How does Twinscroll Work?
The non-gated twin scrolls that TedB and Geoff use and favor are pretty much a no compromise housing. They may give up a wee bit of topend flow, but more than make up for it in improved spoolup velocity and pulse management.
The "gated"( i.e.16G) TS turbine housings, on the other hand, although enjoying certain twinscroll benefits also make certain compromises in the turbine inlet area. If you compare the turbine inlet area on a 10.5 to a turbine inlet on a 9.8, I am sure that you´ll see what I am getting at.
I was really only trying to say that the non-gated twinscroll housing designs in general make relatively fewer concessions in the turbine inlet area than internally gated twinscroll housings(i.e., 16G´s)do. This is due mostly to the convoluted troughs and protrusions required to cast and plumb the dual wastegate bypass ports perpendicular to the scroll axis, within the already restricted space of the turbine inlets. These casting proturbances are, by necessity, more intrusive on the two smaller A/R housings(9.0, &, 9.8) than it is on the 10.5, IMO.
Last edited by sparky; Mar 17, 2009 at 03:07 PM.
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I'm not sure why that should be so difficult to understand. It's the difference between moving the TP from 20%-75% and feeling the engine respond quickly, or feeling like one is waiting for something to happen. A dyno cannot resolve this. I feel anyone who can make their way out of a paper bag can understand it.
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small bump - modified mag is doing a small story on twinscroll in next month's issue, nothing too eye opening for anyone who read pg 1 of this thread tho
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a small bump -- the latest press release from BMW
"Finding new ways to expand the boundaries of what is possible with existing
BMW models has been the singular purpose of the craftsmen at BMW M. Now the
BMW X5 M and the BMW X6 M are the first all-wheel-drive models to offer the
remarkable performance, dynamic driving experience, athletic design, and
premium quality of a BMW M product.
Both models are powered by a newly-developed 4.4-liter V8 M engine delivering
555 hp at 6,000 rpm and 500 lb-ft of torque from 1500 to 5,650 rpm. This new
M engine is the world’s first with a pulse-tuned exhaust manifold encompassing
both rows of cylinders combined with high-performance twin-scroll twin turbo
technology."
"Finding new ways to expand the boundaries of what is possible with existing
BMW models has been the singular purpose of the craftsmen at BMW M. Now the
BMW X5 M and the BMW X6 M are the first all-wheel-drive models to offer the
remarkable performance, dynamic driving experience, athletic design, and
premium quality of a BMW M product.
Both models are powered by a newly-developed 4.4-liter V8 M engine delivering
555 hp at 6,000 rpm and 500 lb-ft of torque from 1500 to 5,650 rpm. This new
M engine is the world’s first with a pulse-tuned exhaust manifold encompassing
both rows of cylinders combined with high-performance twin-scroll twin turbo
technology."
How would you figure that their manifold is not a pulse converter type, as dictated by the description above? Their manifolds run cyls 1 & 4 into one scroll and 2 & 3 into the other, thus separating pulses as much as possible. How is this any different than the OEM EVO manifold?
A true pulse converter will use a venturi shape at the runner end where it meets the collector/plenum. The venturi creates a pseudo-one-way valve that reduces exhaust reversion. This is done by the shape promoting a low loss coefficient to flow in one direction but an appreciably higher loss coefficient in flow the opposite direction.
A shallow angle merge collector flows well in both directions and would not be considered a pulse converter. The purpose of the shallow angle merge collector is to provide a low loss coefficient from runner to collector, but a high loss coefficient from runner to runner. Unfortunately, the loss coefficient from collector to runner is low, there by providing little flow restriction to exhaust reversion generated by the turbine.
Pulse converters are more conventionally used on single scroll diesel engines. The OEM EVO manifold has a venture profile in the runner if you look carefully. Much of it gets ported out when you port the manifold though. The gains are from increased flow area, but it would be interesting to see a company come out with a cast manifold with larger, smoother runners but still used the pulse converter profile.
Last edited by 03whitegsr; Apr 7, 2009 at 07:42 AM.
A pulse converter type manifold uses a particular runner geometry. It has nothing to do with cylinder pairing.
A true pulse converter will use a venturi shape at the runner end where it meets the collector/plenum. The venturi creates a pseudo-one-way valve that reduces exhaust reversion. This is done by the shape promoting a low loss coefficient to flow in one direction but an appreciably higher loss coefficient in flow the opposite direction.
A shallow angle merge collector flows well in both directions and would not be considered a pulse converter. The purpose of the shallow angle merge collector is to provide a low loss coefficient from runner to collector, but a high loss coefficient from runner to runner. Unfortunately, the loss coefficient from collector to runner is low, there by providing little flow restriction to exhaust reversion generated by the turbine.
Pulse converters are more conventionally used on single scroll diesel engines. The OEM EVO manifold has a venture profile in the runner if you look carefully. Much of it gets ported out when you port the manifold though. The gains are from increased flow area, but it would be interesting to see a company come out with a cast manifold with larger, smoother runners but still used the pulse converter profile.
A true pulse converter will use a venturi shape at the runner end where it meets the collector/plenum. The venturi creates a pseudo-one-way valve that reduces exhaust reversion. This is done by the shape promoting a low loss coefficient to flow in one direction but an appreciably higher loss coefficient in flow the opposite direction.
A shallow angle merge collector flows well in both directions and would not be considered a pulse converter. The purpose of the shallow angle merge collector is to provide a low loss coefficient from runner to collector, but a high loss coefficient from runner to runner. Unfortunately, the loss coefficient from collector to runner is low, there by providing little flow restriction to exhaust reversion generated by the turbine.
Pulse converters are more conventionally used on single scroll diesel engines. The OEM EVO manifold has a venture profile in the runner if you look carefully. Much of it gets ported out when you port the manifold though. The gains are from increased flow area, but it would be interesting to see a company come out with a cast manifold with larger, smoother runners but still used the pulse converter profile.
Back on topic...
I personnaly do not understand how anyone would not like the advantages of a twin scroll for daily driving/occasional track usage. The improved spool is worth it's weight in gold.
I have built a couple manifolds. None have had a true pulse converter geometry though as it would be pretty difficult to fabricate and would be much better implemented in a cast piece.
The additional benefit of a pulse converter runner profile is you can use very short runners to reduce exhaust runner volume to improve transient response but still greatly reduce reversion under heavy exhaust back pressure. The shorter runners will reduce pressure losses and thermal losses but have the trade off of not using runners long enough to increase VE through resonance pulse tuning. As with everything, there are compromises to any design.
I'm personally in the longer runner shallow angle merge collector fan club as I would prefer sacrificing a little transient response for higher engine efficiency. But it would be great to see what a short runner pulse converter manifold could do if properly sized to a larger turbo.
The additional benefit of a pulse converter runner profile is you can use very short runners to reduce exhaust runner volume to improve transient response but still greatly reduce reversion under heavy exhaust back pressure. The shorter runners will reduce pressure losses and thermal losses but have the trade off of not using runners long enough to increase VE through resonance pulse tuning. As with everything, there are compromises to any design.
I'm personally in the longer runner shallow angle merge collector fan club as I would prefer sacrificing a little transient response for higher engine efficiency. But it would be great to see what a short runner pulse converter manifold could do if properly sized to a larger turbo.
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