True Dual FAQ
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Q.
What are true duals?
A. Exhaust that comes off each header and goes into an X, H pipe and then has 2 pipes that run all the way out to the exit of the exhaust. Factory exhaust is a Y setup where the stream from each header are merged into a single pipe,
Q.
What kind of gains can I expect with true duals?
A. If you have stock exhaust you will pick up around 30HP by going to duals with a set of headers. If you already have headers and a cat-back, don’t expect a big gain, but some are to be had if the catback is very.
Q.
What are the benefits of duals?
A. Many people believe that duals sound much better than cat-backs. I personally believe that a good dual setup sounds better than any cat-back I have heard. That is the main benefit of duals since they yield similar power gains with y-pipes and duals take bit more work to get to fit.
Q.
What is better, X or H pipe?
A. Typically the X is known to put out slightly more power than H pipes, but not by much. The H pipe is known to have a better sound to it. You can’t really go wrong with either.
Q.
What does dumped or dumps mean?
A. This refers to whether or not the exhaust is run all the way out the back of the car or not. Dumped means that the pipe exit is located underneath the car, usually right before the rear axles. Dumps are pretty loud and have some drone to it, but can be gotten used to.
Q.
Can I have duals and have the pipes ran out the back where the factory pipes were?
A. Yes. It can be done but it usually is a bit expensive to get the pipes ran out the back. This is due to it being fairly difficult to get both pipes over the axle because it is very space limited up there. There are setups that have both pipes going over the passenger side on the rear axle and there are setups that have one pipe over the driver axle and the other pipe goes under the axle. Also, you can buy a new upper PHR to help running 2 pipes over the passenger side of the rear end (see post#2).
Q.
Can the pipes be ran under the axle?
A. Yes, the pipes can also be run underneath the axle successfully with enough clearance. Clearance under the rear end is usually no worse than anywhere else in the system. The suspension unloading causing the swaybar to contact the duals is the only concern and usually not a problem. Using 3-bolt flanges for under-axle setups will allow for pipe removal if the rear end should be dropped.
Q.
What kind of ground clearance will duals give me?
A. Duals usually will sacrifice a little ground clearance. It really depends on how custom they were designed as well as how well they are tucked up. I have seen some where they are very close to the ground and others that are almost at stock height. My duals are tucked up far and I never hit them, I scrape my headers before I scrape the duals. Ground clearance will also depend on the size of the pipes you use.
Q.
What size piping should I go with?
A. The most common sizes for duals are 2.5” and 3”. The general rule is that if plan on lowering your ride, go with 2.5”, if you are going to stay at stock height go with 3”. Anymore than 500HP and you will probably want to go with 3", unless lowering takes priority. There are lowered cars that run 3” with no problems. Both sizes will support plenty of power, more than almost all of us will likely make.
Q.
What are my choices of mufflers for duals?
A. There are quite a few mufflers that work well with duals. Most people use a bullet style muffler with duals which is placed between the X junction and the axles. Some people use single chambered mufflers instead of bullets. The bullets will usually offer the best ground clearance. In setups that go over the axles, the mufflers can also be placed behind the axles. The most common bullet mufflers used are, dynomax and moroso spiral flows. The more common chambered mufflers are flowmaster single chambers and sweet thunders.Borla XR-1 mufflers are good, as are Maganflow 3" core bullet mufflers. Sweet Thunder chambered mufflers "neck down" and reduce flow. Powerstick mufflers are the same basic design but don't neck down. Only available in aluminiumised steel. Stainlees Works offers something similar in stainless steel. Flowmaster 10 Series mufflers are also worth a look.
Q.
Can I run cats with duals?
A. Yes. I run gutted ones just in case the cops ever check. My ground clearance is still good too. You want cats that support the exhuast flow such as Magnaflow's carsound cats. For more powerful setups Metal Matrix CATS are the only sensible option. Random Technology (7000 Series) and Magnaflow offer them, again in 3" core.
Q.
How much does a dual setup cost?
A. It varies a lot. For just a dumped setup with mufflers and no cats look to spend around $400. It depends on the mufflers you choose too. They can be had for less, check around at your local muffler shops for prices. If you plan to go over the axle and out the back it gets more expensive. Some shops charge only a few hundred to extend the pipes out over the axle but I have seen shops that charge over $600 easy to go over the axle. Under the axle isn’t too expensive. Once again, ask around at local exhaust shops.
Q.
What are mandrel bends?
A. This refers to how the pipes are bent. Mandrel bends stay the same diameter in the bends that the pipe is in the straight sections. Non mandrel bent pipes are crushed in the bends, which can choke flow a little.
Q.
Should I have mandrel bends?
A. Probably, why spend the money and not have it done right IMO?
Q.
Should I use mild steel or stainless steel?
A. It depends. Mild steel rusts out after a while, while stainless will last forever. I think it depends on where you are located. If you are in somewhere like Florida mild should be fine but if you are in upstate NY where it snows and is cold I would get stainless. Stainless is typically a bit more expensive than mild, although I have seen places do stainless dumps for $400-$500.
Q.
Do I have to run LT's with true-duals?
A. Maby. The TSP duals system is mean to mate up with LT's (Pacesetters, QTP's, etc.), but can be modified to fit manifolds with some work (welder, pipe, reducers, flanges). The Bassani system is meant to bolt up to stock stuff and doesn't require any. This system can also be used with LT's by doing some modifications. Custom true-duals can mate up to the headlights if you wanted them to.
Q.
Will I have torque arm problems?
A. This answer depends on each individual setup. Some TQ arms will not while others sometimes do. Body mount TQ-arms are extremely hard to work. The TQ arm is not always the limiting factor in clearance. Sometimes the duals are built in such a way that they BARELY clear the factory TQ arm. Lowering the car brings the TQ arm up a bit, and might offer a slight bit of extra clearance. UMI Performance makes a torque arm specifically for this purpose. You can find pictures of it and links to more information courtesy of Ryan@UMI if you scroll down.
Q.
What about my tunnel brace (aka driveshaft saftey brace) and my options for driveshaft safety loops?
A. You can remove the factory tunnel brace if it becomes a problem, this is a must on TSP duals setups. Driveshaft safety loops are hit-or-miss, with most being miss. Do a search on some setups in here and in the suspension forum to find more info. Some people report good luck with the Lakewood units.
Q.
Can I remove the transmission with true-duals?
A. Maby. TheBlurLS1 has removed his several times with TSP true duals. The rear hangers had to be unbolted to allow the engine/trans/exhaust to told and open up access to the top bolts, but the rest of the system was still intact and clamped to the headers. Some systems are built in such a way that it won't allow it, but most should not have a problem.
I personally love true duals and think they sound awesome. I will never go to a cat-back setup. My setup spiral flows and they are tame when just cruising but get loud and mean when I get on it. I have it tucked up real good so I think it has close to the same clearance that a y-pipe would get. Remember that duals are not going to net you tons of peak power over a cat-back setup, although they are known to help with low end power under the curve due to scavenging effects. The main reason for duals IMO is for the sound.
Guys feel free to add anything you wish to this FAQ, I hope it helps you guys out that are interested in duals.
Pictures!
Please post up if you have links to them. If you don't, host them on tinypic.com (or photobucket etc.) and post the URL's with IMG tags (imbedded pictures like below), or post links to the pictures.
02SS:ZEUS -
Over the axle TD's.
TheBlurLS1 -
Under the axle TD's.
Want more clearance? By W8S SS -
http://ls1tech.com/forums/showthread.php?p=6685132 
True Duals, questions answered here. Post YOUR information and pics too! 
