Retards and Decats

[adam cool dude]

I have decatted my skyline. A big increase in power (20+ hp) sounds better and quicker spool up on the turbo also less back pressure.

Decatting an NA car is pointless though as it is reducing back pressure which is good for NA engines.

Negative my car is N/A and has quite a large bore. 2.5" to be precise which is tryed and proven for the SR20. My car has 2.5" downpipe and 2.5" mandrel bent system from the cat back. The cat i had on there which was oem spec lost me 4hp, which i know is not a lot but it all adds up.

 

[Gaijin]

i know a guy that dynod his car with oem cat (96 golf) vs 200 cell, 100 cell and then decat

no repeatable improvements at all

Well its obviously going to depend on the car - a 400bhp turbocharged car is always going to yield better results than a 96 golf!

 

[MeEsH BaKkA]

I have an astra vxr (Oh the shame ) with the Remus upgrade exhaust system. The standard car has a 200cell cat in the down pipe and a 400cell main cat, the Remus is a touch bigger bore and has one 100cell sports cat and the diffrence is huge! Quicker spool by around 4-500 revs and holds max boost for another 500 revs also bumped my power up by 17bhp and torque around the same in lbft.

Oh and it's much louder and pops and bangs which realy gets the girls at mcdonalds going, because everyone knows loudness=chav

 

[MikeHiow]

stupid kids and decats

a lot of cats now have pre and post lambdas. take out the cat, the second lambda gets unexpected signals and puts the ecu in safe mode. the car is slower and overfuels for component protection hence the banging and popping... stupid chavs.

have you looked down a modern cat lately? honey comb structure. you can see through it easily

i know a guy that dynod his car with oem cat (96 golf) vs 200 cell, 100 cell and then decat

no repeatable improvements at all

Stupid kids, writing stupid stuff on the internet.

My map disables the second lambda sensor allowing me to fit a decat, as does most remaps for cars running with a similar setup. The pops and bangs are not a result of overfueling in "safe mode". The other point is, many cars only use that second lambda sensor to throw up an emissions light, making no adjustment to how the engine is run.

Someone already mentioned here that its pretty much pointless on many NA cars, so I'm not surprised that your imaginary friends imaginary ****box saw no improvements with his imaginary tests.

Thanks.

 

[Gaijin]

The pops and bangs are not a result of overfueling in "safe mode".

Indeed some evo owners intentionally "map in" pops and bangs, as a mild, antisocial, ghetto form of anti lag.

I have no such plans to do so.

 

[Simon]

stupid kids and decats

a lot of cats now have pre and post lambdas. take out the cat, the second lambda gets unexpected signals and puts the ecu in safe mode. the car is slower and overfuels for component protection hence the banging and popping... stupid chavs. l

Lol yes thats correct, the ECU thinks the cat is broke and so overfuels to properly finish it off.

The secondary lambda sensor is only there to check the function of the Cat, if the cat does fail then the sensor indicates this to the ECU which causes a check engine light, it doesnt put the car in limp home mode.

 

[Simon]

I have decatted my skyline. A big increase in power (20+ hp) sounds better and quicker spool up on the turbo also less back pressure.

Decatting an NA car is pointless though as it is reducing back pressure which is good for NA engines.

Complete myth, no 4 cylinder NA engine needs backpressure.

My S2000 has a sharper throttle and sounds better with a decat.

 

[Matt82]

Stupid kids, writing stupid stuff on the internet.

My map disables the second lambda sensor allowing me to fit a decat, as does most remaps for cars running with a similar setup. The pops and bangs are not a result of overfueling in "safe mode". The other point is, many cars only use that second lambda sensor to throw up an emissions light, making no adjustment to how the engine is run.

Someone already mentioned here that its pretty much pointless on many NA cars, so I'm not surprised that your imaginary friends imaginary ****box saw no improvements with his imaginary tests.

Thanks.

dear oh dear, who peed on your chips?

 

[Simon]

dear oh dear, who peed on your chips?

Probably the same man who **** in your burger?

 

[MikeHiow]

Indeed some evo owners intentionally "map in" pops and bangs, as a mild, antisocial, ghetto form of anti lag.

I have no such plans to do so.

I'm not sure I'd be keen on that, but its an inherent feature of a turbo engine anyway, seeing as extra fuel is an easy way to cool things down.

 

[NathanE]

If you are getting fumes in the cabin as the result of a decat, I'd suggest your friend tries fitting it correctly.

The ST exhaust is actually quite subdued as standard, and is hardly offensive with the decat either. This is my next mod.

Not the best example on over-run, but just listen to it when he drives off

The problem with that is that people are going to look around for a supercar/sportscar and then be greeted by a Focus.

 

[Janesy B]

Hehehe

 

[probedb]

I know a few mates who have now had their cars decatted, may I ask what the attraction is?

Totally depends on the car. You don't really want much back pressure in a turbo car so removing it removes flow restrictions and gives more power.

My car is actually quieter than before as the old exhaust was louder with a cat in place than the current one with a straight through pipe.

The exhaust fumes smell no different either.

The car is also an old enough import that it doesn't actually need the cat for an MOT which is handy.

 

[Matt82]

Lol yes thats correct, the ECU thinks the cat is broke and so overfuels to properly finish it off.

The secondary lambda sensor is only there to check the function of the Cat, if the cat does fail then the sensor indicates this to the ECU which causes a check engine light, it doesnt put the car in limp home mode.

in my EXPERIENCE, ive seen where the ecu will trim back the fuel mixture further and further try and compensate. the fuel trim ends up out of spec and hence limp mode and CEL lights.

why do you think people bother to make up emulators or disable the secondary lambda function if its only role was to trigger a light?!

 

[Dr Who]

They've done it wrong. Removing the cat should not make the car either massively louder or smellier.

Except for the smell of all the unburnt fuel that is now not being catalysed?

 

[MikeHiow]

in my EXPERIENCE, ive seen where the ecu will trim back the fuel mixture further and further try and compensate. the fuel trim ends up out of spec and hence limp mode and CEL lights.

why do you think people bother to make up emulators or disable the secondary lambda function if its only role was to trigger a light?!

So a minute ago you were telling us it caused the ECU to dump more fuel in to protect components, and now you're telling us it trims the fuel mixture until it fits out into limp mode? If you're going to spout uneducated crap, please at least make it consistent.

People disable them, make emulators, spacers, and even mini cats for the sensor to do just that, turn the annoying big yellow light off on their dash board.

 

[Simon]

in my EXPERIENCE, ive seen where the ecu will trim back the fuel mixture further and further try and compensate. the fuel trim ends up out of spec and hence limp mode and CEL lights.

why do you think people bother to make up emulators or disable the secondary lambda function if its only role was to trigger a light?!

You'll have to tell me more about this then, I'm more than aware of emissions protection ECU strategies for many OEMs.

The CEL is only to indicate the Catalyst isn't working. The secondard sensor should be leaner than the primary (due to the cat converting HC to CO2), if this difference isn't big enough then it suggests a drop in the catalyst's efficiency.

Sticking in more (or less according to your second post) won't suddenly make the cat work again. The reason for a CEL when you decat is that there is no difference between the primary and secondary sensor.

Remind me what you do again, all I tend to read is stuff you make up on the spot.

 

[Leeum]

Saw a big difference ditching the CAT with my 1.6 16V 4 banger - engine seems much more willing to rev. The smell is noticeable when moving the car in/ out the garage but not on the move. If you can smell it from the passenger seat, something is seriously wrong.

My car has dual lambdas, but the post CAT sensor is placed in a metal sleeve so it constantly reads 'clean' air. The sleeve is only to stop the ECU throwing the light on the dash though - the car runs no differently with the second lambda plumbed into the exhaust or unplugged from the loom.

Matt: were you not getting confused with removing the pre CAT lambda sensor? That's the one which adjusts the fuel trims and can put a car in 'limp mode', so to speak.

Because everyone else is posting them...

 

[Gerard]

If you are getting fumes in the cabin as the result of a decat, I'd suggest your friend tries fitting it correctly.

The ST exhaust is actually quite subdued as standard, and is hardly offensive with the decat either. This is my next mod.

Not the best example on over-run, but just listen to it when he drives off

Sounds like water going down a rattling gutter.

 

[thedazman67]

I've got a decat to make the car breathe better, its a bit louder but no popping or banging what so ever. Also it getts refitted by my MOT tester for the MOT then he takes it off again once its passed.