Is "over-spooling" when the turbo spins faster then it is made to/does as standard? Does this not happen when the engine is remapped? ie. the boost is increased to get more power?

Does anyone know which part of the vRS exhaust is the most restrictive? is it the cat or backbox? Surely even custom made exhausts from such company's as milltek put more strain on the turbo then the standard one as they are more "free flow" and allow the turbo to spin faster? :S Cheers.

Can anyone give me an idea how much it will cost at my local exhaust place to cut the 'cat' out? do you have to chop the back box out to get any difference in noise or will just the 'decat' do the job (performance aside)?

Thanks, John

The noise will change but turbos prefer free flowing exhausts which is why mines is straight through with no boxes at all! All I have is the tail piece

Is "over-spooling" when the turbo spins faster then it is made to/does as standard? Does this not happen when the engine is remapped? ie. the boost is increased to get more power?

Does anyone know which part of the vRS exhaust is the most restrictive? is it the cat or backbox? Surely even custom made exhausts from such company's as milltek put more strain on the turbo then the standard one as they are more "free flow" and allow the turbo to spin faster? :S Cheers.

Bump - anyone know the answers?

See I've read different things on here with exhausts but here's wat I've been told

A turbo hates back pressure, the quicker you get the exhaust gasses out the better. And it can actually increase the life of you're turbo because it can breathe a whole lot better. So the best bet is no boxes just straight through free flowing style

Depends on engine type and also type of turbo. Some petrol engines require a certain amount of back pressure for exhaust scavenging. Diesels do not need exhaust scavenging, so the less back pressure the better, unless the car has a VNT turbo, in which case some back pressure is required to prevent over spooling the turbo. The VNT is adjusted relative to engine load and boost demand. It is simple air flow physics, if you remove the back pressure from a VNT setup, the chance of over boost is very real.

Cue the "mines been running decat for 100 years and ragged from cold, and has never gone wrong."

While a diesel only gets a smoke density test at MOT time, and a CAT is not a legal requirement, you still have to consider the environment.

Will a decat destroy the turbo, possibly. Will a decat make the turbo last longer. NO, it's a mechanical impossibility.

I'm not gonna argue with what you say regardless how I drive the car.

As I said I was going on stuff I've been told. In no way am I saying I'm an expert! But regardless of any wee digs I'm not gonna waste my time arguing with you

But I'll end by saying, my car I pay for it, don't like the fact that I rag it from cold fine. If I wanna mention it I will. Don't like it don't read my posts simples!

Mr moggy was only giving the bloke some advice. Why not just read and maybe take a bit of advice from someone who knows a bit about what they are talking about? Not everyone is trying to pick a argument with you. Chill out a bit!

Back OT your car does sound rather nice, even more so for a diesel.

Matt

I've had a bad day, needed a vent so I'll happily apologise.

I love the sound off my car for a diesel, I never once thought it'd sound as good as it does

Depends on engine type and also type of turbo. Some petrol engines require a certain amount of back pressure for exhaust scavenging. Diesels do not need exhaust scavenging, so the less back pressure the better, unless the car has a VNT turbo, in which case some back pressure is required to prevent over spooling the turbo. The VNT is adjusted relative to engine load and boost demand. It is simple air flow physics, if you remove the back pressure from a VNT setup, the chance of over boost is very real.

Cue the "mines been running decat for 100 years and ragged from cold, and has never gone wrong."

While a diesel only gets a smoke density test at MOT time, and a CAT is not a legal requirement, you still have to consider the environment.

Will a decat destroy the turbo, possibly. Will a decat make the turbo last longer. NO, it's a mechanical impossibility.

Ok thanks very much for your informative reply Moggy!

So to sum up - if my car has a "VNT turbo" then it would not be recommended to de - cat / de back box?

Does my car have one? I thought it had a "KKK turbo" :S

Thanks again!

P.S will having my car decatted and/or removing backbox put the engine management light on?

Edited 14 April, 201016 yr by Thirdtimeluck

also why is it only the (Garrett?) VNT turbo that requires back pressure? My car is 05 and pretty sure has a kkk turbo so is it fine to decat it without overspool problems then?

Thanks.

also why is it only the (Garrett?) VNT turbo that requires back pressure? My car is 05 and pretty sure has a kkk turbo so is it fine to decat it without overspool problems then?

Thanks.

makes no difference if it's a KKK or a Garrett, you car's got a VNT turbo

Depends on engine type and also type of turbo. Some petrol engines require a certain amount of back pressure for exhaust scavenging. Diesels do not need exhaust scavenging, so the less back pressure the better, unless the car has a VNT turbo, in which case some back pressure is required to prevent over spooling the turbo. The VNT is adjusted relative to engine load and boost demand. It is simple air flow physics, if you remove the back pressure from a VNT setup, the chance of over boost is very real.

Cue the "mines been running decat for 100 years and ragged from cold, and has never gone wrong."

While a diesel only gets a smoke density test at MOT time, and a CAT is not a legal requirement, you still have to consider the environment.

Will a decat destroy the turbo, possibly. Will a decat make the turbo last longer. NO, it's a mechanical impossibility.

why will removing the cat damage a VNT turbo on a diesel?

makes no difference if it's a KKK or a Garrett, you car's got a VNT turbo

why will removing the cat damage a VNT turbo on a diesel?

Ok thanks for clearing that up

and yes do please tell!

also if any one knows the answer to me previous questions that would be super great :

1. Is "over-spooling" when the turbo spins faster then it is made to/does as standard?

2. Does this not happen when the engine is remapped and the turbo boost increased to get more power?

3. Surely even custom made exhausts specially designed for the car from such company's as milltek put more strain on the turbo then the standard one as they are more "free flow" and allow the turbo to spin faster?

4. Which part of the vRS exhaust is the most restrictive?Cat or backbox?

Edited 14 April, 201016 yr by Thirdtimeluck

My cars an 05 plate aswell. Theirs always a mixed response with de cats which is why I just took the plundge and done it after my remap

The standard VRS exhaust is only slightly restrictive. The back box is HUGE and mostly contains bounce baffles to reduce noise by resonance cancellation. The best way to de-cat, is to remove cat and then have the car mapped. The map can be set up to prevent over spooling by smoothing out the power delivery of the torque.

The thing is though, even though the cat is an open loop system on a diesel, it still removes vast quantities of poisonous gas, that otherwise goes into the atmosphere. That's a moral choice for each individual I guess.

I have seen diesels with straight through exhausts fail an MOT on noise levels. If you have a car mapped for straight through exhaust and it fails the MOT and you have to fix a backbox, ideally it should be mapped again.

VNT Turbos are complex. The variable vanes move so that gas flow rate causes blade speed to remain fairly constant before boost occurs. This reduces turbo lag. Once the taps are fully open, a VNT acts like any other turbo.

The process involved to produce the required boost is also complex. You have the MAF and boost pressure sensors, throttle position, and injector duration, all used to tell the N75 valve, how far to move the VNT actuator. All the while, the exhaust wheel in the turbo, is pushing gas out of the exhaust, against a back pressure, calculated by engineers in white coats, with a slide rule, and PHD in astro physics

If you remove the back pressure, the turbo can over spool, depending on the mapping, and to some degree your luck. Over spool can do one of several things. Oil pressure is finite, and if the turbo spins too fast, the bearing can run dry, and bang, the turbo shaft snaps, or the bearing melts. The turbo bearing is a shell type bearing that requires a constant oil film between it and the shaft.

You can exceed the shaft load if the turbo isn't balanced perfectly. Even a few grams of soot extra on one blade, can weigh a hell of a lot, when the blades are spinning at 200,000 RPM.

The standard VRS exhaust is only slightly restrictive. The back box is HUGE and mostly contains bounce baffles to reduce noise by resonance cancellation. The best way to de-cat, is to remove cat and then have the car mapped. The map can be set up to prevent over spooling by smoothing out the power delivery of the torque.

The thing is though, even though the cat is an open loop system on a diesel, it still removes vast quantities of poisonous gas, that otherwise goes into the atmosphere. That's a moral choice for each individual I guess.

I have seen diesels with straight through exhausts fail an MOT on noise levels. If you have a car mapped for straight through exhaust and it fails the MOT and you have to fix a backbox, ideally it should be mapped again.

VNT Turbos are complex. The variable vanes move so that gas flow rate causes blade speed to remain fairly constant before boost occurs. This reduces turbo lag. Once the taps are fully open, a VNT acts like any other turbo.

The process involved to produce the required boost is also complex. You have the MAF and boost pressure sensors, throttle position, and injector duration, all used to tell the N75 valve, how far to move the VNT actuator. All the while, the exhaust wheel in the turbo, is pushing gas out of the exhaust, against a back pressure, calculated by engineers in white coats, with a slide rule, and PHD in astro physics

If you remove the back pressure, the turbo can over spool, depending on the mapping, and to some degree your luck. Over spool can do one of several things. Oil pressure is finite, and if the turbo spins too fast, the bearing can run dry, and bang, the turbo shaft snaps, or the bearing melts. The turbo bearing is a shell type bearing that requires a constant oil film between it and the shaft.

You can exceed the shaft load if the turbo isn't balanced perfectly. Even a few grams of soot extra on one blade, can weigh a hell of a lot, when the blades are spinning at 200,000 RPM.

Ok thanks for the heads up - don't think ill do a the "pikey" decat but does the Milltek cat back system or "Large-Bore Downpipe and Catalyst Replacement" still produce these undesired effects?

http://www.millteksport.co.uk/exhaust.products.cfm?variantid=102

fair enough, but to my uneducated brain it doesn't sound like a VNT turbo would fair any better or worse than a more traditionally wastegated turbo :S

Ok thanks for the heads up - don't think ill do a the "pikey" decat but does the Milltek cat back system or "Large-Bore Downpipe and Catalyst Replacement" still produce these undesired effects?

http://www.millteksport.co.uk/exhaust.products.cfm?variantid=102

Honestly I don't know, it depends how much research and development went into the products. The tuning market is worth billions of pounds, and frankly a lot of it, is badly engineered over priced tat. Milltek have a pretty good reputation though. But then so did Toyota

Honestly I don't know, it depends how much research and development went into the products. The tuning market is worth billions of pounds, and frankly a lot of it, is badly engineered over priced tat. Milltek have a pretty good reputation though. But then so did Toyota

:S

I'm thinking that "large bore downpipe" is just a bit of shiny pipe with a high price tag

I may save for a nice cat back system from them.. we will see

So I gather the cat is the most restrictive part when compared to the back box? - that generally (it seems) can be replaced to a nice cat back system without and problems?

Edited 14 April, 201016 yr by Thirdtimeluck

:S

I'm thinking that "large bore downpipe" is just a bit of shiny pipe with a high price tag

I may save for a nice cat back system from them.. we will see

So I gather the cat is the most restrictive part when compared to the back box? - that generally (it seems) can be replaced to a nice cat back system without and problems?

That would do just fine. Or leave it standard and spend the money on women and alcohol

^ What Moggy said - give the lovely lady a 'treat' :p