nice keep up the good work

 

huge loss of backpressure.

Some bp is essential



my experience (over 10 years dealing with Nissan/Infiniti)

for N/A
True duals tend to give more torque and broad powerband

Single 3inch tends to give more top end.


tuning can always help any scenario.

for boost, true dual will give more torque than hp especially if you're only revving to 6500

single exhaust allows for more higher rpm hp.


the trick is to hold your torque as long as possible but you'd like to develop your torque as soon as you can. If you build it too late your car will suffer BIG TIME. If you build it too soon, you'll hurt up top.


Exhausts are tricky to deal with. Tony @ MotorDyne has nearly "perfected" this science. He knows what length from headers to y pipe makes most torque etc... If he'd chime in it would be great.

 

tony chime in haha.

and thanks for the answer eric. these are the kind of post i would like in my thread. for all i know you dont agree with what im doing at all but atleast you helped me out by answering a question without flaming me

 

Actually no. Exhaust gas velocity is essential. Not back pressure.



This has more to do with the area of the exhaust tubing vs whether it's dual or single.


Again, exhuast tubing area > configuration.


Agree.


Agree. It would be better just to read all his past posts. It's all there.

 

Kenny,

if i were doing your setup look for a x pipe (canister) from magnaflow.

It'll be a muffler/x-pipe all in one 2 entrances 2 exits. all integrated.

it'll save you from having to make an x pipe and a mid pipe.

 

Jeff, i can see your point but back pressure (at small amounts is essential) Gas velocity does play a HUGE ROLE as well.

kenny If you have 3 cylinders in 1 pipe and 3 in another and they never meet

you will create turbulence in the system, it'll rasp like hell, and power will be horribly effected.


Remember you have a firing order, and they are not in the same banks. each cylinder fires in a sequence. iiirc 123456 and each cylinder is horizontal from each other so creating the x-pipe as soon as possible is ideal for optimal results.

 

No. You never want back pressure ever. You want high exhaust gas velocity. BP is a misonmer in terms.

Think about your theory on exhaust in terms of exhaust gas velocity and it becomes so much clearer. Also you have to remember that it's not one stream of exhaust in the pipe. But a train of pulses traveling down the pipe. One pulling the one behind it.

 

the x pipe is going to be as close to the motor as it possibly can be. its going to be attatched to the cats

 

I think we both understand what we mean lol just word it differently.

But yes same concept !

 

Sorry but 0 back pressure is always desired, it is not needed and is actually bad.

Backpressure: The myth and why it's wrong.

I. Introduction

One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "cars need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory

Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity

Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan GTR use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?

I often wonder how the myth "cars need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a G35 decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?

The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).

VI. Conclusion.

SO it turns out that cars don't need backpressure, they need as high a flow velocity as possible with as little backpressure as possible.

 

No shiet? haha

 

I love the comments, I own G's and can do a little searching online and I have all the answers. Congrats on trying this yourself shelling out 1100 for a exhaust sucks, I have an injen super ses dual exhaust, there is no Y pipe, H Pipe both banks are completely separate and I'm NA, there will be some tricky bends near the rear sway bar, on mine one goes over and one goes under the rear sway bar and my car does not drown if im on the freeway nor did my gas mileage change for the worse.

 

Go open headers.... 0 back pressure....



See where that theory goes.

For the most part that link on the internet is true as far as gas velocity and what not... but as for pressure. It's a theory. I've yet to see a mathematical breakdown to prove otherwise. and with my post experience with both n/a and boosted cars I can tell you it's essential to have minimal but SOME.




You'll understand that some bp is essential (this is tried and tested by me and I've tuned 1,000hp+ cars)

the key element is tuning, but something we must ALL understand is every engine is a different variable. So everything we've come to learn about a previous setup goes out the window and then only our past can apply that wisdom into our current scenario.

 

That doesn't work. Open headers = no exhaust gas velocity.

 

So....

You're saying Pro-Stock and "Funny" cars are doing it wrong?