318 pistons to bring compression up
Wanted to see if someone can point me to the correct stock type pistons to bring a 318 to the earlier 9.2 compression. I currently have a 73 core with flat tops. I see some for sale that have 4 valve reliefs are those higher compression than flat tops?
Thanks
Going from memory, so may be slightly off with the numbers I list.
IIRC 1.755 is the tallest stock compression height 318 piston including the 5.2 magnum.
It takes about 1.80 to get to the blueprint zero deck height on an LA 318, but block machining is all over the place so has to be measured. 5.2 magnum blocks are usually a little shorter deck height but still need to be measured.
For reference I think the high compression factory 340 piston has a 1.84 compression height, and usually sits about .018 to .022 proud of deck height on a factory block, but again your mileage may vary..
If I were going to build a 318 I would likely use the stocktype magnum piston (entire magnum assy if avaialbe) and get the block decked to get as close to zero deck as possible.
Again these numbers are just for info, everything will have to be measured with parts on hand.
Down and dirty cheapo note- I have had several 5.2 magnum engines that I have put head gaskets on. The carbon buildup on the piston tops brought the piston height up a good bit. Leave the carbon on the piston top if you come across a good used 5.2 short block for the free compression bump. Combine it with a Mr. Gasket .028 thickness head gasket for a little more compression.