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Compression ratio pumping loss and race gas

Discussion in '2 smokers' started by greasyfatman, Jun 3, 2020.

  1. greasyfatman

    greasyfatman Long timer

    Oct 18, 2014
    So I brought the compression ration on an air cooled 80cc two stroke up to 162 psi. 162/ 14.7 gives me 11 to 1. 14.7 being atmospheric.

    am I calculating this right?

    Can anyone educate me on pumping loss?

    Also interested in people’s experiences with race gas C12 or anything oxygenated U4.4 in a two stroke.

    going to tag @Strong Bad he seams to have a lot experience with two strokes.
  2. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

    Oct 29, 2007
    Omicron Persei 8
    Back in the day (early 70’s) when I was porting and building pipes for EC Birt & Donny Emler (FMF), 99.99% of what we did was seat of the pants. At the time I don’t think any of us had gone beyond basic math :lol3 . Early days at FMF we had a dirt road out front and a vacant lot next door we used to test.

    The big problem with high compression that we struggled with was from all of the additional heat generated. There was no water cooling so getting a little high compression 2stroke to survive a 30 minute moto was critical. We also didn’t have the exotic race fuels either. The best we could do was the old Chevron Custom Supreme (aka: White Pump) at 100 octane.

    I can remember more than one head that we had to make custom copper head gaskets that were thicker to try to recover from taking too much off!

    We weren’t very scientific, but we sure won a lot of races!!!