scoootie5

I own a MY94 WRX RA and the boost level is 1.1 bar
The fuel cut-out is 1.2ish and I have noticed on Performance Exhausts website that they do a Fuel cut-out raiser.

Has anyone fitted this on their car and does it work?
How far does it raise the limit?

Cheers
Scott

Katana

I'm interested in this too. I tried looking into the DAWES FAQ to see if it's safe for my 92 WRX. I was getting conflicting replies to whether its okay to run in my car because it's not as "cutting edge" like the modern ones. If this is the case, how far can I take it up to before blowing my engine up?

Katana

Help me...please. I really really want to join the DAWES club too.

BugEyed

Hi

Strictly speaking the Dawes cut out raisers is a fuel cut defender not a raiser. It will prevent the pressure seen by the MAP rising above a fixed point, regardless how high the actual pressure achieved is. This comes with some risks - ie. if you have a wastegate problem the boost will rise out of control and potential result in major engine damage. On the plus side, it is a very cost effective way of allowing you to avoid the fuel cut!

Duncan

BugEyed

I'll answer your questions this time!

No, I've not got one fitted, but know someone who has, and it works.

It doesn't have a limit - you can adjust it as high as you like!

Duncan

[Edited by BugEyed - 3/22/2002 8:36:42 AM]

BugEyed

Yet more!

The only problem my friend has had so far is that the settings "creep" with temperature changes, so when set up cold at one reading it crept by about 1/2 psi when hot as installed in the car.

Duncan

[Edited by BugEyed - 3/22/2002 8:39:44 AM]

john banks

A 20p zener diode will also do it.

A fuel cut lifter circuit with a few op amps will also do it.

So will a ball-spring device T'd off the MAP sensor pressure supply. Cosie Convert runs a restrictor in the line to raise fuel cut by limiting how much the relief valve can vent.

He runs 23 PSI on a MY95 WRX RA at 5-6% CO fuelling, disconnected knock sensor, std turbo and intercooler. He sets fuel trim with the fuel pressure AFAIK (running wide open injectors at 100% IDC), and controls knock with water/methanol injection. His car is the fastest Scooby I have been in by quite a long way - substantially pokier than the VF23/Link cars from the feel of it but the short ratios help.

But he really knows what he is doing and monitors EGT, intake temp, knock etc etc.

Turning up the boost on an import is not a fire and forget option, and if done incorrectly you have the opportunity to nuke you engine many many times over. So a proper remap is in order unless you are entirely confident you know what you are doing and are prepared to accept the substantial risk of it all going pear shaped on you.

Katana

Thanks guys, so in theory, I could raise it to say 15.5 psi and not worry for my 92WRX as long as I know what I'm doing right? I just thought that because my car is quite old, she was a tad bit more fragile than the other cars here.

scoootie5

OKay Thanks Guys,

I only want to up the limit a small amount say a couple of psi.
I am not stupid enough to go too high.. I Think???
What is a safe increase from 1.1bar (psi??)

Does anyone know the Conversion website address?

Thanks Again
Scott

C h a z

Would it be possible to put some sort of bleed valve before the MAP sensor so that in effect it was under reading? You would still then have a fuel cut. From what I understand this dawes fuel cut defender removes any fail safes from running too much boost. Can anyone advise as to a safe boost level on my MY97, I was thinking of about 17psi.

john banks

or a resistor on the signal line for about 1p - problem is it changes the MAP signal all the way and scales it. So your atmos pressure reading will be out. I don't know what effect this would have, but I don't like the sound of it. Put a restrictor before the relief valve and you can have a new fuel cut.

C h a z

So another dawes MBC before the relief valve would do it?

john banks

No, a restrictor valve or orifice.

C h a z

... and just when I thought I had a good idea. By orifice I'm guessing a bleed valve of some sort? Couldn't the dawes FCD be used in this position? If I'm wrong again I'll go away to stand in the corner with my pointy hat on with a "D" on it.

john banks

No need for "D" hats


Just make sure you are running rich enough

[Edited by john banks - 3/22/2002 9:22:25 PM]

C h a z

Yipeeee, did I say something that made sense! Who's gonna try the dawes FCD installed before the relief valve then?

john banks

Relief valve = Dawes = ball-spring.
Orifice = restrictor or adjustable needle valve.

You could use a Dawes MBC or cutout raiser as the ball - spring bit and leave the end vented. But the restriction goes between it and the T-piece.

[Edited by john banks - 3/22/2002 9:58:22 PM]

C h a z

Now I'm confused, maybe my head is just not up to this.

[Edited by C h a z - 3/22/2002 10:04:21 PM]

john banks

Can you follow my diagram functionally? If not, what bit do you not follow?

C h a z

with this set up, wouldn't the map sensor never read above 14psi and therefor fuel incorrectly between 14 and 18psi?

[Edited by C h a z - 3/22/2002 11:00:44 PM]

Cosie Convert

Chaz

I have fitted this set up to my 95WRX RA (the one John mentioned)
I have found that the MAP has no measurable effect on fueling. MAF controls this IMHO.
In fact I'm not sure the MAP even influences ignition timing as I have tried different bleed settings and achieved the same level of performance without knock, up to 23 psi !

I would still advise extreme caution if bypassing the fuel cut as I detected knock on my car as low as 17psi. This was before the breathing mods and with a magnex dp with standard exhaust system.

I recommend improving breathing via intake system and exhaust system and monitoring of knock and mixture, before raising boost above 15 psi.

Andy

scoootie5

Looks a bit risky to me...

I think I might invest in a Link ECU with the knock sensor etc before uping the boost.

Last thing I want to do is melt the engine.

I am going to PE next month, Do they adjest the standard MY94 ecu's or is it just the MY98 onwards??

Cheers
Scott

dmel

Just an Op-Amp in the signal line of the MAP with gain say ~0.9 will raise boost held and the fuel cut by that proportion.
You can even take it one step further by having variable gain and thus changing boost settings from inside the car.

Increasing boost this way may increase boost at part throttle but still it could be better than an MBC solution in that respect. Obviously the advantage of quick spool of the ball&spring mechanism no longer applies.

john banks

Is there a hazard from changing the signal before fuel cut though?

I am thinking of the atmospheric pressure reading (mediated by the pressure sources control solenoid) which could be a significant variable for the ECU. To raise fuel cut by 4 PSI you would have to have a gain of 0.9 as you said, and this would make the atmospheric pressure underread also. Are there any effects from this? What is the atmospheric pressure reading used for? Do we know it does not affect fuelling or timing? Agree that there seems to be no input higher up, just a concern over the atmospheric reading. Why not just put a notch in the signal with two op amps as I showed in another thread?

I am wondering though what effect the notch type fuel cut lifter would have on held boost. Only one way to find out

Also I noted that a Superchipped car at 18 PSI had very similar spool up to the Dawes at the same boost. Could this be because there was quite a lot of bleed off anyway and there was no longer so much wastegate creep because of this?

dmel

It is impossible for most (and me) to answer these questions John due to lack of info.
Is it safe to assume that the atmospheric pressure reading is ONLY used to calculate guage pressure? (As the MAP measures absolute pressure)
It is difficult to believe that since the MAP measurement DOES NOT affect fuelling, the atmospheric pressure measurement SHOULD.

[Edited by dmel - 3/24/2002 3:28:18 PM]

Cosie Convert

C'mon you mappers out there
Is the MAP function a big secret or does nobody really know what it does