ryanthomas1 Posted October 4, 2015 Report Share Posted October 4, 2015 Okay guys, I am curious about the comparison here. I have been told the bore of a Z22 is 87.00 mm , going by the old school SAE formula (Bore x # of cylinders / 2.5) I get around 139hp, yet this engine was SAE 85hp rated, so I want to know if it is the formula or was there a change in measuring methods from the 70's to the 80's for SAE. Also, anyone who has access to an old SUN machine, or an Oscilloscope and a Z22 want to do some measurements for me? I would like to know the Internal horsepower (ihp) which is the average cylinder pressure at the power stroke divided by the average pressure of the other 3 strokes. Thank you for your time and resources as always guys, this forum is so great for that. :thumbup: 1 Quote Link to comment
datzenmike Posted October 4, 2015 Report Share Posted October 4, 2015 Early L20Bs were rated at 110 hp but later this was more like 93hp. Same engine just measured differently. The Z22 is more like 98 hp say roughly 100? Before '71 engines were measured and rated as gross hp. These often uses exotic fuels and carb settings, and ignitions and settings, headers, no belt driven alternators, PS air con or alternators, no flywheel and no smog controls whatever. The numbers were ridiculously bloated and high. After '71 engines were measures with everything on the engine as it would be when sold and the numbers were universally much lower. From 10% to 25% less. Both measurements were taken from the flywheel There is no formula for converting from one to the other. If you got almost 140 hp then our L20Bs would be over 130 hp and while I like the numbers you came up with it's not near what they really are. http://www.datsuns.com/tech/datsundyno.htm 1 Quote Link to comment
ryanthomas1 Posted October 5, 2015 Author Report Share Posted October 5, 2015 Haha, thanks, I found the formula in a 1970 automotive mechanics text book from My highschool Quote Link to comment
datzenmike Posted October 5, 2015 Report Share Posted October 5, 2015 Internal combustion engines have too many variables and the efficiency is maybe 30%. There is no formula for working out the expected hp except a theoretical perfect model. Some guesses could be made by comparing it to existing similar engines. 1 Quote Link to comment
ryanthomas1 Posted October 5, 2015 Author Report Share Posted October 5, 2015 Out of curiousity , what do you figure the IHP would be ? I would have to estimate off the compression ratio's , There is actually a formula for thermal efficency but it is partially incorrect becuase it doesn't account for fuel vapor, Quote Link to comment
Stoffregen Motorsports Posted October 5, 2015 Report Share Posted October 5, 2015 That calculation is probably assuming 100% volumetric efficiency. Quote Link to comment
ryanthomas1 Posted October 7, 2015 Author Report Share Posted October 7, 2015 That would explain it, Quote Link to comment
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