Hi all, I recently purchased a Harley, and was thinking about fabbing up a new 2-1 exhaust for it. The Harley brings an interesting challenge that I hadn't thought about for exhaust design. The Twin Cam V-twin has a 45 degree bank angle with a single crank pin, therefore, front cylinder fires, then 315 degrees later the rear fires. 405 degrees after the rear, the front fires. this is why Harleys have their characteristic thump. Quick and dirty math(based on degrees of crank rotation) says that the front primary should be about 12.5% longer than the rear in order for the pulses to meet at the collector end to end. All that's fine and good, but now you end up with differences in primary length, which will affect the powerband of each cylinder... so now what? lol. I haven't seen much good info on odd fire exhausts, most everything is geared towards even fire engines. The bike is a 2010 Fatboy, it's big and heavy, and will be used for cruising, so bottom end, and midrange torque will be more helpful than just max HP. Anyone have any thoughts? Right now, I'm thinking close to equal length, leading into a megaphone and muffler. I feel like the primary length difference would have a larger effect on power difference between the cylinders than collector dynamics, am I wrong there?

-262

Pic of the bike at an abandoned gas station in BFE South Carolina...

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I would tune each cylinder for the rpm range that you want and then add a small balance pipe downstream and call it good.

There will be no scavenging (with one cylinder helping the other remove exhaust) with the uneven events so tune each one for its own pulse.

The 6.8L Ford truck engine fires one side of the engine and then shortly fires the opposite cylinder on the same crank pin. Like a double push deal.

Your deal is similar so do a comparison of events from the rear cylinder (first) to the front cylinder (vs the way you did it). The events will be similar

Tom V.

We did a 6.8L engine that sounded like a Harley at idle, Potato, Potato, Potato (for the Ford "Harley Edition" Truck)

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