Decat pipe options

[R.E92]

The more I read into dynos the less I respect the readouts.

The manufacturer of a dyno makes such a huge difference in the output. Dynojet are one of the more popular ones but are understood to inflate readings by 10%. Mustang dynos under report by 5%.
On top of the dyno manufacturer error the operator can manually massage the figures by putting in bad correction factors for the SAE correction.

The most meaningful metric is 100-200kmh timing. This seems to be the standard at the moment for performance cars. You need to use a 10Hz GPS like VBox or Dragy to measure this though as relying on the speedo for an accurate reading is a non starter. If I wanted to compare the work of a various tuners this would be my starting point.

 

[Anonymous]

The more I read into dynos the less I respect the readouts.

The manufacturer of a dyno makes such a huge difference in the output. Dynojet are one of the more popular ones but are understood to inflate readings by 10%. Mustang dynos under report by 5%.
On top of the dyno manufacturer error the operator can manually massage the figures by putting in bad correction factors for the SAE correction.

The most meaningful metric is 100-200kmh timing. This seems to be the standard at the moment for performance cars. You need to use a 10Hz GPS like VBox or Dragy to measure this though as relying on the speedo for an accurate reading is a non starter. If I wanted to compare the work of a various tuners this would be my starting point.

I think it’s been recognised way back to the early days of readily available dynos for motorbikes that comparing one vs another dyno and as you say even with the same dyno the correction factors is open to unintended or deliberate misrepresentation..

And when you wander ‘off piste’ with a series of engine mods even more so...

On the other hand..

The same dyno on the same day is unlikely to show marked variations so any changes should reflect actual changes to the underlying engine etc..coming from an aviation background I’m well aware how heat, humidity and air density will affect power outputs..plus peering over the shoulder of the operator is key..

The other aspect when dealing with specifically the N20 engine is that you can, if you’re sad, can amass a database of what various tuners publish as the baseline figures and then what they publish as their improvements...

In that context the base figures that most people publish for a relatively large number of N20 engines are surprisingly congruent...

The re-maps do vary more than I would expect, often sometimes counter intuitively, I ponder whether quality of fuel is a factor..

Some tuners seem to be able to get the 18i upto the same or better than the 28i others seem to struggle with better figures from the 28i than the 20i than the 18i..

For me I’ll have the opportunity to see several runs in the same dyno in different configurations..pity there won’t be a ‘normal’ 20i run..

 

[Wing07]

The more I read into dynos the less I respect the readouts.

The manufacturer of a dyno makes such a huge difference in the output. Dynojet are one of the more popular ones but are understood to inflate readings by 10%. Mustang dynos under report by 5%.
On top of the dyno manufacturer error the operator can manually massage the figures by putting in bad correction factors for the SAE correction.

The most meaningful metric is 100-200kmh timing. This seems to be the standard at the moment for performance cars. You need to use a 10Hz GPS like VBox or Dragy to measure this though as relying on the speedo for an accurate reading is a non starter. If I wanted to compare the work of a various tuners this would be my starting point.

I think it’s been recognised way back to the early days of readily available dynos for motorbikes that comparing one vs another dyno and as you say even with the same dyno the correction factors is open to unintended or deliberate misrepresentation..

And when you wander ‘off piste’ with a series of engine mods even more so...

On the other hand..

The same dyno on the same day is unlikely to show marked variations so any changes should reflect actual changes to the underlying engine etc..coming from an aviation background I’m well aware how heat, humidity and air density will affect power outputs..plus peering over the shoulder of the operator is key..

The other aspect when dealing with specifically the N20 engine is that you can, if you’re sad, can amass a database of what various tuners publish as the baseline figures and then what they publish as their improvements...

In that context the base figures that most people publish for a relatively large number of N20 engines are surprisingly congruent...

The re-maps do vary more than I would expect, often sometimes counter intuitively, I ponder whether quality of fuel is a factor..

Some tuners seem to be able to get the 18i upto the same or better than the 28i others seem to struggle with better figures from the 28i than the 20i than the 18i..

For me I’ll have the opportunity to see several runs in the same dyno in different configurations..pity there won’t be a ‘normal’ 20i run..

Good Morning

How did you get on yesterday in Sunderland??

 

[Anonymous]

Hello Wing07...turned out to be a long day and quite complex..the write up is here ... https://z4-forum.com/forum/viewtopic.php?f=23&t=123191

The VSRF pipe is quality piece of work..went on with no issues in itself.. the pipe does add a bit of relatively tuneful noise to an otherwise very quiet car now I defeated the electronic noise generator (ASD)..

You can drive it using short shifting and modest throttle so its very low key..at low speeds on big throttle setings it generates a fair amount of noise that personally I could live without..the 'yoof' will like it, though I'm sure not as much as a six cylinder BMW!

A youtube of the dyno run is here but the cooling fans and rollers make more noise than the car..

https://youtu.be/2NsSMXXRMms

 

[Anonymous]

Just to update based on a day of hooning on relatively unfamiliar roads over 140 miles..

Its difficult given the re-map changes to ascribe what to the re-map and what to the de-cat..

However, there is a nice bark to the exhaust now without being too chavy..the pickup is great and on the roads in the Borders I soon start to run out of room..the auto box does a great job of marrting the power unit to the wheels, in comfort mode its all effortless and quiet quick, in sports mode its generally a big rush and sports+ mode keeps running out of gears (as its doesn;t shift up and runs into the rev limiter at 6.5k)

Sp pickup is much quicker and power with the re-map is in abundance..even though I ponder what more BHP would be like, for the area I frequent its enough, the limited slip diff is now starting to work quite hard, even in the dry with bumpy roads or coming out of tighter corners..

 

[MACK]

Hi,

Posted this in another thread, but just to update this one.....

Finally managed to get to PTorque to have mine remapped on Thursday and to cut to a long story short I'm very happy with the results!

I've posted the printout below, like an idiot I spilt a bit of water on it on the way home!

Will at PTorque told me that on the "before" run on the factory mapping the car ran 190BHP, to which I said "so not really up that much on standard". Will's response was "actual the decat is definitely having an effect". He went on to explain that this engine in this state of tune would normally produce 178-180BHP on his rollers so there's clearly a bit of an increase. Then when he told me the torque had been bumped up to 234 lbft (317Nm) from 199lbft as standard, I could clearly see the value of the decat pipe in isolation. I would also imagine the fresh coils and plugs I fitted, as well as always running it on 99 octane fuel are also playing a role. I remember when I fitted the coils and plugs the car did feel slightly perkier and definitely a bit smoother. Checking back on this thread my " before results" are pretty much on a par with what Pete's (Pbondar) car achieved once the Performance Centre had reloaded a standard factory map back on to it which is also decatted.

Moving on to the after, The car achieved 282bhp and 303 lbft with more available. Will explained that my engine was good for another 15bhp and an extra 30lbft, which if I wanted I could have, but it would be entirely at my risk. He's heard/read the same things a lot of us on here have about these engines letting go if pushed too hard. He told me that they haven't personally had any issues but he's heard stories from others about piston rings being the weak spot and cracking. He did say that in reality I would probably be absolutely fine at the higher outputs for a quick blast and it's probably sustained track abuse that actually causes issue. But he didn't want to take the risk and to be honest nor did I. Don't get me wrong more is always nice but I do like to sleep at night.

On the way back from Wolverhampton on busy M6, M56 and M60 (as well as way too many speed cameras!) I didn't really get to test it but I took it out yesterday evening and on quiet roads the car is a completely different animal. Above 3k revs its ballistic, in 3rd gear you run out of space on most roads before you run out of revs and if you're not careful you'll run out of license very easily too! Honestly the car is more than quick enough for road use, obviously as above, more is always nice but anymore and you wouldn't be able to stretch the engine in anything other than 1st and 2nd gear which would frustrate the hell out of me.

The exhaust note has changed too, the decat alone had changed things, but now with the map there's a much deeper growl to proceedings which is amplified by the exhaust valve bypass switch I have on mine. With the valve open even at low revs/speeds it really does sound like it means business now for a I4. However you definitely want the valve closed for startup and the first few minutes after as it amplifies the air pump which sounds pants and your neighbours will seriously detest you! Yes it's never going to sound as good as a normally aspirated 6 or 8 cylinder, but in its own way it sounds mean, a lot better than it did from the factory. It won't be to everyone's taste with the valve permanently open, but that said with the exhaust valve closed its still reasonable sedate for a sports car.

All in all I'm very happy with the results and well worth the trip to a proper mapper rather than the "man in a van" variety. I learn't a bit while I was there about how these generic mappers operate and also how BMW themselves purposely handicap this particular engine from the factory to fit their product lineups.

 

[Anonymous]

Yes the exhaust note is definitely more aggressive without being a drone..as you say it’s not a six but it’s sounds good in its own right..

The pick up rate seems a lot faster, how much is the de-cat and how much the re-map I’m not sure..it’s plenty aggressive for me..

I’ve got the exhaust valve control in place..glad I kept it as it does mean you can easily drive it in ‘respectable mode’ as you wish/required ..then press the go peddle harder and you get the new growl..

The auto box does a fabulous job of handling it all, far better than a manual..plus now the comfort /sports mode feels very distinct..

Overall good result ..

I’ll study your water cooled chart in more detail beings sad geek..

As an outside had a puncture on Sunday wiping out the front tyre..they were getting close to the wear limits..popped my Team Dynamics Pro Race 1.2 17” 8j 9j with 235/45 17 and 255/40 17 at 34/36 psi and the ride / handling is great ET is 25 front 30 rear

 

[MACK]

Yes the exhaust note is definitely more aggressive without being a drone..as you say it’s not a six but it’s sounds good in its own right..

The pick up rate seems a lot faster, how much is the de-cat and how much the re-map I’m not sure..it’s plenty aggressive for me..

I’ve got the exhaust valve control in place..glad I kept it as it does mean you can easily drive it in ‘respectable mode’ as you wish/required ..then press the go peddle harder and you get the new growl..

The auto box does a fabulous job of handling it all, far better than a manual..plus now the comfort /sports mode feels very distinct..

Overall good result ..

I’ll study your water cooled chart in more detail beings sad geek..

As an outside had a puncture on Sunday wiping out the front tyre..they were getting close to the wear limits..popped my Team Dynamics Pro Race 1.2 17” 8j 9j with 235/45 17 and 255/40 17 at 34/36 psi and the ride / handling is great ET is 25 front 30 rear

When it comes to the exhaust I'm so glad I went to effort of fitting the switch to control it. You may recall from my thread about it at the time that when I bought my car the valve was permanently open which I thought at first might be a coding thing but I later came around to thinking based on the sheer number of other 2.0T E89's reporting the same thing thats is probably a common fault with the ECU controlled earth for the system. Whether its a wiring issue, an issue with the ECU itself, or even something as silly as an unintended consequence of a BMW software update I've no idea. What I do know is the net result was the same as the "Golf Tee Mod".

With the valve open on a cold start the combination of the air pump, the decat and remap are way too much. To be honest it was too much pre the mods with just the air pump, but the mods have significantly amplified this. Once your past those first few minutes of running its fine and I do quite like the added growl it has with the valve open at low revs/speeds that you don't get from the factory, but I'm also glad the switch is there, as at times I tire of it and appreciate something a bit more sedate. I was on Anglesey yesterday, there's some nice A and B roads on the island. I had a number of places to be that meant I had a day where I was driving all over the place, all top down and depending on how I was feeling dictated which "mode" I had the exhaust in. What I did notice whilst do this is the valve position doesn't really seem to impact performance, the engine pulled equally as strongly with the valve closed and open, although I did only take it upto circa 4,500 rpm with it closed, maybe I would have noticed the performance being hampered if I'd redlined it but honestly I think the cat itself was a much much bigger restriction in the exhaust than the backbox valve. I'm increasingly convinced that BMW put it there purely to control noise levels and it has no real bearing on performance.

The journey from Manchester to Anglesey is roughly 100 miles, which is all Motorway and Dual Carriageway. Cruising along at the sort of speeds you do on these types of road and there's still no discernible difference between having the valve always open and always closed. To be honest this does surprise me a bit. Knowing what I know now if I were for some reason to buy another E89 with a working exhaust valve I'd still be tempted to re-wire it through a switch. Only this time I go for three modes. Always closed, as BMW intended and always open. Kind of like a COMFORT, NORMAL & SPORT mode.