Dumb exhaust question
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Joined: Sep 2006
Posts: 3,714
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From: San Ramon, Ca
Dumb exhaust question
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?
6th Gear
Joined: Mar 2005
Posts: 13
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From:
RE: Dumb exhaust question
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'.
Banned
Joined: Sep 2005
Posts: 4,341
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From: Dover, Oh
RE: Dumb exhaust question
ORIGINAL: HawgDoc
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'.
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 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.
Seasoned HDF Member
Joined: Sep 2006
Posts: 25,962
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From: Montana & Arkansas
RE: Dumb exhaust question
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!
Damn... scaring myself with all this stuff I'm remembering from decades ago!
Elite HDF Member
Joined: Feb 2006
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From:
RE: Dumb exhaust question
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.
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Seasoned HDF Member
Joined: Dec 2005
Posts: 5,464
Likes: 624
RE: Dumb exhaust question
ORIGINAL: gunrunner
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.
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.
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.
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Road Captain
Joined: Jul 2006
Posts: 580
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From:
RE: Dumb exhaust question
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?
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?
Cruiser
Joined: Sep 2006
Posts: 230
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RE: Dumb exhaust question
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