Thirty Dollar Boost Control

This is it. The cheapest aftermarket boost control valve we’ve ever seen. Selling for around AUD$30 on eBay, the Turbotech boost controller sets a new standard in bang-for-buck.

So how good – or bad – is an AUD$30 boost controller?

Let’s find out!

The Turbotech Boost Controller

The Turbotech boost controller works differently to most other cheapie aftermarket boost valves. This is not a bleed valve which vents pressure from the wastegate hose.

The Turbotech controller contains a steel ball that is forced down onto a seat by a coil spring. Boost pressure enters through the bottom port of the controller and tries to push the ball off its seat. When there’s enough boost pressure for this to occur, air passes through the top port and reaches the wastegate actuator. Boost pressure is now controlled.

Peak boost pressure can be varied using an adjustment bolt and locking nut. Turning the bolt clockwise increases preload on the spring which means greater boost pressure is required to lift the ball off its seat.

A small hole in the valve body (called an "excess pressure valve") allows pressurised air to escape from between the controller and wastegate actuator following a boost event. This pressurised air would otherwise be trapped against the wastegate actuator and cause poor boost response.

The valve is also equipped with a pair of ¼ inch barbed brass fittings to allow easy fitment.

Installation

If you own a turbo car that has factory electronic boost control (such as a Nissan Skyline, Subaru WRX or Mitsubishi Galant VR4) you’ll need to disable the existing control system before installing the Turbotech unit. This ensures you’ll consistently get the boost pressure that you set.

The easiest way to disable the factory electronic boost control system is to remove the hoses at the boost solenoid (as seen here). We recommend that you then remove all of the existing boost pressure control hoses – everything from the boost pressure source (typically the turbo compressor outlet) to the wastegate actuator. This eliminates problems with unseen hose restrictions and lets you keep the hose route as short as possible – this improves boost control accuracy.

Starting from scratch, you can now connect a new length of hose between the pressure source and wastegate actuator. Cut this hose and fit the Turbotech controller in the correct orientation – the bottom port should connect to the pressure source and the top port should connect to the wastegate actuator. Unfortunately, the direction of flow is not marked on the controller body and there are no mounting provisions – the controller simply dangles in space.

Job done.

If you own an old-school turbo car that doesn’t have electronic boost control (such as a Holden VL Turbo, Daihatsu Charade or Nissan Pulsar ET) the installation process is even easier. Simply cut the existing hose between the pressure source and wastegate actuator and install the controller in the correct orientation.

Tip! When installing the Turbotech controller it’s a good idea to turn the adjustment bolt so that you j-u-s-t blow air through the valve. This gives you a good base for calibration – you’ll be close to the adjustment range that gives your desired result.

Calibration and Testing

Warning! An accurate boost gauge is essential when calibrating a boost control system. It’s also important to use an air-fuel ratio monitoring device to ensure mixtures don’t run dangerously lean. You should also listen carefully for detonation at increased boost pressure. Failure to take these precautions can result in engine destruction.

Before installation of the Turbotech controller, we established a baseline boost curve for our Galant VR4 through second gear and fifth gear. It’s always a good idea to test boost pressure in different gears – in some instances, the extra engine load in high gears will cause the turbo to overboost compared to in low gears.

As seen in this graph, our lightly modified Galant VR4 spikes to 1 Bar boost (14.7 psi) in second gear and levels off to around 0.75 Bar (11 psi) toward 7000 rpm. This mid-range boost spike is quite common when a high-flow exhaust is fitted to a turbo car that employs a conventional (open-loop) electronic boost control system.

This graph shows the VR4’s boost curve in fifth gear running to a maximum of 4000 rpm (with the car travelling as fast as conditions would allow). As you can see, boost pressure builds much faster in fifth gear compared to second gear. By 2000 rpm you’ve got 0.2 Bar (3 psi), compared to around 0.06 Bar (less than 1 psi) at the same revs in second gear. Peak boost is reached by 4000 rpm and, in this particular car, the maximum boost pressure is 1 Bar (14.7 psi) regardless whether you’re in a low or high gear.

Now it’s time we calibrate the Turbotech boost controller.

Fitted to the car (with the adjustment bolt set so we could just blow through the valve), the Turbotech controller gave a peak boost pressure of around 0.7 Bar (10 psi). A safe starting point - but not enough for us. We then loosened the locking nut and turned the adjustment bolt clockwise one full turn. This increased peak boost pressure to 0.9 Bar (13 psi). One additional full turn gave us the peak boost pressure we wanted. Our aim was to reach a maximum of 1 Bar (14.7 psi) and hold it there.

Adjusted to give a maximum of 1 Bar (14.7 psi), the Turbotech controller gives a similar shape boost curve in second gear compared to the standard control system. This graph shows the Turbotech-equipped boost curve (in pink) against the standard boost curve (in blue). Boost pressure is oh-so-slightly improved at around 3000 rpm and, more importantly, top-end boost pressure doesn’t fall away as much as standard. Boost does fall away but we imagine this is a characteristic of the VR4’s relatively small turbocharger which becomes inefficient at high revs – the wastegate probably needs to be shut to hold 1 Bar (14.7 psi) through to 7000 rpm. Incidentally, any closed-loop electronic boost controller or the Silicon Chip IEBC can achieve this.

In fifth gear up to 4000 rpm, the adjusted Turbotech controller provides exactly the same boost pressure curve.

How Quick to Boost? One of the most important aspects of an aftermarket boost controller is the rate of boost rise. It’s likely that you want to get up to maximum boost as quickly as possible. We decided to temporarily remove and seal our VR4’s wastegate actuator hose and (carefully!) measure the fastest possible rate of boost rise. This is a very dangerous process that requires an eagle-eye on the boost gauge. So what did we discover? Well, with no wastegate control we saw 1 Bar (14.7 psi) of boost arrive at 4300 rpm in second gear. This is the absolute quickest that the engine can build boost. Interestingly, we reached 1 Bar (14.7 psi) at damn-near the same revs using the Turbotech controller and with standard electronic control. In this case, it’s impossible to improve on the standard set-up. But at least the Turbotech unit doesn’t reduce the rate of boost rise.

Verdict

Anything that allows you to control boost pressure for around AUD$30 is a winning product.

Fitted to our Galant VR4, the Turbotech controller was successful in providing adjustable peak boost pressure and giving the fastest possible rate of boost rise. Unfortunately, it wasn’t able to hold high boost through the top-end. This is likely to occur in all cars with a relatively small turbocharger.

At the time of writing, the Turbotech controller can be purchased through eBay Australia www.ebay.com.au with a "Buy it Now" price of AUD$29.90 (plus postage). With more than 160 units sold, it seems the allure of an AUD$30-odd boost controller is too much to resist.

And, yes, an AUD$30 boost controller can perform well. We’ve proved it!