Adding more boost with a boost controller!
So I upgraded my turbo kit from Prodigy Performance from the Garrett turbo to the Precision turbo: http://jeeplab.com/showthread.php?26...ull=1#post5400
The improved low RPM response is great, but the peak boost levels are lower with the Precision, and it felt like I was down on power a bit compared to the Garrett. So now it's time to turn up the boost!
I decided on a simple and relatively inexpensive boost controller (compared to how expensive the really sophisticated electronic controllers can get). The Grimmspeed Manual Boost Controller (MBC): http://www.grimmspeed.com/manual-boost-controller/
It's actually on the expensive end for manual boost controllers, but I like the precision and resolution of its adjustments (distinct "clicks", each adds about 0.25 psi). At the other end of the spectrum is cheap ebay boost controllers that look like they were put together from basic plumbing/pipe parts from a hardware store.
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http://www.uselesspickles.com/files/...bc/package.jpg
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http://www.uselesspickles.com/files/...ed_mbc/top.jpg
It comes with a mounting bracket, some hardware, zip ties, and more than enough hose to install it on my turbo setup.
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http://www.uselesspickles.com/files/...th_bracket.jpg
I chose to mount it here by drilling a 1/4" hole (ignore the trimmed plastic above the hole - that was originally done to provide clearance for the charge pipe silicone elbow when the kit was in the stage 1 configuration):
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http://www.uselesspickles.com/files/...illed_hole.jpg
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http://www.uselesspickles.com/files/.../installed.jpg
The included mounting bolt was not long enough. I found a longer bolt at a hardware store, but used the included lock washer. I believe the bolt I bought was a M6x30mm (or maybe 35mm?) 1.00 thread flange bolt. I also used a M6 fender washer on the back side to spread the load of the nut across the plastic.
The boost controller is connected between the boost source and the wastegate. My boost source is on the silicone elbow that mounts to the throttle body, so this mounting location is perfect for minimizing the length of hose used. (NOTE: my wastegate boost source is different than Prodigy's official installation. Click for details)
As part of this install, I also swapped the stage 1 wastegate spring back into the wastegate. This gives me the ability to run at lower boost if I want to for some reason, and also improves how quickly the wastegate can respond once the boost controller allows boost pressure to pass through and reach the wastegate.
Once installed, I just started with the boost controller at its lowest setting, then went for a drive while monitoring my boost. I used the "Torque" app for Android phones/tablets and a bluetooth OBDII adapter.
At its lowest setting with the stage 1 wastegate spring, I saw a peak of 6.5 psi.
The remainder of setup is just pull over, twist the boost controller a bit, go drive and see how much boost you get. Rinse and repeat until you have the amount you want.
With a simple boost controller like this, peak boost is still dependent on engine load. In lower transmission gears, driving downhill, with a tail wind, etc, you won't always hit the target peak boost. So it's important to dial in the boost under conditions where there's enough load on the engine to really reach the max possible boost levels. If I dialed in the boost with a 1st gear acceleration, I'd be over-boosting in all other transmission gears. I dialed the boost in using 4th gear in the 3500-5000 rpm range - high engine load, right in the RPM range that I get the highest boost readings. I stopped when I saw 9.1 psi peak boost. The tune from Prodigy is calibrated for up to 9.2 psi, so that seems safe. Each "click" on this boost controller is about 0.25 psi, so one more click would be too much.
End result: MORE POWER! A very noticeable increase in power. Best power-per-dollar mod I've ever done.
Aside from more power, this style of boost controller keeps the wastegate closed longer while spooling up to the target boost, compared to if you had a wasteagate spring alone that get to the same peak boost. That means less boost lag. At high RPMs where full boost is attainable, from a steady cruise to sudden full throttle, full boost is now reached in about 0.3s. Without the boost controller, the lag was about 0.5s. Just to be clear, this is not a complete delay in throttle response. You get full naturally aspirated power instantly, then it ramps up to full boosted power quickly/smoothly over the next 0.3s.
This decrease in lag also means that peak boost is available slightly lower in the RPM range. Here's a comparison of the boost curve from a 2nd gear full throttle acceleration. Included are the Garrett turbo with the stage 2 spring, Precision with the stage 2 spring, and Precision with the stage 1 spring + boost controller set for a max of 9.1 psi.
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http://www.uselesspickles.com/files/...oost_curve.png
NOTE: I started at lower RPM with the Garrett, so it had a chance to start spooling a bit lower in the RPM range. That may be why is has slightly more boost in the lower RPMs than the Precision.
I'm not sure why the Precision + MBC boost curve tapers off in the upper RPM range more than either of the curves without the MBC. The Precision without MBC seems to taper off a bit more than the Garrett, but it seems that adding the MBC caused it to taper off even more. It's possible that the data is just too "noisy" to draw any conclusions without getting an average of multiple runs. We will never find out for sure, because I'm not swapping turbos and wastegate springs again to gather additional data :)
