For the money the b18C1 is fine. You can find these for around $1,500 while the B18C5 will run at least $4,000. With the money that you save ($2,500) you can pretty much build the engine. You can buy a complete rotating assembley from Eagle that bumps the displacement up to 2 liters for $1,495, this includes your crank, pistons, rods, and rings. Then a good build of the head which I would suggest using all Skunk2 parts, including Cams $500, cam gears $200, Valves $180, valvesprings $150, and retainers $120. that all together is right at $2,600. Of course you will need stuff like gaskets, and main bearings, machine work,ETC, BUT that will be about another $1,000. After putting all of this in your engine you can expect an output of about 250-275 HP naturally aspirated. So considering the GSR motor puts down about 152 HP at the front wheels in stock form you will be gaining 100+ HP.