Put decat and removed mid box, but lost power?!

[The Fatty]

today i had a fun day putting my decat back on after mot, and for the first time fitting a str8 thru center section. the exhaust sounds sweet, so load it set a car alarm off when i drove past lol...but...

im sure theres a loss of power, seems to be really noticable to :S

the engine sounds a bit like a bag of spanners also, maybe its burning to week? i know engines need some back pressure to work 100%, maybe iv got to little now?!

any thought/ideas please!

 

[u33db]

Backpressure is mainly controlled by the manifold...anything backwards of that won't really do much. You'll find the decat will give a bit more power top end but perhaps reduce torque at low revs...you won't have lost power, you'll just have altered where it kicks in.

 

[The Fatty]

^^ well mines completly obisit, it has power from 3k to 4k anything else it just makes a rattly noise and has little power...? maybe i need to get more petrol going in there...

 

[Lunner]

Reset the ECU

GrpN/A rally clios had strasight through exhsusts vbar a tiny silencer either int eh middle or back depending on if they were 1.8/2.0

As u33db says the manifold creats the back pressure, you could run with alomost no exhaust and still ahver a silimar amoutn of back pressure

 

[The Fatty]

i'll give that a try thanks....

but how do you work that out ^^^ ? the point of removing a cat is to allow more to flow thru, thus having less back preesure surely?!!!!

 

[u33db]

Removing the cat will help but its more complicated than that...depends on pipe bore, length of pipe etc

 

[Thomss]

Is this the same for 182's? Could you lose power with decat?

 

[theduck]

almost any performance mod done incorrectly can loose power.

 

[fmp_]

the exhaust will be tuned from the factory, and whislt putting a decat on will increase power (as no thick cat for gasses to get through), it will not porduce as much power as a decat, but with an expansion box/silencer.

taken from gmc motorsports site, about their BTB exhaust for the saxo (which a BTB for the clio 182 will be available soon)....

Another reason to fit the BTB unit is a bit more technical, most people want to take the CAT off as they sap so much power, the problem is taking the CAT out and substituting a straight pipe is not really correct. OK, this will certainly give you the power back the CAT takes away through restriction but this causes another problem. When exhaust gas comes out of the cylinder it produces sound/pressure waves that travel up and down the exhaust system, if these S/P waves can be controlled correctly they can be harnessed to draw extra gas from the cylinder and so make the engine more efficient. These S/P waves are controlled by the cam timing and the pulses go down the exhaust until they meet the first expansion chamber, silencer, CAT (anything that causes the size of the exhaust bore to rise significantly). As soon as the gas reaches this expanded section, the S/P wave stops and goes back to the cylinder head, as this wave hits the back of the valve it bounces back and causes a suction pulse that helps pull more gas out the next time the valve opens. The problem is the distance from the first expanded section to the cylinder head is critical, to get this pulse action working correctly, if this distance is not correct the wave goes back at the wrong time and hits the gas coming out of the valve and so stops the gas coming out rather than helping it. This is what happens when you take the CAT out, you no longer have an expanded section in the correct place and the S/P wave will go down the system until it reaches the first silencer box before returning. Before CAT's were fitted, this was the reason all cars had an expansion boxes in a similar position to where they now fit CAT's.

 

[u33db]

Interesting although i doubt you'll notice any difference on a road car, especially since so many other things (beyond the exhaust) will alter the conditions.

 

[benji&eka]

you will lose out lower in the rev range with a decat, don't forget the engine has been tuned for use with the cat.

 

[The Fatty]

the exhaust will be tuned from the factory, and whislt putting a decat on will increase power (as no thick cat for gasses to get through), it will not porduce as much power as a decat, but with an expansion box/silencer.

taken from gmc motorsports site, about their BTB exhaust for the saxo (which a BTB for the clio 182 will be available soon)....

Another reason to fit the BTB unit is a bit more technical, most people want to take the CAT off as they sap so much power, the problem is taking the CAT out and substituting a straight pipe is not really correct. OK, this will certainly give you the power back the CAT takes away through restriction but this causes another problem. When exhaust gas comes out of the cylinder it produces sound/pressure waves that travel up and down the exhaust system, if these S/P waves can be controlled correctly they can be harnessed to draw extra gas from the cylinder and so make the engine more efficient. These S/P waves are controlled by the cam timing and the pulses go down the exhaust until they meet the first expansion chamber, silencer, CAT (anything that causes the size of the exhaust bore to rise significantly). As soon as the gas reaches this expanded section, the S/P wave stops and goes back to the cylinder head, as this wave hits the back of the valve it bounces back and causes a suction pulse that helps pull more gas out the next time the valve opens. The problem is the distance from the first expanded section to the cylinder head is critical, to get this pulse action working correctly, if this distance is not correct the wave goes back at the wrong time and hits the gas coming out of the valve and so stops the gas coming out rather than helping it. This is what happens when you take the CAT out, you no longer have an expanded section in the correct place and the S/P wave will go down the system until it reaches the first silencer box before returning. Before CAT's were fitted, this was the reason all cars had an expansion boxes in a similar position to where they now fit CAT's.

im guessing this wouldnt apply to mine then, as my decat is simpley a real cat with the insdes removed, thus being an expansion chamber yeah?

 

[fmp_]

applys to 99% of cars.

 

[Thomss]

Hmmm I'm getting a de-cat on Tuesday to do with my AAS CAt-back system.
You think I will lose low down power with a de-cat on?
Still a little un-shure to get a de-cat or not

 

[Dave.]

Reset the ECU

How the hell do you do that?? will it matter if i have a rp N ecu?? :S

 

[The Fatty]

did a 0-60 today...around 12 to 14 seconds...wasnt the best run think it could have been a bit faster...have had it faster with cat on...

will reset ecu tonight, simply disconnect bat yeah? gd gd

 

[Dave.]

dont think you will gain a massive amount without the cat tbh fatty, as your not going to have a massive amount of gasses as the engine is quite small, will make a difference, maybe feel a bit revvyer but doubt youd get too much more m8

 

[Lunner]

Removing the innards is you problem.

The exhaust gasses enter that and swirl around creating turbulance, and slow down, aim is to getvteh gasses out as wuick as possible, hence straight through sections, and strraight through silencers.

To reset the ECU simply unplug the battery negative terminal for an hour or so.

You can't do an accurate 0-60 on a stop watch, and certainly not with teh speedo, as on clios true 60mpoh is about 65 on the clocks

 

[Lunner]

dont think you will gain a massive amount without the cat tbh fatty, as your not going to have a massive amount of gasses as the engine is quite small, will make a difference, maybe feel a bit revvyer but doubt youd get too much more m8

You do NOT loose low down power with a cat, this is a myth.

You will gain possibly 1-2 bhp, more if you have it mapped properly. What you will notice is it will pull alot better towards the higher revs, when you have more exhaust gasses being expelled, and then engine will feel 'ferrer' at higher revs.

I can supply brand new de-cats for all mk1 clios (MK1 CLIOS ONLY) for £35 delivered