justin8260

Hi Guys,

I had an Impreza STI PPP 305bhp (or at least that was what they are meant to be right?) , 2 years ago, and now after a bit of a break, I'm after another one.

Basically I'm after the same again, but with a bit more power. Ideally 330 - 350bhp.

I've seen a few examples that fit the bill, but they all seem to have either the Hayward and Scott turbo back exhaust system, or the Nurspec R exhaust system. Both have decats.

My question is would these need remapped again if I was to swap the decat for the likes of a Cobra Sports cat? Dead against the idea of driving around with a decat, so I don't see that as an option.

Anyone know of a good cheap alternative sports cat that would fit with aftermarket exhausts or that would fit with the prodrive exhaust?

Cheers for any tips from experience guys.

Justin

justin8260

anyone able to help Here?

urban

iTrader: (1)

It would need remapped.
Put it this way, my old 05STI PPP was simply remapped by Andy Forrest and made approx 340 bhp.
Decatting would have released maybe another 10-20 bhp, but in my opinion its not worth the hassle come MOT time.

PPP'd STI's never made 305ps, they were usually always shy of this.

justin8260

Thanks Urban!

And agreed re. decat being more hassle than worth (for me anyway).

Actually got my new motor today, 53 plate black STi, standard.

So I'm thinking, uprated fuel pump, sports panel filter, and a ppp exhaust system and Andy Forrest remap (as not too far from me). Should be good for at 330bhp I'm hoping.

Justin

urban

iTrader: (1)

Yes, uprate the fuel pump and fit a ppp exhaust system - I think they make quite a nice noise, unlike those daft nurspec drainpipes.
Service, new filter and maybe fresh plugs too in there too.
When I did the power runs, it showed 331, 334 & 337.
But its not the power, its the torque you'll appreciate most and you'll generally have a much more drivable car.

PPP cars in my opinion are pretty dead until approx 3.5K, then they begin to run out of puff about 5.5K - doesn't give you much to work with.
My car pulled strongly and had 1.4bar boost from 2.7K, pulled strongly to 7K where it tapered down to 1.25bar.
No point reving them to 7K anyway, grab another gear about 6.5 and begin again.

DmcL

why would you need a remap for a decat or fitting a sports cat or even standard cat? the ECU has built in measures for compensating air/fuel ratio based on lambda feedback.. you dont go running for a remap when winter becomes summer because the IAT/MAF sensors have been used to cooler weather and now its getting warmer...

only reason for a remap regarding decat to cat or vice versa is if it causes a fault code and subsequently a check light in the dash.

feel free to correct me if im wrong here.

**jay**

iTrader: (1)

You are taking a huge restriction out the exhaust(cat) the car will over boost so needs mapping.

Turbotits

iTrader: (2)

The point being without a re map theres very little gains to be had. And as above de catting without a map on a newage car will probably cause boost spiking and/or over boosting

DmcL

how much overboosting are we talking? the ECU has loads of maps and compensation maps, etc, etc. id have thought in an overboost situation the ECU will detect the amount of boost, detect the air/fuel ratio and trim fuel and ignition accordingly as maps are created with high and low areas beyond normal operating conditions to account for such instances. perhaps if overboost is too much for ECU compensation then even hitting a boost/fuel cut or something along those lines. ECU's always have safety strategies/measures in place.

now, im not saying anything power wise here as opbiously for best results in terms of HP/TQ then mapping is needed and ideally for the specific setup and can be tweaked after changes or additional mods but from an "it should still run ok" point of view id think fitting a decat system in place of even a standard system and standard cat shouldnt make the car unsafe to drive or unsafe to put the foot down.

trying to learn myself a bit about the modern subaru ECU's and exactly how they operate particularly relating to boost as all my mapping background is on old BMW's with no factory O2 sensor so all tuning was manual and it ran what it was told to with the only variables being IAT and coolant temp. have mapped a couple turbo setups on the same system with great results, just ramp down timing and ramp up fuelling as boost comes on. ofcourse the subaru ECU's are far more complex and have boost specific compensation maps and maps relating to boost contro, etc. all of which im completely unfamiliar with but will hopefully get my head round since downloading romraider and checking out a stock tune and looking at the various maps. some make sense, others ill need clarification on.

Turbotits

iTrader: (2)

The ecu can only adjust within the perameters put into it. If its boosting more than it will ever expect then it cant adjust anything that high up the scale. mine spiked upto around 25psi when i de catted. The ecu just isnt set up as standard to expect or control boost that high

DmcL

but if it spiked higher than the ECU is set to compensate for then the ECU would basically go "oh ****" and cut something in an attempt at engine preservation such as boost/fuel cut.

dont know the conversion from bar to PSI off hand but in first time looking at the maps in the ECU lastnight i did see boost related maps which were tabbed up to 1.6-2 bar or so which would be around that or higher.

also if it was not compensating then id think at a spike up to 25psi then you would have seen a very lean condition, possibly detonation and engine damage given how fragine the pistons seem to be in these engines.

Turbotits

iTrader: (2)

Your last statement. I.E. Lean running,det etc. Thats why decats need mapping for. Youve answered your own question

DmcL

not quite.. there is an O2 sensor in the exhaust and the ECU knows what boost pressure the engine is seeing and has maps to compensate fuelling/timing accordingly. if it doesnt compensate enough to prevent a dangerous lean condition then whats the point of it having O2 sensors, pressure sensors and maps specifically for compensation of abnormal engine actions such as overboost, etc.

id expect a remap to be necessary on the old stuff i tune that has no boost input or O2 sensor as there is no compensation but a modern ECU with more maps, more safety measures and more sensors should step in to save the engine in some manner if the ECU is not mapped to suit the mods. ofcourse without suitable mapping best results cannot be obtained so it would require a remap in that respect but thats not what im talking about, im just talking about the engines ability to operate without damaging itself.

bluenose172

iTrader: (2)

Fuel cut is a lot lower than 25psi on a standard car. DMcl the ECU won't react exactly in the way you assume to an over boost situation. Boost control will kick in and probably end up oscillating all over the place. The overboost may or may not cause det, this may or may not cause the rough knock control to activate and reduce the IAM, if this falls to below 4 or 0.25 (16/32bit), then boost control will be disabled, and a high det fuel and ignition map will be used. This isn't a situation you want to get in.

bluenose172

iTrader: (2)

The factory O2 sensor can't detect a lean condition in open loop.

bluenose172

iTrader: (2)

To the OP, I would at least have a mapper check the car, you may or may not need a tweak.

DmcL

this is the stuff i want to be hearing.. not just you cant because stone cold said so

not sure what IAM stands for and also what does the number 4 or 0.25 represent? was actually looking at that map among others lastnight and thinking i have some sussing out to do here.

whats so bad about high det fuel/ignition map? obviously it will impair performance but with no instances of det it should work its way back into the normal maps again until the next instance of overboost and/or det.

regarding boost control oscillation.. why does it oscillate? these and the above are the sorts of things quirky things outside of the normal ignition/fuel tuning i like to know as on the old BMW stuff i have found areas not relating to power where improvements can be made. if its possible to tune boost control maps for less oscillation and also tune maybe IAM or rough det depending on whether necessary and what other maps may be used before these to prevent an arising problem from becoming critical to engine health. maybe possible to retune relevant maps to cap boost to a set level in the event of abnormal spiking as apposed to heavy oscillation and chances of det maps not acting swiftly enough, etc, etc, etc.

i like to know how everything works and generally keep plugging away until i do. started with the old BMW's after a cheap chip and thinking "i can do better", year or so later and i find myself in small time business with people chasing me down for chips lol

to the OP, dont take my posts as saying you dont need to get the car mapped. you definately should, im just going off on a bit of a tangent.

bluenose172

iTrader: (2)

I'm on an iPad and have been drinking so ill be brief.

All the information you'll ever need about the working of the Subaru ECU is available to trawl through in the various stickies over on the Romraider forums.

DmcL

cheers, read a few articles on scoobypedia just now.. one explaining accelerated ECU learning. also read something regarding IAM. also nice to know the safety features in the ECU an be improved so as to not be such a nuisance if they happen to be triggered when modding/tuning/etc.