is there a hp diffrence with tailpipes vs. turndowns

[Nixon1]

Well if you've got a 4.10 posi rear, you should have plenty of low end....that extra low-end torque might actually be a hinderance to you, in terms of traction issues. But I would expect the loss to be upwards of 10 ft lbs down low...but that depends on how much power you're pushing. It cuts bottom end torque down and changes the power curve around a bit, but MIGHT add a little on the top end...but don't quote me on that. What kind of diameter are we talking about here on your pipes...do you have 2.5 in. or 3 in.? 2.5 should be right about perfect for power.