Last week we covered the use of the Delta Throttle Timer DIY electronic module to control the action of a factory or aftermarket blow-off valve (BOV). By using a solenoid and a one-way valve in the vacuum line, we could make sure that the BOV didn’t open at idle (and at other unwanted times) but that it still vented to the atmosphere with a satisfying Psshhht! each time the throttle was snapped shut. (Go to The $70 Electronic Blow-Off Valve for more on this approach.) But this time we’re going to push the concept one step further and use a fully electronically-controlled BOV. That’s right – there’s no vacuum feed at all; instead the opening and closing of the BOV is done purely electronically. And furthermore, an electric BOV is used as well! Electronic BOVsA BOV is just a big capacity valve that opens when there’s a strong manifold vacuum present. Well, that’s how all standard ones work, anyway. In fact, what the valve is designed to do is vent the pressure build-up that otherwise occurs between the closing throttle and the still-spinning turbo. (For more, see ‘How BOV’s Work’ at the end of this story.) That pressure build-up in front of the throttle body only occurs when the throttle is being closed. In fact, more accurately, it occurs only when the throttle is being closed fairly quickly. So if we monitor the output of the throttle position sensor, and if the voltage falls rapidly, we know that the throttle is being closed fast. And on a turbo car, that means a boost pressure build-up in front of the throttle. The way that this voltage can be monitored is to use an electronic module that constantly watches throttle position and triggers a relay when the throttle position sensor output voltage falls fast. Normally, this would be very hard to do but thanks to Silicon Chip (www.siliconchip.com.au) electronics magazine, a complete solution is at hand. They’ve come up with what’s called the Delta Throttle Timer and it’s a device that can be used to do all the hard control work. Since you only ever want the BOV to open when you’re quickly lifting your foot off the throttle, it’s ideal in this application. Furthermore, the Delta Throttle Timer incorporates a timer circuit so that you can keep the BOV open for a preset time. But how can an electrical relay trigger a BOV? Well, what we do is replace the BOV with a large electrically-controlled solenoid. Feed power to the solenoid and it opens, venting the excess pressure. Don’t feed power to the solenoid and it stays shut. Easy, huh? The Electric BOVThe solenoid that you use as the BOV can vary from well-priced to extremely cheap. And from incredibly durable to shorter lived. Let’s start at the top end of the range.
The Goyen Controls CA valves are the pick of the bunch. Tested for an incredible 1 million cycles, they will last literally for the life of the car. They can also hold boost pressure without the slightest concern. The CA valves are part of a series called the “T series reverse jet pulse dust collection” valves. They use a pressure-cast aluminium body, a nylon-reinforced Buna N elastomer diaphragm and are suitable for temps from -40 to 82 degrees C. The valves are available with different electrical coils – in this application you need a 12V coil. The valve shown here is a 1-inch design; they’re also available in sizes from ¾ inch up to an incredible 3 inches! To shortcut your chase, the 1-inch valve is catalog number CA25T. Goyen
valves are manufactured in The price is about AUD$115.
The alloy Goyen valve is the top-line – but what if you want to keep things right down at the budget end? In that case head for your local garden irrigation shop and have a look at the plastic water irrigation solenoid valves that they have available. These valves are available in a variety of sizes, with the pictured ¾ inch size the smallest that you’d use in this application. (Note that despite the plumbing size being the same as the smallest of the Goyen jet pulse dust collection valves, the actual flow-put of these water valves is lower. However, they still vent plenty of air and so can be used.)
Larger garden irrigation valves are also available. This one easily pulls apart (the screws are undone as part of this process) so that the internal spring can be replaced with a stiffer one if that’s required. Despite garden irrigation valves being normally used on 24 volts AC, they generally work fine on 12V DC. They’re also pretty good at holding pressure, but obviously their durability won’t be anything like the Goyen valve.
So that’s the solenoid valve sorted, now what about the control system? The Delta Throttle Timer
As mentioned, the Delta Throttle Timer was developed and designed by Silicon
Chip
www.siliconchip.com.au
electronics magazine. It is one of a number of projects that will be covered in
a unique Silicon Chip publication - High
Performance Electronic Projects for Cars - which will be available from
newsagents in
The book will be an absolute must-have for DIY modifiers. The electronics design and development of the Delta Throttle Timer were carried out by the skilled and modest electronics engineer John Clarke, while I came up with the concept and did all the on-car development. (During this period I wore a different hat to an AutoSpeed contributor, working for Silicon Chip Publications as a freelance contributor.) So while by no means should the Delta Throttle Timer be seen as an AutoSpeed-developed project, we’re very happy to endorse it. (The Delta Throttle Timer is sometimes known as QuickBrake. This is because the module was first used as a quick brake light trigger in the March 2004 Silicon Chip magazine Increase your driving safety with Quick Brake .) The ModuleIf you have assembled other electronic projects before, the Delta Throttle Timer (or QuickBrake) kit shouldn’t cause you too much trouble. There are 18 resistors, 13 capacitors, 13 semi-conductors, assorted terminals, the relay and two trim-pots. Solder and hook-up wiring is supplied. Follow the instructions carefully – in fact to gain the article in full colour (important when following a component overlay) we suggest that you subscribe to the on-line version of the article at Quick Brake . However, if you’re not confident with component identification, component polarity and soldering, buy the fully built and tested version – then only a few simple connections to the car are required. Neither version comes with a box, however the Delta Throttle Timer (we’ll call it DTT from now on!) fits straight into a 130 x 68 x 42mm plastic electronics ‘jiffy’ box. Alternatively, you can put it in any box that you want, making sure that the bottom of the printed circuit board can’t come into contact with anything metallic (which could cause shorts).
When you have either built the kit or received the built-up module, have a good look at it. Orientate it so that the relay is on the right. Now you’ll have two sets of terminals on the left and a long strip of six terminals on the right. The top-left terminal connects to ignition-switched 12V – that is, a battery positive supply that is on when the ignition is on. The terminal right below connects to ground – in other words, to the car’s metal body. The lower left terminal has two inputs but as they’re connected together, either one can be used. This input is for the wire that connects to the throttle position sensor.
Before you can connect the signal input to the throttle position sensor you need to find the right wire on the sensor. To do this you’ll need a multimeter. Set the multimeter to Volts DC and connect the black lead to the car’s body. Turn on the ignition. With the other multimeter input, back-probe the working throttle position sensor until you find a wire that has a voltage on it that varies with throttle position. Typically, this will be in the 1-4V range and the voltage will rise when the throttle is opened. This is the wire that you tap into for the DTT signal. Connect up these wires to the DTT. (Note that the throttle position signal wire doesn’t need to be cut – the DTT just taps into it). TestingNow that you’ve made these connections you can do some testing. Then turn Pot 1 (Sensitivity) anti-clockwise as far as it will go. (Note that these are multi-turn pots so you may not come up against a positive ‘stop’ when you get to the end of its rotation.) Turning the Sensitivity pot anti-clockwise increases sensitivity. Next turn Pot 2 (Time) clockwise to decrease the period that the timer will stay on. Finally, check that the moveable link is in its right-hand position, which causes the DTT to turn on with fast throttle lifts. Switch on the ignition, wait for 10 seconds, push down and then quickly release the throttle. The LED should come on and the relay pull-in for a short time. (The 10 second delay after switch-on is needed because the DTT has a built-in pause to avoid false-alarming when power is first applied.) Then turn the Time pot anti-clockwise a little to extend the relay’s ‘on’ time. The range of adjustment is from 1/10th of a second to just under 2 minutes - in this application around a second is fine. Adjust VR1 clockwise until the DTT responds only when the throttle is being lifted moderately quickly. The PlumbingIf your car already has a blow-off valve, you can use the standard fitting that connects to the intake system between the turbo and the throttle. If the car didn’t come with a BOV (and/or you’ve changed the intake plumbing) you’ll need to organise a new fitting. We suggest that it is placed as close to the throttle as possible – this keeps the air passing through the BOV cooler (as it’s after the intercooler) and also is nearer the beginning of the pressure wave that builds when the throttle is closed.
Setting Up
If you’ve got the DTT working properly (LED lighting with throttle lifts and then staying on for about a second) you can now connect the output relay to the solenoid. The wiring connections are shown here. Start the engine and make sure that it idles as well as it did before the modification. Wait until the initial start-up delay of the DTT has elapsed and then (if the engine is warm!) blip the throttle hard. Depending on the size of the turbo, you’ll probably be able to hear the BOV open on each quick throttle release. Go for a drive, making sure that the engine behaves perfectly but the BOV is venting to air on each sharp throttle lift. If the engine wants to stall, you’ve probably got the DTT Timer set for too long an ‘on’ period, so adjust the Time pot to shorten this.
ConclusionA fully electronic BOV – especially one using the big Goyen valve – has the ability to shift a huge quantity of air and so reduce the pressure build-up (and pressure waves – see below) to near nothing. It’s also easy to vent it to atmosphere without making the car run badly, has full electronic adjustment of when (and for how long) it functions, and can even be way cheaper than an off the shelf aftermarket BOV! Sounds like a winner to us...
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