Tried venting your factory blow-off valve (BOV) to the air? Engine didn’t like it, did it? You might have got those Pssshts! that you were after but you also got a bad idle and black smoke. The reason for those unwanteds is that the BOV was open at idle – not just when you were quickly backing-off the throttle.
But now we’ve got a solution for you. It’s an instant intelligence upgrade for your BOV! Instead of just relying on manifold vacuum to trigger it, this version adds electronic control to your existing BOV. You don’t need to buy a new BOV, you get a perfect idle, and you get an atmosphere-venting BOV!
Oh yeah, and from as cheap as about seventy bucks....
How It’s Done
So what’s the secret? Instead of the BOV always seeing manifold pressure, what we do is put a solenoid (an electrically-controlled on/off valve) in the hose. Now the valve sees manifold vacuum only when we want it to – that is, when we feed power to the solenoid and it opens. You don’t want the BOV open at idle? Easy – just keep the solenoid shut! (Click on any of these diagrams to give a bigger view.)
The other tricky part is opening that solenoid just when we want the BOV to trigger. 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.
The Delta Throttle Timer (DTT) constantly monitors throttle movements and when it sees the throttle being opened fast, it trips a relay. It knows what the throttle position is by monitoring the output of the throttle position sensor. Since you only ever want the BOV to open when you’re quickly lifting the throttle, it’s ideal in this application. Furthermore, the DTT incorporates a timer circuit so that you can keep the solenoid (and so if there’s enough engine vacuum, the BOV) open for a preset time – eg a second.
There’s only one other trick. Because the boost pressure acting on the BOV helps keep it shut against leakage, we still want boost to reach the factory BOV even when the solenoid’s shut. And this is easily accomplished by putting a one-way valve around the solenoid, so that boost can act on the BOV but vacuum only triggers the BOV when we want it to.
All starting to sound too hard and expensive? Not really. If you can wield a soldering iron and recognise electronic components, the Delta Throttle Timer control module will costs you only AUD$24.95 as a kit.
The one-way valve that you need can be salvaged from the brake booster of a heap of cars at wreckers (this whole handful cost AUD$2). If you are sourcing these valves look for cars that place the valve in-line in the manifold > booster hose rather than building them into the booster itself.
And then all you’ll need in addition are two or three ¼-inch brass T-pieces (about AUD$4 each from a pneumatics or hydraulics supplier) and some hose. Oh yes, and some hose clamps.
But let’s take it all step by step.
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 Australia, New Zealand, or online through the AutoSpeed shop. 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)
If 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 Increase your driving safety with 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).
Now that you’ve made these connections you can do some testing.
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.
Any solenoid valve that can hold boost pressure and be worked by 12V can be used. This includes industrial 12V quarter-inch solenoids like those made by Goyen (they’re often used as LPG shut-off valves in LPG cars), boost control solenoids out of turbo cars, or even the valves often used in the vacuum hose plumbing of cars. The latter won’t be suitable for mega boost but in practice they’ll work fine in most street applications.
The solenoid and one-way valve are plumbed into place as shown here. (Click on the diagram to enlarge it.) You may need to use some rubber hoses of different diameters to adapt the one-way valve to suit the rest of the plumbing. As mentioned, the cheapest source of one-way valves is to raid the wreckers and find some brake booster valves, but another approach is to use one of the valves shown in this story - Do-It-Yourself Peak Hold. Make sure that you get the flow direction of the one-way valve the right way around!
Here’s what the assembled solenoid and one-way valve bypass look like.
Extensive testing showed that one additional part needed to be added to the system. This is a vent between the solenoid and the BOV. Without it, there’s nothing to stop vacuum being retained when the solenoid shuts – so keeping the BOV open all the time! A small vent stops this vacuum being retained while having no affect on the opening of the BOV. One approach to making the vent is to solder up one arm of a brass T-piece, then drill a small hole through the solder plug. Even easier is to insert a piece of hard plastic hose in the plumbing and make some small holes in it with a hot pin.
Don’t forget to disconnect the side of the factory BOV that normally connects back to the intake system ahead of the turbo so that the BOV now vents to the atmosphere.
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. If there are other problems check the orientation of the one-way valve and that the vent in the plumbing between the solenoid and the BOV is working.
By using the DTT and a few bits and pieces of plumbing it’s possible to revolutionise the way in which the factory BOV works. And of course this approach isn’t confined to factory BOVs – if you have an aftermarket one that produces the sound you want but causes the engine to run badly, just the same approach can be taken with that valve too.
Next week: installing a completely electronic BOV system – there’s no vacuum feed needed!