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Re: Dean's point is the important one...
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Posted by Dean (more from Dean) on Wed, 31 Dec 2003 12:54:10 Share Post by Email
In Reply to: Dean's point is the important one..., Jeff in ATL, Wed, 31 Dec 2003 10:23:02
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A further point concerning boost droop.

With a MBC or MBC+A fed from the turbo compressor hose barb, there is a lot of boost droop created by this arrangement, as the engine gets the MBC set point minus pressure drops across the IC and other restrictions.

With the MBC+A pressured from the TB or manifold, the MBC will make the turbo work harder at higher flow rates to maintain the boost. There can still be boost droop as you reach the limits of the turbo. (But the charge air will be hotter and less dense in any case and torque will droop in ant case.)

With a change from the original nasty IC to the Viggen IC, the charge air is cooler at higher flow rates and the turbo is working less hard to create the pressure at the TB or manifold. This means that the wastegate will be further open and the turbine back pressure is less and that translates into greater shaft HP and also reduces residual exhaust gasses in the cylinder after the exhaust valve closes. That increases the volumetric efficiency and the engine will then take in a greater amount of fuel and air. Its a win-win situation. In the same manner you can see how flow restriction reduction has a compound benefit. So the Viggen IC, which also removes the turbo compressor discharge silencer, TBTC mod and air box mods all are needed.

With the T7, folks were thinking (because the T7 limits peak air mass flows instead of pressure) that reducing intake flow restrictions would have no benefit. Not quite. When you reduce flow restrictions with the T7, you do get more power! The turbine back pressure is reduced. I was really impressed how a JR filter in the 9-5 Aero really spiced things up! And I was not expecting much as the filter looked so small.

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