True Dual Exhaust

[William]

Another fantasy of mine: "True Dual Exhaust" with a 3" or 2.5" Pipe

 

What are your recommendations?

Is there a risk running the 2nd pipe too close to the RIGHT of the Fuel Tank?

 

The below is only a 1st trial layout for the route of the 2nd pipe. I probably need to

bring that muffler closer to the front to have more maneuverability in routing

the 2 final exhaust pipes:

 

 

William

[Tungsten]

If you are talking true dual from the engine then forget it, there is no room to route a dual exhaust down there. Also, a single pipe will always make more torque than 2 pipes. If you want duals from the muffler then it's do-able but there is too much headache going by the fuel filler line. I looked into it before and it's not worth doing because the routing will get insane especially with bigger pipes. I barely stuffed one 2.5" down there. I built my own system too!

[Kingman]

True dual exhaust with 3", 2.5", or probably even 2" would net you less power and torque than a single 2.5"-3" pipe. Duals aren't a good setup for a VG.

[Tungsten]

Duals aren't a good setup for a VG.

 

Agreed

[sewebster]

Why does the number of pipes matter?

[RJSquirrel]

2 1/4" or 2 1/2" single exhaust is all you need. If you were going to go duals, you'd only need 1.5" pipes.

[RJSquirrel]

Why does the number of pipes matter?

 

It's not so much the number of pipes, but the order the exhaust pulses flow down the exhaust. One pulse helps draw the next one along (scavenging). With duals, you effectively create two 3-cylinder engines where each side won't pulse often enough for the next one to scavenge properly. If you want to understand more, I highly recommend the "Scientific Design of Exhaust & Intake Systems" by Smith and Morrison. It's not very math-intensive, and is a pretty easy read. It was written in 1971, so its dated, but the principles are all there.

[Tungsten]

That's a great book.

 

If you notice, most if not all dual exhaust systems also feature an X-pipe or an H-pipe to increase the torque because of this theory.

 

Some cars have dual mufflers all the way in the back to make them quieter and to reduce exhaust back pressure at the same time.

[sewebster]

It's not so much the number of pipes, but the order the exhaust pulses flow down the exhaust. One pulse helps draw the next one along (scavenging). With duals, you effectively create two 3-cylinder engines where each side won't pulse often enough for the next one to scavenge properly. If you want to understand more, I highly recommend the "Scientific Design of Exhaust & Intake Systems" by Smith and Morrison. It's not very math-intensive, and is a pretty easy read. It was written in 1971, so its dated, but the principles are all there.

 

Hmm, interesting. Thanks for the reference!

[nunya]

Why does the number of pipes matter?

image is everything!

[Tungsten]

 

I was close to doing this on a pathy once...

[sewebster]

 

I was close to doing this on a pathy once...

 

Exhaust pipe and rock slider all in one!

[Tungsten]

It was a stupid idea, I scrapped the project.

[Slartibartfast]

So he threw it on the GROUND.

[Tungsten]

Me? I never made it, my drawing went in the garbage.

[1994SEV6]

The above people are correct. It's not about the number or size of the pipes, it's about the flow. Of course, the number and size of pipes directly affect the flow.

The scavenging (I think it's called) is true. I'm not exactly sure how it works in regular gasoline engines, but this is what makes 2stroke diesel engines work. Without this, all of the fuel would just fly right out of the exhaust.

 

check out the animation at the top http://en.wikipedia.org/wiki/Two-stroke_engine#Different_two-stroke_design_types

Edited December 4, 2011 by 1994SEV6

[ahardb0dy]

That's usually why a single exhaust will use bigger pipe than duals, the cat back I had on my V8 dakota, single was 3" but usually they do duals in 2" to 2.5" but on a V6 it would be different, I had 2.25 single on my hardbody and it ran fine and sounded great. I knew a guy long time ago that ran single 3" on his 4 cyl toyota pickup, was loud but no idea how it ran.

[1994SEV6]

That's usually why a single exhaust will use bigger pipe than duals, the cat back I had on my V8 dakota, single was 3" but usually they do duals in 2" to 2.5" but on a V6 it would be different, I had 2.25 single on my hardbody and it ran fine and sounded great. I knew a guy long time ago that ran single 3" on his 4 cyl toyota pickup, was loud but no idea how it ran.

 

The bigger the pipe, the louder it will be. You don't necessarily want it to be loud. If it just lets too much flow through, then it won't perform properly and it will just be loud as hell all the time. And it wound even sound good.

 

If you have a big fat pipe then you will have lower MPGs and less power.

[Tungsten]

The bigger the pipe, the louder it will be. You don't necessarily want it to be loud. If it just lets too much flow through, then it won't perform properly and it will just be loud as hell all the time. And it wound even sound good.

 

If you have a big fat pipe then you will have lower MPGs and less power.

 

Yes it will be louder with a bigger pipe but you want the size to match the RPM range that you use the engine in. Since a VG30E typically runs to 5000 rpm on acceleration you want something that will not choke the engine out at that speed. I had really good luck with a 2.50" pipe but you can also use a 2.25" just fine.

[Nefarious]

My pathfinder had true dual exhaust from the previous owner(3" body lift so ample space). It was with dual 2 inch pipes flared out to 3 inch tips. Dual mufflers. The reference to it splitting the motor up into two 1.5 litres was pretty accurate. It sounded like 2 Chevy Sprints with 3 inch exhaust racing each other.... It sounded like poop...

Also keep in mind the VG30E only has a single oxygen sensor, so if you don't run an X pipe(with o2 sensor mounted right in the x pipe) then you have only 1 bank of cylinders being monitored by the o2 sensor... Not the best idea. I bought the truck that way and just yesterday I spent cutting out the entire dual exhaust system in favour of a much simpler, cleaner and more efficient Y pipe into a single 2.5 inch side angle exit. You will have much better flow and exhaust scavenging... That's the way I would go with it! Well that's the way I am going with it...

Edited December 5, 2011 by Nefarious

[Tungsten]

If you want dual exit you can get a single in and dual out muffler assuming you can stuff those pipes under there.

[MY1PATH]

to get efficient true duals out of a pathy I think you need to use 1.5" pipe to keep the pulse velocity up.

 

Now Dual exit isn't a bad idea and using a single in dual out muffler is the best place to do it because the muffler is where the exhaust slows down the most (and thus loses heat and creates turbulence) so why not give it more room to expand and exit at this point to counteract the slowing action of the muffler baffles.

[William]

Based on the views and opinions on this TOPIC, I'll go ahead with this project as follows:

 

 

1. I'll replace all the RED-marked pipes with a 2.5" diameter pipes

2. I'll replace the YELLOW-marked stock Muffler with one from FLOWMASTER (Please recommend a model/size!)

3. I'll keep the GREEN-marked pipe as is 'cause that's where the O2 sensor goes! Right?

4. I am considering replacing the BLUE-marked stock Catalytic Conv. (The Magnaflow one is nice but pricy!!!), What do you think?

5. I am puzzled about the remaining PINK-marked pipe. It is rusty and should be replaced. Can I put a regular 2.5" pipe in its place?

 

What do you think?

 

William

[sewebster]

Couple general comments. If you're going to be switching out pipe to a larger size, I'd make changes to the entire system. If you leave a stock piece in the mix then it will be the constriction point, and most of the improvement from the rest of the changes will be lost. Also, the "red" pipe sections from the manifolds to the Y junction don't have to be as large as the rest of the system because they only carry half the amount of gas. So if you wanted a 2.5" system at the rear end then you only need 1.75" (cross sectional area scales with radius squared) diameter pipes up front.

[Tungsten]

use 2" downpipes then y-pipe them into a 2.5" collector and go 2.5" from there

make your own pipe with a o2 bung and throw everything factory in the garbage

for a 2.5" muffler a flowmaster 50 is a good choice (if you want flowmaster)

then magnaflow high flow or no cat at all

Edited December 6, 2011 by Tungsten