Speedo Accuracy

I have an 81 Vector with a 115 Merc turning a 23 pitch ss prop. (It's the white w/ blue chines one used in the old sales brochures). I'm questioning the accuracy of the speedo. Does anyone have a chart or graph showing the relationship of pressure in the pick up line to the reading on the speedometer? 

                                                           Thanx, Rick S.



I used to have a chart that gave the pressure to mph numbers but I lost it somewhere. Medallion instruments published it and if I remember 100 psi was 88 mph. I'll try to obtain one and post it here. 

Thanks for the question,



Please submit whatever questions you have to IHRTechTalk@yahoo.com.  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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