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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
I hear keeping the exhaust events in tact is one of the goals of a turbo exhaust. If that is the case, then some length to the equal length primary tubes might make for some benefit.

This is part of the reason a split scroll system works well. By matching up cylinders that exit the motor the events are more able to hit the turbine wheel in tact.


As copbait73 brought up, equal length also helps reduce the differences in residual pressure that will be present when the exhaust valve closes at each cylinder.

Seems even if we have some 20psi of pressure resident in the exhaust headers at full boost this dose not compare to the pressure and speed the gasses come out of each cylinder.

The pressure in the headers is going to appear in waves and with waves there are high pressure parts and low pressure parts.

If the exhaust valve closes during a high pressure part of the wave, less exhaust is going to exit. Low pressure, more will exit.

If this is the case, it dose not matter if each cylinder is getting exactly the same amount of fuel, there will be different levels of residual exhaust remaining in each cylinder and this will effect cylinder fill.

If so this could result in some cylinders running leaner than others and result will be seen with a variation in temperatures per cylinder.

Maybe we do not want to think of it as savaging like on a N/A motor but there seems to be something to this beyond letting the exhaust events just exit in a more orderly manner.

On a street motor where the duty level is modest this is probably not a bit deal. Under hight duty like in competition, it could become a very big deal.

Last edited by 911st; 01-17-2010 at 03:26 PM..
Old 01-17-2010, 03:23 PM
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