How much HP can you pick up on a 351w if you use a torque plate when boring? What are the benefits? Is it worth $150 to go back in a .030 bored block and use the torque plate and go to .040? How much HP am I paying for?
The torque plate is usually a 1 inch thick plate, with the four cylinder openings. You bolt this thing down to spec, and then hone the block under the same conditions as having the head bolted down.
The theory on Torque plates is that when you bolt the head down on the block, the bolts "stretch" the cylinder into more of a square shape. Now this is VERY slight, and I have been told that the Chevy's are worse for tweaking than Mopar or Fords.
You're not going to gain HP really, it's more about making the cylinder as round as possible under what would be the torque of the head bolts, instead of without.
You have a greater chance of rings sealing using it, but I have never used them, and all my engines sealed fine.