if i have a gm502 short block,what gains will 110cc heads give me over 121cc heads,far as hp/tq?

Try the ROSS Racing Piston web site's Compression Ratio Calculator.

Input your piston dome/flat-top/dish, type, headgasket thickness and chamber size for both sizes and it will tell you pretty close..

Try to hold quench at .035" to .045" or so and the piston stock, "down in the hole" dimension is generally .025".

I really like ta play around with it b/c it's fun to sim. motors....

pdq67