[335i E92]

Afternoon All

Now starting to think about my next 2 upgrades and have decided on a Forge intercooler which is quite straight forward and upgrading the down pipes which i believe isn’t quite as straight forward.

I can see that you can get high flow down pipes with or without cats. I've done some research and read somewhere that Tony had catless downpipes and ended up cooking his secondary cats. Tony is this correct mate??

As most of you know i have a DMS remap so i will also be taking advise from Mike & Rob as to which is best and if they provide an updated map to compliment the new hardware. I will feed this back on here when i have the info.

In the mean time does anyone have any opinions as to the pro's and con's of total de-cat downpipes v high flow downpipes with cats. Obviously i know the decats will give more flow but is this advised, will it pass an mot, cause bad smells or throw codes?

On dyno runs ive seen the total decats only offer around 4 more bhp than wider downpipes with cats.

Over to you...

[m1bjr]

The swap to no cats isnt purely to realise more power.
Removing a large obstruction to the turbo exit has more important benefits.
Thermal and pressure related, it might actually extend turbo life as they won't be fighting so hard to hit the boost targets
Think spool time and thermal efficiency here

Shame about another remap though, with a JB3 you just pick another optomised map from the list and drive

[335i E92]

Originally Posted by m1bjr

The swap to no cats isnt purely to realise more power.
Removing a large obstruction to the turbo exit has more important benefits.
Thermal and pressure related, it might actually extend turbo life as they won't be fighting so hard to hit the boost targets
Think spool time and thermal efficiency here

Shame about another remap though, with a JB3 you just pick another optomised map from the list and drive

Afternoon!

Ta for the input

I know a total decat will reduce back pressure and allow the turbo to spool quicker and with less effort which is all good.

My concerns were what if any are the downsides of completely deleting 2 cats? Emissions? Fault codes? Burning the secondary cats?

The above concerns are why i'm thinking a higher flow downpipe with built in cats might be safer?

Anyone?

[m1bjr]

Well, seems there are plenty around who have removed the primary cats with no other issues.
You will get codes though, but there is normally a fix offered by popular tuners.
I know the JB3 for example simulates a 'correct' voltage from the affected O2 sensor to stop it happening.

With a remaining cat pair I know of others who still pass emmissions okay and have no odd smells - one cat per line is adequate to stop this.
TBH if you go to the effort and expense of this job, then why bother with half arsing it
What dps did you have in mind, and from where?

Heres a related thread :
http://www.e90post.com/forums/showthread.php?t=422222

[335i E92]

I agree I would much rather have the total de-cat if its safe to do so, i just need an little more convincing that i'm not going to be causing other problems.

Does everyone agree total de-cats are ok and will pass emissions test etc??

Tony, did you have problems with your de-cats??

[Alpina_B3_Lux]

Originally Posted by 335i E92

I agree I would much rather have the total de-cat if its safe to do so, i just need an little more convincing that i'm not going to be causing other problems.

Does everyone agree total de-cats are ok and will pass emissions test etc??

Tony, did you have problems with your de-cats??

I'm not Tony, but I can tell you it's correct that after having driven with catless DPs for some time, the higher exhaust temperatures had burned out his secondary cats. He then replaced these with metallic race cats from HJS.

You can also run completely catless, i.e. also remove the secondary catalysts. Then you won't pass any emission testing, of course (unless you swap the cats back in) and you may get some smell issues. Which is why I went the same route as Tony and got me some quality metal cats. Also, the noise the exhaust makes then may be a bit much - I'm fine with it right now but wouldn't like to have it any louder (I got a Bastuck exhaust, but on a sedan which has a resonator more than the E92).

I also first had the catted version of the downpipes (AR ones too). There's a difference in performance and sound to the catless version, although it's not enormous and not very noticeable. With these the chance that you cook your secondary cats is certainly lower, and emission testing shouldn't be a problem. Depending on your software version, you may still have to run a O2-sim though (from BMS for example), unless DMS can also deactivate the catalyst codes (not all tuners can do that) which get thrown now even with catted DPs in some cases. Catted DPs also are more expensive, obviously.

Alpina_B3_Lux

[doughboy]

Originally Posted by 335i E92

I agree I would much rather have the total de-cat if its safe to do so, i just need an little more convincing that i'm not going to be causing other problems.

Does everyone agree total de-cats are ok and will pass emissions test etc??

Tony, did you have problems with your de-cats??

I asked Tony and others about this.

You'll pass an MOT only if your secondary CATs are good and hot enough to work properly. Normally from cold the primary CATs heat up very quicky and perform their duties well early in the engine warming period.

Your secondary CATs won't get hot enough if the car is idling. Also the VOSA specified minimum oil temp for our N54 engine MOT emmissions test is only 60degC, which is pretty cool, so it will probably fail if tested from cold.

Tony has to find a 'friendly' MOT station, make sure you arrange a 'spirited' drive into the garage to get things good and hot then get it tested pretty sharpish and you'll be OK.

Not ideal, but worth a go.

Don't forget Tony's car has had some pretty extreme useage for several years, is a testament to the N54 that its still going TBH.

I think more regular useage, even with no primary CATs would not burn out your secondary units.

[335i E92]

Thanks for the response chaps...

I'm still a little confused as to which option to go for although I'm leaning towards decated. I understand that after a long periods of hard driving I will start to melt the secondary cats. However I will never track the car and generally any spirited driving is done in short spells.


I know a good local dealer that I rekon will be "friendly" when it comes to mot's so as long as dms don't strongly advise against the fully decated downpipes Im thinking this might be the way I'll go. I suppose if I'm going to open up the flow I might as well do it properly as with my style of driving it's unlikley to burn out my secondary cats, you all agree?

My only other concern would be the exhuast note, will this be much louder with a full Decat?

[335i E92]

Not decided what make I'm looking at yet, possibly the AR Design ones.

Although they are quite expensive, anyone suggest any good makes??

[doughboy]

Originally Posted by 335i E92

My only other concern would be the exhuast note, will this be much louder with a full Decat?

You still have the secondary cats and the main rear silencers remember. I asked the same question to someone with AR de-cats and they said there was no noticeable noise increase.


Defo AR -From what I gather, the AR pipes are the ONLY ones to get.

Not only are they fabulous quality and fit, but they are the only ones that will fit a RHD car properly without fouling the power steering.

Remember to spec RHD fitment if you buy!!

They're a thing of beauty - almost too nice to hide under the car!!!

http://www.ardesign.info/catalog/ard...ipes-p-72.html

Get em bought!

[335i E92]

Originally Posted by doughboy

You still have the secondary cats and the main rear silencers remember. I asked the same question to someone with AR de-cats and they said there was no noticeable noise increase.


Defo AR -From what I gather, the AR pipes are the ONLY ones to get.

Not only are they fabulous quality and fit, but they are the only ones that will fit a RHD car properly without fouling the power steering.

Remember to spec RHD fitment if you buy!!

They're a thing of beauty - almost too nice to hide under the car!!!

http://www.ardesign.info/catalog/ard...ipes-p-72.html

Get em bought!

I think you've just persuaded me, they do look the ones don’t they!!

Are you going for these?

I had my car in Woods yesterday for break pads and talking to Mike he has a 335i in at the mo with downpipes, Forge intercooler and stage 2 evolve. He said it is unreal and would absolutely obliterate the v10 M5.

I’m gonna speak to Mike at DMS today to confirm if he is able to supply a relevant map update for the Forge intercooler & AR Design catless down pipes. If the response is positive then I’ll go for it.

I currently have the forge DV’s and once I’ve upgraded to the below that’s it for me engine wise. Initially I didn’t think that I would upgrade anything beyond the standard remap. However I’ve learned a lot on this forum from you guys and feel the below additions are not just to gain a tad more power just as importantly to reduce temps and back pressure on the turbos as I plan to keep this car for a good few years.

Last engine mods:

AR Design catch can
AR Design catless downpipes
Forge Intercooler
Oil change every 5 k

Do you all agree?

[Alpina_B3_Lux]

Originally Posted by 335i E92

My only other concern would be the exhaust note, will this be much louder with a full Decat?

Only changing the DPs will not result in a very noticeable change in the exhaust note. It's when you change (or delete) the secondary cats that it gets noticeably louder. As you do not intend to do this (and I would agree that with your driving profile that should be ok), you will not have to worry about the exhaust noise.

Originally Posted by 335i E92

Not decided what make I'm looking at yet, possibly the AR Design ones.

Although they are quite expensive, anyone suggest any good makes??

AFAIK the AR are the only ones that make perfectly fitting DPs for RHD cars. There are other good options for LHD cars (Macht Schnell for example), but even then I would still go with AR as all components I've had from them until now were of great quality.

Alpina_B3_Lux

[Yahoo]

Interesting thread!

I can vouch for AR catless downpipes - they are excellent. I would say that the exhaust note is significantly improved with these. No drone, but a more aggressive tone and slightly louder. I have disabled the exhaust flap (aka golf tee mod) which makes the exhaust sound great - particularly with the DPs.

FMIC is a must - very highly recommended. I have the AMS one which has a similar core dimension to the Forge unit - but has slightly better flowing end tanks imo.

Catch can - another must. I have the BSH one which seems to work nicely.

Regular oil change - defo!

Remap - I have just had an Evolve stage 3 remap on my car (review to come). Very impressed so far though - buttery smooth 420bhp at 1 bar, very nice!

At these power levels, the only other thing that needs considering is an air intake. I know that others on the board don't think this is necessary - but I would prefer to be safe that sorry. I would certainly look at a high flow panel filter at a minimum. Additionally, I have manufactured a secondary air intake into the stock airbox. The is piped to a filter behind the near side fog light / brake duct. This provides extra cool air which can only be a good thing. This doesn't provide cooler AITs - but does provide the engine with as much 'free flowing' air as it could want when running power levels 1/3 above stock. Some say the stock air box is restrictive, others don't - read up and make you own mind on this.

Happy modding!

[doughboy]

You've got the bug now 335iE92 -

What about the wedding? hope you're not spending the savings?

[335i E92]

Confused.com...

Just had a long chat with Rob at DMS, who as most of you will know is very well acquainted with the the N54 engine.

Firstly they can tweak the map to accommodate the Forge IC and downpipes no problem and indicated that 400bhp or slightly over will be a safe level to take it to.

However...

When discussing the option of cated or de-cated downpipes Rob was very much in favour of the cated option. He said de-cated work very well with n/a engines but not as well on turbos due to the turbo not getting enough back pressure. As a result of this you lose a little power in the lower revs when on part throttle compared to a total decat. Also he did mention the potential emissions situ etc etc

He did say though at full wot it would not be as noticeable but we don’t all drive at full wot constantly, the roads are generally to busy and full of pot holes. For normal day to day part throttle driving the cated downpipes will apparently deliver more low down grunt which is what makes any car feel smooth and enjoyable.

Ideally we need someone with experience of both to move this thread forward. I know Tony gets leaned on quite often on here for advise, however i believe he was on catless and is now on cated so come on TONY.. Please

Anyway there's the update, what do you all think of the above spanner in my in works??? any opinions???

Doughboy, wedding is still on, i'm sacrificing lots of social events to accommodate these mods, the ying and yang is all good.!!

[335i E92]

Hi Yahoo

Already got a K&N panel filter boxed up ready for fitting after the downpipes & ic.

[Yahoo]

Originally Posted by 335i E92

He said de-cated work very well with n/a engines but not as well on turbos due to the turbo not getting enough back pressure. As a result of this you lose a little power in the lower revs when on part throttle compared to a total decat.

I am not an authority on this, so I'm not really sure.

I have read on the FI pages about back pressure benefiting the turbos and to the contrary, back pressure being a negative also.

One significant benefit of free flowing DPs is quicker spool up time - this makes the throttle significantly more resonsive giving that large capacity NA engine feel. Although back pressure might improve mid range power (as per your post above) - I would have thought that more back pressure would have a negative effect on spool up time and therefore percieved turbo lag.

[seanblee]

I'm pretty sure that reducing back pressure (thus decreasing exhaust gas velocity) on an NA can up peak power but move peak torque up the rev range, but I'm also pretty sure that's not applicable to FI. Turbos work best with zero back pressure on the turbine.

http://www.tercelreference.com/terce...st_theory.html explains it all pretty well.

[E92Fan]

Originally Posted by 335i E92

Afternoon!

My concerns were what if any are the downsides of completely deleting 2 cats? Emissions? Fault codes? Burning the secondary cats?

Originally Posted by Alpina_B3_Lux

I'm not Tony, but I can tell you it's correct that after having driven with catless DPs for some time, the higher exhaust temperatures had burned out his secondary cats. He then replaced these with metallic race cats from HJS.

Originally Posted by doughboy

I asked Tony and others about this.

You'll pass an MOT only if your secondary CATs are good and hot enough to work properly. Normally from cold the primary CATs heat up very quicky and perform their duties well early in the engine warming period.


Don't forget Tony's car has had some pretty extreme useage for several years, is a testament to the N54 that its still going TBH.

I think more regular useage, even with no primary CATs would not burn out your secondary units.

Sorry, bit late to this thread. And a bit shocked to read one of the 'expert' opinions a bit later on...

I've had AR Design catless downpipes for almost two years, and they've been absolutely excellent in all aspects. I went for catless downpipes to leverage the most power out of the engine, and also because I personally was not worried about emissions or check engine lights (I had a plan for this).

The standard system has two sets of cats as you know, one in the downpipes and the secondary cats in the main exhaust section. The engine ECU employs a before and after lambda probe setup around the primary cats in the downpipes - this measures the effective catalysed exhaust post cat and compares this reading to the one taken before the cat. If the readings show a catalysed exhaust, then all is well for the ECU. The problem with a de-catted downpipe is that the lambda probes are now largely useless.

There are two ways around this - one is to use a simulator of some sort to correct the return voltage of the post lambda sensor, to fool the ECU into thinking all is ok. This is fine, but the values will change depending on the relative efficiency of the engine at the time, so the simulator may in some cases 'drift' out of spec.

The other way of 'fixing' the lambda probes is to relocate the post probe to behind the secondary cats in the main exhaust. This is a bit of work, about an hour or so, but does result in a fully catalysed signal being sent back to the ECU without any form of simulation.

This is what I initially did on my car, and it worked absolutely perfectly.

You could go for high-flow catted downpipes from AR Design - these will eliminate any need to mess around with lambda probes or simulators, and will ensure that you pass any MOT, but they are still more restrictive than the decat downpipes and therefore you don't release as much power from the engine. Don't get me wrong though - the high-flow cat downpipes still produce a good power increase from the engine.

As far as passing an MOT goes, as long as you have standard OEM secondary cats in the main exhaust section, and they're warmed up before the actualy MOT test, you'll sail through the emissions test without any problem. If however you have changed the OEM secondary cats to something a little less restrictive, then you'll have a problem or two to surmount

Originally Posted by 335i E92

I'm still a little confused as to which option to go for although I'm leaning towards decated. I understand that after a long periods of hard driving I will start to melt the secondary cats. However I will never track the car and generally any spirited driving is done in short spells.

My only other concern would be the exhuast note, will this be much louder with a full Decat?

Actually, you won't melt the secondary cats at all, especially under the style of driving that you suggest you do. I only melted the secondary cats because the exhaust gas temperature of my car was abnormally high, due to the type of remap I was running at the time, and also because I'd just completed 35+ laps of the Nurburgring in one day, and the engine was more than raging hot

The secondary cats melted due to the absolutely extreme heat that I generated with the engine, and this is abnormal to everyday use. I wouldn't worry at all about the secondary cats on a normal car.

Originally Posted by 335i E92

Just had a long chat with Rob at DMS, who as most of you will know is very well acquainted with the the N54 engine.

However...

When discussing the option of cated or de-cated downpipes Rob was very much in favour of the cated option. He said de-cated work very well with n/a engines but not as well on turbos due to the turbo not getting enough back pressure. As a result of this you lose a little power in the lower revs when on part throttle compared to a total decat. Also he did mention the potential emissions situ etc etc

Good God, he's got that a bit backwards.... and as an aside, he knows bugger all about the N54 engine itself. The ECU, yes he knows about, a lot about, but the engine itself.... DMS remap ECUs - they don't build engines, and they certainly aren't turbo specialists. They should stick to doing what they do best.


Normally aspirated cars NEED a bit of backpressure to ensure their engines run well. Especially if the exhaust manifold is not pulse tuned to match the engine. Backpressure is a by-product of exhaust velocity. The greater the exhaust velocity, the greater the performance of the engine because exhaust velocity helps to scavenge the cylinders during the blowdown process (ie the exhaust gases are expelled quicker). However, to increase exhaust velocity on a N/A engine, the discharge of the exhaust collector (ie the exhaust) needs to be made smaller in diameter. However, this also increase the backpressure. Too much backpressure voids any increase in scavenging performance derived from the increase in exhaust velocity. Too little backpressure means the exhaust is too big, and therefore not enough scavenging is taking place. There has to be a happy medium here, but the bottom line is that backpressure is needed to a degree.


On a turbo-charged car, there are no ifs nor buts - the idea is to reduce backpressure in the exhaust (post turbine) as much as possible. Turbos can be very simply split into two parts - upstream of the exhaust turbine (ie turbo inlet manifold) and downstream of the exhaust turbine (ie the exhaust itself). An exhaust turbine operates via a pressure ratio - for any given turbine inlet pressure, you will get the highest pressure ratio across the turbine when the exhaust backpressure is the lowest possible.

On the front side (upstream) the pipework needs to be smaller than normal so that exhaust velocity can be increased. This faster gas speed helps the turbine to spin up as quickly as possible, which helps to boost torque early on in the rev range. This maximises the performance of the turbo on the input side.

On the exhaust side of the turbo, which is where the downpipes and exhaust come into play, it is of paramount importance that there is as little backpressure as possible. Minimising the pressure downstream of a turbine makes most effective use of the pressure that is being generated before the turbine.

The N54 engine is even more critical of backpressure, because it uses small turbos. Small turbos generally operate at a higher turbine pressure ratio than big turbos/turbines, and so are generally more sensitive to the backpressure post turbine.



There is absolutely no doubt that a decatted downpipe will work better on the N54 engine than a catted downpipe (of the same diameter and shape) There will be a greater performance hike. Of this there is no dispute.

However, this performance hike has to weighed against the disadvantages I've talked about above - poorer emissions and concerns with lambda probe effectiveness. There is a bit of an increased rasp to the engine note with full decat pipes - I like it actually and it's not at all noticeable when cruising on the motorway. It won't sound as loud as my own car, mainly because I'm using full metallic race cats and a larger bore exhaust all the way through.

Originally Posted by 335i E92

Ideally we need someone with experience of both to move this thread forward. I know Tony gets leaned on quite often on here for advise, however i believe he was on catless and is now on catted so come on TONY.. Please

I have never had high-flow catted downpipes. I know many people who do and they have been very happy. More power, no potential problems. Some of these people have since changed to decat downpipes, and are even more happy, although have had to be a bit creative with the lambda probes. No big issue in my opinion.

You have to weigh up the pros and cons of each. I guarantee you there will be a performance increase over the OEM downpipe, purely because of the increased diameter of the pipework. As far as a 'special' remap goes, actually there isn't any need for one. Turbo spool up will be faster in any case and exhaust gas expelled more quickly. If you wanted to make more power than just that released by upgraded downpipes, then yes you need another remap to increase boost pressures slightly.


Incidentally, to the OP - if you want or need my input, PM me and I'll get involved sooner. Hoping that I'll just come across the thread is not a good idea, as I just don't have time to read everything.

[m1bjr]

I agree.
And as I alluded to in post 2, a turbo doing less work will increase volumetric efficiency.
Of course, you may well need more intake air flow by this point on this engine too.
Forget the CIA, it is provemn to make little difference if the IC is effective.

[E92Fan]

Originally Posted by m1bjr

I agree.
And as I alluded to in post 2, a turbo doing less work will increase volumetric efficiency.
Of course, you may well need more intake air flow by this point on this engine too.
Forget the CIA, it is provemn to make little difference if the IC is effective.

Spot on - an efficient turbo increases VE significantly and reducing exhaust backpressure aids in this quest.

I have deliberately ignored the subject of intake air flow, as that would be confusing. In the context of the OPs question on downpipes for the N54 engine, it is sufficient just to change the downpipes to 3" diameter decat pipes without significant need for improved intake air flow.

It is my opinion that the OEM intake is actually quite sufficient for decent power output, and it is more advantageous to go for an uprated intercooler instead to lower charge temperatures.

If after that it is determined that more effective intake air flow is required, I personally would advise against an open cone intake system, whether it be single or dual cone, as there is significant heat expelled from the engine and this increase in heat would potentially negate any increase in air flow. Far better to fit a secondary air intake into the standard airbox, with a separate filter, mounted behind the nearside fog light area in the wheel well.

[m1bjr]

Well Tony, thats another topic for hot debate
Real world testing suggests that reduced Pd is of greater benefit even allowing for slightly elevated IATs.
On a turbo engine, the IC largely negates the increase in IAT with an open cone filter in the engine bay.
But the decrease in pressure drop from the cone makes a greater difference to the VE of the system.
The issue being not the air filter itself, but all the associated piping and airbox that causes a pressure drop.

I was exploring this theory at length with the Engineers at TDI South recently.
In particular, the effect is not much at all given the car is moving and so the engine bay is supplied with air.
Its one of those subjects that will always be up for debate