[XutvJet]

Originally Posted by AmuroRay

Also, you were slower because your average power was less - you don’t really have those issues in a boosted car.

Not at all. It was where the new power was and the stock redline. The car needed the extra rpm to wind out in order to take advantage of the power. I learned a very valuable lesson about ideal shift points and torque multiplication. The most important take away being that just because power peaks at XXXX rpm doesn't mean that's where you shift. In almost all cases, you need to be shifting 200-500rpms PAST peak power in order to maximize acceleration. It's all about torque multiplication, powerband shape, and gears ratios on the upshift. So many people get this wrong but it's not surprising because most haven't made hundreds and hundreds of 1/4 mile passes to understand how it all works.

Contrary to popular belief, ideal shift points for all EWG N55s with stock turbos and running gasoline is between 6800-7000rpms depending on gear.

[AmuroRay]

Inspired by my post here https://f87.bimmerpost.com/forums/sh...7&postcount=18 on the differences why the F87 makes more power than other tuned N55s, BMW claims that along with the intake airbox being dethrottled (which we have tested this to be true) they have done the same to the exhaust.

https://www.bimmerpost.com/goodiesfo...l-training.pdf

Intake air system
The air intake system is in principle comparable with that of the N55B30O0 engine. The most important changes in the air intake system are adaptation of the intake silencer housing. On the N55B30T0 an additional opening is provided in the bottom housing section, to optimize the power potential and for dethrottling purposes

4.1.6. Exhaust system
The exhaust system was newly developed for the F87 BMW M2.
Differences in the exhaust system:
• Vacuum operated exhaust flap replaced by electrical exhaust flap.
• Dethrottling of the exhaust system for optimum gas exchange.
• Exhaust routing adapted to F87 BMW M2.
• Sporty exhaust sound combined with ASD to the vehicle occupants.

I also read into it more - and I believe the exhaust sizing is actually undersized for a lot of guys, especially the ones running huge turbos/boost.

The 2JZ Supra has basically the same stock exhaust flow through the head (155CFM) but have seen 66WHP by moving up half an inch
https://www.motortrend.com/how-to/mo...ust-test-tech/ This is again confirmed on the S55 cars using a larger center 3.5 midpipe with 20whp on stock tune/boost.

Basically, the more boost we run, the greater the restriction it becomes. The graphs showing a handful of HP at peak is because on the stock tune, the cars are only running 7-10psi that tapers to redline, though there is a (claimed) significant increase at the low end.
Changing a muffler isn't an exhaust system, and unfortunately, there isn't really any R&D in most aftermarket parts - so who really knows what those $1,000 mufflers do (nothing) or what's the true optimal size for FBO 16-18psi. I would be it's larger than stock.

With that being said, I picked up a AWE 3" midpipe to pair to my MPE...though I might to a better muffler, we'll see.

[AmuroRay]

I installed the AWE midpipe, and the fit...well it fits. It was welded to the MPE, and they have almost the same diameter pipe. It does rattle against the body brace at times on cold start though. As promised - tedious data collection for your information











Pre: https://datazap.me/u/amuroray/milvs-...31-32-33-35-40
RPM| Boost| WGDC
3500 | 18.5 | 87.3
3700 | 18 | 87
3900 | 18.39 | 84.9
4100 | 18.1 | 85
4300 | 18.5 | 85.1
4500 | 19.39 | 83.1
4700 | 18.5 | 86.3
4900 | 18.39 | 83.4
5100 | 19.1 | 84
5300 | 19.1 | 88.2
5500 | 19.89 | 90.1
5700 | 18.5 | 89.4
5900 | 17.2 | 88.2
6100 | 16.6 | 87.8
6300 | 16.1 | 87.9
6500 |



Post: https://datazap.me/u/amuroray/exhaus...30-31-32-33-40
RPM | Boost| WGDC
3500 | 19.2 | 84.7
3700 | 18.7 | 86
3900 | 19.2 | 84.2
4100 | 85.1 | 85.1
4300 | 19.8 | 84.2
4500 | 20.39 | 82.8
4700 | 19.7 | 82.7
4900 | 19.3 | 82.3
5100 | 19.3 | 83.5
5300 | 19.1 | 89.9
5500 | 19.3 | 88.7
5700 |
5900 | 17.6 | 89.6
6100 | 16.3 | 86.2
6300 | 15.9 | 86.6
6500 | 15.5 | 86.9


You can clearly see that the difference is a trend of more boost AND a LOWER WGDC. I believe there are bigger gains with a bigger exhaust, but there is nothing commercially available off the shelf.

I actually picked the wrong log to compare to (on the "pre" log side) Oh well, the trend is there. I'll update it after work when I'm not exhausted, no pun intended.

[AmuroRay]

I was playing around in VD - I'm just waiting for a day that's cool to hit the dyno - every day its 90F+ easy.

First graph is the "VVT change only" tune - I compared it to my BEST run with this tune before and after the exhaust. Dates are listed on the picture -
First run temps: 88F ambient, Second run temps 83F. I'll note the post exhaust run has some timing drops pre 4500RPM which account for it losing a bit of power over the pre run down low.

The second graph is the "Standard" tune before and after the exhaust. Again, this is the best run of each. Approximately 88F for the first run and 85Fish on the second

The last graph is a comparison between the two tunes. The VVT changes add torque, but lower the power on the top end. (The torque gain might not even be the changes, but the Lift profile from Valvetronic map being modified) VD does not really have the ability to correct for ambient temp and humidity, so take this for what its worth: Something fun to look at.

But the there is a trend that the upgraded mid pipe did add power, and after seeing the connection to the downpipe where the stock part necks down, it's not hard to see why. The car sounds a little more raw and has a touch more NHV. Otherwise is pretty much the same.