Engine temp running too hot
too much ignition timing advance
engine """compression-ratio"" too high
hot spots in combustion chambers
idling too high
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any of the above &/or any combination of the above, can cause running on &/or Pinging
I`m definately not a fan of minis (or any cars for that matter) pinging &/or running on... there is definately no need for it,,, there`s definately no reason to even want it that way
as i`ve said before (many many times) most engine reco shops don`t even have a burette (device that allows you to measure the volumes within the combustion chamber) & even if they did they most often don`t use it... The compression ratio needs to be kept to a reasonable level (9.5:1-ish) so that pinging & running on doesn`t occur with the fuel you commonly use, or damage will be the result,,, if your mini pings &/or runs on, then sooner or later the signs of premature engine damage will be evident
stalling the car to stop it running on also damages the engine,,, it hammers, stresses & fatigues the pistons & rings
If your engine has been built for road use & to use pump fuel but with "too-High" compression ratio, then you really should be looking at having it relieved or add some octane booster to your fuel
& no,,, most valve saver products are not octane boosters at all,,, in fact they are most often the opposite,,, they are only meant to add some valve & valve-seat lubrication which generally detracts from the octane rating of the fuel (unless it`s lead based which is now illegal)
Building an engine with 10.5:1 (or higher) compression ratio is generally "NOT" the way to go... there`s very little difference in performance between a mini engine running 10.5:1 comp ratio & the same engine set up at 9.5:1,,, (noticable but very little) providing that all else is adjusted to suit.
you can normally advance the ignition some more with the lower comp ratio to help re-gain some response, but also it alows you to de-tune (retard) it for when good fuel is not avaliable
However,,, retarded-ignition type engines generally run hot,,, so if you think you can get away with a high comp engine & then just retard the ignition till it stops pinging ,,, then you have been miss-guided as the engine now runs hotter & will need even more retarding of the ignition to combat the running on, hence it runs even hotter
it`s a viscious circle & this situation is all to damn common these days,,, there`s no need for it & if you have an enginbe that you know is too high compression, then you really should take "measures" to correct it,,, (Pardon the pun)
If your mini does ping or run on & If you`re not sure what your compression ratio is,,, then i`d suggest you have it proffesionally tuned (by an experienced mini mechanic) & then look at how it`s running,,, if it still runs on or pings then you can almost bet your left testicle that your engine has way too high a compression ratio & you should have it relieved
"Race-Cars" run high compression ratios with big "RACE" cam shaft profiles & they "NEED" to run very high octane fuels,,,
road cars run road fuel & should run road compression ratios & road cams
If you want a "Compromise" engine like a Rally motor, then keep comp ratios at (or around) a tad lower than 10:1 to keep thing safe & help them last
If you have a very large capacity road engine (1400-1500ccs) then you can get away with slightly higher comp ratios (10.5:1-ish) but must be kept in tune or damage will occur, especially to piston ring lands & head gaskets predominantly
end rant
