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I did some reading, crunched some numbers, and thought I had it down. I follow along the tutorial on Garrett's website just fine. But, I decided to look at the map for my 1996 F350 7.3L Powerstroke and it doesn't make sense. Even at full tilt my math shows the turbo barely spinning and not doing much. I had the same conclusion for the 1993 7.3 IDI turbo, the 2001 Silverado Duramax, and the 2001 Dodge Cummins. What am I doing wrong here???

1993 7.3 IDI turbo was rated [email protected] and [email protected]

If the turbo were disconnected, and assuming 80% VE at 2000 RPM, the motor naturally pumps: (444cuin/1728/2*1400*0.8=144CFM >> 144CFM*0.0709lb/[email protected]°F=) 10.21 lb/min MAF Garrett's suggested 18:1 AFR and 0.36 BSFC for 105 HP give: (MAF=HP*AFR*BSFC/60 >> 105*18*0.36/60=) 11.34 lb/min MAF.

If the turbo were disconnected, and assuming 70% VE at 3000 RPM, the motor naturally pumps: (444cuin/1728/2*3000*0.7=270CFM >> 270CFM*0.0709lb/[email protected]°F=) 19.13 lb/min MAF Garrett's suggested 18:1 AFR and 0.36 BSFC for 190 HP give: (MAF=HP*AFR*BSFC/60 >> 190*18*0.36/60=) 20.52 lb/min MAF.

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So at max torque, which is supposed to be the engine's most efficient, with the pedal to the floor, the turbo is barely spinning, and at max inefficiency. And even at max hp, full tilt, pedal to the floor, the turbo barely touches the high efficiency island. Wouldn't it make more sense to have the turbo at maximum efficiency in the midrange, dropping off on the high end as the motor does as well? To my idiot mind it seems like the factory turbo is way too big.

I must be doing something wrong, and it's driving me nuts. Can someone please correct me?
 
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