i have some OLD LCengineering 4 into 1 1 1/2 inch primary into 2 1/4
its not so much the design with these motors as much as size of the primaries and size of the exhaust tube, at least 1 1/2 inch and 2 1/4 inch
the stock 22R exhaust on a 20R is a improvement and probably the best for a rock crawler, but if roaring down the freeway is your thing, contact www.lcengineering.com