De-cat on standard map, anyone had problems?

[TehMarchant]

So I am thinking on hitting my cat out and I was wondering if anyone has actually had first hand problems with doing this on the stock map.

 

I don't mean a mate of yours having problems but has anyone personally had problems with this?

 

Ryan

[sepulchrave]

Why bother with this wanton act of vandalism? It doesn't make the engine any more powerful, it doesn't make it sound any better, it just makes the emissions worse which is bad for you and everyone around you, diesel particulates cause lung disease and can trigger asthma attacks.

[JamieFabia6Y]

So I am thinking on hitting my cat out and I was wondering if anyone has actually had first hand problems with doing this on the stock map.

 

I don't mean a mate of yours having problems but has anyone personally had problems with this?

 

Ryan

 

I had no problems with mine when fitting a full milltek system with Decat... Then had a mufflerectomy

I personally love the grunt of mine when flat out!

Some people aren't very keen on the noise but all down to personal preference I suppose!

And if you don't want to contribute to harmful emissions or the noise then consider a high-flow sports cat...?

[Jrjg]

No problems here with mine, although if I could of had a sports cat downpipe made to fit a gtb I would of done. As the fumes from the car now smell awful. Not to mention the little cloud I get every morning on startup.

JRJG

[hutchysrs50]

I like my cat

[Hardcore]

I ran a full  straight through 2.5" turbo back system on my old PD130 Ibiza FR on a standard map.
I got a small amount of boost spike at lower revs but not enough to cause any danger for the turbo or any problems with anything else. 
EML didn't come on ever and never went into limp mode either.

 

 

Why bother with this wanton act of vandalism? It doesn't make the engine any more powerful, it doesn't make it sound any better, it just makes the emissions worse which is bad for you and everyone around you, diesel particulates cause lung disease and can trigger asthma attacks.

 

It makes the engine more powerful at lower revs by allowing the turbo to hit full boost earlier with the lack of restriction beside it. 
If you're driving the car hard as well all the time it can help prolong the life of the turbo as there isn't a red hot cat beside it, slowly cooking the turbo over time.
I personally think it sounds much better.

The cat does nothing to reduce diesel particulate emissions. That's a DPF you're thinking of.

[sepulchrave]

I ran a full  straight through 2.5" turbo back system on my old PD130 Ibiza FR on a standard map.

I got a small amount of boost spike at lower revs but not enough to cause any danger for the turbo or any problems with anything else. 

EML didn't come on ever and never went into limp mode either.

 

 

 

It makes the engine more powerful at lower revs by allowing the turbo to hit full boost earlier with the lack of restriction beside it. 

If you're driving the car hard as well all the time it can help prolong the life of the turbo as there isn't a red hot cat beside it, slowly cooking the turbo over time.

I personally think it sounds much better.

The cat does nothing to reduce diesel particulate emissions. That's a DPF you're thinking of.

 

Read this:

 

https://en.wikipedia.org/wiki/Catalytic_converter#Diesel_engines

 

None of what you say is true on a standard unmapped engine, the standard exhaust system including cat is not restrictive at all until much larger turbos are fitted, there is enough headroom in the injectors and inlet/exhaust setup to allow ~220BHP, no other supporting mods are needed, an FMIC is recommended due to rapid heat soak of the standard IC, but other than a turbo and a map nothing else is necessary.

Turbo spool is controlled by the ECU varying the pitch of the vanes via the N75 vacuum solenoid, it is not affected by the exhaust system. EGT is purely a function of how rich the map is, rich maps cook turbos, nothing to do with the cat at all.

How you justify your own mods is a matter for you, I'm simply trying to provide accurate and responsible advice to the OP.

[dannycook96]

no problems so far mate.

[Hardcore]

Read this:

 

https://en.wikipedia.org/wiki/Catalytic_converter#Diesel_engines

 

None of what you say is true on a standard unmapped engine, the standard exhaust system including cat is not restrictive at all until much larger turbos are fitted, there is enough headroom in the injectors and inlet/exhaust setup to allow ~220BHP, no other supporting mods are needed, an FMIC is recommended due to rapid heat soak of the standard IC, but other than a turbo and a map nothing else is necessary.

Turbo spool is controlled by the ECU varying the pitch of the vanes via the N75 vacuum solenoid, it is not affected by the exhaust system. EGT is purely a function of how rich the map is, rich maps cook turbos, nothing to do with the cat at all.

How you justify your own mods is a matter for you, I'm simply trying to provide accurate and responsible advice to the OP.

I'm providing accurate first hand information as well.

Before my free flow exhaust system was fitted the car would boost to approx 1.4bar and hold it there through all the rev range.

It was progressive power delivery and and with the tyres i was running, if i floored it in the went it would sometimes spin the tyres a bit in second (in the wet) (without touching the clutch or coming off a corner) but never in 3rd.

After the exhaust system was fitted with the same stuff everywhere else on the car it was able to spin the wheels much more violently if flooring it in the wet and would occasionally do it in 3rd as well.

Peak boost was also up to 1.52 bar and rather than being a progessive power delivery like before it was a much larger surge of power when the turbo hit full boost. 

I've been told the boost spike happens due to the turbo overspooling itself for a moment befure the ECU can adjust the fuel. The same reason why cars with generic maps on them sometimes can throw an overboost fault code after having a decat done.

The turbo started to boost about the same RPM, but hit full boost approx 100-200rpm sooner on my Ibiza

You are correct in the fact that the exhaust system is fine for cars up to 220bhp but that's not evidence that gains can't be made from changing the exhaust system itself. 

Here's a real world dyno where real gains were made simply by removing the backbox. (6bhp)

 

 

Edited 4 July, 2016 by Hardcore

[sepulchrave]

Here's a real world dyno where real gains were made simply by removing the backbox. (6bhp)

 

 

 

...and remapping, hardly comparing apples with apples, the remap alone could have found the extra power, no need to remove the backbox.

 

Excuse my scepticism but I have masses of experience with tuning all types of petrol engines from singles all the way to V8's, turbo and N/A, and I can tell you that the exhaust system on a petrol FGT can indeed make a big difference but diesel VNT's simply don't obey the same rules at all, this is largely due to the much lower EGT and the higher mass of the end gases.

 

I'm sorry but 6BHP difference between two separate runs is well within the margin for error for a rolling road, you could get that just by leaving the car overnight so the intercooler was stone cold before the run. The black-eye dude is SELLING something.

 

Engineers painstakingly developed the standard exhaust system to maximise performance and economy and minimise emissions, not a mechanic who got a slap from the missus for coming home ****ed.

[Hardcore]

...and remapping, hardly comparing apples with apples, the remap alone could have found the extra power, no need to remove the backbox.

 

Excuse my scepticism but I have masses of experience with tuning all types of petrol engines from singles all the way to V8's, turbo and N/A, and I can tell you that the exhaust system on a petrol FGT can indeed make a big difference but diesel VNT's simply don't obey the same rules at all, this is largely due to the much lower EGT and the higher mass of the end gases.

 

I'm sorry but 6BHP difference between two separate runs is well within the margin for error for a rolling road, you could get that just by leaving the car overnight so the intercooler was stone cold before the run. The black-eye dude is SELLING something.

 

Engineers painstakingly developed the standard exhaust system to maximise performance and economy and minimise emissions, not a mechanic who got a slap from the missus for coming home ****ed.

 

The standard exhaust system also is built to minimise noise which reduces efficiency at certain RPM ranges due to restricting the flow of exhaust gasses.

I studied Automotive Engineering for a few years at college many moons ago before working in the motor trade so i'm well aware of how things are designed.

The 6bhp gain on the video was peak power. There may have been bigger gains in either torque or bhp at lower RPM ranges. You're right, it's possible that it was done at a different day where humidity or ambient air temp was different but coupled with my own experience and dozens of others on various forums with the same engine i'm convinced that a de-cat will help the turbo reach peak boost quicker and a full 2.5" turbo back system gives a good torque increase over the lower rpm range.

If you think that a de-cat or free flow exhaust on a PD diesel engine doesn't affect anything then why did mines suddenly have a boost spike from it's regular 1.40bar before the exhaust to 1.52bar on it's standard map?

Why was i getting much more aggressive wheelspin in the wet and a more aggressive delivery of power when coming onto full boost?

 

[expostmanpat]

I loved mine, no problems. As for any advantages, well it was the only mod to the engine and imo it sounded better, oh and it would sit at 135 mph all day (gps) with cruise set on the autobahn but i never tried the same trick with the original exhaust so dunno

[sepulchrave]

 

The standard exhaust system also is built to minimise noise which reduces efficiency at certain RPM ranges due to restricting the flow of exhaust gasses.

I studied Automotive Engineering for a few years at college many moons ago before working in the motor trade so i'm well aware of how things are designed.

The 6bhp gain on the video was peak power. There may have been bigger gains in either torque or bhp at lower RPM ranges. You're right, it's possible that it was done at a different day where humidity or ambient air temp was different but coupled with my own experience and dozens of others on various forums with the same engine i'm convinced that a de-cat will help the turbo reach peak boost quicker and a full 2.5" turbo back system gives a good torque increase over the lower rpm range.

If you think that a de-cat or free flow exhaust on a PD diesel engine doesn't affect anything then why did mines suddenly have a boost spike from it's regular 1.40bar before the exhaust to 1.52bar on it's standard map?

Why was i getting much more aggressive wheelspin in the wet and a more aggressive delivery of power when coming onto full boost?

 

 

I'm sorry but your first sentence is just nonsense, the standard exhaust system isn't restrictive at all until larger turbos with higher gas flows come into play. This is at about 220BHP, so until you have a large hybrid increasing the pumping efficiency of the engine then the exhaust makes no difference. There are hundreds of forum members who know this, it's common knowledge.

 

Your argument that changing the exhaust system changed the characteristics of the power delivery is entirely reasonable, why you think that boost spikes are desirable is beyond me but my argument rests on the fact that you CANNOT have more BHP unless you have more air and more fuel and both these things come from a remap, not from an exhaust system. If you like lots of noise and pollution then go for it but it will NOT make your car any faster.

[faboka vrs]

I've seen decats cause turbo's to over boost low down on some cars and then not on others. Tweak the n75 map low down to bring it back and your left with it being the same as before you chucked money at your car to remove the cat.

The vrs has been around since 2003. Many people have fitted revo, jabba, custom code, impossible performance, forge, oscarli, awesome, shark, etc etc. Fitted decats, "performance exhausts", "performance airfters" removed the EGR to "improve flow", had the map tweaked and then dyno'd again. Results pretty much same as it was with just the remap.

You will never Google a true comparison as no one advertises or probably bothers to log air to fuel ratio on a diesel. Hates off to the dyno operator that log AFR and use this to setup the fuelling in the maps. Most just dump a load more fuel in, seen X% across the board many times. Customer then comes along or back with a super dupper exhaust and airfilter and wants the map tweaked. Mapper just dumps more fuel in making it run richer. Hay presto more torque lower down but not much peak power if any due to the turbo on its peak of flow. Or they up the boost and more fuel. But wait you could have just done all of this on the standard hardware and saved a few quid.

[Hardcore]

I'm sorry but your first sentence is just nonsense, the standard exhaust system isn't restrictive at all until larger turbos with higher gas flows come into play. This is at about 220BHP, so until you have a large hybrid increasing the pumping efficiency of the engine then the exhaust makes no difference. There are hundreds of forum members who know this, it's common knowledge.

 

Your argument that changing the exhaust system changed the characteristics of the power delivery is entirely reasonable, why you think that boost spikes are desirable is beyond me but my argument rests on the fact that you CANNOT have more BHP unless you have more air and more fuel and both these things come from a remap, not from an exhaust system. If you like lots of noise and pollution then go for it but it will NOT make your car any faster.

You're misunderstanding what i'm saying. I said that just because the exhaust system can handle power up to 220bhp, that doesn't mean to say you can't improve the performance of the car by changing the exhaust.

Just to clarify, you think these items inside the exhaust flow gas as well as a straight pipe?

 

 

 

A little overboost on a standard map is fine. 1.52bar boost spike is still less pressure than a lot of remaps out there.

Perhaps it's the overboost that makes the car pull better at lower revs.

You haven't explained how the wheels would spin more aggressively in the wet with the same set up on tyres and same bit of road etc before after my exhaust was fitted.

There's dozens of threads over dozens of forums with dozens of people in each thread stating they felt a definite improvement in the surge of power when initially hitting full boost with a decat on a PD130. 

[faboka vrs]

more boost more air (to a point) will help burn the fuel its running rich.

If you want to run more boost then have the map tweaked to give it more boost. No need to remove or replace things.

Think of it like this. You have a door frame (exhaust) which is big enough to get 1 person through (airflow) without touching the sides. Will making the door frame bigger allow the person through quicker?

[TehMarchant]

Awesome replies guys, I may have put a big bar through the middle of my cat today whilst giving my car his 5000 miles oil change

[Hardcore]

Any change in how it drives?
 

[TehMarchant]

Any change in how it drives?

 

I think it does feel a bit faster now, but it could all the psychological. Hoping for a mufflerectomy soon. Then it'll sound like a jet fighter.

[sepulchrave]

I think it does feel a bit faster now, but it could all the psychological. Hoping for a mufflerectomy soon. Then it'll sound like a jet tractor.

 

FYP.

[jpderv]

Why bother with this wanton act of vandalism? It doesn't make the engine any more powerful, it doesn't make it sound any better, it just makes the emissions worse which is bad for you and everyone around you, diesel particulates cause lung disease and can trigger asthma attacks.

Lol you e obviously never had a decat done then I can personally verify that taking the backbox off and a decat give me 12bhp and 11lbft gain as which is noticeable on the road for me atleast car sounds emence and boosts earlier also.

One thing I would say is log boost afterwards as when I had my full straight through fitted I got slight boost spike this is on a big turbo so may be worse on a small one.

And on the plus side I got £120 for my cat from the scrappy which payed for the materials:)

Oops my apologies sepulchrave :( should have read the full thing I got 12hp gain but I'm running around the 250bhp mark I agree on a standard car there's not much to gain but the sound is good if nothing else

Edited 9 July, 2016 by jpderv