[MOD.Works]

I really don't mean that a 4-stroke engine needs back pressure. But the collector is just as important as the headers and you have to think of the whole rest of the exhaust after the headers as a collector. Bigger is not always better.
But the exhaust rear section a 70mm diameter is certainly enough for a 300hp engine. Especially when the front and middle section is a double exhaust.
If the Y-piece was immediately after the headers, then a 76mm single exhaust would be better.





I just don't understand why my N52 does what I wrote before.

Here is a comparison with the flap closed and open. Drove in the same place and direction, first with the flap closed and then open. Red= flap closed and Blue= flap open.
I don't have exactly the same Log for the MD rear pipe. But the airmass shows that the loss is even slightly greater in the high rpm range.

[AmuroRay]

You can see you lost power with the flap closed (more back pressure) and OEM mufflers aren’t an upgrade, they don’t flow that well to begin with.

Your issue is likely the collector location - it’s too far back. You should move it towards the end of the transmission/drive shaft area (or even a tad closer) to the engine. It’s too far back to take advantage of proper scavenging.

Finally, again, the piping diameter is only an issue prior to the collector, after the merger, there is no detriment by going larger, just smaller.

[MOD.Works]

Originally Posted by AmuroRay

You can see you lost power with the flap closed (more back pressure) and OEM mufflers aren’t an upgrade, they don’t flow that well to begin with.

Your issue is likely the collector location - it’s too far back. You should move it towards the end of the transmission/drive shaft area (or even a tad closer) to the engine. It’s too far back to take advantage of proper scavenging.

Finally, again, the piping diameter is only an issue prior to the collector, after the merger, there is no detriment by going larger, just smaller.

At first I thought that I would install a Y-pipe near the headers.
I painted the front pipes with the old school methods and saw where the paint wears off first. And I also used Pipemax in the calculation. A good place for the Y piece would have been a little before the first bend.
I didn't dare to do it. I was afraid I would lose low end torque, especially knowing I was going with the N54 intake. I read writings, e.g. e46 M3, where low torque was lost, after a new exhaust with a Y part near the headers was installed.

I think a good place would have been to find the Y part by trying a different place and running a Dyno. I made a safe decision and went near Stock. As e.g. SuperSprint has done.





Today I drove a little longer with the flap open. A few WOT pulls before the "Dyno" pull.
I got better results with the flap open. I think it might be a matter of adapting a little.

I'll try my test pipe sometime later. I need to install a straight through muffler on it. With which to get the sound down.

Red = Flap open
Blue= Flap closed

[AmuroRay]

So it was an adaptation issue.
Question, where did pipemax tell you to put the merger? And what were the recommend sizes?

[MOD.Works]

Originally Posted by AmuroRay

So it was an adaptation issue.
Question, where did pipemax tell you to put the merger? And what were the recommend sizes?

It depends on what Peak RPM uses in the calculation. This calculation is 6200RPM peak. The new version of Pipemax recommends large diameters for the exhaust pipe. Double pipe more than 2.5 inches and single 3.5 inches. I didn't go that big.
I don't have all the cam specs for the N52B30. But I think I'm close enough.

H-Pipe Location= 510,678 or 255,339 mm X-Pipe Location= 2042,714 or 1021,357 mm
( both H-Pipe and X-Pipe locations are measured from Primary Tube ends inside the Collector )

Here is a table for different Peak HP RPM.

Best TQ + HP Tuned Collector Lengths= 100,963, 201,926, 403,852, 807,703, 1615,406, 3230,813 mm long 7500RPM
Worst TQ + HP Loss Collector Lengths= 151,444, 302,889, 605,777, 1211,555, 2423,110, 4846,219 mm long

Best TQ + HP Tuned Collector Lengths= 109,203, 218,406, 436,812, 873,623, 1747,246, 3494,492 mm long 7000RPM
Worst TQ + HP Loss Collector Lengths= 163,804, 327,609, 655,217, 1310,435, 2620,869, 5241,738 mm long

Best TQ + HP Tuned Collector Lengths= 118,999, 237,998, 475,997, 951,993, 1903,987, 3807,974 mm long 6500RPM
Worst TQ + HP Loss Collector Lengths= 178,499, 356,998, 713,995, 1427,990, 2855,980, 5711,961 mm long

Best TQ + HP Tuned Collector Lengths= 130,851, 261,703, 523,406, 1046,812, 2093,623, 4187,247 mm long 6000RPM
Worst TQ + HP Loss Collector Lengths= 196,277, 392,554, 785,109, 1570,218, 3140,435, 6280,870 mm long

Best TQ + HP Tuned Collector Lengths= 145,503, 291,006, 582,011, 1164,022, 2328,045, 4656,090 mm long 5500RPM
Worst TQ + HP Loss Collector Lengths= 218,254, 436,508, 873,017, 1746,034, 3492,067, 6984,135 mm long

Best TQ + HP Tuned Collector Lengths= 164,111, 328,221, 656,442, 1312,885, 2625,770, 5251,540 mm long 5000RPM
Worst TQ + HP Loss Collector Lengths= 246,166, 492,332, 984,664, 1969,327, 3938,655, 7877,309 mm long

Best TQ + HP Tuned Collector Lengths= 192,310, 384,620, 769,239, 1538,478, 3076,957, 6153,913 mm long 4500RPM
Worst TQ + HP Loss Collector Lengths= 288,465, 576,929, 1153,859, 2307,718, 4615,435, 9230,870 mm long

Best TQ + HP Tuned Collector Lengths= 229,292, 458,585, 917,170, 1834,340, 3668,679, 7337,358 mm long 4000RPM
Worst TQ + HP Loss Collector Lengths= 343,939, 687,877, 1375,755, 2751,509, 5503,019, 11006,037 mm long

Best TQ + HP Tuned Collector Lengths= 259,160, 518,320, 1036,641, 2073,282, 4146,563, 8293,127 mm long 3500RPM
Worst TQ + HP Loss Collector Lengths= 388,740, 777,481, 1554,961, 3109,923, 6219,845, 12439,690 mm long

Best TQ + HP Tuned Collector Lengths= 372,600, 745,200, 1490,401, 2980,802, 5961,604, 11923,207 mm long 3000RPM
Worst TQ + HP Loss Collector Lengths= 558,900, 1117,801, 2235,601, 4471,203, 8942,405, 17884,811 mm long

Best TQ + HP Tuned Collector Lengths= 541,964, 1083,928, 2167,856, 4335,712, 8671,423, 17342,847 mm long 2500RPM
Worst TQ + HP Loss Collector Lengths= 812,946, 1625,892, 3251,784, 6503,568, 13007,135, 26014,270 mm long


Best TQ + HP Tuned Collector Lengths= 818,101, 1636,201, 3272,403, 6544,806, 13089,611, 26179,222 mm long 2000RPM
Worst TQ + HP Loss Collector Lengths= 1227,151, 2454,302, 4908,604, 9817,208, 19634,417, 39268,833 mm long

Stock pipes are about 2100 and 2200mm long. I made slightly shorter ones and they are almost the same length. I don't remember the exact measurement, but about 1800mm or a little more.

[AmuroRay]

Originally Posted by MOD.Works

It depends on what Peak RPM uses in the calculation. This calculation is 6200RPM peak. The new version of Pipemax recommends large diameters for the exhaust pipe. Double pipe more than 2.5 inches and single 3.5 inches. I didn't go that big.
I don't have all the cam specs for the N52B30. But I think I'm close enough.



Here is a table for different Peak HP RPM.



Stock pipes are about 2100 and 2200mm long. I made slightly shorter ones and they are almost the same length. I don't remember the exact measurement, but about 1800mm or a little more.

Peak power on the 3SIM is about 6500-6600R, and 7200RPM on the N54, you might have low balled yourself a bit. The cam specs can be found on the BMW technical manual for the N52/N54