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Many have asked about true dual exhausts for Harleys. There are some advantages and some disadvantages to the systems.

True duals will loose a bit of torque on the bottom end from the loss of scavenging but some like them for looks and sound in any event. It's a personal preference for the most part. They will also remove some of the heat on the newer bikes from the under leg area because of the absence of the pipe from the rear cylinder that exits out the right side.

You also have to be careful which mufflers you run when you change the pipes to true duals. The stock muffler on the left side on 07 up bikes has very little flow to force the exhaust to exit to the right muffler which provides scavenging. This is due to the baffling in the muffler on the later models.

Using the TD setup with stock mufflers will cause a problem for the rear cylinder because there will not be sufficient flow to exhaust the cylinder. Changing to slipons like Vance & Heinz , Reinhardts or the equivalent will solve this problem and allow both cylinders to breathe properly.

Reinhardt True Duals have a stepped header design and end with a larger diameter pipe then the stock setup. The Reinhardt true dual mufflers only work with the Reinhardt true dual head pipes.

Also see this tip...
Full-Sac exhaust - Harley Davidson Community
 
I have the Fullsac true dual system with my stock mufflers. The mufflers are catalysts and each side appears identical internally, and now they sound balanced and identical. With this arrangement the performance and ridability seems unchanged. My passenger appreciates the lower heat on the right side after removing the crossover. I figure the substantial back pressure of the stock cans provides balanced back pressure despite the slight length differences of the pipe, since the pipes have little obstruction. My FLHT is basically stock (new carb needle) and performs like an enrichened stock bike. I've read the 2006 stock mufflers sound better than other years. IMHO this is true but they are still a little quiet for me. My experience has proven that loud(er) pipes can be a safety advantage.
 
There's one thing here to be very careful about when using the stock mufflers on a TD setup.

The stock mufflers regardless of the look are sometimes not balanced as far as backpressure internally, like in the case of the 07 bikes where the left side is used basically as a sound chamber more so than an outlet. The pipe in the left side is only a short perforated piece about 6" at the rear of the muffler unlike the right side where it is a flow through muffler. The purpose of this setup is to force the rear cylinder to exit mainly through the right muffler and give better scavenging to the exhaust.
If these mufflers are used on a TD pipe setup, you will run into a problem with the rear cylinder not being able to exhaust properly and it can damage the engine.
Running a TD setup requires a balanced set of after market mufflers or a pair from HD that has equal exhaust flow through both.
 
Not true. My "07 SE mufflers are identical inside.
I know this because I took them apart and removed the converters in both of them. Should have taken pictures but didn't.
 
The bike I bought had Rinehart true duals with SE stage 1. Is there a way to bring the noise down a touch? If not,i may go back to OEM,and I am sure it would have to be set up again.
 
Ok I'm concerned about my recent purchase now. today i ordered the fullsac TD kit and Screamin eagle slip on mufflers for my 2004 Roadking and was about to order the stage one SE air breather kit, I know that I will have to have my system re-maped to run correctly, but after reading all the comments about the back pressure on the rear cylinder on the newer bikes, should this be a problem with my 2004 and will the stage one air breather be any benfite to the preformance of my bike.
Thanks for any advice you can give my
 
The Screamin eagle slip on mufflers will be OK because they aren't made like the stock mufflers. As far as the remapping, get a TFI and use that instead. The remapping done by the dealer will only return your mixture to the factory lean condition. The TFI will add what you tell it to add and the bike will run better and a bit cooler.

Look through this section for info on the TFI, It's an easy install and works well. There's even a discount link for it too.

Diagnostics and Fuel Injection Related - Harley Davidson Community
 
I emailed Fullsac and asked about using the TD kit with the stock mufflers on a 2007 FLHTCU. This is the reply I received:

Hi Jim
The stock 07 mufflers are not the same left and right. No damage will occur if you were to use them but its not recomended.
Poor performance and even worse sound quality will be the result. If you want it as quiet as stock, use a set from a 05 or earlier.
They are interenally identical. I hope this info helps.
Steve George
Fullsac Performance
928-505-2912
Fullsac Performance - Quality Performace Parts for Harley Davidson Motorcycles



[FONT=&quot]-----Original Message-----
From: Jim Harvey [mailto: removed]
Sent: Friday, May 21, 2010 08:54 PM
To: removed
Subject: Question from Fullsac website[/FONT]
In installing your true-dual conversion kit on a 2007 Ultra Classic, is it necessary to replace the slip-on mufflers with aftermarket? I?ve heard conflicting stories. Some say the left factory slip-on is designed to handle about 20% flow because of the factory rear Y-pipe and that when it handles 100% of the rear cylinder, it creates too much back pressure and overheats. I understand that any change to the muffler would be an increase in performance over the stock mufflers but I'm not quite ready to sink that kind of money into it quite yet. But, I don't want to cause an imbalance in the engine or have it throw my O2 sensors off and have it result in internal damage either.
Advice?
Thanks in advance,
Jim Harvey

 
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