[SEL] One for the mathematicians out there :-)

Jerry Evans jerrye at databak.co.za
Fri Oct 29 08:38:08 PDT 2010


Hi All,
         It's Friday afternoon here and this ole brain refuses to work this 
problem out :-)

         I want to do a compression test on a small aircooled Chinese 
Diesel engine and need to modify a normal auto tester to do this.

Here are the details that I have:
         i) Compression ratio is 19:1
         ii)Bore×stroke [mm] - 86×70
         ii)Displacement[Lit]  - 0.406
         iii)Rated power/speed(kW/r/min) 5.7/3000  6.3/3600 (not necessary 
for the calculation but included for interest sake)


         Or, if you prefer it in Imperial Measurements:
         i) Compression ratio is 19:1
         ii)Bore X Stroke (ins.) - 3.386" X 2.756" (As Near As Dammit)
         iii) Displacement[Cub. ins] - 24.77564
         iv)(Horsepower = 7.6 H.P. at 3000 rpm to 8.4 H.P. at 3600rpm (again, not 
necessary for the calculation but included for interest sake).

         What I need to know is what the pressure should read on my 
compression tester (either in Bar, KG per Sq CM or Lbs per Sq. Inch).

         The piston is flat topped but the head has a smallish domed 
combustion chamber but for these calculations I would think that it is O.K. 
to call it  flat (I realise that this would make the answer greater but I 
only need to be close).

         Alternatively someone may just know what the reading should be and 
you don't need to do all this maths on a Friday afternoon :-)

         I want to do the tests tomorrow morning so would appreciate any 
answers in the next 12 hours please. Bear in mind also that I only get the 
SEL Digest version which is due in about the next 1 1/2 hours so if you are 
reading this on the SEL List please copy the mail to me "Off List" at the 
address above. - Old engine list members do not need to do this. (He gets 
pushy now as well !!!)

         Thanks in advance guys.

Keep the revs up (or down)
Jerry Evans
Near Johannesburg in Sunny South Africa.
Etched Brass Engine Plates made to order:
<www.oldengine.org/members/evans/plates/index.htm>  


More information about the sel mailing list