Why does Harley run two pipes off the rear cyl ? Is it to equalize the pipe length? Does that work? Does it help it run cooler? I almost thought it was for looks. There is a gap there. It really stands out with some after market exh/systems. I like the 2 into 1 idea. The Thunderheader is a good example, The way the rear pipe routes forward it really opens that area up. I guess that falsee would work, but almost $300 extra for a non functional pipe ?? What do you guys think?

 

A large portion of the rear cylinder exhaust goes out the right muffler anyway, it's the free-er flowing path. The left side balances the bike out visually. True duals are not a great idea because the rear exhaust must make a u-turn right out of the head... while the front has a much easier path to follow. The key in top performance is EQUAL power from every cylinder. A two-into-one is a good design (I do like Thunderheader) if you don't mind the visual unbalance. I don't think H-D will ever drop the left muffler on 'baggers'... it's part of the 'style'.

 

I like the 2 into 1 look.

 

I do not believe that the shape of the headers has anythin to do with power as to if they are staight or tied into a pretzel. As long as they are equal length.

 

Stock bagger exhaust SUCKS[:'(]....True Duals DO work great with a precise dyno tune. Ya wanna race or ya wanna ride? Choose your combo and tuner carefully!

 

I think I understand some of the modern engrg. reasons for two into one. But many decades ago we kids were playing with pipes into megaphones that had the phone's waist diameter near the end of the exhaust line and using some formulas we found somewhere that would create better breathing by using the perfect length of pipe to use the sound waves and tempo of the exhaust valve beat to blast the exhaust out. Change dimensions and then the backpressure and the sound wave scavenging would increase HP. Wonder if that was just a bunch of flooey or is also part of what the engrs. try to do with modern exhaust design?

Damn... scaring myself with all this stuff I'm remembering from decades ago!

 

2 into 1 systems `are the best for power and torque, thats why the stock system is like it is, its basicly a 2 into one system being 80% of rear cyl. exhaust goes out right side with 100% of the front cyl. exhaust. true duals might look kool but they will rob torque and move the power band up higher in the rpm range. Many sacrafice that power for the look.

 

Not sure I totally agree with you on this one. 2 - 1 pipes are the best for power and torque, no arguement from me here. The part I am struggling with is that true duals are for looks. My experience has been, when properly tuned, the true duals make more overall power. The rpm range may shift with true duals, but you can't just look at the peak numbers. You need to look at the area under the tq and hp curves. I think true duals increase this area.

My theory (and I am definitely not an expert) on the factory bagger exhaust is that it causes contamination problems in the rear cylinder. Because those exhaust gasses get split between the right and left pipe it causes turbulence at the Y junction. The turbulence dramtically slows down the exhaust exiting the head. This creates a "traffic jam" and actually causes some of those spent exhaust gasses to get sucked back into the combustion chamber due to the vaccuum effect created by the engine.

Again, that's just my theory. Someone can set me straight.

 

How much power are we talking though?


The non-pipe side of a bagger just doesn't look right to me and they look odd from behind.

I'm willing to sacrifice a few ponies to keep the look.

I was just wondering if anyone dynoed a 2-1 vs a true dual using the same setup otherwise. How much difference is there? I know there IS a difference but how much?

 

I have a set of the V&H Dresser Duals on the ' 07 RK Classic and I dont know what the 2-1 systems are pulling down but on the Dyno I am pulling 75 HP and 90 FT. LBS.......Hell thats good enuff for me and I LOVE the sound