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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Twin Scroll Turbo and Headers

OK, I have read about a twin scroll turbo and why it is an advantage many times and never quite got it but I think I have had a brake through moment.

First, a 4 stroke motor must turn 720 degrees to complete a full cycle of every cylinder.

Second, a stock 930 cam is open for 200 deg of exhaust duration, an SC 220 deg, and a C2 230deg.

Thus, in 720 deg of motor rotation there is an exhaust valve open at least 1200 degs of the time! That is , 40% of the time, or more, tw

That means that 100% of the time there is a 40% or more over lap where two exhaust valves are open at the same time with a 6 cylinder motor!!!

On a connected exhaust manifold, any time there is overlapping of exhaust events, pressure will be elevated in the exhaust manifold and this will inhibit the exhaust cycle of the closing valve.

Now the fun stuff:

If we split the motor to into what is principally two 3 cylinder even fire motors things can improve dramatically.

With a split system having three cylinders on each side we then have an exhaust valve open 600 deg out of 720 degrees of motor rotation.

This gets us no over lap of to exhaust events!

Now we can get more exhaust out of each cylinder for less contamination of the incoming charge, it will run cooler, and we can even run more timing for a further increase in motor efficiency (VE) at the same boost levels.

Potentially important stuff with significant opportunities to improve our performance.

Old 06-01-2010, 04:14 PM
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