So 2 into 1's are the best for increased performance on stock motors and others, True Duals are next from what I've read in this forum. My question is why does HD go to the expense of using a Y pipe? HD could easily use 2 pipes and at less cost both in materials and labor. I am thinking about just going to rinehart slip-ons and skipping the true duals. So why the Y pipe?

 

....it is kinda Harley's way of doing a two-into-one while still maintaining the classic dual-pipe look that most prefer. By having the Y-Pipe it helps balance the exhaust, which aids inn "scavenging" which is the process by which a tuned exhaust sucks unburnt gasses out of the cylinder to set up-up for the next combustion stroke...techical enough for ya?...that's why on a stock bagger if you put your hand over the end of the rear-jug pipe(left side looking at the bike from the rear), you would swear that the rear jug has almost no compression compared to the right.

 

I just installed a Fulsac kit...making my bike a 'true dual'.
Temps on the right side decreased dramatically.
I feel no loss of power, and no increase of exhaust
noise (I have stock mufflers).
For me, the main reason for the change was because the
passenger complained of HEAT on the right side. I can not get
rid of the passenger, so the heat was a factor. Noise is a factor also..
so with the Fulsac kit.......I think I am ahead of the game (so far).
Armrests come next.....(I miss my Fatboys SOLO seat).

Chuck

 

They call it "free torque" - the Y pipe adds a bit more torque.

 

Don't care about performance issues and so far haven't encountered any heat problems.For me, the Y pipes lookbetter than any alternative.

 

As I have stated in other threads, the stock HD bagger exhaust of a near optimal solution for most rider's needs. Great low end torque and good balance of horspower, figuring most riders don't need hp just good torque. The system is made to act somewhat like an expansion chamber on a 2 stroker. It gives tons of volume for the exhaust gases from both cylinders to mix and even out (somewhat) the alternating blasts of exhaust from two huge cylinders. All this provides a pretty decent flow with good back pressure.
And exhaust scavenging is the amount of BURNT fuel / air mixture that is removed from a cylinder prior to the next intake stroke. Leaving more room for fresh mixture. Over-scavenging is the removal of some un-burnt raw fuel / air mixture. This happens with free flowing exhaust systems, small exhaust valves (increased velocity not volume) and cams with high dgrees of overlap.
There is not a thing wrong with keeping the stock system and doing just mufflers if you like. Might as well do the stage 1 thing then and re-map.
You can grind away that peice of the cross-over pipe that hangs down into the main pipe, it will gain some power and change the sound somewhat. This is the infamous "Y-pipe modification".
Good luck whichever way you decide to go. Nice scooter.

U

 

True duals are not next in performance after 2 into 1s, the stock Harley exhaust is (and in many instances better than some of the 2 into 1s). The original mufflers on the stock exhaust are the limiting factor. Put free flowing muffs on and you will, generally speaking, have a more efficient system than a true dual system. For someone running a basically stock engine, sometimes sound and appearance are the more important considerations. The preceding posts are not incorrect.

 

TxFx is basically correct. On stock or near stock bikes (stock cams, heads and pistons), the stock system with the Y-pipe modification will out perform true duals, you just don't need all that flow.
BUT, the same applies to a 2-1 on a stock bike, too much flow for the motor and performance will not improve much if at all. I have seen it get worse, too lean.

U

 

..........Actually it's a little of both BURNT and UNBurnt gasses, since there is no such thing as 100% burn during power stoke..so we're both right[8D]...the point was that scavenging helps suck out WHATEVER is left in the chamber...don't be so picky...