what is a true dual

[james1981]

is it dual straight from the headers ?

 

[Lil-Pony]

a true dual straight pipe has no cross over x pipe or h pipe, while true duals will have a h/x pipe to help the engine some how, forgot exactly how, it has something to do with back pressure sucking the gases out of the cylinders when the exhaust valve opens or something

 

[Power-Ranger]

true dual exhaust is one exhaust system per bank of cylinders. On a V type engine, that would be a manifold or header on the head, a dedicated pipe going to the cat, then muffler, then tail pipe. (some of the components could be omitted obviously) The other bank of cylinders has the same thing on it... separate from the other pipe.
Stock systems on a v type engine will *generally* have the manifolds on each head, then into a 'Y' pipe, where the left and right pipe come into one. then go the length of the vehicle. Some will have a single catilitic converter, others will have one per side, and some will have 2 cats per side, then the pipe merges into one with one muffler.
The reason for wanting a free flowing exhaust is to help it get rid of the exhaust... to make room for the fresh charge of air/fuel to come in. The old over simplification of 'look at your engine as an air pump' comparison works here. You can't pump air in, if you haven't gotten the old air out. MPG can increase too... but that is normally more of a theoretical increase, or too marginal to see in real world applications. One can go too far with free flowing exhaust too. Off idle performance (low end torque and throttle response) will suffer and even hurt MPG.
Many late model trucks with custom exhaust will have the stock single system, and get the muffler cut off, a louder free flowing muffler installed, then another 'Y' pipe to split it into two pipes, and have 2 tail pipes out the back. This is not true dual exhaust.
The X pipe and H pipes are custom pieces on a true dual set up, it connects the two systems without combining the two into one. The reason for X and H pipes is to help balance out the exhaust pulses and have a very very very slight increase in how the exhaust system scavenges the exhaust from each cylinder. This is actually getting into the more complicated aspects and into the higher power motors.
True dual exhaust systems are hard to do on most cars and trucks due to the computers running them. It is also illegal (at the federal level) to mess with the catilitic converter. This includes relocating it, or even adding more than the car came with. So if your car only came with one cat, there is no legal way to run a true dual exhaust system. Many states don't have inspections and so will never know what you've done with the cats, but it is still a possibility to get a rather huge fine for messing with pollution control devices. This is also why most exhaust shops wont do modifications like this. Once they do the work, they are liable for what happened to the items tampered with on your car.... and you are liable too if you are aware of the illegal mode... so the EPA can now fine two people.
There is more to it than just a loud muffler and the number of pipes... it is more of a science. It is easy science, but if not done right you wont get the benefits that you could get in a properly engineered system.

 

[85_Ranger4x4]

There are some cars (mustangs) that come with a factory h pipe dual exhaust and there are some trucks (newer F-150's) that are favorably set up for duals too.

My '02 F-150 has two cats per bank, a little snippy at the y where they join together after the cats and duals go on 100% emission legal.

It was freaking expensive and only lasted 3 years though...

 

[Frank The Tank]

H and X pipes are for sound only.

Most commonly 'true duals' refer to any exhaust that doesn't go to a Y pipe to make two tips exit the rear.
A 2.3 with true duals would require 2 mini headers pulling from 2 cylinders apiece.

To me a true dual has no cross pipes and no Y.

 

[85_Ranger4x4]

H and X pipes are for sound only.

No, they balance exhaust flow.

 

[Frank The Tank]

I'm going to go ahead and disagree with you.... Yep I think ill do that.

So does Larry Meaux tune your exhaust for you? If not I bet a straight pipe makes more usable power. Also I bet if you change the cam in that mustang tuned from the factory your factory cross pipe is now useless.

It sounds better with a cross pipe. But without trying every combination on an engine that will never be modified or changed. Your most power and best bet will always be a straight pipe.

And don't forget the mandrel bends or it's garbage anyways for what your talking about.

 

[dieseldane]

H and X pipes are for sound only.

Not really...

No, they balance exhaust flow.

Pretty much. H pipes and X pipes do different things. An H pipe allows for an area for exhaust pulses to expand, and don't really flow from one pipe to the other. An X pipe allows the pulses from one bank to help scavenge the pulses from the other bank.

So does Larry Meaux tune your exhaust for you? If not I bet a straight pipe makes more usable power. Also I bet if you change the cam in that mustang tuned from the factory your factory cross pipe is now useless.

It sounds better with a cross pipe. But without trying every combination on an engine that will never be modified or changed. Your most power and best bet will always be a straight pipe.

Sound better, for sure! Do you mean pipe or pipes? For most street driven vehicles a single outlet with good headers and properly sized pipe will perform the best.

Now of course you could tune the primary length and size, collector shape and size, muffler placement, four into one vs. four to two to one vs. zoomies, etc. etc...

And don't forget the mandrel bends or it's garbage anyways for what your talking about.

Full agreement there!

Now for the original question since we've thrown a bunch of crap out there that the OP probably isn't familiar with since they are asking what a constitutes a true dual setup, I have a few spare minutes and think this is a case where a picture is worth a thousand words.

Don't be hatin' on my MS Paint skills!

 

[85_Ranger4x4]

I'm going to go ahead and disagree with you.... Yep I think ill do that.

So does Larry Meaux tune your exhaust for you? If not I bet a straight pipe makes more usable power. Also I bet if you change the cam in that mustang tuned from the factory your factory cross pipe is now useless.

It sounds better with a cross pipe. But without trying every combination on an engine that will never be modified or changed. Your most power and best bet will always be a straight pipe.

And don't forget the mandrel bends or it's garbage anyways for what your talking about.

Straight pipe is great for peak power, they also make an engine peaky. You lose power on some places in the powerband to gain elsewhere, usually down low.

I really don't care for the sound of an X pipe, the H pipes don't make enough of a difference in sound for me to pick out of a crowd. Both of my trucks have truelly true duals, I like the way they sound and the one with an OEM engine did gain power over the single stock exhaust.

Mandrel bends don't make a huge difference on a stockish engine. It is like a river where most of the flow goes to the outside on a bend to a certain point anyway.

 

[gw33gp]

H and X pipes are not just for sound. My 69 Fairlane Cobra with the 428 CJ engine came from the factory with an H pipe as pretty much all of the 428 CJ and SCJ's did. Ford would not do this just for sound. It helps to balance the pulse pressures in each bank and typically results in better torque giving better low end power.

I remember when the first X pipe was used in NASCAR. It did have an unusual sound but was outrunning all the other cars. It did not take long for the other teams to figure out this new technology. They could care less about the sound. They just want to go faster.

 

[Mac]

Ford has been using the "H" pipe on their dual exhaust since '65', sure didn't do it as a cost savings. Not going to argue about any HP gain but probably made a better DD.
Dave