Originally Posted by Litle brother (Post 10716116)

As the heading says, I want to challenge you all to come up thoughts about how to come up with the best x-pipe design for a 911 with RSR cams.

Run discussion [emoji123]

Bill Verburg, Steve Weiner, others....ideas, thoughts ?
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Originally Posted by Bill Verburg (Post 10717048)

It depends on the noise restrictions that you need to live w/



In general the best performance from an even fire engine like a porsche flat 6 is 2 separate sides or a tri y type that spreads the torque out a little bit. An x on these types of engines will also dissipate noise a bit better.



The best quiet system is a separated catless 993 type

like this, I used 993 turbo side mufflers instead of n/s 993 side mufflers because they are a better design that flows better. On a 911 w/ the right rear oil tank this won't fit

http://forums.pelicanparts.com/uploa...1578854019.JPG



so 3 to 1 headers make for a very efficient design, size depends on the engine size and rpm design range, you almost have to use a rear mounted muffler and the bigger the case the more sound absorption will be had. I like the idea of redesigning the interior of a stock banana muffler though the factory design is fine too. I wouldn't join the 2 sides, I'd have parallel opposite flowing perforated internals as long as possible w/o bends in them.



You want the pipes to terminate in as large a cavity as possible to generate as large a return signal to the valves as is possible to get, a bell shaped exit helps, the perforated pipe would be wrapped w/ f/g or ss wool.



This partially shows why a x over on these engines isn't desirable form a performance perspective, if you look at the valve events on any one ide they are separated by 180° from the same event in an adjoining cylinder, looking only at the exhaust events E1 ends 180° before E2 which ends 180° before E3, the exhaust events are an asymmetric blob of hot gases that rapidly move through the pipe leaving a partial vacuum behind them. The enter the collector w/ a small vacuum at the tail which helps to suck the next blob into the collector and and then repeat. When the sides are connected this sequence is disrupted, it can be a positive or a negative depending on the detail and rpm(timing of the gas blobs) but if implemented it has to be done carefully as w/ the design of the dollector itself, the gases have to be gently merged together

http://forums.pelicanparts.com/uploa...1578854584.gif



Exhaust events are orange, others colors are intake or internal events that don't generally concern the exhaust

http://forums.pelicanparts.com/uploa...1578855249.gif