Mad Hammer

iTrader: (55)

When I got my MY98 STI RA it had full de-cat and it was detting a little. I re-fitted a standard downpipe and problem was solved. However I miss having a de-cat downpipe and now I have all monitoring gauges.

I wondered if I re-fit a de-cat downpipe and use a Dawes I have lying around to control boost creep (which was probably happening before with de-cat but had no boost gauge at this time) will this help solve the problem of det until I can afford re-map ?

Clive

The_Judge

Before fitting a Dawes, you could try slackening off the wastegate actuator arm. If the arm's too tight, it could lead to overboost. Or you could try drilling out the restrictor bore slightly. This should help the wastegate solenoid control the boost better...

Mad Hammer

iTrader: (55)

Thanks for your reply, currently boosting at 18 psi max overboost with 16 sustained with cat downpipe fitted. So 2 psi is not a problem with cat fitted.

By drilling the restrictor bore, do you mean on the dawes ? If so to how many mil ?

The_Judge

Are you saying your max boost is 16psi with the OEM downpipe, but 18psi with the de-cat downpipe...?

Depending on MY, and whether you've a 2 or 3 port wastegate solenoid, the restrictor is somewhere in the vacuum hoses, between the compressor and wastegate solenoid/actuator. On mine (MY00), it's just before the T-piece, in the hose from the compressor. If you look carefully, you'll see a slight bulge in the hose, where it's located.

As to how many mm, it's more like how many 0.1mm...! For instance, if the standard is around 1.1mm (not sure exactly!), increasing this to 1.2mm might be more than enough...

Mad Hammer

iTrader: (55)

With my OEM downdipe I am getting 16psi sustained with 18psi overboost. I don't know what it was previously boosting at with de-cat as there was not a boost gauge fitted when I purchased car.

If I fit a dawes to control boost will I not be doing away with the need for the restrictor in the pipes to the solenoid ?

I suppose what I am trying to get at here is if I fit de-cat downpipe and set boost with dawes to a sustained 16psi rather than use solenoid, will I be protecting myself from overboost associated with de-cat therefore minimising the issue of det.

The_Judge

Again, going on my own, the MBC replaces the hose with the restrictor in, and obviously removes the wastegate solenoid from the equation.

Yes, pretty much. The only reason you wouldn't fix the problem with a Dawes, would be if the wastegate itself wasn't venting enough exhaust gas, and so even fully open, boost would still climb.

Mad Hammer

iTrader: (55)

Would you therefore suggest seeing how the Dawes operates on my current set up before fitting de-cat downpipe ?

Clive

The_Judge

Either would work. Just bear in mind if you fit it before the de-cat, you'll probably have to adjust it after the de-cat, as you'll probably get another 1psi of boost due to the better breathing. I doubt whether the wastegate itself would be a problem, as you're not running a big turbo with loads of boost...

Mad Hammer

iTrader: (55)

Fitted Dawes last night and now get a solid 17psi with no overboost whatsoever. Will change downpipe tomorrow if I have time and see what the results are.

If I set boost @ 17psi with de-cat downpipe are my only benifits going to be earlier spool up as I am running same level of boost. Therefore no actual power gain ?