Boost Question > MY05 STi
 

Hi Guys,

I have just fitted a Defi boost gauge to my STi and wasnt expecting it to be boosting over 1.2bar. However it does seem to be....

Basically its boosting as so:

• 1st Gear = Needle twitches quite fast between 0.9 and 1bar

• 2nd Gear = Needle twitches quite fast between 1bar and 1.1bar

• 3rd & 4th = Needle more stable, gets to 1.2 at about 3.5-4k revs then tails off to about 1-1.1bar as it climbs.

• 5th & 6th = Needle hits a stable 1.4 bar at about 4k and holds through to 5.5k where it starts to tail off again. (I havent had enough revs to see what it does in the uppers here but it appears to start to tail away steadly after 5.5k in 5th)

• Fuel = Tesco 99

• Temperature is about 9 degrees

Does this sound normal? I thought i read in a thread somewhere that a standard (non PPP) STi would only boost 1.2bar?

I also notice that it drops to almost -0.8bar when im on over-run, which seems really low compared to a mates Evo (although i know this is like apples for pears, but i thought they would be closer in terms of their behaviours becuase they are both similar'ish)

It feels really nice and clean still when its pulling, and the boost gauge sensor it fitted just before the Dump Valve with a T-Piece which all has a very tight seal (i purposely bought a larger metal T-Piece because the Defi item seemed to have a tiny bore compared to the hose connected to the Dump Valve).

Thanks for any assistance in advance,

Ant

The boost target for a standard MY05 STi is around 17psi or 1.2 bar, are you sure it hasn't been 'played' with? The boost you describe in-gear and when you let off the throttle sounds fine/normal.(i.e. low load/lower gears won't make as much boost as the longer gears)

Ye, its definately not been played with because i have had it since new. I had it on a couple of rolling roads about a year ago and it made bang on book figures, but it was ran in 4th which it isnt peaking to 1.4 in. The RR graph on the first one was showing intake temps up in the 30's and it only made 1.1bar on that one.

It feels really smooth and clean when its pulling, and it has been very very loved. ie: servicing 1k before it should be, properly run in from new, allowed to warm up before any load is placed on it, Tesco 99 / V-Power pretty much exclusively (couple of tanks of 95 have had to be used but i was very careful with not pushing it when it was) etc...

Im probably un-nessecarly worrying... i just wasnt expecting to see 1.4bar