I’m hoping that some of you guys that spend much of your waking hours thinking about how to get more flow through a port might have some ideas or different approaches for optimizing exhaust flow out of a turbine housing (something that I’ve never heard any real consensus on on ‘blown’ lists or boards).
Flow coming out of a turbocharger’s turbine housing tends to rotate in the same direction or opposite direction of the turbine wheel depending on it’s relative speed. The problem is that swirling flow does not work well in a tube, and a goal to maximizing flow out of a turbocharged engine is to convert this as quickly as possible to turbulent/laminar airflow like in a conventional exhaust.
Everyone seems to agree that a straight or gradual bend coming off of the turbo that is roughly the same size as the rest of the exhaust is the worst.
There appear to be 3 trains of thought about optimizing flow:
- Most turbo manufacturers suggest that you want to increase the cross section of the exhaust pipe leaving the turbine at roughly a 12* angle till you basically reach the outside world (enough not to pose a restriction to the swirling air, not enough for that flow to separate from the walls of the exhaust). Totally impractical for everyday use, and even most race cars. Some larger turbos even have the start of this taper built into the discharge of the turbine housing. They seem to suggest that in a real world application that you just increase to whatever you have room for and then accept your losses…
- McInnes (holds a bunch of turbocharging patents) suggests that the way to go is to quickly increase the crossection of the outlet to a large size for 18-24” and then neck down to your normal exhaust, the idea is the quick expansion and the chamber disrupts the swirling flow allowing things to settle down and flow well through the smaller pipe leaving the chamber
- OEM’s and a few others subscribe to the thought that you should put a sharp, 90* turn right at the turbine housing, and the flow will not be able to ‘stick’ to the inside surface of the turn and disrupt the swirl (I’m not sure I buy this since I’ve seen tests of ‘banjo’ outlets in tight packaging applications that suggested that they flowed more then a traditional 90* bend).
One thing that I’ve played with (and I’m noticing a few import tuners are starting to try this) is to put a vane or even an X shaped vane in the exhaust right after the turbine keep the flow from being able to swirl in the pipe.
Anyone have any thoughts on what would work best? This is a difficult thing to test since the only accurate way that I could think of to do this is to test it on an engine dyno where you can easily change packaging and measure exhaust pressures and spool times.
Flow coming out of a turbocharger’s turbine housing tends to rotate in the same direction or opposite direction of the turbine wheel depending on it’s relative speed. The problem is that swirling flow does not work well in a tube, and a goal to maximizing flow out of a turbocharged engine is to convert this as quickly as possible to turbulent/laminar airflow like in a conventional exhaust.
Everyone seems to agree that a straight or gradual bend coming off of the turbo that is roughly the same size as the rest of the exhaust is the worst.
There appear to be 3 trains of thought about optimizing flow:
- Most turbo manufacturers suggest that you want to increase the cross section of the exhaust pipe leaving the turbine at roughly a 12* angle till you basically reach the outside world (enough not to pose a restriction to the swirling air, not enough for that flow to separate from the walls of the exhaust). Totally impractical for everyday use, and even most race cars. Some larger turbos even have the start of this taper built into the discharge of the turbine housing. They seem to suggest that in a real world application that you just increase to whatever you have room for and then accept your losses…
- McInnes (holds a bunch of turbocharging patents) suggests that the way to go is to quickly increase the crossection of the outlet to a large size for 18-24” and then neck down to your normal exhaust, the idea is the quick expansion and the chamber disrupts the swirling flow allowing things to settle down and flow well through the smaller pipe leaving the chamber
- OEM’s and a few others subscribe to the thought that you should put a sharp, 90* turn right at the turbine housing, and the flow will not be able to ‘stick’ to the inside surface of the turn and disrupt the swirl (I’m not sure I buy this since I’ve seen tests of ‘banjo’ outlets in tight packaging applications that suggested that they flowed more then a traditional 90* bend).
One thing that I’ve played with (and I’m noticing a few import tuners are starting to try this) is to put a vane or even an X shaped vane in the exhaust right after the turbine keep the flow from being able to swirl in the pipe.
Anyone have any thoughts on what would work best? This is a difficult thing to test since the only accurate way that I could think of to do this is to test it on an engine dyno where you can easily change packaging and measure exhaust pressures and spool times.
Registered User
Ya that 12 degree taper is unconventional, but the 90 degree bend right after the turbine discharge is what I have always seen and heard. I seem to think that such a sharp bend would cause some backup in the exhaust gasses and add more back pressure than could be had, but I dont know a much better way.
The splitter idea you mentioned, with an x shaped in vane sound like it would really work. Have you done this to an actual turboed engine? Seen any benefits or gains in doing this?
One way to test this would be a flow bench, with a swirl meter that they use to test for swirl in flow testing of heads. If there is still swirling gases after this vane, or any other test subject then we will know if it would help.
I think something that might be interesting to test is using some kinds of muffler technology with different vanes (like WS6 TA said), and chambers used in mufflers like Corsa and Flowmaster make.
Hunter
The splitter idea you mentioned, with an x shaped in vane sound like it would really work. Have you done this to an actual turboed engine? Seen any benefits or gains in doing this?
One way to test this would be a flow bench, with a swirl meter that they use to test for swirl in flow testing of heads. If there is still swirling gases after this vane, or any other test subject then we will know if it would help.
I think something that might be interesting to test is using some kinds of muffler technology with different vanes (like WS6 TA said), and chambers used in mufflers like Corsa and Flowmaster make.
Hunter
A long time ago tried about an 8” long X shaped vane (cut a slit in 2 pieces of sheet steel, tack welded them together and then tack welded it in the down pipe), and I know someone else that’s tried something similar (I think that the just put a single vane in). Both cars showed a very obvious decrease in spool times (the one that I played with was spooling 500-700rpm sooner, maybe more).
A couple of days ago I ran across a subaru/import tuner in Australia selling downpipes with a similar arrangement.
A couple of days ago I ran across a subaru/import tuner in Australia selling downpipes with a similar arrangement.