Quote:
Originally Posted by TomSaintJames
I found a compression ratio figure from an FAQ thread on turbobricks. 9.7:1 seems to be the ticket with the 531 head. However, IIRC the 530 head has a slightly smaller combustion chamber, so will end up slightly higher.
What is the issue with compression and turbo forced induction? Without investigating my two guesses would be actually getting the fuel/air into the combustion chamber being difficult at such high compressions and/or too great a force on engine internals = bent rods or other ruin.
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Sort of the right consequences but not for the right reasons Tom.
Primary problem is detonation aka pre-ignition, knocking, pinking, pinging and similar phrases. It can cause problems in the little ends but before that, it has a tendency to overheat the piston crowns, resulting in a big hole where the piston should be.
In extreme cases, con rods can get broken and make a bid for freedom through the side of the block.
As a side effect, it also reduces power output.
The forced induction pushes extra air into the cylinder so when the cylinder compresses, the heat goes up further. If the compression ratio is too high and/or too much boost or too low a octane rating fuel is used, it has a tendency to self-ignite the mixture before the time it should for maximum power.
If you remember Boyles Laws from your physics days at school, you'll get the idea fairly quick.