Exactly how much I don’t know. Maybe 5 to 10 lbs. they are the same engines for the most part. The B18 has a different grind on the crank and longer rods different pistons, and some of the internal head parts are different. But its all pretty much the same in weight. I have had both in my 91 CR-X and there was no noticeable deferent’s in handling. If it where me doing it all again I would go with the B16, it’s cheaper. Use the money you save to get the Crower stroker kit. That will make your little B16 a 2.0