Hi Chaz, I think you probably have got the information you need from numerous previous posts, but I'll chime in anyway and hope to clarify the matter a bit.

Chad: "...I guess no one knows [about compression ratio], as I cannot find the info in the factory manuals either."

I have looked a bit and also do not find a specific number. Some mfrs publish a number, others do not. Those who do not have the better idea IMHO, because testing under different conditions will yield pretty different numbers. Numbers will vary according to 1) Altitude 2) Spark plugs in or out 3) Throttle open or closed 4) Battery state of charge 5) Starter motor condition 6), 7), 8), ask and I will think of some more.

Oh, 9), this is critical, accuracy of gauge. Unless you are using some high-dollar equipment, like SnapOn, different gauges can easily vary by 10# or more. So absolute numbers even if the mfr provides one, are very problematical.

The better measure is measurement across cylinders with the same gauge and the same conditions (throttle, plugs, etc), looking at differences in readings from highest to lowest. Difference over 15% highest to lowest may indicate an existing or incipient problem. Repeated testing to establish a clear pattern and eliminate random variations is highly recommended. Results should be correlated or confirmed with other testing.

Compression testing alone may have been the best measure of some things back when dinosaurs roamed the earth, and I was there then. Nowadays it is seldom done because there are better methods, even on old engines.

posted by 208.53.82...

• What are normal compresions for 1974Sonett V4?..., Chaz, Thu, 4 May 2006 09:29:16
  • Interesting f/u..., Chaz, Sun, 7 May 2006 10:28:32
  • No one knows compression psi?..., Chaz, Thu, 4 May 2006 23:28:04
    • Re: No one knows compression psi?..., kansas, Mon, 8 May 2006 17:17:30 <-- Viewing This Message
    • Re: No one knows compression psi?..., Mikael H., Sat, 6 May 2006 07:37:39
    • Re: compression psi?..., JimH, Fri, 5 May 2006 00:50:11
      • Re: compression psi?..., Wiliebill, Fri, 5 May 2006 19:48:33
        • Awesome. Thank you. What compression ratio?, Chaz, Sat, 6 May 2006 04:54:05
          • Re: compression ratio?, JimH, Sat, 6 May 2006 07:35:38
            • Not what I meant..., Chaz, Sat, 6 May 2006 10:16:51
              • Re: Not what I meant..., Wiliebill, Sat, 6 May 2006 20:05:55
                • Re: Not what I meant..., paratrooper34, Sun, 7 May 2006 07:28:05
                  • Re: Not what I meant..., Wiliebill, Sun, 7 May 2006 08:09:18
                    • Re: Not what I meant..., paratrooper34, Mon, 8 May 2006 12:20:58
                      • Re: Paratrooper files, Wiliebill, Mon, 8 May 2006 21:24:57
                      • Paratrooper, is that from V Saab or Internet?, Chaz, Mon, 8 May 2006 15:41:15

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