I am looking to increase the boost on my car moderately (currently 12psi probably to 15-16psi) and I have ordered a bleed valve and fuel cut-off gizmo which allows the fuel cut-off to be retained but at a higher level.

I attended the dyno day and looking at the figures compiled by Paul, I can see that my car is running the least amount of boost.

My question (finally!) is what is the limit to increasing boost before ignition and fuelling changes become strongly advisable ?

I know that the standard fuel cut is set at 15.5psi and would assume that Subaru didn't "pluck this figure out of the air". I also have read on this BB that the car runs rich as standard which seems to indicate that there is a little room to manoevre.

I am not disputing that the PE Phase 1 option is a much better solution (and will be my eventual path) but what are the safe limits of this sort of set-up ?

All informed opinions welcome (but please no scare-mongering!)

Thanks

Gavin

Sorry to say there are no general safe limits. One car is rich another may be lean, If you must do this then best to take it to PE and put it on the rollers, fuel may be ok but timing will not be and it will be down to the individual car as to what can be done. PE will tell you what is happening as you increase boost with the bleed valve.
The Superchiups conversion is basically this, and when quizzed abouts its safety all that came back was, we haven't heard of any cars blowing up but ... if you limit the map sensor then, as I'm sure you've seen posted, the safety boost trip does not work so you are taking the chance that a pipe does not come off. Best to clip all the turbo control pipes in place firmly, make sure you do the map sensor pipes as well.

Good luck, and don't wait too long to do the Phase 1

Bob

Where did you order your bits from and what was the cost ?

I am looking to do the same.

What is the purpose of the fuel cut-off "gizmo" ?

And is yours a 99 model ?

ta

Bob / Lee,

Thanks for the responses.

I ordered the parts from

Gavin, Im really interested to see how you go on with your mod. Ive recently had my car (RB5) to Well Lane Dyno where because of the low boost(11.5lb) it was topping out at somewhere near 25bhp less than the other similar MY99s(232 against 245 to 249bhp). Ive spoken to Pete C who has told me to get it to the dealer to check for air leaks on the boosted side, My dealer looked at me blank faced. Im awaiting a reply from David Power. What car is yours & what sort of figures are you producing. Ive driven a mate of mine MY99 and it does seem slightly quicker, especially in 3rd gear.

Tony, I don't remember if you were still at Well Lane when Richard Hardaker had his 98 on the rollers, he had a problem with his boost (1st run only 10 psi, other runs dropping to 10psi above 6000 rpm). He took his car to his dealer, they changed his waste gate solenoid, he is now getting around 15 psi peak dropping down to about 13 psi - might be worth asking your dealer to swap/check the solenoid. I lent Richard an old boost gauge I have, if you want to borrow it give me a shout.

Tony,

I would follow Edward's suggestion and get a dealer to check the boost solenoid as an initial step. It sounds as if your car has a fault rather than needing an increase in boost from standard.

I have a 94 WRX automatic (dyno figures are on Paul Strong's site - at the wheels only). On a previous visit to PE, I got an approximate figure of 215bhp at the flywheel.The boost is correct at 12psi but I feel that increasing it to 15psi will not cause problems (I'll get it checked at PE).

The parts will be despatched from Oz on Monday so I'll give some feedback when they have been fitted and I get down to PE.

Thanks

Gavin

[This message has been edited by GavinP (edited 28-08-1999).]