flat top vs dish pistons
- Thread starter ray6966
- Start date
8) a flat top piston is as indicated flat on the top, though it might have valve reliefs cast in. a dished piston has a step down from the edge of the piston, this can be fairly shallow, as little as .001" to fairly deep, as much as .1" 
. playing with dish depth adjusts compression ratio and flame travel.
. playing with dish depth adjusts compression ratio and flame travel.
Back in the early 70's when everyone pretty much had to suddenly drop the compression of their performance motors there were some pretty big dished pistons. Cadillac has some that were in the 40cc range.
Howdy Back Ray:
Our sixes have always had dished pistons. Dish designed pistons have several advantages over flat-topped pistons in an engine with a wedge type compustion chamber. They aid quench effect, minimize knock, and offer a slight increase in power. The advantage of using a flat-topped piston in place of the OEM dished pistons is to increase the compression ratio. The OEM flat-topped pistons come in two dish sizes; 6.5 cc for most all 200 and 250 applications (same piston) and 13 cc for the Calif Emmissions engines of '66 & '67. The flat-topped pistons frequently used in 200/250 are from the Tempo HSC engine. They do have some valve reliefs. Another option with 250s is an .085" taller piston from the 255 V8s. They have the typical 4 eyebrows of a V8 type piston.
If you're interested in higher compression, milling the deck of the block to achieve zero deck height and/or milling the head mating surface. Milling these surfaces also re-establishes a true mating surface for good seal.
Questions?
Adios, David
Our sixes have always had dished pistons. Dish designed pistons have several advantages over flat-topped pistons in an engine with a wedge type compustion chamber. They aid quench effect, minimize knock, and offer a slight increase in power. The advantage of using a flat-topped piston in place of the OEM dished pistons is to increase the compression ratio. The OEM flat-topped pistons come in two dish sizes; 6.5 cc for most all 200 and 250 applications (same piston) and 13 cc for the Calif Emmissions engines of '66 & '67. The flat-topped pistons frequently used in 200/250 are from the Tempo HSC engine. They do have some valve reliefs. Another option with 250s is an .085" taller piston from the 255 V8s. They have the typical 4 eyebrows of a V8 type piston.
If you're interested in higher compression, milling the deck of the block to achieve zero deck height and/or milling the head mating surface. Milling these surfaces also re-establishes a true mating surface for good seal.
Questions?
Adios, David
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