Originally Posted by
Fabrik8
Speaking of that, stroke and other rod/crank geometry has an effect too, because that changes the expansion ratio (which is just the compression ratio on the other side of TDC, but is actually at least as important) and how fast the cylinder volume changes.
Motorcycle engines go over 12:1 on pump gas very easily, but that doesn't mean that the particular engine you have in mind will be able to do the same. Like I said, it's all about geometry and engine design.
I'm going to over-simplify this a bit for some of these guys around here. As it's not a perfect logic, but it will apply in their case.
Almost every high-rev motorcycle engine that uses high compression has 2 items in common that differ drastically from a Honda 4-Cylinder - They are OVER SQUARE, and they have a high Rod/Stroke ratio, most of them above 2:1....
Also, Formula1 engines make 800 hp on a 2.4L V8, using 94 octane, and they also happen to be very OVER-SQUARE, with Rod/Stroke Ratios upwards of 2:1.... They don't have cams, so they have ultimate valve control, and some of them run higher than 15:1 compression....
They can do that due to having unilmited control of the valves, an engine design that is optimal, and combustion chamber shapes/volumes, piston designs, etc., that are so space age it'd make the average person just wonder....
So yes, it can be done.
For a Honda 4-cylinder of a B18 design, the GSR/TypeR will handle it slightly better than the B18B/B20 due to the shorter stroke and higher rod/stroke ratio.
As Fabrik8 pointed out, IF you're going through all the trouble to polish the chambers, de-burr everything, remove all sharp edges, and ceramic coat everything, you can actually gain power on a street 12:1 Honda engine, as you can keep the timing and make use of the compression.
Otherwise, you'll probably run into detonation, followed closesly by turning the timing down or destroying the motor, so you may actually lose power....
BTW, of all the B-series engines, the B16 is most tolerant of high compression from a design standpoint.