ScottishMenace

I know there have been several threads on this so I am aware of the fix for spiking at 1.7 bar. However can someone tell me where all the cats are located and what I should be changing for maximum benefit. I have a Magnex back box at present.

Thanks in anticipation.

Dave Allan

mutant_matt

Cats are in the downpipe and centre section. Removal of both of these for a freer flowing exhaust with the standard restrictors seems to cause spiking in the 1.5bar region. Adding an OEM up-pipe to this seems to raise this to 1.7bar.

There are a couple of peeps on here who have solved this with different restrictors (Jonno and Deep Singh off the top of my head).

Matt

mutant_matt

Sorry, when I said OEM up-pipe, I meant to say Aftermarket - muppet, sorry

Matt

raybotha

Just a note , there are 2 cats as mentioned , 1 in the downpipe and one in the short pipe attached directly there after . The centre pipe only has a resinator in it and is straight through . I went BPM down pipe with 3" system to back including a small resonator in the centre pipe , about where the above mentioned 2nd cat was .
Now here's the thing . I got a 1.5 bar spike , but note you only get this between 3-4500 rpm thereafter it does not spike at all .
Also when I fitted my standard back box onto this 3" I got significant part throttle and low down torque increases and it only spiked to 1.3 ish bar . But still pull hard .
The spiking low down upsets the ECU as it pulls back boost too far then sends it to standard again . This effect apart from the high spike disappears after about 50km's driving . I am convinced however that the total milage for the ECU to calm down is also dependant on the amount of times you restart the car which seems too help . So stop off for a coke etc.

Although the car performs well with the standard back box it has a measureable increase above 5500rpm that is unexpected and really feels awesome with the free flow unit. A totally confidence inspiring powerband . I was getting people hooting and waving in delight , strangers , as I played with the cars rev range on the highways .

Am going too have a drag with my brother too see what the onroad difference is between the 2 , he also has an Sti VII - standard .

A note , I am running 102.6 racing fuel (this in itself give a well worth while performance increase over 97 octane) and never noticed any pinging at all with the boost spikes . Take a corner in second gear and floor it and hold on , four wheel drifting . I never would have believed the difference in power , much greater than on a WRX . Feels like a motorbike .

Sorry too go on friend but I just fitted it yesterday .....

Good Luck ,
Ray

Pete Croney

LOL

Deep Singh

Ray,who makes this racing fuel? I thought it was difficult enough to get 98 RON fuel in SA.

raybotha

Aaah , now there's a thing Mr. Singh . Amazing what a few phone calls will achive . There are 2 makes available . Most Shell garages now stock 20lt tins of 102 in the forecourt . It is however high in lead , more so than standard leaded fuel . I personally know of some STI owners that have used it for 20 ,40 and 80 000km's without changing cats or lambda sensors . No surging , just good power . Then there is BP 102 fuel that I get from the depot . They are more than willing to sell it , also 20lt drums . A lot of local racing teams use it . The crunch is that it is a low lead fuel with a 1/5th the lead content of the Shell .
I have tried all sorts of solutions , toloune , nulon , NF .... but none compare with racing fuel for throttle response , smooth delivery and damn good power and revability . As my brother sais "it feels as if thats what a Subaru should go like" . The cream of the crop is the Sasol unleaded 102 but we got banned from buying it when we depleted their stocks . Deep I'm commited to racing fuel from now on , my car loves it . I stock some tins at home and some at work . No probs . It costs about 25% more than PULP .

Get some if you can .

Ray

Deep Singh

I see Mr Botha! Unfortunately nothing of this sort exists in the UK.On sale at garages anyway,probably available to racing teams.Interesting though as I've been in email contact with a fellow country man of yours called Rupert Van something who was having difficulty even getting hold of 98 RON fuel.Next time I speak to him I'll point him in your direction if thats ok.
Cheers,Deep
ps,Rupert mentioned an intercooler tilt mod that was all the rage out there,have you had this done aswell?

Big Goon

Do a partial de-cat like my car, junk the standard back box, center, and small cat after the downpipe, then replace with ScoobySport or whatever you fancy, mine sounds much, much better and pulls a bit stronger lower down the rev range.

Reasonably easy to put back to standard should anybody start whining about warranty issues.

GDBSTi

Hi Deep
Rupert here, Ray is talking about leaded racing fuel, only available in 25 litre tin cans (low lead) BP and (high lead) Shell. We only get maximum 97Ron Unleaded at the pumps in coastal regions. In Johannesburg they only have 93Unleaded!!!However we suspect the 97 is actually 98,5 but not quotable due to infighting in the petroleum industry in SA. In fact when we first got 97 Unleaded at the beginning of 2002 it was
cheaper than 95 Unleaded, but since it was only sold by one company called ENGEN not Shell,BP etc they complained and the government forced a price rise above 95 Unleaded.

The TMIC tilt mod is not well know in SA but in Australia. I heard about it on the MRT forum and I am spreading the word here.

raybotha

Deep , Big and Rupert , Howzit ,

Guys let me tell you a story . As mentioned I replaced dp with a BPM unit ,took off the rear straight through silencer and replaced it with a STI VI backbox . Immedietly the car was easier to drive , better off the line and wheel spun front wheels in first off the robot form just pure acceleration in a straight line . The ECU was still battling to contain the overboost , but it was down from 1.4 bar to 1.3 bar (with STI VI bacbox on now) . Damn I couldn't believe it . When I got home I fitted the origional STI VII back box and noticed with dissapointment that the throttle response was slower , slower off the line , and not eager to rev up , especially after 6500rpm . Now , my brother has the same STI VII with a Prodrive backbox on ,minus the second smaller cat , so we head off for a drag . From 3000rpm in third gear we floor it , my STI now with STI VI backbox on literally pulls a car length in fornt and keeps pulling in fourth ahead at the same pace . Tommorow I will put the straight through backbox back on ; the ECU is now limiting the boost spike to 1.25 and is smooth , and we will see if this helps from the bottom up . The f/flowing back box definetily helps from 5500rpm onwards , feels like a good old cam kicking in , although I may need to drill the restrictor a little . Mine is .75mm standard . The car is an absolute bomb .

Rupert I wouldn't mind that info about the intercooler . The reason I haven't bothered with cooler is I've heard my STI ping with 95 in , in midwinter at -2Deg C , but I know the waterspray helps . Game to try though if you get a chance . BTW Rup' I drove in the PPP STI VII the other day with Dawie from Sub' SA and it feels very strong and smooth , also just a little louder than the WRX PPP setup . That was on 93 too !!!

Ray

Deep Singh

Hi Rupert thanks for mailing me the tilt mod link.
Ray,I'm confused.The STi6 centre and backbox does;nt bolt straight onto the 7 does it?

Deep Singh

Also have you retained the resonator thingy in the mid section?

GDBSTi

Hi Ray,

TMIC Tilt mod pics in your mailbox

Hi Deep,

Have you tried the Tilt mod yet?

Reduce by 1/4mile time from 14,6 sec to 14,0 sec

Will vist dyno 24th August to check any gains there but do not expect cooling gains to be picked up at a static dyno. Perhaps with the fans on we will see cooler intakes with the tilt mod.
Keep you posted.

Ray, does the PPP consist of an all cat removal i.e. complete turbo back prodrive catless exhaust system, also does the bb of the PPP look the same as the current WRX PPP bb. Its finishing is poor for my taste. I hope they make a better looking bb for the STi. Any news about release date yet?

raybotha

Hi friends ,

Deep , in response to your questions : Yes all backboxes I have tried PPP , STI VI / VII and others all fit standard and free flow centre sections . Thats what makes it so much fun , I have ramps that I drive the rear of the car up on (just cheap makes from an automotive retailer) and its 2 x 14mm spanner nuts / bolts to be removed . Have done this 4 times so far and gasket still good . Yes I replaced my mid section with 3" because the twindump dp was just a little short of the mark and wouldn't bolt directly on . Here we don't suffer emmisions tests . I still cant believe the difference in performance of the STI back boxes so I lined all 3 up next to each other and there are slight changes . The piping inside the 6 box is bigger , the build quality and attached pipeing worse , looks like a cheap job with varying diametres bacause of poor bending equipment . Sakemoto have come a long way ... I also got my brother to tape the sounds of them so we could analyse that on the HIFI (that was fun)The perfomance of a 3" with a standard backbox versus a standard pipe with a PPP rear backbox encourages a lot of theorising on my part . Just goes to show how restrictive that front cat is . Although the turbo whines more at pull off the pipe is as quiet as a lamb ...
Just out of interest any silencer midway detracts from performance , I seen this on a dyno , the boost comes in earlier and gives more power without a centre resonator , even with a bigger backbox (more restrictive) as I'm experiencing here . Top end power however is limited by backbox restriction eventually . So , more flow , more go .

Rupert thank you for the e-mail , I got the picks . What exactly did you use for spaces . Can you confirm if only the rear side is lifted .
The PPP has a full decat pipe on , including PPP downpipe , but uses the same back box as you feared . Personally Rup' I thought the build quality was good .... They where going to get some kind of periscope to look inside the engine to make sure their was no ill effect on the internals from det . The OK date was a month from that day (2 weeks ago) so I expect another 2 to taking orders . Will pop past and find out for sure for you . I think I should emphasise that they are approaching this rather causiously and want the car to be reliable on 93 RON , some compromises in performance are inevitable (hope this doesn't cause an outcry) but as Dawie sais it is fully factory warrenteed .UK PPP will run higher boost - 1.3 I believe. If you are interested Johnathon from Subaru SA is bringing in odds and ends from STI JAPAN that you might want to consider , give him a call he's still feeling out the customers and will bring in on demand .

Ray