What's the compression ratio on my 73 Comet with 302, also if I installed a set of the 68 302 4x heads that are 53.5 cc, what would my compression ratio be then
I have 54cc aftermarket heads on my .030 over 302. My static compression ratio is a little over 10 to 1.
Stock is 8:1. Those heads would bump it to somewhere between 8.5:1 and 9:1. I have '66 289 heads (54.5cc) with flat top pistons and it's around 9.5:1. Your stock motor would have dished pistons...
Plus approx .030 taller deck, so pistons are likely to be in the hole. Apparently was easier to machine less off deck surface than redesign a low compression head.
The heads will bump it a half point. Big question is, has this motor been rebuilt ? Very unlikely it hasn't at this late date so the stock ratio may not be in effect here.
Okay, well the engine currently in my Maverick is a '68. The original '73 302 shortblock is sitting in the garage...
There is a date code stamped on the block near the distributor hole. Is that where you found it is a 1968? Because some mistake the casting code on the side of the block - the C8OE - as meaning the block is from 1968 - that casting code on the side of the block is just when the block was designed, not when it was made.
Here is a pic of where to look - just above the oil pressure sending unit - this pic shows a 1972 date
That would be the build date. (first time I've seen this stamping) The date the block was cast would be where the casting numbers are found above the starter. A 73 block is .020 taller than the earlier blocks, which can easily be milled off.
Unless engine has been through a commercial rebuild, orig date should be there. Some years back I pictured the stamp on my orig Comet block.(killed by photobucket) Stamp on my '69 Fairlane 302 1969, June, 19th day, B has no meaning other than a assembly code(my guess it refers to line of assembly). Car has a July 1 assembly date. Here's a scruffy old '68 289 I have in corner. 1968, March, 2nd day... V assembly code. Found the Comet pict. 1972, June 7. This car has a June 23 build date.
It was the D4 Engineering code blocks (74 thru 77) that had the .02x" higher decks Even if the 68 block has been rebuilt it may have cheap rebuild kit pistons with low crowns, extra thick head gaskets, etc. The only way to really know the compression ratio is to measure it. Then we can discuss dynamic compression ratio...
It's definitely a '68. It began life as a 289, but I swapped in 302 crank & rods. Saved my '73 for a future build. So which is it? '73 or '74 that has a .020" taller deck?...
Blocks that have a number cast into the side starting with "D4" (1974 design) have the higher deck height. Don't remember if they were .023" or .026" higher, it's been awhile. In '78 they went back to the original deck height with the "D8" (1978 design) blocks.
