Compression ratios

[SidewaysFeltham]

Surely, aren't you confusing cylinder temp with gas temp?

The main reason some cylinders run hotter than others is because of compromises in the block design, siting of bores, one to another and wall thickness: as well as less effecient coolant flow. Bearing in mind the whole thing 's a compromise.

If the swept volume of each cylinder is the same: the compression ratio is identical, cylinder by cylinder, since the combustion chamber siszes are identical and the gasflow has been correctly sorted to ensure that the same weight of charge is received by each cylinder, then the combustion process should be pretty much the same.

One cylinder normally runs hotter than another because the mixture it's receiving is too lean; which means the jet for that cylinder needs sorting (if carbs) or the injection/injector needs looking at.

The whole point about the process is balance: balance of reciprocating bits: balance of gasflow; balance of BMEP, cylinder by cylinder.

If the Air:Fuel ratio delivered to each cylinder is identical (within whatever tolerances have been set), then the combustion temp should be pretty much identical. Unless there is something wrong with a plug, or the chamber or the squish design, which has caused an uneven flame front, for example.

And this will introduce precisely the sort of imbalance one is seeking to avoid, since it will make the engine rev lumpily (even if this isn't detectable, bearing in mind the revs and time/rev at say 9,000 RPM), and limit the engine's own acceleration, life, power output and rev potential.

Thats why blueprinting is so critical for classes which use standard engine bases.