Finchinater

Settle an argument. Is the higher CR like 11:1 have higher actual compression than a 8:1. Always heard for forced induction you would need a lower compression ratio. Without the forced induction, which ratio would have higher actual compression. And with it which would. My friend seems to think that you would have lower pressure in the cylinder with the higher CR. It doesn't make any sense to me. Please educate us both.

Finch

breakmyfootoff

You are referring to 2 different types of compression, static and dynamic. Static compression is always the same, it is the ratio between the cylinder volume at TDC and BDC. Dynamic compression factors the amount of air being added to the cylinder. To make a long story short, naturally aspirated an 11 to 1 engine will have more compression than an 8 to 1 engine. With boost either engine would have higher dynamic comression ratios but the engine that started with a higher static CR would still have a higher dynamic CR. A low compression engine with boost will most likely have a higher dynamic CR than a high compression engine that is naturally aspirated due to the higher volume of compressed air being forced into the engine. Forced induction will add volume similar to a oh no, Ive gone cross eyed.