hi, just fitted my 02 sti uk (stock)with full 3" decat exhaust, also changed the up pipe and manifold but now when i boot it i get a kinda hiss sound like airs escaping from somewere quite hard to find as only does it once booted, also revs ok up to limit but top end @ about 110 mph it feels a bit judery.

I have checked all hoses that were taken off sti panel but no leaks.. and no engine checklight comes on, also once i have worked this problem out will i need to remap to get full power now decated ?

Cheers

 

a remap would definatly get you the most from the decat zorst, you dont have to remap but you may start to get overboost and over fueling so the safest thing would be to have it done,

as for the sound your hearing this may be the turbo you can hear, mine does it now ive decatted too. more of a whistle type noise rather than a hiss but i think yours is a different turbo to mine seen as yours is the STi

 

cheers 4 the quick reply, somebody else said it could be the turbo noise, i thought maybe mr garage guy had not put the air box back correctly or a bent hose, always best to see what the modders on the forum say

Next job ecu remap then

 

be very carefull indeed, fully decatting, up pipe and manifold could totaly screw up the AFR, needs to be checked for definate.

the juddering sounds like overboost, take it very steady till you get it checked out

 

hmm i think im gonna put the (downpipe) first cat back on after turbo because i can see the lambda sensor is before second cat then at least i can 1) save up some dosh 2) find a good mapper thats not a million miles away, cheers for your help guys

 

Is this a problem exclusively for STIs as I keep reading about decat=overboost and spikes?

 

nope, any scoob, or at a guess any turbo car.

the cats add a slowing point in the exhaust system so when you remove it you allow the gas to flow more freely. because the turbo works on exhaust gas to pressurise the inlet gas, you suddenly free up the exhaust gas and do the same with the inlet so it spikes.

some classics can (i emphasise some) get away with it, but always. and new age tend to not like it at all (although some do get away with it). it can alter the air fuel ratio so if you having a decat then personaly i'd at least have it checked out after fitting and if needs be mapped

 

Makes sense. Thanks for the reply. I have a decat downpipe waiting to be fitted, as well as the decat second pipe that is already fitted. I will leave the up pipe as it is for a mo. Will that make any difference without a remap, and will the aforementioned problems still be apparent?

Thanks

Myles
PS Sorry to hijack the thread tunesguy, and I hope the 110mph is on a private road!!!

 

More scaremongering!!

You're engine isn't going to blow up just because you've replaced the exhaust system. To get the best from it yes get a remap but all this about your engine being in jeoardy is complete and utter rubbish.

Your airflow metre is there for a reason. It measures the air going into your engine and fuels accordingly. By freeing up the flow with a new exhaust you'll be taking more air in at a faster rate. However, an exhaust system will only give a small increase in flow compared to a new bigger turbo which will definatley require a map.
There will be certain tolerances built into the system and a new exhaust will fall within them.

I know this because I had a tubular manifold, and a full 2.5 inch decat system on my RB5 this car did around 20,000 miles in this state without issue.

You'll get some pops and bang and the car will be noisier but please don't be worried about it the engine going pop because of an exhaust change. It wont!!

Hope that helps

Daz

 

would have thought with your tech knowledge you'd understand things a bit better than that.

ok heres a couple of questions. i'll even answer them for you

can too much boost destroy your engine if its high enough?

yes it can

can your car, after a decat, over boost?

yes it can

is over boost too much pressure so management backs off?

yes it is


so therefore it can kill your engine if the management isn't quick enough and the boost spikes to high.

so what i have said is correct, admitedly on the worst possible case, some classics get away without overboosting and some don't, new age tend to more often than not. so best bet, if you do decat, get it checked rather than doing it and going out, booting it and getting overboost.

now the last comment says its juddery, that sounds like overboost, now go read the top again.

 

Going back a few years John Banks had boost spike problems with a de-catted Bugeye STi. He eventually sorted it by drilling out the restrictor

Boost spikes not a problem on the de-catted bugeye WRX though

Shaun

 

Ta Daz. Pops and bangs are goooood! Thanks for your advice also!

 

Complete and utter drivel.
The amount of increased boost required to destroy an engine is NOT going to be caused by an exhaust change no matter how well it flows.
That's the bottom line!!!

 

Daz

The man talks sense.

Simon

 

Which man??

 

It might not destroy the engine, but as John Banks and others have found out decatting the bugeye STi may lead to loss of boost control and reduce drivability.

Does that make sense LOL

Shaun

 

Total loss of boost control just by changing the exhaust? Get real.

I cannot believe the rubbish I read on here some times. Next we'll be reading that not using the recommended windscreen wash will cause the whole car to corrode into a pile of dust.

Let me try and make myself clear. Changing the exhaust is not going to make your engine suddenly explode. Niether is it going to make your turbo overboost to the point the engine can't cope and goes bang.

Worst case scenario is a few pops and bangs out of the exhaust slightly higher fuel consumption and in the most extreme circumstances some slight iregularities on boost i.e a reduction in the car smoothness. It will hardly be noticeable, won't cause any damage and can be easily solved with a remap.

I still cant get over people are saying swapping an exhaust system will cause engine failure!!

I bet these people closed their Halifax accounts last week too!!

 

TOTALLY agree with daz all an exhaust does is remove the unwanted gases how ever you gain power buy the speed the gases are released into the atmosphere so i cant see how mayjor engine failure can be caused by a simple exhaust change, doing internal mods yes but otherwise


mat

 

By decatting from the turbo back you are just letting the crap out of your engine escape quicker.
You are also removing back pressure from the turbo, so everything moving away from engine cant see how damage can be done.

 

well all i'll say is you have been warned, you pays your money you takes your choice, can sit, type and argue all nightif people realy want to, which i dont lol

 

Dazdavies..

decatting the UK Bugeye STi led to problems with boost spiking....and problems with "spirited" driving.

Well documented all those years ago by John Banks, a marine engineer called Andy Forrest and another unknown by the name of Mark Aigin..

Shaun

 

Shaun,

I'm not disputing that what I'm disputing is the claims that your engine will blow up, or you'll and I quote " loose total boost control" just by changing an exhaust. I'm sure Andy, Mark and John would also agree with what I'm trying to say too.

I've said for best results get it mapped but it's not an absolute must and you're engine isn't going to go bang if you dont. People shouldn't be scaremongering saying this will happen. That's all i'm trying to get across.

Jesus! why cant people seem to grasp this.

I'll try this one last time.

CHANGING AN EXHAUST WITHOUT A REMAP WILL NOT CAUSE YOUR ENGINE TO GO BANG!!!.
I cannot put it any plainer than that folks

 

perhaps i am being a bit alarmist, however it is the absolute worst case

 

Daz..

I think we all agree that de-catting a bugeye STi won't make it explode but may have problems with boost spikes.. LOL

Shaun

 

Quite possibly but this won't happen in all cases. Even if there are boost spikes they won't be anywhere near big enough to destroy an engine.

ps It's nice to have a debate on here for a change without it turning into all out warfare

 

Daz

I've got a WRX Bugeye with a few mods

The Bugeye STi is a bit of a dark horse as Subaru changed so many things from the Classic STi.....but just failed LOL

It's still my favourite for bang per buck performance with minimal mods....cheap as chips

Shaun

 

I'm currently considering binning my type R project infavour of either a bugeye STI or a WR1. Can't quite bring myself to do it after all the work has gone into the shell.

 

lol, tbh i think we all agree though that the outcome of decatting is very much a not gaurentied to either work properly or not work properly lol

 

What is gauranteed is it won't blow your engine up

 

stranger things have happened