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How to determine optimum shift points?

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Old 09-24-2010, 09:13 PM
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Ok, I have installed the Precision 74GTS off my Blazer on this truck. I put a .96 housing on the 74mm (the 67mm had a .81) I am now running it at 10 psi vs 6ish with the smaller turbo. Going to the dyno tomorrow-anyone care to make a guess what it should make?
Old 09-25-2010, 03:10 PM
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I thought the shaky line on the dyno graph indicated valve float or valvetrain instability?
Old 09-26-2010, 09:46 AM
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Well, it made 422 horsepower and 451 torque. Graph is even shakier now and it still nosedives way before it should. Dyno operator thinks the valvesprings are weak. I think its a combination of valvesprings, the "all terrain" tires, and the tune.

The next step is to put some 317 heads on to lower the compression a bit. I will do some good springs at that time. In the meantime I am planning on getting the tune in better shape....
Old 09-26-2010, 09:54 AM
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congrats on the new power... if the turbo didn't change anything, then I would agree its probably the valve springs...



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