MY99 UK Turbo with PP ECU - Can i decat downpipe?
 

Hi folks,

I have done my reading on here, and I have gathered some information but just want to make sure...

I have a MY99 UK turbo 2000 AWD, with no engine mods, but a PPP ECU. I have the centre section decat pipe and a back box. I always put in V-Power (no matter how much my wallet tells me not too).

My friend has given me a decat downpipe and tells me that it should make a big difference and to whack it on. I have read that the decat downpipe will create over boost problems and lead to fuel cut, I think.

I have also read about the restrictor pill, and that that can be drilled out in 0.5mm instalments until the best size is found, and run the car like that.

Is any of this a good idea? Should I leave it how it is, how prodrive meant for it to be? Or can I give it a go with drilling the restrictor pill?

Also, if I can do this, is there anything that should be done? Next on my list will be the panel filter, as I said above, that’s how prodrive wanted it to be...

Any help appreciated.

Thanks, Matt :thumb:

Think it may over boost but at the end of the day if you get the pipe for nothing mate and fit it yourself you can only swap it back over if it doesnt work out tbh as its an easy job to fix.

It can cause big issues, no matter what anyone say's to the contary, if they had a generic remap and then replaced an item like a catted dp with a decatted dp it will overboost and can det.
Your best off doing 1 of 2 things, keep the car as standard (you wont gain much anyway from just a decat without a remap) or 2 replace the ecu with a standard unit and get it remapped (adding the downpipe at the same time).

Tony:)

Thanks Tony, that was the reply i'm waiting for.

As its a UK Classic, with PPP ecu, i think i will just leave it it as it is... Im only 23, and couldnt insure a JDM, but do want to start properly modding on a classic STI, so i think i may just keep the UK classic standard as the STI is better to start with anyway...

Thanks a lot mate :thumb:

I had a ppp ecu on my MY2000 uk,and fitted a decat downpipe,car did not seem to suffer,and still pulled 1.1 bar with no hesitation. I too read that it could lead to overboosting,but being as i only had it fitted to my car for 16 days,before i changed the ecu,turbo,etc,cant really say that it will definetley overboost as mine appeared to run fine ,without any mods to the t piece or the restrictor pill.

Hmmmmm........ Guess i'll await more replies.... Thanks Midnight :thumb:

I done it too, when I had my PPP ecu. But at the same time I fitted a boost controller, to cap it at 1.1 bar, so never experienced any overboosting because of that.

But it wasn't long before I looked for a standard ECU to have mapped, just because I wanted to take things further.

As Tony says decatting the PPP can cause issues - the most likely of which will be a tendency to overboost/spike. As already said some cars will do it some won't, depends on a number of factors, not least the temperature of the ambient air - and in any case there is a simple fix for it

If you want to try the decat downpipe, it'd be worth getting a good quality boost gauge first, driving round with it on for a couple of weeks so you get to know the natural boost response of the car, and then fit the DP. If you then see any unpleasant spikes/oscillations on the gauge, you can take some remedial action - which will most likely be drilling out the restrictor orifice in the boost control pipework a little bit.

Mine was on the car a good 2.5yrs, ran 1.1ish normal, decat pushed that to 1.25-1.3bar :eek: saw det on that on cold days, knocklink loved me, always ran her on super unleaded as per Prodrives instructions.
Eventually drilled the restrictor pill out a little, still it wasnt worth the effort when a remap would have given me safer power.

Tony:)

Hey guys, Thanks for all the replies...

The last thing I want is to hurt my engine or worse.

I have a boost gauge plumbed in, it’s a mechanical one, and I don’t think it is too accurate (my mate gave it me, it is one of the ones that you can press the button and it changes to 7 different colours (I think that means it is inaccurate)). I think the most I’ve seen on it on a nice cold evening in 5th gear was a bout 18-19psi - should I be worried? I haven’t felt any type of fuel cut in my car... Just a thought, I also have RomRaider so may go out and check that against my boost gauge to see if there is a difference.

I'm trying to steer clear of fitting it, also for MOT purposes, however, if I feel I need to test it out, is it easy to get another restrictor pill if I mess up mine, or want to change it back?
Also I know that these ECU’s are one of the best for a MY99-00 (for a standard car – plug in 40BHP at the least i think), and wouldn’t want to remap this ECU... so would sell this one and map a standard one, which also seems like a long procedure.

Please keep the replies coming.... :thumb:

Thanks, Matt

Grief, where to start. It's impossible to tell you whether you should be worried or not on the basis of that. 19psi is 1.31 bar - which is miles above the boost target (of around 15-16psi). Not sure where fuel cut on a PPP is but wouldn't be surprised to see it lower than 1.3 too. As such this tends to point more to an overreading gauge than anything else. Does it hold at 18-19 then drop back lower, or get up there and stay there, or constantly oscillate up to that level, or what?

Yes, definitely do that. Easy way to work out what's what. As above you either have a significantly inaccurate gauge or a problem. Better to know which.

You can get spare restrictors from your local Subaru dealer for a couple of quid each so that isn't a problem. As for MOT time you can just refit the standard downpipe.

Re. "long procedure", not quite sure what you mean - mapper will map a standard ECU just as quickly as he would a PPP one so it's not "longer" in that respect. In either case he'll most likely start from his own base map. As you say, if you are going down that route, the most financially effective way to do it is to sell the PPP ECU as it is and use a standard one for the remap.

Thanks Splitpin, i will check on RomRaider tonight and see if the gauge is over reading - suspect it is - i should have mentioned you can get them on eBay for about 20-30 pound...
But to answer your question, it would get up there and drop back down. I don't think I've ever seen it stay up there.

I have an MOT friendly test station so i not need worry about that, don't really know why i mentioned it.

With the "long Procedure" i meant that its just a bit long to get another ECU and change them over to get a map on there... I'm lazy and cant be bothered to do anything! :)

Oh, and thanks for the heads up with the pill, if i need to i can take a trip to Subaru.

Thanks a lot for your help, I will report back with the gauge problem, which i think it is...

Thanks a lot!!

over reading boost gauge
 

Hi, My boost gauge is over reading, which is a good thing. RomRaider has told me that in 4th gear i hit 15.82psi at 3032RMP, it held it for a little bit, and then started drop down. My boost gauge on the hand read about 17-18psi. So that has cleared up that matter, thanks :)

As for the decat DP i may try it out, I'm not too sure. I think i will leave it for the moment as I'm really not bored of my car and don't need extra power yet.

If anyone else wants to leave some comments about when they put a decat downpipe on a PPP ECU and the running issues they may or may have not got...

Thanks, Matt

Good stuff, that makes sense - and your logs suggest that the boost is where it should be at the moment. The bottom line with this gauge is that even though it's inaccurate, as long as that level of inaccuracy remains consistent, it's still usable in a compare and contrast scenario - especially for spotting spiking.

As far as other people posting comments, btw, you'll probably not find anything "better" than you've already got. Bottom line is that each car behaves slightly different - especially a decade after being assembled. To a large extent it doesn't matter what happens to other cars, when the only thing that really matters is what yours does.

whack it on and get it mapped. no problems, job done. sleep well.

If your happy with it then stay with it, however if you decide to sell your ppp ecu , you could get £300- £350+ for it and buy a STD ecu for £40 - £80 & either get that mapped or buy a bigger turbo, and map that .

Thats what i plan to do i think... maybe even get rid of UK spec car and get an STI - better place to start i think..

Thanks for everyone's help :thumb:

Heard ppp ecu with decat downpipe is a no no. What about a 100 cell sports cat though? Would you still get the same problems?

Anyone?

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