Ok,
Heres a small explanation i did for another topic but ive altered slightly to make it more suitable for this one..
Detonation in any engine can be caused by a number of things....
1) Excessive cylinder pressures:
This is created by having the maximum PCP earlier than 10deg ATDC. This is of course why we have an advance curve in teh first place, to keep our PCP around the 10 - 20 DATDC area under all conditions.
2) Excessive heat:
Cylinder head and combustion chamber temps can give rise to detonation and far more damaging "pre ignition" (Pinking as you know it) This is simply due to reaching what is in effect the fuels flashpoint.
3) Wrong or poor fuel:
As above, we want a fuel that burns slowly otherwise we will again exceed the PCP target area and cause massively excessive cylinder pressures that will blow holes in things. (Yes, optimax will burn SLOWER than say, sainsburys crap)
4) Excessive advance:
This again is a PCP issue and the first clue you will have is she will feel probably her fastest ever... then boom
5) lean mixture:
Lean mixtures = hotter burn, again taking us across and back to the heat problem. Lean mixtures also burn and flash faster so taking us to the pre PCP area problem.
6) Excessive EGT.
Often created by a combination of teh above. This will put excessive heat into the exhaust valves with corresponding heat and pre ignition problems as desribed above.
7) Excessively hot/cold ICT.
Hot and cold air has an effect on ICP and also AFR. We need to richen as the air cools and lean off as it gets hot. Failure to do so will make our advance curve WRONG. Beware.
And a question from that post that was also relevant to this one in a way so ive left it in:
So if i make it run say 11.2 afr very rich will that cool it down enuuf not to det thru heat and where would the det really occur in 4th 5th gear only????
Detonation in an engine is usually very slight.
A very slight problem will only usually kill an engine if it occurs for a sustained period. So if we have say, det at 5500rpm (common for YB).
In 1st gear flat out she spends maybe, what? 1/4 second there?
In 3rd gear flat out she spends maybe, what? 1.5 seconds there?
In 5th gear flat out she spends maybe, what? 5 seconds there?... Boom.
Hope this helps somewhat.
