
Originally Posted by
wobbly
RVP, is something of a hobby horse of mine at the moment.
Forever, so many people have had big issues with deto in KZ2 kart engines, and after reading several references in DynoTech magazine
about the effects I decided to do a test.
I ran our SKUSA Honda125 on the dyno one morning on fresh Avgas.
From a huge number of track tests where I have recorded the Altitude Density ( RAD ) and the egt, I have a straight line jetting chart that I know is
absolutely accurate.
RAD = 97% = 165 jet,I can simply go ahead with that and be tuned perfectly.
The baseline run gave the exact result as I would have expected,with the egt smack on 1340* and the deto first red light flickering at peak torque.
I left that fresh fuel in the dyno tank, with its normal breather to atmosphere sitting overnight.
Luckily the RAD was exactly the same the next morning, so I reran the test,and holy shit it was a complete surprise.
The egt had dropped nearly 100*F,with no changes whatsoever.
The power was down dramatically ,like 2 Hp in just over 40.So I leaned it down as you would - trying to regain the power and the egt number.
But as I leaned down, the power DROPPED, the deto lights started to warning flash,so I stopped right there.
The light front ends had all flashed off from the fuel, and as the DynoTech articles had said,the fuel simply wont vaporize entering the crankcase - it flows into the engine as big globs.
The globs dont burn efficiently,thus dropping the egt, and power simply goes away,badly.
I think I stated on here before that at the SKUSA World Finals this year we were allowed to use the 98VP racegas,or VP C12,a WAY better high octane race fuel.
For some reason we simply could not get the C12 to work on track,so I went to the VP race truck and asked them could they open a brand new drum of C12 for me.
They did, and completely the reverse to what one would expect, as the lid was unscrewed,NO vapour pressure went WHISHHHHH.
The fuel had No RVP ie it was "off" ie useless.
C12 has a published RVP of 9psi ie it should woooosh like hell.
The short of the story is that not only does fuel degrade VERY quickly, causing deto if left even overnight - hard starting in cold weather would be super likely if the light fractions wont vaporize and give
the engine something to actually burn, not drown on.
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