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That means that at low rpm where TS counts the most, your pulses are hitting turbine wheel not exactly at same time intervals, but pulse, one short pause, pulse, one long pause.
Ive talked with senior Akrapović exhaust developer and he said exactly the opposite.
He said if I go to the trouble of making TS, it is much better to try and get it to its full potential, which is equal length and calculated piping diameter.
I live 4 km away from Akrapović HQ so I hope to get some help from them when I get to exhaust piping.
Akrapovic makes beautiful exhaust pieces. How about you get them to build us some headers since your so close
Originally Posted by Voith
Ive talked with senior Akrapović exhaust developer and he said exactly the opposite.
He said if I go to the trouble of making TS, it is much better to try and get it to its full potential, which is equal length and calculated piping diameter.
I live 4 km away from Akrapović HQ so I hope to get some help from them when I get to exhaust piping.
The main benefit from the twin scroll in a four cylinder engine comes from reducing the exhaust blowdown interference. That is, you don't get one cylinder blowing exhaust right after EVO into another cylinder during overlap. The pipe length doesn't matter, you'll get this benefit regardless. This I would classify as a fact.
There are of course some pulse tuning effects that can be concentrated to specific rpms if the pipes are equal length. While one should never leave anything on the table, this is much less important that the elimination of the exhaust blowdown interference.
My personal opinion is that one should focus on getting the pipe diameters right, avoid any small radius turns, get the merge angles as shallow as possible, and get the best thermal barrier to retain as much heat as possible. The pipe length differences between cylinders are less important. This is an opinion, not a fact.
Lol, maybe it is in Akrapovic world, but in 944 world where there are so many compromises needed to be done, it doesn't matter pretty much at all. You can make things lot worse or better with tune.
If you are going through the trouble of making things equal length, then start by moving turbo to the exhaust side of the engine. You get much more effect. But for me the main purpose of twin scroll is pulse separation to reduce exhaust blowdown like ptuomov said and thus increase knock resistance.
We have tried both equal length and inequal length on 4cyl and 6cyl engines, the difference is not measurable tbh.
Akrapovic makes beautiful exhaust pieces. How about you get them to build us some headers since your so close
It all stops at $$$. They can and will make titanium everything and tune it to whatever makes you happy but invoice will have some pretty big numbers on it.
I hope I bump to Igor the owner, he could have some sympathy for enthusiasm.
The main benefit from the twin scroll in a four cylinder engine comes from reducing the exhaust blowdown interference. This I would classify as a fact.
No, that is not true. Main benefit is two separate bursts of kinetic energy to spin the turbine wheel. Timing of them is as important as any similar device. Bycicle for instance.
Originally Posted by Raceboy
If you are going through the trouble of making things equal length, then start by moving turbo to the exhaust side of the engine
Basically the lack of space on the exhaust side is why i am asking the question in the first place
I want to move the turbo to the hot side of the engine, to reduce all piping as much as possible, thus reducing spoolup and while it seems doable while making two-lenght manifold, things get pretty tricky when i try to think of a way to make a allround four equal runner manifold.. That's why I started wondering if it's worth the hassle. Might be a matter of which will works better - equal lenght with turbo on the stock side, or much nearer to the combustion chambers but with two different lenght equal lenght pipe pairs..
What does high CR has to do with getting exhaust pulses equal? Turbo on the intake side of engine on 944 is just another compromise made by Porsche on that car and is so far from the best performance solution that it is not even funny. As I said, if you are going through the trouble of equal length manifold, even more benefit is having the turbo on the exhaust side and having the runners as short as possible (with correct diameter of course).
BTW, one of the main reasons for going twin scroll in my application was to have low exhaust blowdown and therefore better knock resistance. Works perfectly so far.
You can go Akrapovic or whatever but during the time you are building your engine, I drive and enjoy it
? Turbo on the intake side of engine on 944 is just another compromise made by Porsche on that car and is so far from the best performance solution that it is not even funny.
Interesting. Mazda Skyactiv is pump gas 14:1 CR turbo. The reason why it can pull that off is VERY long exhaust header.
1. How responsive the turbocharger is
The longer the manifold runner length, the more area that needs to be filled by exhaust gasses to build the pressure and heat required to spin the turbine of the turbocharger. Short tube header manifolds, with their small runner areas are excellent at transferring the energy of the combustion of fuels in the engine to the turbine. This allows the turbo to spool several RPM sooner than a long tube manifold.
2. How much exhaust reversion the engine experiences.
One of the problems with short runner length manifolds is that they suffer in the power department when it comes to all out peak HP. This is mainly due to something called exhaust reversion. Exhaust reversion is when exhaust heading out of the combustion chamber in the exhaust manifold reverses direction, and heads back towards the combustion chamber. This causes exhaust gases to not completely evacuate the cylinder. The cylinder will therefore have not only less room for clean air and gas to enter the chamber when the intake valve opens, but also that air will be hotter and more prone to pre-ignition and detonation. Longer tube manifolds help to keep the exhaust gases flowing in the right direction and don’t allow reversion from cylinders to other cylinders. One of the huge benefits of a twin scroll divided set-up is that it pairs exhaust runners who are 180 degrees apart from each other in their firing order together. This cuts WAY down on exhaust reversion. For example, on a four-cylinder motor you would pair cylinder 1 with 4 and 2 with 3.
3. Exhaust flow
Longer tube headers before the turbo allow for more area before the restriction of the turbine wheel of the turbo. This added area allows for more expansion and flow of the hot exhaust gases. This increase in area provides you flow just like going from a 2” to 3” exhaust ads exhaust area and gains exhaust flow.
4. Detonation Suppression
Longer tube headers allow for more exhaust flow and hinder exhaust reversion. This helps in controlling combustion cylinder temperatures by allowing more area for fresh cool air to enter the combustion chamber. Since cylinder temperatures directly correlate to detonation, it is important to keep them as cool as possible.
Long tube vs short tube turbo header design
So it looks like you have choices to make when it comes to designing or picking out a turbo manifold. The length and design of the manifold will greatly control the responsiveness of the turbo, and the compression or ignition timing you will be able to run without causing detonation or pre-ignition. Short tube headers will provide a fast responsive turbo, while a long tube header, like the one on the Mazda sky motor, will allow you to run higher compression, more advanced timing, and have higher exhaust flow. There is no best option here as it really depends on what you’re going for with your set-up. Whatever you choose, now you can make an educated decision for your goals.
You started your build in 2008 so yours wasn't exactly fast either.
I was driving the car with another engine for almost all the time, removed it before paint job. But had several other Porsches to drive with
And trust me, Porsche did not put the turbo on the intake side because of knock resistance. It was just a turbocharger longevity issue that was present on 931. As was turbocharger waterpump etc.
Like any other manufacturer, Porsche is also trying to find ways how to reduce number of warranty claims and if they can reduce this, by say even 0.5% they are willing to sacrifice performance easily by 10% and just raise boost level a bit instead.
A few goodies came - 20mm swaybar - non adjustable yet, but we're most likely going to move the mounting point a bit; and ultralight mirrors - probably the cheapest upgrade at $6 a piece (brand new).
The decision has been made - if there is no condition i forgot to consider, i will put the turbo behind the front lamp. With only minor modification to the frontright frame, there's just enough space for a perfect fit of a carrera gt lamp, a simple heatshield and the big holset hx40s. This sweet spot allows me to shorten the exhaust manifold by 57% from 160cm (63") down to a mere 69cm (27") measured from head to turbo housing. Furthermore it's all four runners equal lenght and they are separated all the way up to the twin scroll housing. I wonder how responsove this setup will be.. I don't expect miracles with such a big turbo but everything's possible i guess..
06-22-2015, 06:50 AM
