ok i have a b18c spec r, now i think my compression is at 10 or 10.5 to 1. i'll have to check on it. but you can usually go one point higher on the compression. the b 18c1 is a gsr engine with either 165 or 175 hp. it does not come with a limited slip differential. the b18c spec r comes with limited slip, and 200 horse power. another difference is that the type r has different cams and higher compression. another is it has different intake and exhaust manifold, you have to get a special flange for the cat also. i run 93 octane