I'd say you're pushing your luck as it is. 91' had the b18a, right? So, is the b18b a replacement motor? They should be the same, but does the tach match the motor? (ie. is 7500 really 7500?). My b18b redlines (stock) at what, 6800? Better learn about this motor's crappy r/s ratio before you go revving the ish out of it.