When you go through all the trouble of installing new pistons, throwing on a new set of heads, and swapping out camshafts, the worst thing that can hamper your “happy ending” is getting a less-than-expected horsepower gain. Don’t let that make you reconsider all the time and money you’d just spent, ’cause what it all really boils down to has nothing to do with what you’ve done—it has to do with what haven’t done: exhaust.
While “true” duals definitely give a V-twin’s trademark sound a real improvement (at least in the ears of the operator!), the same can’t always be said on the performance side. Unlike a V-8, splitting the cylinder head air outtake can have the opposite effect, ultimately taking away the backpressure the motor needs. That was the case with our ’96 Road King: after all that work at Bennett’s Performance, once the motor was freshened and buttoned up, we immediately noticed that the existing dual (un-muffled) exhaust wasn’t restricting flow as much as it was restricting horsepower—68 hp @ 4,800 rpm is quite respectable all things considered, but this motor still had some untapped power to be achieved.
In order to unleash its full power, we installed a Rinehart 2-into-1 complete exhaust system. Along with giving the Road King a completely different sound (much throatier), it also gave it the ability to put out a more respective 75 hp, which we found out thanks to some dyno runs at Quaid Harley-Davidson in Loma Linda, California. The peak torque didn’t change much, but what did was the overall horsepower range, giving the bike plenty of pull through all the gears. HB
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