Hey guys, my motor is at the machine shop and the machinist was asking about how far the pistons sit in the bore at TDC. Atleast thats what I think he was asking. Does anyone have this info? I didnt buy the pistons new so Im not really sure.

 

well it depends on a lot of variables that are not even that consistant from the factory
first and foremost what is the deck height on your block?????
once you know this you need to know what the compression height is on your pistons
your rod length and your stroke

here is a quick equation to figure it out
(stroke/2) + rod length + piston compression height....... once you do that subract that number from your deck height
a positive number will tell you how far in the block the piston sits a negative number will be present if the piston actually sits above the block deck at tdc

have fun

 

Well he was talking about puting the crank in and pistons and rods in the 4 corners. Takeing measurements from there and then deciding what to do with the deck on the block. I wish I could remeber what he asked for. Im think it had to be compression distance.

He said it should have been on a card with the pistons. But I didnt get a card

 

if you know the pn on the piston go to summit website they have specs on most of the pistons

 

The piston manufacturer should have included the recommended quench distance (top of piston to head "plane"), usually 0.040". Several engine builders have mentioned that 0.035" for a street/strip engine is the current "sweet spot". Race engines are usually built with less quench with each builder having his preferred setup.

The quench is calculated from the piston top "plane" to the bottom of the head "plane". It is basically the sum of the head gasket thickness at compression plus the distance of the piston "in the hole" (distance from piston top plane to deck top). LT-1's deck heights and resulting "in the hole" distances vary all over the place. My block had readings in the 0.028" to 0.032" range.

My suggestion: Decide on your target quench (0.035 to 0.040), decide on your head gasket thickness, substract the gasket thickness from your target quench and you'll have the target piston height "in the hole". Deck the block to reach this piston height. Example: For a 0.040" target quench with 0.026" gasket thickness the piston height in the hole should be 0.014". If the actual piston height is 0.028" in the hole, then the machinist will need to cut the block 0.014".