[chiphead]

So a lower compression engine can still make good peak power. But the tradeoff is loss of idle quality and ragged low speed behavior. You take a combination running well at 10.5 and drop it to 9.5, it's going to get lazy at lower RPMs. If you use a smaller cam to gain back the street manners, peak power is reduced further than just the compression ratio change alone indicates.

This is why everybody (including me) is trying to push that edge of 9.5, to use larger cams and mitigate the low RPM penalty. This is also the big upside of roller cams, you can get large valve lifts without the huge duration penalty of FT cams. This gives good power in streetable RPM range, below 5500. This is the street section, where port velocity is kang.