I can just about guarantee you that catalog uses negative numbers for domes and positive for dishes, just like the two Speed Pro examples I posted, since the Speed Pro is essentially the old TRW pistons using the same part number.
My 1989 TRW catalog shows a 2295 dome piston as 13.1/12.1 cc. No plus or minus.
It shows a 2266 as "flat head" (no cc rating) cause its a flat top with no reliefs.
It shows a 2355 (six pack, four relief flat top) as minus 7cc.
It shows 2399 (my 454 chevy piston, small dome, with an exhaust valve relief) as 13.8 cc. (No plus or minus)
All of these are in a column marked "effective dome volume".
