Sizing of header for turbo build

[Undutched]

Dear Pelican,

I have been working on my 4.0 964 NA-T conversion for half a lifetime and several lifetime savings, or that's the way it feels.

In any case, some help would be great! Since this is a custom build, why try to save a few bucks if it could be outstanding, right?

Specs:
Xtreme cylinder heads with 44,5mm ports on the exhaust side. At .500 lift around 213CFM on a flow analyzer at the exhaust ports. Intake a little over 300.
4.0l crank
Elgin C2 Super cams

So twin wastegates and GTX40 are in the plan, but more importantly are the headers themselves.
Should we start at 45mm and after collector 57mm? From my experience too large is easily attained, but neither do I want a bottleneck. Same question on how to and if to do stepped primaries and whether to use anti-reversion. Equal length or short runners? Does it all make sense on a turbo?
If I look at Turbokraft (beauties, btw) or Rarlyl8 (great communication), they all look different and all cost more or less the same, but since I need a full custom job, pointers would be great.

The jig which we are going to use allows for some adjustments (slip-on fit or bolted as attached). This is an exhaust from the same builder, so if you have suggestion please let me know.
Exhaust pictured by TT Exhausts from the UK.

[Raceboy]

45mm is good and no need for bigger than exhaust port.
You will want them as short as possible. For the power goals you aim I would go with twins, you get much shorter exhaust and lighter impellers etc making spoolup better which is important for a car that could be called even remotely a streetable.

With big single twin-scroll is also good but exhaust manifold volume will be much bigger than needed.

FWIW I am doing 2.5liter short stroke (66x90) 911 engine and it gets twin IHI ball bearing turbos capable of 300 hp each. Lighting fast spool.

[RarlyL8]

That's a lot of engine with a turbocharger!
Key to turbo header design is velocity. Counter intuitive to normally aspirated builds, the flow must restrict as it makes its way to the turbine which increases its speed. The exhaust ports you site at 44.5mm are huge. Piping with this ID would be 1 7/8"OD. Decision on primary and secondary size depends on projected HP output at X000rpm at x.xbar boost. That is the first question that needs to be answered. How the car will be used, where the powerband is preferred, and specifics on the turbo specifications also will be needed information.
My starting point would be 5th harmonic equal length 1.75"OD bumped primaries and equal length 2.25" secondaries (the secondaries on the set you have pictured are too long) to improve off boost performance and torque. Split volute T4 flange with twin waste gates.

.

[Undutched]

Originally Posted by Raceboy

45mm is good and no need for bigger than exhaust port.
You will want them as short as possible. For the power goals you aim I would go with twins, you get much shorter exhaust and lighter impellers etc making spoolup better which is important for a car that could be called even remotely a streetable.

With big single twin-scroll is also good but exhaust manifold volume will be much bigger than needed.

FWIW I am doing 2.5liter short stroke (66x90) 911 engine and it gets twin IHI ball bearing turbos capable of 300 hp each. Lighting fast spool.

It may be easier and I agree to an extent on using twins, but on my last engine the smaller Turbos didn't perform as well as the BW EFR. Turbos have gone a long way and I like the idea of one large turbo. In general I would agree though!

Originally Posted by RarlyL8

That's a lot of engine with a turbocharger!
Key to turbo header design is velocity. Counter intuitive to normally aspirated builds, the flow must restrict as it makes its way to the turbine which increases its speed. The exhaust ports you site at 44.5mm are huge. Piping with this ID would be 1 7/8"OD. Decision on primary and secondary size depends on projected HP output at X000rpm at x.xbar boost. That is the first question that needs to be answered. How the car will be used, where the powerband is preferred, and specifics on the turbo specifications also will be needed information.
My starting point would be 5th harmonic equal length 1.75"OD bumped primaries and equal length 2.25" secondaries (the secondaries on the set you have pictured are too long) to improve off boost performance and torque. Split volute T4 flange with twin waste gates.

.

Brian, thank you for the input.
Power: As you may know we need "Autobahn-proof" engines, so it should be capable of roughly 800, but won't see that power 95% of the time hoping to have an easily drivable car with low to midrange torque with less than 1 Bar, with seldom use of higher boost, so basically 600ish HP. The plan used to be to use E85, but it all but vanished here in Germany.

Using 1.75" to 2.25" was our idea as well (had to check in Inches). The primaries were measured to be around 65cm (25in) Thank you on the note with the regards to the length of secondaries. I have looked at your site maybe a thousand times over the last years and didn't notice this.
It seems some use equal length secondaries and others don't (like turbokraft or BB).

[JakobM]

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.

[RarlyL8]

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.

[JakobM]

Originally Posted by Undutched

Using 1.75" to 2.25" was our idea as well....

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

Originally Posted by Undutched

.... It seems some use equal length secondaries and others don't (like turbokraft or BB).

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

[Undutched]

Originally Posted by JakobM

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

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

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?

[RarlyL8]

I am uncertain on the terminology of "bump the port primaries".

At 44.5mm the exhaust ports are larger than the 1.75"OD primary pipes. A transition must be made by matching the primary flange ID to the port ID and bumping the primary to 44.5mmID at the port outlet. This creates a smooth transition and helps velocity. The port gasket should also be 44.5mm.
Yes secondaries should be as short as possible and equal length if possible.

[JakobM]

We are not that far from each other, I am located just north of you in Dänemark :-)
I have been tig-welding custom turbo headers for many years. Twin scroll only, and all kind of cars. Happy to share experience.
Yes, good that you get the sunken separation wall corrected, that would mess up every penny you spend.
You want your primaries to port match your exhaust openings from cylinders
You want short as possible routing from exhaust valve to turbine wheel
You dont want to go too big on secondaries, as you will run equal length and twin scroll.
Ideal you want to have turbo centered at the back (for short routing) of the engine and build short secondaries around that. Twin scroll, two wastegates. Then forget rest and you are good to go
Normally best practice is very short secondaries and in the dimension so they fit to tig weld the T4 split bank flange. Such dimension is ok short as velocity for a single puls drops dramatically. If your welder is skilled, then he can press fit the secondaries to fit flange and use the walls from the 2x secondaries as the separation wall. Makes an easy and simply layout with correct flange inlet. Or you can put in the 5mm thick wall instead, and weld secondary inlet around it.

Note: this is Turbo macro tuning, and not NA micro tuning, so other factors are in play and priorities in regards to back-pressure, velocity, temperature, turbo efficiency etc. Burns or who ever commercial business you will ask have their products to promote and sell. Burns make collectors for both NA and turbo. Turbo is much different, you will have single scroll, twin scroll, equal length, un-equal lenght, and outlet diameters from merge collector are NOT the same for all these different applications. It is not that difficult to cut and weld your own collectors just like burns and others. Make a jig for the saw, and you have what you need to tig-weld your own collectors with free pick on outlet dimensions. Just because they are a business, dont mean they are correct when pointing at a product for you to pick and buy. Look at the example of the sunken separation wall - you will find those business out there (plenty for porsche offerings as well), who sell twin scroll headers with such sunken separation walls. They have absolutely no clue what they are building in that perspective.
It is both fun and pays off to make your own header

[Raceboy]

Fully agree with Jakob, as short as possible and keep pulses separated.
But I would still go with twins, just take some modern turbos. Twin turbos themselves keep the pulses separated.

[Neil Harvey]

Looking at the system posted here, the detail at the turbo flange sunken or not and the secondary sizes will not be an issue. Yes, maybe the behavior of the pulses will be effected by these features but in this system they will not be a issue.

The biggest problem with this system is the positioning of the wastegates. So far from the turbine will create a huge delay in response, regardless of secondary size or turbine design.