912ULS Power output

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912ULS Power output

Postby alan » Wed Oct 12, 2005 9:46 am

The information I have read states 100hp when using Rotax intake and exhaust systems. I will be using the Just Aircraft exhaust and two K&N intake filters. Does anybody know what kind of power loss will result?

Alan
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Postby alan » Thu Nov 03, 2005 10:05 am

What, nobody flys behind/before a 912ULS?

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Postby mr157ifhz » Sat Nov 26, 2005 2:03 pm

Ok. Havn't been on this site for a month or so.  I fly in front of a 912s in a Titan Tornado.  It has the stock ss exhaust, and the little stinger as it's excuse for a muffler. Never flown it any other way. Why do you think you will have a performance loss with your aftermarket stuff? Could well be you gain power over stock, not lose it.  On the Titan list some are claiming more power when switching to individual air filters, as opposed to the Rotax airbox.  
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Postby alan » Sun Nov 27, 2005 12:05 pm

I was just going by what the Rotax site said. I don't know enough about why they would say "100 hp only with Rotax intake and exhaust" to guess why. It does make sense that with a more open intake and exhaust you would make more power, but they imply you will make less.

More is always better.

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Postby Sean_Caranna » Mon Nov 28, 2005 6:40 pm

A quality exhaust will perform better than a more open system because it will improve cylinder scavenging.

Basicly, scavenging draws the burned gasses from the cylinders. A tuned exhaust system will increase the level of scavenging which leaves more free volume to draw a clean intake charge into the cylinder during valve overlap. This gives the engine gets more air and fuel to compress increasing horsepower and torque.

The quote below is from a car site.

Cylinder scavenging occurs every time one of the exhaust valves open. As a valve opens the burned gases begin to exit into the header pipe. The piston will be on the upward swing and will force most of the gases out of the cylinder. However, when the piston nears TDC, the intake valve starts to open letting in the "new" air/fuel mixture, even though the exhaust valve is still open slightly. This is called valve overlap and in most cases it causes the outrush of exhaust to actually draw more incoming air into the cylinder. So, by making the exhaust pulse stronger, you get more draw on the incoming charge of air and gas.

But wait, there's more to this story. Just after the exhaust valve closes the exhaust trapped in the header pipe loses any push from behind. This causes the pressure in the tube to drop. At the same time the exhaust gases in the tube begin to cool and lose velocity. When this occurs, the exhaust gases stall until the valve opens again and more gases enter the pipe. Fortunately, the other cylinders are constantly pumping, and forcing gases past the stalled tube in the collector. This creates a pressure differential in the collectors which helps draw on the tubes with low pressure.
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