Good call Heather. :D I run 15-40 TURBO DIESEL oil in mine. My engine is also ported/polished- way tweeked out, It works amazing! Diesel oil is WAY classed above gas engine oil. EG: Dragsters run STRAIGHT 80-90W oil..The rule of thumb is:The more load/strain ya put to your bike engine, the HIGHER the viscosity ya need.(to a point)If ya ride mildly,them thin oil would be better as its thinner and puts less parasitic drag on the engine. ;D Hope that helps! :D