[XutvJet]

So there are plenty of dynos out there showing N54s and N55s motors gaining around 20+whp and 30wtq throughout the powerband and around around 10-15 whp and 20-25 wtq without any tuning. However, you constantly read from vendors that adding a Stage II tune to account for the downpipe will take "full advantage" of the downpipe and gain more power. So what is the tune changing between the stock downpipe and aftermarket downpipe maps?

I can't find on the interwebs anything that indicates exactly what is being changed other than the same regurgitated stuff. Is it air/fuel ratio, timing, boost, something else that's changed? If they are adding boost, well that is largely why there's more power. Just curious.

[Jnat]

Are you aware that BMW uses load based tuning? If you are then you will also understand that basically, the least amount of everything will be used to achieve a requested load. So in short, the higher the back pressure on the exhaust side is, temps will be higher than you would want or prefer. In other words, a restrictive exhaust/downpipe will require the turbo to work harder to achieve its requested load, therefore reducing performance or at the very least, more wear and tear due to heat.

[Poochie]

From what I've gather by reading between the lines of everyone's feedback is that with a downpipe, sports or decatted, it's not about the overall numbers but the fact it allows a freer flowing exhaust, hence less strain on the turbo's load, with or without added boost..

I was on the fence about possible getting a sports cat but I gradually moved away from the idea because of a few issues here and there I've read about and honestly the minimal/ambiguous power gain is not as appealing to me VS the possible risk of an error light or blowing out the stock charge pipe.

That's just my opinion though, you might find more value in it, depending on your needs and setup.

[hwntime]

Originally Posted by Poochie

From what I've gather by reading between the lines of everyone's feedback is that with a downpipe, sports or decatted, it's not about the overall numbers but the fact it allows a freer flowing exhaust, hence less strain on the turbo's load, with or without added boost..

I was on the fence about possible getting a sports cat but I gradually moved away from the idea because of a few issues here and there I've read about and honestly the minimal/ambiguous power gain is not as appealing to me VS the possible risk of an error light or blowing out the stock charge pipe.

That's just my opinion though, you might find more value in it, depending on your needs and setup.

The OEM chargepipe will eventually bust with aggressive driving with or without an aftermarket DP.

[XutvJet]

Originally Posted by Jnat

Are you aware that BMW uses load based tuning? If you are then you will also understand that basically, the least amount of everything will be used to achieve a requested load. So in short, the higher the back pressure on the exhaust side is, temps will be higher than you would want or prefer. In other words, a restrictive exhaust/downpipe will require the turbo to work harder to achieve its requested load, therefore reducing performance or at the very least, more wear and tear due to heat.

Yes, I am aware of the load-based tuning employed on these cars and I do understand the relationship between restriction aft of the turbo and heat. It seems to me that the DME in stock form is already good at accounting for an aftermarket downpipe because it makes quite solid gains with the stock tuning.

It sure seems to me that the tuners are more comfortable with pushing fractionally more boost with an aftermarket downpipe thus that's where the extra power is coming from.

When you look at comparison dynos for Stage 1 tunes (no downpipe) vs Stage 2 tunes with a downpipe, there isn't a ton more power being gained beyond what we typically see with adding a downpipe to a stock tuned N55.

[Poochie]

Originally Posted by hwntime

The OEM chargepipe will eventually bust with aggressive driving with or without an aftermarket DP.

I still have a year of factory warranty left, so if it blows out, it would be replaced for 'free.' After my warranty expires, I might explore the possibility of an aluminum pipe.

However, I've been using a Dinantronics stage 1 for over a year, on hard WOT and my charge pipe is still fine. I even gave it my own, personal torture test and it held to my demands. So I'm pretty confident I'll be ok.

BTW, using an aftermarket charge pipe or downpipe - tampering with any emission control device, in general, would void my warranty with BMW and the supplement coverage with Dinan, so there's that also.

I'm not a boy scout but I don't like spending unnecessary money, so I would like to retain what's left of my coverage instead of forfeiting for ambiguous power gains.

[Jnat]

Originally Posted by XutvJet

Yes, I am aware of the load-based tuning employed on these cars and I do understand the relationship between restriction aft of the turbo and heat. It seems to me that the DME in stock form is already good at accounting for an aftermarket downpipe because it makes quite solid gains with the stock tuning.

It sure seems to me that the tuners are more comfortable with pushing fractionally more boost with an aftermarket downpipe thus that's where the extra power is coming from.

When you look at comparison dynos for Stage 1 tunes (no downpipe) vs Stage 2 tunes with a downpipe, there isn't a ton more power being gained beyond what we typically see with adding a downpipe to a stock tuned N55.

I think all of what you just said is correct. I would add that on our EWG cars, we have the 4 inch down pipe (stock cat) and your right, up to a certain amount of boost, it will be able to keep up. Maybe the better question is at what point does the stock cat become a restriction therefore a stoppage and or loss of power. Also, with some past vehicles I've had including an N54 I used Cobb. I've seen a lot of data logs and over the last 7-8 years learned a lot about tuning. Most tuners up the timing (very little) obviously but are reluctant to push it because they have no idea what we're gonna do, meaning Octane, E, bolt on's ect:. I advanced the timing, upped the load requests and leaned the fuel using Cobb's software and I def can tell you that the off the shelf maps, probably all OTS maps are conservative, for safety. My last thought, comparing Cobb OTS maps and MHD OTS maps, MHD is much more aggressive and more dialed in. IMO...

[XutvJet]

I installed the HJS Euro 6 300 cell downpipe yesterday and I'm on the stock tune. I drove around for about 50 miles and whoa....it was everything I was looking for. A nice bump in power below 5500rpms, a little power above 6000rpms, generally less lag, a more willing and flexible feeling engine, ~10-15% louder exhaust volume depending on throttle with the MPE plus more turbo whistle, and still completely docile inside.

[Jnat]

Keep us informed on the MIL with no tune... and good luck... i'm thinking of trying the VRSF 200 but i'm not thrilled with the O2 placement as it appears to be right in the cat? I don't see that being the case with the others. Where was the O2 placement with the HJS?

[XutvJet]

Originally Posted by Jnat

Keep us informed on the MIL with no tune... and good luck... i'm thinking of trying the VRSF 200 but i'm not thrilled with the O2 placement as it appears to be right in the cat? I don't see that being the case with the others. Where was the O2 placement with the HJS?

The first O2 sensor on the OEM cat sits inside a void between two cats. The HJS Euro 6 has the same arrangement and it sounds like the VRSF and Fabspeed 200 cell downpipes do the same.

I will do a review of the HJS Euro 6 in a few weeks once it's fully broken in and the ECU is fully adapted. I went with the HJS Euro 6 because it has OEM build quality, a very high quality and long lasting 300 cell HJS cat, and is the least prone out all the downpipes to throw a code because of the 300 cell count vs the others that run a 200 cell count.

[ghost.M]

I'm not an expert but stated plainly, the turbo is more efficient without a catalytic converter behind it. Greater efficiency at any given boost pressure/rpm will mean more power, and a "Stage 2" tune will adjust the DME to take advantage of the increased efficiency. To your point the DME is perfectly capable of adapting, and it does; however without cat, the rear 02 sensor readings will be outside of OEM spec which is why it will throw a code. In addition to increasing boost and adjusting AFR etc, Stage 2 tunes will clear the CEL or completely code out the rear 02 sensor so the DME doesn't limit performance and can enjoy the increased turbo efficiency . I'm sure you can run a Stage 2 tune with the stock cat in place, but you would likely overwork the turbo if routinely driven hard since the tune is designed for a more efficient arrangement than the stock cat permits. Also, Stage 2 tunes usually make the oem throttle overrun function far more exaggerated which could eventually lead to premature failure of the stock cat.

Again, I'm not an expert, just trying to explain this as best as I can without getting too technical.

[NewM235Owner]

Im curious why you started with a downpipe rather than a tune, like BM3? I'm about to throw away the last year of my 5 year warranty and was thinking BM3 first, and later a downpipe, and just curious why you did it the other way around, especially considering the cost difference for a catted DP. My thought was that BM3 would give me a lot more bang for the buck than a catted downpipe. Not judging your choice, just gathering data so I can decide what to do first. Also, I was looking at the 200 CEL vs. the 300 cel HJS, which they also say won't throw a code. Is there some advantage to the 300 CEL over the 200 or did you just feel like the 300 was less likely to throw a code? Thanks.

[XutvJet]

Originally Posted by NewM235Owner

Im curious why you started with a downpipe rather than a tune, like BM3? I'm about to throw away the last year of my 5 year warranty and was thinking BM3 first, and later a downpipe, and just curious why you did it the other way around, especially considering the cost difference for a catted DP. My thought was that BM3 would give me a lot more bang for the buck than a catted downpipe. Not judging your choice, just gathering data so I can decide what to do first. Also, I was looking at the 200 CEL vs. the 300 cel HJS, which they also say won't throw a code. Is there some advantage to the 300 CEL over the 200 or did you just feel like the 300 was less likely to throw a code? Thanks.

I went with the downpipe before a flash tune because I'm not overly obsessed about power. I'm more interested in improving a cars performance and responsiveness all the while still making it fully streetable and not causing compromises in drivability. I want a car that I can hustle on the backroads with power that is tractable and doesn't hit like a sledge hammer and roast the tires too much instant torque. Everything I've read about catted downpipes installed on stock tune M235s and N55 M2s has been quite positive. The downpipes gain solid power across the entire power band plus it reduces lag and makes for an amazing sound. That's what I want.

I know a flash tune gains a lot more power, but I've always wanted a quality downpipe for the reason noted above. I may go with a flash tune in the future, but I want to give it another year or so so they can work out all the bugs and I want to see how N55s hold up after the tunes being on market for 2 to 2.5 years. I do have the Dinan Sport and have run it since last March. I've found that the best setting is Sport (2-2.5 psi over stock), but sometimes I don't even like it because it can impact driveability negatively because it makes the throttle jumpy and there is more initial lag than stock. So, for now, it's turned off so I can fully gauge the gains of the downpipe.

I went with the HJS Euro 6 downpipe because:

1) It has a very high quality 300 cell cat.

2) Due to it being a 300 cell cat greatly reduces the chances of a CEL. I've never heard of the HJS Euro 6 DP throwing a CEL.

3) The 300 cell cat flows nearly as good as the 200 cell cat used in the Fabspeed DP.

4) The 300 cell cat won't be quite as loud as the Fabspeed DP.

5) Most importantly, the HJS Euro 6 DP looks and feels dang near OEM and isn't that much more expensive than the Fabspeed DP. Fitment was perfect. The Fabspeed DP looks totally aftermarket and I'm not a fan of their revised catted Fabspeed DP design on the turbo side as they really cheaped out with the revised mounting flange. It no longer has an internal seating ring and makes me question it's sealing capability over time and heat cycles.

[NewM235Owner]

OK, that makes sense, thanks a lot, gives me something to think about. Regarding the DP, I have an MPE and really don't want it louder, but I know a new DP is going to add some sound, so the 300 CEL probably would be better for me than a 200 from that perspective.

[XutvJet]

I am nearly 45, routinely haul my family in the car, and I'm extremely picky about mods and will yank them if they compromise driveability. The increase in volume is not significant inside the car. It's still totally sane. No drone, no vibrations, etc. Yes, it is louder, but it's nothing extreme. It sounds so damn good. It's like the MPE on steroids.

I will do a detailed review in a couple weeks once I get more miles on the downpipe and the DME fully adapts.

[Jeff@TopGearSolutions]

Originally Posted by NewM235Owner

Im curious why you started with a downpipe rather than a tune, like BM3? I'm about to throw away the last year of my 5 year warranty and was thinking BM3 first, and later a downpipe, and just curious why you did it the other way around, especially considering the cost difference for a catted DP. My thought was that BM3 would give me a lot more bang for the buck than a catted downpipe. Not judging your choice, just gathering data so I can decide what to do first. Also, I was looking at the 200 CEL vs. the 300 cel HJS, which they also say won't throw a code. Is there some advantage to the 300 CEL over the 200 or did you just feel like the 300 was less likely to throw a code? Thanks.

The tune would provide more bang for the buck power over any other modification.

The tune will also add to the power for further modifications. Increasing boost, fuel and ignition timing, depending.

The 300 CEL HJS is extremely unlikely to throw a code, while the 200 CEL appear to be hit or miss.

[mike@x-ph.com]

Originally Posted by NewM235Owner

OK, that makes sense, thanks a lot, gives me something to think about. Regarding the DP, I have an MPE and really don't want it louder, but I know a new DP is going to add some sound, so the 300 CEL probably would be better for me than a 200 from that perspective.

200 CEL is pretty quiet .. Fabspeed downpipe do not throw a code either