advise on overboost
 

just bought first impreza a jap import 1998 sti which had a £7,000 engine rebuild with cosworth pistons 8,000 miles ago,
it went in for an oil service today and was told it is over boosting due to large exhaust and no cat. it has aturbo timer which is set to alarm for boost at 1.1 bar and it hits 1.25 bar for a second or two before going back to 1.1.
he said the best way to stop it is to fit a cat back on.
has anyone got any advice on how much boost is ok and whats the best way of turning it down

hhmmm
 

If i were you mate i would'nt worry to much.....but i'd probably see if you could have it remapped.

Phil

Well with all jap imports we know that there they run 100 ron and are usually mapped for that kinda fuel. They are also usually tinkered with, so in my opinion you should get the car thoroughly checked to make sure u know exactly whats on it. Then get it tuned for the UK fuel depending on what you are going to run on regularly.

"Overboosting" now do you mean compared to standard or is it actually set to a certain boost and its going over that. Maybe the car is set to boost to 1.2 ... wouldn't surprise me on a jap car. My friend got one and it was set to 1.4 bar ... !!!

Neways i hope that helps

leeps

Overboosting - normally refers to when the engine boosts so high that the ECU cutout comes in and the car feels like you just hit the brakes AFAIK!

Do you mean that the car boosts higher than you expect? What kind of turbo timer have you got - I have never heard of a turbo timer that measures boost?

If its an STi Japanese model I would not have thought that 1.2 bar is too much boost for it - however take it to a reputable Impreza specialist and get it checked out!

Make sure you never put ordinary umleaded fuel in it - as it is only 95RON in the UK and the Jap cars run on either 100RON or 102RON fuel.
I have had an engine blow up when ordinary unleaded was put in rather than super unleaded - went 6 miles then bang!! went No.3 piston!!

First of all, you could try cleaning the boost solenoid.

If that makes no difference, check the restrictor hasn't become clogged at all.

If it hasn't, you could try a slightly bigger restrictor.

Or fit a manual boost controller.

Alternatively, if you're not hitting fuel cut, you could get a boost gauge to keep an eye on it, and a Knocklink. If the boost levels are consistent, and you're not detting, don't worry about it.

As already mentioned, if you're not using SUL/Optimax/BP Ultimate + octane booster, a remap is essential... :)