I've been reading back and forth here, and I simply cannot figure out what is the better route: a single exhaust w/ a y-pipe or a true dual with an x-pipe. I know that velocity is king when it comes to exhaust, and I see things on both sides pulling me in that direction. Does anyone have any hard evidence to suggest which would be better in the case of F/I?

 

i dont have hard evidence but it is suggested, and i have heard that the dual set up is more beneficial to the FI up stream. if you really want to boost it up, some people go with the custom manderal bent exhausts, designed for their particular application.

 

I've done some of my own research on this topic and have come to the conclusion that on a NA Z, catback dual exhausts make gains on the top end (5k+) vs. upgrading the Y-pipe and going with a single pipe (dual tip) exhaust improves on the torque more and mid-range power.

I've got highflow cats and a borla, and comparing my Z to a stock Z dyno chart shows me making not much more power up to about 5k and after that I see gains of 35-40rwhp over other stock Z's on the same dyno (with the help of other mods besides exhaust).

 

Wow, this seems to be a very confusing area, the exhaust. I've been researching this issue, too & one Pro says duals gives you upper end HP but you may loose out on low end torque, while the dealership mechanics say that staying with the single Nismo system beefs up the torque & mid rage power, too. I hate to loos out on the low end torque & power. What is the right thing to do?

 

yes i am really confused too. clarification on this would be greatly appreciated as i am fairly new and my next mod will be an exhaust. I guess i know a little less then the others, but i was also wondering if i got this correct: If i get a y-pipe then i cant have a TD because that has an X-pipe instead, thus if i go with a y-pipe i have to go with a single pipe? sry if i sound stupid but im just confused :|. Why couldnt they make an encarta or some encyclopedia on this stuff :\

 

If you are very confused, then just check out what JDM tunner's Z Race car used. Mostly are single pipe, single outlet. Like Greddy Racing Titanium or Amuse Titanium racing.

 

Exhaust is an area the what SEEMs like the logical choice is not or is often not the correct choice.

Just saying true duals or Y pipe ignores the design and execution. Most pipes on the market are TOO big for near stock engines. Because of this it isn't unusual to actually loose low and mid range power over even the ugly stock parts. Since these are for the most part street cars... that see the vast majority of drive time in the low to mid rpm range... this could be considered a mistake.

I have said it before and will say it again... go with the smallest diameter pipe that gets the job done.

Y pipes and X pipes (and to an extent H pipes) all contibute to low to mid rpm power in V8 systems. Some have argued that the V6 config works better as 2 isolated banks of 3 cylinders (running true duals). Y pipes and X pipes work VERY much the same as accelerators of exhaust energy that reduce reversion. Either will work very well if the X or Y section is formed correctly and the piping diameter is SIZED correctly.

 

A dual system is only better if the stock system is too restrictive. However a less restrictive single pipe is even better than the dual. Once, again, if the stock exhaust is not restrictive, changing the exhaust won't give any performance gain, and may even give you a loss of low-mid range torque.

What is the correct pipe size? It should be equal to the combined cross-sectional area exiting the header, be it single or dual.

Given appropriate sizing, a single is better. Here are the reasons:

1. Usually less weight
2. Usually fewer connections
3. Less exhaust gas drag to to less gas-pipe interface
4. Higher exhaust temp energy to due less dissapation of heat, secondary to less surface area for a given diameter pipe.

So.....single is better providing the piping is of corerect diameter.
NISMO is really the best designed exhaust for this car.

 

i respectfully disagree that a single is better, because the y pipe has to merge two exhaust streams which can interfere with the velocity of the exhaust gas, creating an impedence at the merge. a true dual will flow better bc it does not merge 2 pipes into 1

 

Its all about wether your NA or Turbo.

A turbo needs the largest exhaust pipe diameter w/ the smallest amount of backpressure possible. Hence the reason large diameter dual pipes are so popular w/ turbo's.

A NA Engine however needs a certain amount of backpressure to function properly. Now walking the edge between too much and too little is complicated, regardless- a NA engine needs alot more backpressure than a turbo.

 

that is not true. backpressure is bad, velocity is more important

taken from nissan performance mag, tech section

"Some self-proclaimed motor gurus state that you should not run too large of an exhaust tube on your car because engines need a certain amount of backpressure to run correctly. Although the statement about not running too large of a tube is correct, the assumption about engines needing backpressure is not. Remember this, it is one of the most common performance misconceptions out there. Read on and you will be able to argue with and break off any self-proclaimed expert on the subject!

You need to have the lowest backpressure possible to produce the maximum power by keeping pumping losses low. Too big of an exhaust pipe causes power loss, especially low-end torque. This is because a big pipe has less exhaust stream velocity than a smaller pipe. Velocity is essential to get the best scavenging (or sucking) effect from tuned headers, which we will discuss in more detail later in a future installment. To simplify things, if the exhaust gas flow is kept high with good velocity, a vacuum can develop behind the closed exhaust valve allowing even better scavenging when the exhaust valve opens on the next exhaust cycle. Good scavenging is even more critical on valve overlap, the part of the 4-stroke cycle where both the intake and exhaust valves are open, especially with longer duration performance camshafts.

If the exhaust pipe is too large, the flow will be sluggish with low velocity and the scavenging will not be good. Remember that a good exhaust has low backpressure and high velocity. The only possible exceptions to this rule are for turbocharged or nitrous motors. It is almost impossible to put too big of an exhaust past a turbocharger as a turbo depends a lot on the pressure differential across its turbine to get power recovery efficiency. A turbo engine can have an exhaust gas volume about 1.5-2 times more than an equivalent displacement naturally aspirated motor. NOS motors also have a pretty high exhaust volume and require a bigger exhaust if they are to be optimized for NOS operation."

nissanperformancemag.com

 

the only way to prove that would be to dyno both systems with same diameter piping....then you will have your answer...else its all speculation.

you could also argue that one design is better than the other....because all of the exhaust systems out there use different sized piping, routing, etc....so you would have to dyno each design on the same car to find out which is better.

hence, no one is going to do that so all you're going to get is theoretical speculation...although interesting and conversational...its not fact

 

Back pressure is bad to a certain extent. A NA motor w/ no backpressure would lose HP.

 

I'm always willing to run an experiment if we get ppl to chip in for the dyno costs. Only thing is I don't know anyone with a spare nismo exhaust sitting around. Maybe we can get an exhaust vendor or manuf to sponsor the test?

I'm running the borla true-dual right now and i'm pretty sure I haven't gained any low-mid torque (even possible I lost some). But i'm certain it's helped my top end hp past 5k.

 

im sure performance nissan has all kinds of nismo exhausts lying around.

 

if someone had access to a dyno where you could do several runs that would be great....changing the exhaust systems out wouldn't really take that long.....that would be cool....an exhaust shootout....its been a long time coming

 

i could provide the stock exhaust as baseline :|

 

I think what you will really find if you compare apples to apples (ie "true" duals vs Y pipe + cat backs, that on this car, it makes little difference what route you choose. Simply put, go for the exhaust you like the look/sound of. When combined with a Y pipe, the "non dual" exhausts offer nearly identical performance to the "duals".

Compare the popular "duals" with the nons, and you'll find amazing similarities in pipe diameters..only some small design differences exist between them all, be it NISMO, Fujitsubo, Apexi, Greddy, RSR, etc etc etc etc

Adam

 

Maxipad, while you were correct is saying that a turbo wants the lowest backpressure possible you are INCORRECT in you above statement. PoWeRtRiP posted a good reference to explain why. The whole "backpressure" myth has been around since the first person realized that a big pipe can hurt low/mid RPM power. This is an example of making a correct statement "big pipe hurts low speed power" combined with an INcorrect statement as to why.

The TRUTH is that a VACUUM would make more power. There are lots of reasons why but just one is that much of the pressure from the burning fuel is released very early in the exhaust event. This happens while the piston is still going DOWN during the power stroke. The exhaust valve opens well before bottom dead center on the powerstroke. Once the piston begins moving UP it is working against ANY pressure in the cylinder. Adding VACUUM not only reduces this pumping loss it can actually MAKE horsepower by PULLING the piston up. In some highly refined racing type systems that maximize velocity with tuned headers and merge collectors... this actually happens.

Not trying to slap any hands here... just wanting to kill this often spoken myth.

 

Here is the funny thing about the whole "backpressure" myth, no matter how untrue it is, it shows up on every board I have ever been to.

STOP the Backpressure Myth

Good job PoWeRtRiP and JBrady

Chris