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Join Date: Jun 2014
Location: Germany
Posts: 38
Originally Posted by JakobM View Post
Great project!

Looking at the header pictured the guy who build this seems to have misunderstood how Twin scroll works just as many other manufactures. Or I see it wrong on the picture. I see on the picture the divided "wall" in the turbo flange is SUNKEN into the collector!??! meaning all pulse separation is gone right there! And the split "wall" is way too thin also if height even was correct... Same issue when people go with a "Y" shaped WG design ending in one open shared WG on a twin scroll header/flange and call it true separation...What they have is a destroyed twin scroll system! It has to be 100% separated, as in 100% closed banks any where in the system to carry the name "true separated". Otherwise it is a simple open system inside, but may look like twin scroll outsite and advertised as such. Your choice of two wg's are the way to go, but make sure to get that flange "wall" up in correct same height and aligned with the same separation wall on the turbine housing, and get it thicker to seal properly.
To be honest. I never thought of this or better said, never thought to think twice of it. Thank you for this info!
And when it comes to the basics I have found many willing to build an exhaust, but in 12 of 13 cases it stopped at questions of anti-reversion collector design. It is very hard finding experts other than the internet these days and even fewer willing to share their experience.

Originally Posted by JakobM View Post
I would not go 2.25' secondaries when building equal length. Back pressure is fine already. Secondary becomes an extension of primaries on equal length design, and primaries now have two dimensions. Only if our flat six engines fired 3 cylinders parallel in each bank I would go for such diameter secondaries. Secondaries are not used on twin turbo headers either besides getting a collector pipe to fit inlet flange. Each of the 666 ccm3 cylinder pulses (4L / 6 cyl) would slow down in 2.25' extended primary and loose energy before they go to work again in the turbine - those pulses run alone and separated

Un-equal length headers still have pulses separated (separated in different spread out pattern) if build correct, and typically gain higher velocity due to the lack of long secondaries. Twin scroll housing help unequal length headers to separate pulses even more, as it gives an extra "cylinder cycle time" in between next pulse in each bank to spread out pulses for each side turbine. Meaning, equal length becomes less important factor to separate pulses on twin scroll setup and is sacrificed for higher velocity instead
So the length of the header is fine, as long as the pulses at the Flange (Twin-Scroll) are strictly separated? I have looked at Bill Verburgs Exhaust stuff in this regard.
The problem is that the exhaust is being built in a different country, so comes off of a standard setup. I have phoned Burns Stainless and they noted 1,75 to 2,25 as well, but noting secondaries should be "as short as possible".

Originally Posted by RarlyL8 View Post
Yes if your going to the trouble to build custom headers and have the space then equal length secondaries are an added plus. The tuned sound tells you that the pulse timing is optimized. To finish off the build I would bump the port primaries and port match the inlet flanges then also port match the T4 split plenum with that of the turbo. This match also needs to include the T4 turbo gasket. This attention to detail simply helps optimize everything. The gains are diminishing of course but using that level of detail on the entire build will make a difference.
I agree on the attention to detail hence I wanted input from the vast knowledge on this forum to see whats needs to improve. I am uncertain on the terminology of "bump the port primaries". Do you mean anti reversion? or stepped up in diameter to the first collector?
Old 02-14-2019, 06:03 AM
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