So, I've required this bike that I'm told needs 110 octane fuel and I'd like to establish whether it actually does or not. If I were to measure cylinder pressure with a compression tester would that be enough information for an educated guess?
Reading about the subject, pressure is not the only factor in octane requirement and I imagine experience and careful jetting are key?
I haven't even found a table that shows compression versus octane.
Would a compression test be done with a cold engine or a warm engine?
Should a compression test be done before a rebuild, would assembly lube affect the compression test, I imagine it would.
Thanks
Compression is an indicator of potential octane required, that's it.
How well that octane combusts is they key.
Squish/ign timing/pipes/transfers all play a big or moderate role adding up to more that just a compression test.
You can get a basic idea of your compression ratio, if you have compression psi numbers, with this calculator -
https://best-calculators.com/everyday-life/compression-ratio-to-psi-calculator/
squish needs to be measured as does head volume. as stated above, its an indicator. imho, anything over 135-140 psi on an aircooled rd350 is pretty high and would def need different considerations. I have seen where porting was aggressive and cold cranking showed 110-120 but as the rpm rose the cylinder pressure got out of control. so to automans point, compression is just an part of it.
Thanks for the replies. At some point in the near future I'm going to disassemble the engine to change the main seals, have a look at the clutch etc. I'll measure the height and width of the ports, measure the amount of squish etc. If I could post the information here then perhaps you guys could take a look at it?
I would, love to here, many others also.