Somewhere you picked up some misinformation.

The B23E is listed at 10:1 compression ratio. It uses the same block as the B23F, which was 10.3:1 compression ratio. That's right, the F engine was higher compression than the "high compression" E engine. The reason is that the 405 head on the B23E engine has 2cc more capacity in the combustion chamber than the head used on the B23F (probably a 398 head, but could have been 160, both essentially the same).

Use the 405 head from the B23E. It has a greatly improved intake port compared to the B230FT head (which would be a 530 head, and have the 2cc smaller combustion chamber). If you look down the intake port, you might be able to tell just from looking that the B23E head is larger. On the roof of the port, there should be a small ridge in the middle where it comes to the valve guide and the air splits to go around the valve. The B230FT head won't look quite the same, being more smooth there.

If you don't know what I mean by 160, 398, 405, 530...there's a number cast in the head on the exhaust side above the #2/#3 ports. It's "1000 xxx" where 'xxx' is the 3 digits used to identify the head casting.

The B230FT engine had 8.7:1 compression because of the pistons that were used, not because the head gives lower compression. The B230F (9.8:1) and B230FT use the same head design, the difference in compression is all from the piston dish and design. 7.5:1 compression comes from the B21FT, not the B230FT.

Measure the combustion chamber volume and you should come up with close to 51.7cc for the B230FT 530 head, and close to 53.7cc for the B23E 405 head. If either has been shaved in the past to clean up the surface, it may measure a little less.

--
forums.turbobricks.com