Anyone else interested?

[toasty]

Was thinking on the weekend what a great car I have.

Only real problem with the Biturbo is that the Air intake path is weak with many notable weaknesses (F pipes, Throttle body, Dump valves & Intercooler endcaps)

I guess this affects both the S and RS4 and I would imagine Dump valves generally are a problem for all turbo charged Audis.

Anway, I thought a boost guage would be a good addition to my car, as any of the above problems would result in lower boost, apart from perhaps a damaged DV which could potentially stay stuck shut and therefore result in more boost, especially at low revs when the DV should be open.

I don't really want a boost gauge as I've not seen on that suits the rest of the interior, so I was thinking of a simple 2 led display which could easily be fitted into a switch blank plate or similar (same sort of size as a alarm led)

The idea is that one LED will illuminate Green when there is some boost (i.e above atmospheric pressure) and go red when maximum boost has been reached.
The other LED will illuminate green when there is a vacuum holding the DVs open.

It won't give you a continuous reading of boost pressure, but would be set to illuminate at max boost so that you know it's been reached (i.e no air leaks etc..)
And the other LED would light when there is a vacuum which will mean that the DVs are both in good shape as if they had damaged diaphrams the vacuum would leak out.

I think by just using these two leds should give the full intake system a healthcheck. What you should expect to see is the vacuum led on at low revs and on a trailing throttle.
If it never comes on then the DV diaphram is ruptured or one of the vacuum pipes has come off.

If you have the boost LED on at low revs and the vacuum LED is illuminated also then the DV must be stuck shut.

If you see the boost led never goes red (i.e max boost) then there is a leak in the system somewhere or a DV stuck open.

I'm going to make one for me, would anyone else be interested. Not sure of the cost yet, but you are looking at about £10 in parts plus the cost of a pressure sensor for the boost and a vacuum sensor for the vacuum. (I'm still trying to track some of these down)

[Nige_RS4]

Hi Dan, yep, I'd be interested, but a boost-only LED gauge(no vacuum) would suit my needs more. I't would fit nicely in the cup holder on the 99.5 car.
Any idea on how you would calibrate the LEDs?

Nige.

[johneroberts]

I think this has been tried by a couple of people here and the loss of boost due to linkage is considerable, so be aware that in theory it may work, but in practice another matter.
Cheers
jr

[Bushy]

Indeed JR is right, also another real problem is a suitable guage

Some of our cars have boost spikes up to 1.7 but most guages peak at 1.4, which is where a chipped car peaks, alledgedly

SO that together with joint leakages make it very very hard to get consistant readings

Even boost guages you can buy dont always meet the range requirements of some modded cars

But if you get it sorted put me down for one

[LittleSkull]

O.CT makes a really nice one (1.5 bar)
http://www.stratmosphere.com/oct_s4_boostgauge.htm

[Dippy]

And the other LED would light when there is a vacuum which will mean that the DVs are both in good shape as if they had damaged diaphrams the vacuum would leak out.

I don't think so: Even if both diaphrams were damaged, the vacuum at the intake would be the same.

Having had a boost gauge for about a year now, I feel I can say with authority that to try to diagnose any problem other than limp mode (which is pretty obvious anyway), you need a complete reading: It will be the RATE at which boost is applied that suggests a problem, not the absolute value.

[toasty]

Sorry Dippy I disagree [img]images/graemlins/tongue.gif[/img], yes the car would create the same level of vacuum, but I'd link the vacuum sensor in with a T peice in between the two DVs, that way if either were damaged then the vacuum would leak out of the broken diaphram and the sensor would detect this loss of vacuum.

Something like this:
dodgy drawing

Hope this makes sense.

Good point about boost loss through the system JR and Bushy, however I think this can be minimised by mounting the pressure sensor directly into on of the pressure pipes.

As for calibration, well all cars would be different, I'd be looking for a sensor capable of measuring at least 2bar, which would give a voltage output proportional to the pressure (say 5volt per bar, but this is arbitrary)

You could then adjust when the lights come on by adjusting a small variable resistor. personally I'd calibrate mine using a multimeter and a variable voltage source, so if using the example above I was looking for 1bar max boost then I'd apply 5volts to the circuit and adjust the resistor until the LED just came on. Someone like Bushy would probably be looking for more like 1.4bar and so 7volts etc...

Woudl probably just use a vacuum switch for the vacuum line rather than an actual sensor, i.e just on or off would suffice.

But you could just keep incrementing the resitor until thrashing the car didn't cause the LED to light and then just back it off a bit. (providing of course that your car is running ok at the time of the test)

[toasty]

O.CT makes a really nice one (1.5 bar)
http://www.stratmosphere.com/oct_s4_boostgauge.htm

Now that is nice, and good value for $400 I reckon. However, you'll be looking at a lot less than $100 for mine, it's more stealthy and easier to fit. The guage is ideal for those who want to know the actual values, for me I just want to know that the car is working.

....plus I love making stuff. [img]images/graemlins/grin.gif[/img] ..... I went out on Saturday to buy a Macbuster (device to allow you to copy DVDs onto video) you can get them for £30 easy. I ended up in Maplin, bought all the bits I needed (plus loads I didn't) total cost £60 [img]images/graemlins/blush.gif[/img] but it's unique and I had fun building it.

[Paul-RS]

Have you guys seen the Defi's ?

www.Defi-shop.com

"Defi Link System" -> "Defi-Link Meter BF"





ok. not up on the dash, but look great. and match your RS4 (and s4??) lighting?

im toying with the idea of the boost one for the s3. With white backlight shown. not the horrid green one..

ok lighting for me will be different( S3 has white needle and red lights) but if i could stealth install it somewhere... or maybe have it removable and hidden in glove box, then clipped to cup holder or so, then i think it would be ok...

not cheap mind you.

[Paul-RS]

Oh and Dan...

SK Pang has a sensor that read boost and Vacuum, tho your need to knock up electronics to use it.

there is a data sheet for it there too....

http://www.skpang.co.uk/boost_guage.htm

[toasty]

Nice one Paul,

I didn't know SK did anything like this, and I bought a VAG COM lead from him a while back, so I know that he's very talented.

My system will be a lot simpler than his for two reasons:
1) I want it to be discreet, just two leds
2) He's better at electronics than me! [img]images/graemlins/blush.gif[/img]

I'm using the same sensor as him, but will use something simpler for the vacuum detection to reduce cost.

I've got the bits, the design and the location of the leds all planned out, now I just need to build it.

I'm thinking one led for vacuum status:
On = vacuum i.e DV's open in recirculation mode
Off = no vacuum i.e DV's shut = boost

The other led for Boost Pressure:
Off = No/minimal boost.
On (green) = Intermediate boost pressure.
On (red) = Max Boost reached.

From these two leds (you'll notice that one is Bi-Coloured) I'd expect to see the following in a car that was working properly

Sat at idle - vacuum light on, boost light off
Accelerating - vacuum light off, boost light from off to green to red
Trailing throttle - vacuum light back on, boost light (quickly) from red to green to off.

Should be fun [img]images/graemlins/grin.gif[/img]

[PhilT]

Better watch you don't get confused with the traffic lights [img]images/graemlins/colflash.gif[/img]

[johneroberts]

Paul,
a little over the top for me im affraid [img]images/graemlins/033102bigblink_1_prv.gif[/img]
Carlos Fandango might be interested though [img]images/graemlins/biggrin3.gif[/img]
Cheers
jr

[johneroberts]

And that photo?
were you in warsaw in poland this week?
Cheers
jr

[Paul-RS]

Mori Posted them on TS.

seemed relevant so i swiped them [img]images/graemlins/wink.gif[/img]