cascadia Posted January 3, 2013 Share Posted January 3, 2013 Hello all, I'm putting a 27 Pontiac Six back on the road after a 50 year hibernation. It was stored correctly and shouldn't be that difficult. I just completed a compression test and I'm seeing around 60psi on all cylinders. I'm trying to get an idea of what a benchmark number should be, haven't found anything on the web, any experts out there that can weigh in? Link to comment Share on other sites More sharing options...
aussiecowboy Posted January 3, 2013 Share Posted January 3, 2013 Easy to calculate. Atmospheric pressure is 14.7psi. Multiply by the compression ration (about 5.5 to 1 I think) gives 80.85. Subtract the original 14.7 (as your compression gauge reads atmospheric pressure as zero) gives you 66.15.So in a perfect world, in a brand new engine that leaks no compression it should be 66 psi, so your 60 is excellent. Further to this I compression tested my 29 Pontiac a little while back which had a good tight running engine, it made 55 to 60psi on all cylinders. You're good to go! Link to comment Share on other sites More sharing options...
aussiecowboy Posted January 3, 2013 Share Posted January 3, 2013 Compression ratio is from memory only, check the manual and you can adjust the calculation accordingly.Post some pictures when you get a chance. Link to comment Share on other sites More sharing options...
cascadia Posted January 3, 2013 Author Share Posted January 3, 2013 Thanks for your input, I'll post a pic tomorrow. Link to comment Share on other sites More sharing options...
Guest Posted January 3, 2013 Share Posted January 3, 2013 According to the "Mechanical Features" manual that I have for the Series 6-27 Pontiac the compression ratio is 4.9 to 1 so your engine's rings and valves are in good shape. Link to comment Share on other sites More sharing options...
cascadia Posted January 3, 2013 Author Share Posted January 3, 2013 That's good news, thanks for the information. Here's a picture of the gentleman I bought the car from, he's 80 years young. He bought the car in 1956 and drove it until 1960 when it was put up on blocks. Link to comment Share on other sites More sharing options...
aussiecowboy Posted January 3, 2013 Share Posted January 3, 2013 Wow, what a beautiful car. I'd give my left nut to own that one! Link to comment Share on other sites More sharing options...
nzcarnerd Posted January 12, 2013 Share Posted January 12, 2013 This looks to be the car that is on ebay at the moment. Oddly enough it has had an engine change at some time as the engine has a 1928 number. Link to comment Share on other sites More sharing options...
aussiecowboy Posted January 12, 2013 Share Posted January 12, 2013 Indeed it is, same user name. Link to comment Share on other sites More sharing options...
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