I've heard of grinding the top edges of the bores on a big block chevy to help unshroud the valves a bit. I'll assume that the bore diameter, valve diameter, and the amount of valve lift will all play into how effective this is.

Does anyone have experience doing this?

Any pics?

Any opinions?

Raymond

 

Some of the factory blocks even came with a little relief machined in. What size valves and what bore size? It only makes sense if you have big valves relative to the bore. I think it's pretty standard practice with big valves. As to quantifying the results??? A good machine shop will likely be familiar. As long as you didn't get too crazy with, I can't see a downside. If the top ring is close to the crown I guess you would need to consider that.

Rich

 

The bore size will be 4.310 with a 2.25" intake valve and a 1.88" exhaust valve.

 

Dont have any back to back dyno numbers for ya either way, but its common practice in the BBC world. I have a drag boat motor at the shop I can get a couple pics of where it is relieved.

 

It works on SBC & LT1 too. Is it worth the cost

I think so.

 

One of my old 454 blocks has been cut. It also had a bunch of other stuff done to it such as a receiver groove in the deck for o-rings. I have no idea what size valves or how much lift was on the cam from the previous owner of the block.

With a typical open chamber BBC head, you shouldn't need to unshroud the valves any more.

You could always install the crank and cam. Install a head and valve train for one cylinder then turn the crank over and look down the cylinder to see how close the valve is to the cylinder wall.

 

Sounds like a reasoanble thing to try.

Rich