by Fred Dodd


Buick 455 engines left the factory with cast aluminum pistons with 
dished tops.The only non-dished factory piston used was the forged  units
offered as part of the dealer-installed Stage program.The Stage 2 and
non-stage pistons were the same as cast units.1970 compression ratios
were 10-1, 1971  and later ratios were 8.5-1.Most of this drop in 
compression was due to the deeper dish in the pistons.The Stage 2 forged
pistons were a flat  top design with a trench type valve relief. Stage
two pistons were rated at 11-1.The 1971-1974 pistons are similar design
if not identical. I took three measurements from each of the pistons
pictured. First is compression height or distance.This is the distance
from the centerline of the wrist pin to the top of the piston.
I measured this with a dial caliper from the top of the pin hole to the
top edge of the piston. Adding 0.500 gets you to the pin centerline as the
pin hole is 1.00 in diameter. Second I measured the dish volume. I did this
in the same manner as one would measure combustion chamber cc in a 
cylinder head. I sealed a flat piece of plexiglass with a hole in it to
the top of each piston then filled the dish with fluid from a graduated
cylinder. The measuring cylinder that I used held 10cc and originally was
used to measure medication. There are some real accurate devices available.

Disclaimer: I do not claim to be an all-knowing expert on anything, let 
alone piston design and manufacture. I am the owner of the pistons 
photographed in this article and have taken the described measurements to
the best of my capability. If anyone has better or more detailed 
information on this subject, I would love to hear it and I am more than 
willing to edit this material accordingly. This is an attempt to put a 
collection of piston and piston related info in one place.

1970 stock piston (LEFT) and 1974 stock piston (RIGHT) note the major difference in the dish depth. 1974 piston will yield close to two full points less compression.

left to right…Forged dealer-installed Stage2 piston, 1970 stock piston and lastly the 1974 stock casting. Forged piston with trench type valve relief yields a full point higher compression than the 1970 casting.

Close up of the 1970 piston dish. Dish is 5/32” deep. Volume of dish is about 25cc.

1974 dish, can’t see end of ruler, but depth is a bit more than 1/4". Dish Volume is 42cc.

Close-up of the Buick over-the-counter Stage 2 forging. Good view of the valve relief trench, slipper type skirt and if you look closely, you can see drilled oil return holes in bottom ring groove, instead of the machined slot in all other pistons shown in this article.


Piston on left is the Federal-Mogul hypereutectic alloy cast piston. On the right is a Speed Pro L2353F forged piston. Black on the skirt of the forged piston is the new anti-scuff coating.

Any Questions?? Fred