I have an HJR 421 Cub with aggressive dune port :thumbsup: I ran it one trip with stock swinger...it was fun...but unable to use more than 1/4 the power! Went with a swingarm shop +6. I can now use all the power for duning but the front still comes up at will in any gear...just more controlable...if you plan on dragging a lot...go with at least a +8"