What compression did you get his motor up to?You would need to put more compression in the engine with the 640 cams. You will make more power, and torque at a higher RPM, but lose low end torque. Everything will shift to the right on your dyno sheet. A large rear tire, always hurts horsepower numbers. A small rear tire will always show more power on the dyno. Did your tuner check air pressure in your rear tire, before dyno work. Also a hot tire will show less power on the dyno. Send me a copy of your dyno sheet.
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