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Low Buck Boost

Assessing the cheapest aftermarket boost controller on the market...

By Michael Knowling

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The automotive aftermarket is already flooded with turbo boost control systems, so what makes the new PowerUp MBC (manual boost controller) from Balistik Motorsport stand out? Well, in a word, price.

Retailing for just AUS$99, the MBC is the cheapest boost-up device you can purchase off-the-shelf.

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The MBC is a pneumatic bleed valve, which works on the same principle as one of the AutoSpeed boost control systems (the one comprising a ball valve, needle valve and T-piece, covered at ["Project EXA - Part 3 - DIY Boost Control"]). Although the MBC is slightly more expensive than our previous approach, it has the advantages of easier sourcing, easier installation and - of course - it's prettier to look at.

Before we delve into how the MBC operates, it's best that we scrub up on some background knowledge of factory wastegate control systems...

Outline of Wastegate Control Systems

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In older factory turbo cars, a rubber hose is used to channel boost pressure directly from the turbo compressor outlet to a wastegate actuator. The pressure inside the hose acts upon the spring-loaded wastegate actuator diaphragm, which - in turn - opens the wastegate bypass. Once the wastegate is opened, the turbine receives less exhaust gas and - as a result - manifold boost pressure is limited.

Modern turbo cars use a similar approach, except an electric solenoid valve is usually tee'd into the hose between the compressor outlet and the wastegate actuator. When certain engine criteria are met, this solenoid valve is pulsed by the ECU to bleed some of the pressure that the wastegate actuator diaphragm would otherwise receive - determining the manifold boost pressure attained.

The PowerUp MBC shares the concept of bleeding pressure from the wastegate hose to increase boost. Unlike an electronic controlled solenoid valve, however, the amount of pressure bled by the MBC is determined by a preset adjustment dial. Here's how it works...

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The MBC is plumbed into the hose connecting the compressor outlet to the wastegate actuator. Boosted air enters the MBC through a barbed hose fitting, which incorporates a pinhole-sized opening. This tiny opening serves as a restriction to airflow through the wastegate hose - it slows the airflow, enabling the bleed to vent the appropriate amount of pressure. We're told this helps maintain stable boost pressure across the rev range.

Following the restriction, boosted air follows a machined passage inside the MBC's aluminium body. An internal 'T-junction' separates the air that flows to the wastegate or the bleed to atmosphere.

The division of airflow is determined by the position of the adjustment dial; turned fully clockwise, the base of the dial's adjoining shaft blocks the air from the bleed outlet. Turning the dial anti-clockwise, however, raises the base of the shaft off its seat, allowing a portion of air to escape up and out through the bleed. A large circumferential o-ring - which is purely for cosmetics - hides the bleed outlet from sight.

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Balistic Motorsport tells us extensive testing has led to the use of a tapered tip shaft, which - apparently - gives improved boost stability. A small rubber o-ring is fitted around the shaft - about half way up its length - to prevent pressure seeping out through the top of the valve. This o-ring also prevents the adjustment dial from moving through vibration.

Pressure that's not bled to atmosphere flows out the MBC's exit fitting and makes its way to the wastegate actuator diaphragm. Receiving an artificially low boost pressure signal, the wastegate will now remain closed at higher boost levels and - as a result - the turbo generates more boost.

That's the theory.



Installation

The PowerUp MBC arrives in a kit comprising the bleed valve body, a 150mm length of ¼-inch rubber hose and an installation guide.

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The first step is to disconnect the existing rubber hose from the wastegate actuator. Next, push the MBC's ¼-inch brass barbed fitting (the one with the restriction) into the open end of that hose. The supplied length of ¼-inch rubber hose can then be used to connect the wastegate actuator to the MBC's purple barbed fitting.

Note - depending where you want to locate the MBC - it may be necessary to install a longer length of hose from the compressor outlet to the MBC, and from the MBC to the wastegate actuator. This allows the MBC to be located in a more accessible position inside the engine bay.

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Unfortunately, the MBC has no provisions for mounting, so instead you'll have to let it dangle in space supported only by its attachment hoses. These hoses can, however, be clamped or cable-tied into position to partly secure the MBC.

Once the MBC has been plumbed into the wastegate hose, we strongly suggest you go out and buy clamps to secure each hose fitting - the last thing you want is a potentially catastrophic over-boost because you left out a few $2 hose clamps...

And for Vehicles with Factory Electronic Boost Control...

Fitting the MBC to vehicles equipped with electronic boost control requires only slightly more effort.

In most instances, the factory bleed solenoid should be completely disconnected from the wastegate hose; the MBC slots into its position as the sole pressure bleed.

You can leave the solenoid's electrical wiring intact, as this should ensure there are no ECU problems.

Calibration and Testing

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First and foremost, an accurate boost gauge is essential when you're adjusting boost pressure levels. Where possible, it's also a good idea to have an air-fuel ratio metering device installed to ensure mixtures don't go excessively lean at high boost.

Note that the services of an assistant is also essential - it's too dangerous for one person to attempt to drive the vehicle and watch the tacho, boost gauge and air-fuel ratio meter all at the same time.

Now we can get into it.

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Ensure that - as soon as it's installed - you seal the MBC bleed by turning the adjustment knob fully clockwise. There are markings on the side of the MBC body to identify which way to turn the dial for more or less boost.

With the MBC sealed, zero wastegate hose pressure should be bled from the line. This means peak boost pressure should remain as standard or, where a factory electronic boost control bleed solenoid has been disabled, less than standard. (Most cars with factory electronic boost control run relatively weak wastegate springs.)

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Interestingly, top gear testing in our demo Holden VL Turbo revealed the MBC was already having an effect on boost pressure - even before we'd opened the bleed. In this graph you can see maximum boost (50 kPa) was unaltered, but pressure built earlier in the rev range. This rapid boost rise is caused by the airflow restriction in the entry fitting to the MBC - the restriction delays the arrival of boost pressure at the wastegate actuator. This is a trait commonly referred to as 'wastegate delay'.

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With everything functioning correctly, we could then move on to adjusting the MBC to bleed some wastegate hose pressure. We began on our VL Turbo by opening the adjustment knob one full turn (ie 360 degrees). Make sure you don't open the valve too much in the first instance because you can never tell how much extra boost you'll get for a given adjustment.

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On the VL Turbo, opening the MBC valve one complete turn gave almost the boost increase we were after. A top gear peak boost spike of 75 kPa was seen at a low 2000 rpm, falling to a steady 70 kPa towards the redline.

This kind of boost curve - a fairly early pressure spike followed by a boost pressure stabilising at a lower value - is typical of bleed-type boost systems. As far as we can determine, a drop of turbo efficiency at high rpm is the cause - since the boost control doesn't have a feedback loop which would enable more exhaust gas to be pushed through the turbo to maintain the same boost, the manifold boost pressure drops.

Grab the Right Gear...

When calibrating a bleed-type boost controller, it's important to focus on boost pressure throughout the rev range in top gear and at very high engine load (such as when climbing a hill).

Adjusting the bleed to deliver, say, 100 kPa (1 Bar or 14.5 psi) in first or second gear might seem enough of a set-up exercise, but - be warned - manifold pressure will rocket even higher when you put your foot down climbing a hill in top gear. The extra engine load makes it easy to get ten or twenty percent more boost than you thought was the maximum...

The only way to discover the absolute maximum boost pressure is to perform full throttle tests in top gear.

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The problem associated with top gear testing, however, is the prohibitive road speed involved - you don't want to be distracted by tachos, boost gauges or air-fuel ratio meters when you're driving at around 250 km/h... Ideally, we'd like to measure boost during a top gear run from idle through to the rev limiter, but - in the name of public safety - we suggest another approach.

A short-cut way to identify the absolute pressure peak involves looking at the boost trend in a lower gear.

Make a charge through the entire rev range in - say - third gear and take note of the rpm where peak boost arrives. Experience has taught us that pneumatic bleed systems give a boost peak at the tail end of the initial spool up period. In our VL Turbo, for example, we saw a third gear boost peak arrive at approximately 2500 rpm.

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Next, make a charge up through top gear from the lowest rpm the engine can tolerate. Expect peak boost to arrive at slightly lower rpm than it did in third, because of the increased engine load. Our VL Turbo was quick to boost from very low rpm, peaking at 2000 rpm.

Based on the boost trend obtained from our third gear run, we can safely say the boost value seen in top gear at 2000 rpm is our VL Turbo's absolute maximum.

As seen in the above graphs - which we chose to run to 4000 rpm - boost pressure settled to a lower value following the initial spike at 2000 rpm.



After pondering our existing 75 kPa boost peak, we decided we'd chase yet a little bit more pressure - therefore, we opened the adjustment dial another complete turn...

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After this second stage of adjustment, we recorded a new 90 kPa boost ceiling in top gear. This 90 kPa peak arrived at the same 2000 rpm point as previously and from there pressure tapered downwards, then holding at 80 kPa. These were pretty much the sort of boost settings we were after, so no further adjustment of the MBC was required.

With our absolute maximum boost pressure set in top gear, we wanted to see how much boost we could generate through one of the lower gears without adjusting the bleed. First gear was impossible to test due to wheelspin, but we could j-u-s-t maintain traction through second gear on a grippy dry road.

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This graph compares the second gear boost pressure curve for the standard wastegate configuration, when the MBC was added, once it had been opened one turn and - finally - our 'open two turns' setting.

As you can see, the second gear boost curve has a similar shape to that measured in top gear. Due to the lower engine load, however, everything arrives later in the rev range - instead of peak boost arriving at 2000 rpm, for example, it's delayed to 3000 rpm.

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Just we'd seen in our top gear data, adding the MBC made boost come up quicker in second gear but without exceeding the standard wastegate setting of 50 kPa.

Opening the bleed one complete turn saw a 70 kPa boost pressure spike at 3000 rpm, tapering to 60 kPa towards the redline.

Finally, winding the bleed dial out two turns saw an 85 kPa peak followed by 70 kPa held. Interestingly, this represents a slightly larger pressure drop-off than we'd measured in top gear - top gear dipped 10 kPa from its peak pressure, while second gear fell 15 kPa.

In normal driving, the VL Turbo has been transformed by the installed and calibrated MBC - a hard charge up through the gears confirms it's a much, much quicker beast. It also climbs onto boost earlier, giving a heap of low-down torque and response. This rapidly building boost spike can be dangerous on a wet road, however; floor the throttle at around 80 km/h in third gear and the back-end will break traction and skew sideways. Exciting stuff - if you know it's coming...

Atmospheric Variations...

In addition to boost variations across different engine loads, the ambient temperature can also have an affect on bleed-type boost control systems.

As ambient temperature drops, a given engine produces more power. This results in increased exhaust flow, which - in turn - produces more boost pressure.

If you want to be ultra careful setting up your wastegate bleed system, it's best to do it when it's coolest. This will minimise the chance of your set boost ceiling being exceeded late down the track.

Also - if winter is coming around - you might want to double-check any existing bleed valve settings.

Summary

The PowerUp MBC proves the point that pneumatic boost controllers give the biggest bang for the buck of any type of turbo car modification.

The MBC performs quite well. For a bleed system it delivers quite good manifold pressure consistency across various engine load and rpm - it doesn't give the boost stability of an electronic system, but it still performs competently.

Another positive is that it's considerably easier to install than a ball valve, needle valve and T-piece system; there's also less likelihood of making a plumbing error. On the other hand, there's less versatility in the setting up - you can't alter the main valve's sensitivity by varying the size of the restriction, for example.

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Finished in anodised 6061-T6 aluminium, the MBC comes from BalistiK Motorsports backed by a 12-month warranty. Being such a simple device, there's not much that can fail - except don't do what we did and completely unwind the adjustment dial while 'checking it out'... The little o-ring seal on the dial shaft can get torn as it comes up through the valve's threaded collar. Oh well, lucky it's an easily replaceable commercial seal that costs next to nothing...

There are a few aspects of the MBC that we'd like to see improved. It'd be nice if hose clamps were included in the kit and the supplied installation guide needs to be rewritten - the current one is very disjointed and awkward to read. Most important, however, the lack of mounting facilities means it's difficult to mount the valve to - say - the inner guard.

For AUS$99, however, you can't go wrong with the PowerUp MBC - this is as cheap as power gets.

Contact:

Balistik Motorsports Int
0409 014 990

www.powerupbov.homestead.com/powerup.html

mugen1@mt.net.au

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