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I'm in the mood for an awesome exhaust on these cars. No one has built one yet! I wan't to see equal length runners, twin scroll exhaust, twin wastegates, and three exhaust pipes out the back (two: 1 7/8" wastegate pipes and one 3" turbo exhaust pipe. If the pipes are too big they will weigh more and slow down the escaping exhaust gasses by cooling to fast and take up too much room. I want all the header pipes made out of 321 ss and from the turbo or wastegates back out of 304 ss. I would like to see "v" band clamps for easy removal for inspections. I want the exhaust out the back because that's how Porsche designs the areodinamics of the car. Not a wastegate dumped under the car creating a hot pocket. There is no disadvantage of using a twin scroll turbo, only will help with our cars!!
So grab your pens and pad and draw up your best design. I'll show you what I scribbled down. Its time to come up with the best exhaust design. If Hondas have it and we don't i feel incomplete.
I like the idea of a twin scroll setup. a few have done it. cannot remember on the outcome though.
But i had a waste gate exhaust to the back. takes up quite a bit of space. although i used a 2.5" pipe (all i had) but rather use a 2.5" with both gates leading to it.
making the twin pipes to the turbo would be the challenge.
1 - space
2 - correct sizing. to big to much backpressure. to little to much back pressure.
having a RHD car making it easier for the crossover just more challenging for the 4-1 headers.
Subaru guys find some pretty good top-end power with equal-length pipes versus their stock unequal-length manifolds. It does change the sound of the exhaust though, and sacrifices some low-end power, but your previously-stated goals should be OK with that
I made twin-scroll crossover for my 2.5 16v turbo. But really, making twin scroll equal length, especially on 944 engine gives very little reward in relation to the effort needed. There are so many other areas that would need to be addressed first with much less effort.
Twin-scroll affects spoolup much more than equal length and having it both does not mean even bigger cumulative effect sadly.
Twin scroll ftw. Bought AC/DC TiG welder recently just for this purpose.
I will try and use efr internal wastegate and simplify things. Two wastegates and all the plumbing is a bit of overkill.
TS benefits are proven and quite dramatic both at low and high end.
Btw: square tubing is not ideal for exhaust construction, it causes more drag and turbulences.
From another forum(camaros.net):
Originally Posted by Toby Keen
My profession is commercial and industrial heating, ventilation and air conditioning (HVAC). I will explain by saying that the air will tumble in all four corners of a boxed tube. Therefore, it would take a boxed tube of approximately 1.25 times the size of a round tube to do the same job. The surface area example is a good one.
When we design a duct system for an HVAC system, friction is the largest consideration. There is approximately 1.25 times the friction in a square duct than there is in a round duct that delivers the same amount of air, measuring for static pressure loss in the two using a straight pipe. We use turning vanes in a square duct and 1.5 (1.5 times the diameter of the round pipe) elbows in the round or oval duct to prevent further static pressure losses.
Turbulance = static pressure loss.
By the time a header pipe was made big enough to accomplish it desired goal, the pipe would be too large to save any space over a round pipe.
Twin scroll and dual wastegates has been done before. As stated above, I don't think the overall gains were worth the cost and effort. Very interested to see what avenues you go down to see project completion.
Twin scroll and dual wastegates has been done before. As stated above, I don't think the overall gains were worth the cost and effort. Very interested to see what avenues you go down to see project completion.
The one I showed above is made for my 924 2.5 16v and it works exactly as expected.
So square tubing is out of the design all together! What about the idea of a rear mount twin scroll turbo. It can set where the muffler is now. You can remove the heat shield above the muffler for more space and replace it with a design that will work best for the parts chosen. That way you don't get heat soak from the crossover to the oil pan. Also heat soak from the turbo to the intake manifold. Wastegates are dumped in the back by the turbo. There is a LOT of room where the muffler hangs. It will help turbo longevity due to cooling just a little more before hitting the exhaust turbine. And I seen an intercooler pipe with fins on it on eBay, that consept could be used on the intake side in place of an intercooler, as it will run from the back of the car to the front next to the exhaust, it would take place of the intercooler. Then have more room for oil coolers where the intercooler sat, and not worry about heat soak from a front mounted intercooler to the A/C system and radiators for those of you that have one of those, or heat from the stock intercooler location to the engine bay. You could use any intake manifold you wanted because there's no turbo in the engine bay taking up the room. The spare tire area can be removed also. It's not like we use it! So on that note, you could modify the spare tire area by whatever means you take. I was thinking of having an oil resivoir and water resivoir back there for the turbo and have quality electric pumps for them, and have small water and oil coolers for the turbo mocked up by the redesigned spare tire area. Or you could run just oil lines from the engine and not use water. It's a design, it's flexible. Let me know what you all think.
Also with a rear mount turbo setup, it makes it easier for me to make an intake manifold for my 85/86 928 4V head turbo swap. I can use the 928 intake manifold flanges and use the 944 S intake manifold I have. A bonus is the intake pipe from the turbo will tie in at the rear of the engine and that's where the throttle body is on the S intake. Also don't need all that brake booster/starter/steering knuckle heat shielding. And don't need a fancy turbo mount. Or fancy intake manifold. With the S and S2 cars this would be ideal as they are the DOHC engine with big flow heads and not much modification is needed on the intake manifold. And the exhaust is already set up to due a twin scroll piping coming off of the catalitic converter pipe. Just cut the pipe after the collector before it merges to one and keep two separate pipes all the way to the turbo. You can use turbo headers and a regular 944 cat pipe for the two pipe flange with the pipe coming off it for those parts.well the head I'm using you can use the turbo headers. But with the 944 DOHC head the exhaust headers will have to be addressed. As they are the three bolt flange not the two bolt flange.
Last edited by Humboldtgrin; 09-13-2015 at 07:16 PM.
09-10-2015, 08:15 PM
Designing: equal length runner twin scroll turbo exhaust
