Yen1969 t1_j4yw2yc wrote

The primary reason for lower compression ratios on engines with forced induction is that the compression process (from turbocharger or supercharger) heats up the air, and even with an intercooler, the increased temperatures raise the risk of pre-ignition (or detonation, or knock). Higher octane increases the auto ignition temperature, allowing for greater pressures in the same engine without knocking. The engine static compression ratio can also be lowered to reduce how much the air will be heated by the compression stroke.

But this is actually not necessary. It is just an extra safety margin that is favored by people who really really don't want to take more risk than necessary. For example there is a turbocharger kit for the Porsche 11:1 CR flat 6. It is limited to 4psi, but it still provides a rather large increase in power, because you will make more power for a given boost pressure with a higher CR.

However... all of this is largely beside the point of your question. There is an easy way to shortcut all of the nuances of the variables when you are looking for cylinder pressures: Torque. More cylinder pressure = more torque on the crankshaft. So the way to get the answer to your question is to examine different engines with different CRs, different boost pressures, etc... And just look at what makes more torque.

I have had the same 1.8L engine boosted, and dynoed, at pressures from 5psi to 15psi, and with CRs of 10.5:1, 9.5:1, and 8.6:1. (and have had other non-boosted versions of the same car/engine) All on 93 octane, so that was a controlled variable. I could run more boost on track without knock with the 8.6:1, but the torque/power peaks didn't actually vary much. Naturally Aspirated doesn't change this. Cylinder pressure is directly related to torque.

Anecdotally, I vastly preferred lower boost and higher CR for a given power level, since the turbo reacted quicker from a higher off-boost mass going through the turbine, and when spooling it gets to it's lower peak boost much faster. The end result is that the car had much better partial and transient throttle dynamics, which made road course "racing" (non competitive) vastly better


Yen1969 t1_j4rax2b wrote

Electricity and water don't mix, unless you are using water as an analogy. Then it works so well basically all the time.

The way I see it, you can fill a reservoir from lots of little streams, or even massive rivers. Sending 8.4 cubic miles of water (77.3 trillion pounds) at Hoover dam all at once (the reservoir's capacity), and it's gonna fail.


Yen1969 t1_iz10g2f wrote

Another minor point:

Most wool sheep can still shed their wool, but it is usually a sign of being stressed or sick. I expect that if left to "go back wild", the first n generations of sheep will probably shed their wool when heat stressed in the summer. Not at all healthy for them, but those that survive from being easier/faster to shed would likely begin to self-correct back to become shedding sheep again.

Source: I have a small Southdown flock and used to have Dorper/Katahdin crosses. We had one ewe that lost around 70% of her wool mid winter last year from an illness. We saved her, but not the twins she carried.