john510 Posted August 12, 2023 Report Share Posted August 12, 2023 A question for Datzenmike.I sold an L-16 to guy trying to restore and old 520 truck.That engine had 240z flat top pistons .80 thousands over stock bore.What's the displacement now ? He wants to rebuild it and has questions. Quote Link to comment
datzenmike Posted August 12, 2023 Report Share Posted August 12, 2023 L16 is an 83mm bore and 73.7mm stroke for a total displacement of 1,594cc The L24 is also 83mm bore so???? I don't know about that. Over size pistons max out at 1mm or 0.040". But assuming he is correct about being 2mm or 0.080" over, that's an 85mm bore same as the L18 and L20B... 85mm Pi r2 X 73.7mm = 417.99cc X four cylinders = 1,671.995cc Compression... stock head...................... 10.40 closed chamber head.... 9.9 open chamber head...... 9.17 Quote Link to comment
john510 Posted August 12, 2023 Author Report Share Posted August 12, 2023 1 hour ago, datzenmike said: L16 is an 83mm bore and 73.7mm stroke for a total displacement of 1,594cc The L24 is also 83mm bore so???? I don't know about that. Over size pistons max out at 1mm or 0.040". But assuming he is correct about being 2mm or 0.080" over, that's an 85mm bore same as the L18 and L20B... 85mm Pi r2 X 73.7mm = 417.99cc X four cylinders = 1,671.995cc Compression... stock head...................... 10.40 closed chamber head.... 9.9 open chamber head...... 9.17 Ok thanks.I measured the bore when I took my A87 peanut head off and replaced it with a U67 head.It was 85mm I just didn't know what displacement would be.I doubt he'll find new rings for those pistons. Quote Link to comment
datzenmike Posted August 12, 2023 Report Share Posted August 12, 2023 I doubt they are L24 from a 240z. L18, and L20B are both 85mm but never in flattop. Can you post a picture? Do the flattops have small valve relief cuts in them????? Quote Link to comment
john510 Posted August 12, 2023 Author Report Share Posted August 12, 2023 10 minutes ago, datzenmike said: I doubt they are L24 from a 240z. L18, and L20B are both 85mm but never in flattop. Can you post a picture? Do the flattops have small valve relief cuts in them????? Yes they have very small relief cuts.I bought that car 35 years ago so just going on what the owner of it told me.Didn't the early Z cars have flat top pistons ? Quote Link to comment
datzenmike Posted August 13, 2023 Report Share Posted August 13, 2023 Better get your ruler out. Those could be Z20 pistons that are '85mm and come in 85.5mm over size. However they have a much shorter pin height than the L series pistons that are all the same height. L series, from center of the pin bore to the top of the piston, are 38.1mm while the Z20 pistons are 31.75mm. This means that a Z20 piston installed on an L16 rod will stop 6.25mm below the top of the block. Basically no compression. You would need rods that are 6.25mm longer than the L16 rods or about 139.25mm. L13 rods are 139.9mm which is better but about 0.6mm too tall. You could mill this off the piston tops. Measure from the center of the pin bore to the piston top. This will resolve the question of what piston this is. Quote Link to comment
john510 Posted August 13, 2023 Author Report Share Posted August 13, 2023 The piston tops were nearly flush with the top of the block.That motor was built in 1987.Was there a Z-20 back then ? I'm just going off of what the previous owner told me back in 1989 when I bought it.I thought the L-16 pistons had a different pin height than the L-18 or L-20B ? Quote Link to comment
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