hit 309g/sec with a EWG and stock turbo. (Unless you had a fat MAF curve) How many volts? On a stock intake? Now I have a goal in mind for mine.

Can you recommend a particular actuator that would work well with a VF-52 and supporting mods?

http://shopping.kinugawaturbo.com/kinugawabilletadjustableturboactuatornissansd33-tpatrolht15-bht15-2-1.aspx

Here is where I got mine.

^Thanks^ Where the springs you needed supplied with the actuator, or did you have to purchase them separately?

1.0 Bar installed

 

0.3bar, 0.5bar, 0.8bar, 1.0bar, 1.2bar, 1.5bar, 1.8bar and 2.0bar Springs are available on our shop.

Look I got some more tonight! 16.75 psi @ 6000 rpms, and 15.9 psi @ 6500.

It was a bit lower in the low rpm because I turned my ebcs down a bit, trying not to explode my stock tmic.

Actually I think this speaks volumes. You can clearly see here that with the stock spring and either boost controller you getting roughly the same thing at redline. Certainly a nice bump in torque with the GS unit.

Now compare that with a higher spring and you get a much wider torque band, and some high end power!

Any thoughts on the turbo's adiabatic efficiency at those flow rates? What about applying similar principles to the VF40?

I haven't looked for compressor maps for these turbos, nor would I have a decent guess for VE on these engines, but it would be interesting to see turbo outlet temperature data as well.

Thank you for sharing your findings.

On my SR20 running a Garrett turbos, I have less zigzags and keeps boost till redline (though I'm usually running 15psi or less). I wonder if Garrett wastegates (Diaphragms and springs specifically) are better quality then what IHI uses.

Restrictive Intake: I hear all too often that people are claiming the stock intake is restrictive or I couldnt break X whp with the stock intake. Now in a larger setup certainly you will max out the Maf by exceeding its range 1-5 volts. A larger MAF housing allows less signal at a given flow so there is some truth behind this yet, at VF52, VF39, etc flow rates its pretty unlikely you are maxxing out your MAF.

I built a custom intake out of the stock MAF housing to test this. With MAF housing staying same diameter and with 3" 45* elbow my MAF scales were still 20% off (25% with a flow stack). I don't think MAF diameter is the only thing at play here, I think it's overall airflow through the MAF plays a big roll.

What I don't get is this: With a hot wire maf, more airflow would cool the wire more, requiring more electricity to warm up the wire, hence increasing the MAF voltage, but in reality intakes cause MAF voltage to drop and not raise up.

Any thoughts on the turbo's adiabatic efficiency at those flow rates? What about applying similar principles to the VF40?

 

I haven't looked for compressor maps for these turbos, nor would I have a decent guess for VE on these engines, but it would be interesting to see turbo outlet temperature data as well.

 

Thank you for sharing your findings.

Certainly I would like that info too. Also would be a great way to compare with all the hybrid turbos on the market. No reason why the VF40 cant hold a little more up top.

On my SR20 running a Garrett turbos, I have less zigzags and keeps boost till redline (though I'm usually running 15psi or less). I wonder if Garrett wastegates (Diaphragms and springs specifically) are better quality then what IHI uses.

 

 

 

I built a custom intake out of the stock MAF housing to test this. With MAF housing staying same diameter and with 3" 45* elbow my MAF scales were still 20% off (25% with a flow stack). I don't think MAF diameter is the only thing at play here, I think it's overall airflow through the MAF plays a big roll.

 

What I don't get is this: With a hot wire maf, more airflow would cool the wire more, requiring more electricity to warm up the wire, hence increasing the MAF voltage, but in reality intakes cause MAF voltage to drop and not raise up.

When you have a soft spring rate and are using a boost controller to achieve a higher target, you generally get more oscilation has the solenoid modulates across a pressure and flow range. So I'm doubtful there major difference in quality. Just how much the port can flow, size of flapper, and spring rate.

Would the actuator you referenced fit on a VF40? I have a bnr 16g that's in a regular VF40 housing and am wondering what my options are for an upgraded actuator.

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Would the actuator you referenced fit on a VF40? I have a bnr 16g that's in a regular VF40 housing and am wondering what my options are for an upgraded actuator.

 

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You may want to ask the company selling it ? call them.

I emailed them. They weren't very helpful. Maybe a phone call would be better.

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Would the actuator you referenced fit on a VF40? I have a bnr 16g that's in a regular VF40 housing and am wondering what my options are for an upgraded actuator.

 

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It should fit. It has slots so it works with a variety of bolt hole locations.