So I had a thought about modifying factory boost control....

[Hotwire]

Don't know if this will work as not 100% sure on the operation of the factory solenoid, BUT here goes...

The factory boost solenoid (as far as I can tell) relies upon a voltage signal from the ECU to determine how much pressure to bleed off. Varying the pressure bled off ultimately leads to boost increasing/decreasing at the manifold.

NOW if the voltage from the ECU is such that if the volts are DECREASED to increase boost pressure (i.e, 1V is no bleed off down to 0V = maximum bleed off), then my idea may work.

Basically, by fitting a variable resistor (POT) in the circuit from the ECU, and providing a voltage drop accross the POT, this would increase boost pressure

Now the limits are dependant upon just how much the factory solenoid can bleed off, and how much voltage is being seen at the solenoid for "maximum" boost. If it is presently 0V for max boost, then this will do nothing. If the solenoid however see's say 0.5V for max boost, and this can be decreased down to 0V, then a boost increase will occur.

To determine if this works I will need to attach a volt-meter to the solenoid outputs of the ECU and take the car for a drive. No idea when I might get the time for this, but it's something I'd like to try.

If anyone has any other input, or would like more clarification let me know. Alternatively if someone wants to try this, I'm all ears. My idea is to be able to create 2 circuits in parallel, low boost for when my wife has the car, and high boost for when I drive. By having switchable resistors (and 2 MAPS on my SAFCII) I'll hopefully get the best of both worlds

Cheers
Lee

 

[Kenneth]

Hi Lee,

The factory boost control runs a solenoid, which in turn is pulsed.

This means that it only gets either a full 12V or 0V. This means that a variable resistor would not work.

The boost control line does look like a voltage if you use the DC voltage measurement on a multimeter, but this is because it measures the average voltage.

If a 12V source spends 50% of its time at 12V, and the remaining 50% of its time at 0V, then the multimeter will measure it as 6V.

This is how the boost controller works. When it wants to bleed lots of pressure off from the wastegates, it applies the 12V for longer so that the solenoid spends a higher percentage of its time open. The more time it spends open, the less pressure reaches the wastegate.

I hope that makes sense.

For further reading, google DUTY CYCLE and PULSE WIDTH

 

[Hotwire]

Aww crap, that's what I was afraid off - that it would be a pulsed signal. oh well, scrap that idea

 

[matchtheclown]

My idea would have been around running the pot off a seperate power source and thus having a free / cheap MBC.

However seeing as it's a duty cycle thing, unless you want to design your own circuit to control it your not going to be able to do it.

 

[Hotwire]

There is a pulser circuit made by Autospeed guys:
http://www.autospeed.com.au/cms/A_110512/article.html
but at $60, its not a cheap upgrade and you may as well use an MBC (turbotech) at half the cost as it won't allow you to easily modify the boost setting without adjusting the duty cycle and frequency POTs on the unit, which kinda defeats the purpose.

 

[Kenneth]

If you are going to go to that length, look up the digital pulse adjuster (or the purpose made boost adjuster)

It costs a bit more, but will give you much better control.

I have been thinking about it for some time, and what you want is to be able to control the BCS (boost control solenoid) based on engine RPM. This way you should better be able to avoid the usual dip in boost pressure at higher RPM without being tripped up by the big boost spike at between 3000 and 4000 RPM which is usually where people experience fuel cut.

 

[2000VR-4]

Dont be a jew and spend $80 on a GFB gated controller, I have had mine set at around 14psi since Feb and not a single spike or boost cut

 

[Hotwire]

Jason, it wasn't about being a Jew. I was looking for an easy low cost 2 stage boost controller so I could keep it at low boost when my wife drives the car, and have high boost when I drive it (which is only about 20% of the time now). My wife is scared of me turning up the boost on her, and I don't fancy paying $350+ for a Japanese EBC, or even the Jaycar units at $200 odd assembled.

 

[Guest]

hey, My dad and I actually altered the ECU on my saab 9000 aero, we basically put in a chip that altered the voltage fooling the ECU, it ran normal up to around 10 psi and from there fooled it to run an extra 4 or so psi. It worked pretty well, normal driving was just the same but when I put the boot into it it upped the boost all the way through the revs which my manual boost controller failed to do.
But yeah you really do have to do tests on what voltage is running at what psi, dad made the chip himself and we had to change it a few times to get it running smooth, at the moment between the manual boost controller giving high boost at low revs and the ECU chip being altered to get high boost at high revs it has worked pretty well.