eddiebeef

Does anybody know what pressure the wastegate opens at on

1.)standard impreza turbo
2.)prodrive turbo (240bhp)
3.)wrx (260bhp)

Cheers

john banks

0.5 bar for all Subarus AFAIK.

eddiebeef

so where does the extra power come from then??

john banks

Just because the wastegate pressure is the same doesn't mean the ECU has to run the same boost, and that some turbos don't flow better than others.

The actual opening pressure depends on exhaust flow through the turbine, exhaust back pressure, wastegate size and bleeding off of boost from the actuator diaphragm by the wastegate solenoid.

But the actual arm will move at 0.5 bar +- tolerances. Boost control is achieved by making the diaphragm see only a proportion of the compressor outlet pressure. This is achieved closed loop (with variable gain depending on boost error) depending on boost targets, max/min duty cycles with compensations on some models for temperature/pressure.

[Edited by john banks - 1/20/2003 11:11:10 PM]

eddiebeef

It doesnt matter what flow rates etc you have thru the exhaust turbine - pressure is pressure- as soon as the pressure reaches a certain limit the wastegate/pressure relief valve whatever u want to call it will open. I think wot u are talking about is bleed valves which fool the wastegate into thinking that the pressure is lower than it actually is - hence u get more boost before the wastegate opens. I dont think these are standard fit on production cars so there must be a difference in springing in the wastegate or if it is electronically controlled a difference in the ecu programming???

john banks

Yes, suppose so. What I am saying is that the factory boost controller is an electronically controlled bleed, so yes the ECUs have different duty cycles and boost targets. In addition, some turbos are not far away from boost creep and others have the wastegate blown open easily at high RPM by EXHAUST flow not by boost pressure on the actuator. The different cars also have different restrictors off the compressor outlet which adjusts the control bandwidth of the factory boost contoller - which is narrow on the crap flowing 2 port solenoid models.

The ECU boost control on the Scooby is pretty standard stuff for a factory turbo car and there is lots of stuff out there on this method of control.

Fair to say that the boost control is a multivariable phenomenon, and not reducible to one single factor like wastegate spring strength.

[Edited by john banks - 1/21/2003 9:22:39 PM]

eddiebeef

In a way I see where your coming from but it sounds like a complicated solution to an easy problem. There's not much point in having a wastegate designed to open at a certain boost pressure if the exhaust vacuum created sucks the wastegate open at high RPM!
This means that the diaphragm is not actually doing anything??

The simplest and most effective way of increasing boost would be to just change the cracking pressure of the valve would it not?

eddiebeef

Or do you mean that the exhaust pressure that builds up inside the manifold at high rpm actually causes the valve to 'blow' open?

john banks

Yes. Since exhaust back pressure on a small turbo can be considerably higher than boost pressure (and the boost pressure that the actuator sees is reduced by the work of the factory boost controller). The exhaust housing is just too small so the wastegate flap is literally blown open. Stronger wastegate helps, but you can have a x.y bar actuator on a turbo which will not make that boost at high RPM.

eddiebeef

Is the wastegate opening controlled through the ecu from a pressure sensor in the intake system and activated by a solenoid or is it just a mechanical valve? Do the systems vary depending on MY or are they all utilising the same design??

john banks

The former. Basically the same except some use a 3 port solenoid, some use 2 port.

eddiebeef

so it cant be modified by simple means!!

john banks

Yes it can. Alter the manifold pressure sensor signal and change the size of the restrictor. This method let me run 22 PSI and 295 BHP on a 215 BHP car (with a few breathing mods and a different turbo). Cost £5 if you are any good with a soldering iron.

eddiebeef

so u can get a new turbo and the mods for £5??

Tell me where to get them!!

eddiebeef

do you know what output signal equates to what pressure?

john banks

Nah, I meant the MAP signal modifier was a fiver, but just make sure it isn't detting if you are going to do this! It is engine blow up no problemo scenario if you get it wrong.

On the MY99/00 UK fuel cut is about 4V on the MAP sensor (17.6 PSI). The car as standard aims for 13.7 PSI held boost. About 0.1 V per PSI very approx, so to defend from 12.6 PSI you need a clamp above 3.5 V, ideally you would have it step back in to give a new fuel cut.

Someone somewhere will have a link to the DIY FCD thread....

john banks

http://www.scoobynet.co.uk/bbs/threa...D=70491&Page=1

Here is one of them If that doesn't faze you there is a DIY EBC using a uC and a further DIY FCD thread entitled "DIY FCD results" which had my final cheapo really simple design, but it does mean soldering and making up a board with an 8 pin DIL on it. In the end I had the offer to remap ECUs instead - much easier but it was all good fun and I learned a lot from all the bolt ons

eddiebeef

sounds easy enough, should be able to rig something up for in car control and just tweak it whilst at the wheel

CHEERS!!

john banks

Do lots of research first, and be paranoid about detonation. Good luck and don't blame me if it goes pear shaped. No reason it should, but use caution. Seeing your profile I expect you know what you are doing.

Knocklink is a good idea, nay essential.

eddiebeef

On the fuels side of things I am experimenting with a setup for running on methanol fuel. Not sure if a scooby has been run on MeOH before. Taking it one step at a time at the moment. I have another car that I use as a bench test. Its not only the ignition and fueling that are to be dealt with but other things like corrosion, lubricity and the problems encountered with hygroscopic fuels. Applying it to turbo engines is the next step!

john banks

There was a recent thread (well last few months anyway) about naughty fuels, additives etc and these octane mad guys were using paint thinners IIRC. Andy F has used methanol through an injector, think he has also put it in the tank.

eddiebeef

You cant just use methanol as a direct replacement for gasoline as the densities and volumes required are all different. A lot of people say yeh I tried methanol and i got loads more power. Its all bull****, I calculated that replacing with methanol will actually cut power. You only see the benefits when you modify the fueling and compression ratio. Approx twice the volume of methanol is required when cf gasoline so..........

john banks

Andy does modify the fuelling, found it runs leaner, but it apparently good at suppressing knock.