# Smaller exhaust == better low end torque?



## se7enty7 (Jun 18, 2002)

Okay.. I have read that the *ideal* exhaust size is 2 inches for a ga16. Is that ideal for high rpm or low? I want my car to stay fairly peppy.. I do NOT want to have to redline to get any power.. Should I get 1 3/4 mandrel instead?


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## Ninety-Nine SE-L (May 5, 2002)

2" is the optimal size for the GA16. Any bigger, you lose the constant flow of pressure which puts more work on the engine to PUSH the exhaust out (like trying to sip water through a 2 1/2" wide straw..or PVC pipe). If you go any smaller, you're building too much backpressure and restricting the flow (like sipping water through one of those little coffee mixer straws). I have 2" exhaust and my low end is better than ever. I can peel that f**ker GA16 out with an auto and 205mm wide tires (something I couldnt do before, even on stock 170 tires).


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## zeno (Sep 17, 2002)

> 2" is the optimal size for the GA16. Any bigger, you lose the constant flow of pressure which puts more work on the engine to PUSH the exhaust out (like trying to sip water through a 2 1/2" wide straw..or PVC pipe). If you go any smaller, you're building too much backpressure and restricting the flow (like sipping water through one of those little coffee mixer straws).


Agreed....I like your analogy  



> I do NOT want to have to redline to get any power


I don't know about the ga16 but there is a lot of extra power to tap into at the higher rpms in the sr20de if you can get your hands on a JWT ECU or G20 ECU. Check out the dyno chart for your car to learn where you begin to lose power on the rpm scale. However; if you have mods. then you throw off the stock hp/torque curve. You can always dyno it yourself to figure it out.

Unfortunately, we own 4 bangers and redlining is kind of the name of the game.


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## IXLR8se-r (Apr 14, 2003)

zeno said:


> *
> Unfortunately, we own 4 bangers and redlining is kind of the name of the game. *



couldn't have said it better myself :thumbup:


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## himilefrontier (Jan 21, 2003)

Remember also that exhaust pipe sizing is more dependant on how much power your engine makes than on displacement.An engine with a given horsepower level-no matter what the size- will always need a certain pipe size(although it may be larger on a engine with more internal mass due to power lost to internal friction ,reciprocating mass and pumping losses).A 400 hp 350 Chevy will have roughly the same airflow requirements as a 400 hp SR20.This is because in order for an engine to make power, it must combust a given amount of fuel and that amount of fuel also needs a given amount of air to burn properly.All fuels have a given amount of energy per given volume(measured in BTU's or British Thermal Units) and no matter what you do,this will remain a constant.So, while a 1.6 liter 115 hp engine may be optimized at a certain pipe diameter, it is because of power output and not engine size that it does that.That's my lesson for today!


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## zeno (Sep 17, 2002)

Is this going to be on the midterm?


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## himilefrontier (Jan 21, 2003)

Yeah, you're all gonna get tested on this stuff later so you better pay attention!

NEXT CHAPTER:Quantum Mechanics and how string theory will be the realization of Einstein's failed attempt at his Grand Unified Field Theory!


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## Guest (May 18, 2003)

Please supply some evidence to support this statement... I'm not sure that I agree at this time. Your sipping from a wide straw analogy doesn't make much sense to me. Lets take electricity... the larger the wire diameter, the less the resistance for a given length of wire. Why wouldn't this apply for an auto exhaust? Hell, people at the dragstrip run open headers to race... according to your thinking... that must be awful.


*2" is the optimal size for the GA16. Any bigger, you lose the constant flow of pressure which puts more work on the engine to PUSH the exhaust out (like trying to sip water through a 2 1/2" wide straw..or PVC pipe). *


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## Ninety-Nine SE-L (May 5, 2002)

true, the bigger you go, the less backpressure and resistance. Resistance=bad and it is important to get rid of it as much as possible. Unfortunately, exhaust gasses and electricity are 2 different things. With a n/a engine, only one thing pushes the exhaust gas out and that is the piston. The exhaust valvs open and the piston pushes out the fumes using some of the engines energy. 

When you have a smaller exhaust, backpressure is your biggest enemy. With a larger exhaust, you get rid of that resistance, however there is a problem, in your exhaust system, that piston gets a bit of assistance by a suction within the exhaust system. 

Like I said, you can best understand it by thinking about a straw with water. Something you probably remember from elementry school, imagine 2 glasses sitting on 2 different steps of a staircase. The glass that is higher up is full of water and the one on the lower step is empty. If you take a U-shaped straw and stick each end in each glass and you start the flow by sucking the water from the lower end, the water will continue to flow into the lower glass until the top one is empty. This is all done because a velosity has been created and gravity has chosen the direction of the flow. (If you still cannot imagine it, think about siphoning gas out of a fuel tank).

back to the car, the exhaust system works the same way, the flow of gases also has velocity within the pipes and therefore, there is a suction that literally pulls the exhaust gases out of the cylinders freeing up the engine of the old gases and taking some stress off the piston. Now, a 1.6Litre can only create so much exhaust at a time (especially at low RPMs), so if the exhaust is too big, the gases move slower (there is more space to fill) which means the velosity is slower and the suction is less (once again putting more stress on the piston). also, it i's too big, there may even be some reverse flow going on within the pipes b/c there just isn't enough exhaust to fill up the pipe completely.

I hope this is a better explanation


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## sentrapower93 (May 11, 2002)

IMO unless your running a turbo, a 2" cat-back is all the GA16DE will ever need...


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## Ninety-Nine SE-L (May 5, 2002)

well of course, the 2" is dyno proven to be the optimal size for a N/A GA16DE. If you have a turbo on the car, things change. With a turbo, bigger is better. The gasses are being forced in and foced out, so there is no need for the suction of a properly tuned exhaust system.


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## Guest (May 18, 2003)

Nonsense, who says exhaust gasses and electricity act totally different??
How about electricity and water?... they act the same... the bigger the pipe... the more water you can get through it with a given water pressure. Same for electricity... the bigger the wire diameter... the more current can flow through the wire for a given pressure(Voltage). Now why would exhaust gasses through a pipe act any differently...



1997 GA16DE said:


> *Unfortunately, exhaust gasses and electricity are 2 different things. *


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## Ninety-Nine SE-L (May 5, 2002)

bgriffey said:


> *Nonsense, who says exhaust gasses and electricity act totally different??
> How about electricity and water?... they act the same... the bigger the pipe... the more water you can get through it with a given water pressure. *


 yes, but if there is not enough water to fill that pipe completely there will be air in the pipe. I'll try to do some kind of image, I'm not explaining this well.


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## Ninety-Nine SE-L (May 5, 2002)

here:


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## Guest (May 18, 2003)

OK, what you have shown here has to do with turbulence. I'm not sure this applies when the inside of the pipe is very smooth. Turbulence has to be started by something in the airstream. I know of no such object inside the pipe that would start such a phenomenon...



1997 GA16DE said:


> *here:
> 
> 
> 
> ...


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## Rama (Mar 8, 2003)

ok remember electricity is energey and its existence doesnt take up space with you deal with a solid or liquid where ever the liquid or solid doesnt take up space a gas will and same when you release a gas into an area that isnt sealed it wont be the only gas that takes up that space too much of an opening and you'll get air coming in from both directions unless there is something pushing the air from the other end the other end in this situation is the engine. So what stock GA16DE puts out wont be nearly the same as the people running open headers and I wouldn't necessarily call it awful either different situation because it's a car with different output.


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## Ninety-Nine SE-L (May 5, 2002)

well, I said it the best I can, maybe mike kojima could put it better.


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## Ninety-Nine SE-L (May 5, 2002)

hopefully these articles explain it better than I can:
http://www.nissanperformancemag.com/july02/revengeofthenerds2.php
http://www.nissanperformancemag.com/august02/revenge_nerds/


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## Rama (Mar 8, 2003)

I got what you meant but here is something from the first link that mike said 

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.

that's basically what you were getting at


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## himilefrontier (Jan 21, 2003)

I'll add this(or maybe restate it).An engine's airflow requirements vary by RPM and power.At lower rpm's,it's smaller,higher=larger. Simply put, a street engine has different requirements than a race engine that will run in the upper rpm band all the time.At higher engine speeds, the exhaust will"stack up" if the tubing size is too small.At lower rpm's you can actually over scavenge the engine and loose some torque because of insufficient cylinder filling(most street engines like a little EGR at lower RPM's) with too large an exhaust.After saying all that, I think a 2" exhaust should be fine for a relatively stock GA16DE but inadequate if you plan on making significant increases in VE(Volumetric Efficency) by either a turbo or other mods that add significantly to the engine's airflow requirements.


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## Guest (May 19, 2003)

The problem I'm having is... what's the principle behind this statement? Anybody can say anything... but please back this up with some science.


*I got what you meant but here is something from the first link that mike said 

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. *


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## Ninety-Nine SE-L (May 5, 2002)

ok. well, the velocity is the speed at which the gases move throughout the pipes. Given a constant amount of exhaust exiting the engine, a smaller pipe will have higher pressure and higher velocity b/c the gasses build up quicker in a pipe with such small volume. In a larger pipe, there is much more volume to fill per inch in the length of the pipe, therefore the pressure and velocity are much less.

small pipe = high pressure, high velocity
large pipe = low pressure, low velocity

like Mike kojima says, you want low pressure, but you also want high velocity.

The low pressure is good b/c everyone knows resistance is bad.
the high velocity is also good b/c as the speed of the flow increases, the gasses (which do have mass and take up volume..unlike electricity) start to gain momentum. This momentum creates a 'Sucking' action at the exhaust ports which pulls the fumes from the engine and takes some stress off the upwards motion of the pistion.

If you cannot understand what has already been said in this thread, I suggest you take a physics course. BTW, in that picture, there is some turbulence going on, but what I am trying to show is the gases are moving around more to fill the pipe up completely.


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## Guest (May 19, 2003)

You just keep saying the asme thing over & over without any reasonable scientific explanation...


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## Mecho1.6 (May 8, 2003)

this is simply explaind. 1997 GA16DE said it properly but forgot to say that if the pipe is to big you loss the vacume affect, true that a 400 horse 4 cylinder will require a larger pipe but it is also pushing out more exaust gas, so you wont loss the vacume on that 400 horse engine with say a 3 in pipe like you would withe a 115 horse engine with a 3 in pipe.


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## BIGBULS (Sep 24, 2002)

What isn't scientific enough for you? Because they don't quote any laws out of a Physics book? These explanations don't make enough sense?

How about this: Why don't you go put a 3in exhaust on your NA GA16De, and go race somebody else with a 2in exhaust.....do a full gear pull, from idle all the way to redline. Guess who is going to win.......oops...not you.

It's simple. Enough gas velocity within the outgoing exhaust stream creates a vacuum/suction. This helps scavenge the cylinders. This creates more power. Simple.

Yes, backpressure IS bad, but go too big, and you lose velocity, and therefore the scavenging effect. So..........

Go get a 2in diameter exhaust (mandrel bent) if you believe us.......if not, go buy a banana, and stick it up your tailpipe.


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## BIGBULS (Sep 24, 2002)

Actually...since you have a Spec V, you'd probably want a 2.5in exhaust......this discussion was about GA16DE's...........but you get my drift.


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## Mecho1.6 (May 8, 2003)

i know this, 3 in is way to big for a stock GA16DE i have a 2 inch i was just explaining why 3 is to big


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## sethwas (Apr 30, 2002)

Well,
Ideally you want a pipe that expands with high rpm, and contracts for low rpm. This way you don't get a pipe that is 'optimized' for one exhaust velocity. However it doesn't exist so you have to compromize, or focus on either low end or high end.

Seth


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## Guest (May 20, 2003)

Huh??? That is nonsense... there is no vacuum effect. A vacuum effect would be a venturi action. The only way to do that is to have a high perpendicular air flow over the end of the tailpipe. There is no such air flow present.



Mecho1.6 said:


> *this is simply explaind. 1997 GA16DE said it properly but forgot to say that if the pipe is to big you loss the vacume affect, true that a 400 horse 4 cylinder will require a larger pipe but it is also pushing out more exaust gas, so you wont loss the vacume on that 400 horse engine with say a 3 in pipe like you would withe a 115 horse engine with a 3 in pipe. *


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## bahearn (Jul 15, 2002)

He means harmonics in the header. 

All this arguing is pointless since pipe size doesn't make much difference once past the last merge of the collector. Just get a 2-1/2" exhaust and don't worry about it.


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## Guest (May 21, 2003)

You have debunked the claim of the large exhaust being detrimental to performance... which I fully agree with... and do you also agree that the larger pipe will help the performance?



bahearn said:


> *He means harmonics in the header.
> All this arguing is pointless since pipe size doesn't make much difference once past the last merge of the collector. Just get a 2-1/2" exhaust and don't worry about it. *


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## UNISH25 (Aug 12, 2002)

WOW! This post is really heating up!

Hmmm...4 years of engineering school..Thinks of gas flow as liquid flow. It's both the same thing really! Except gas is a less dense material than liquid.

Here is bernoullis law of flow fluid dynamics...
Bigger diameter=higher pressure, smaller velocity.
Smaller diameter=smaller pressure, higher velocity.
Bernoulli's principle 101!

This same principle applies with our GA16s exhaust flow.
We have to find a piping that balances the pressure as well as the velocity of the exhause gas. If the pressure and the velocity is not balance correctly then we get a bad flow of exhaust gas.

Now as you guys all know. Air always wants to go from the high pressure to low pressure. So we have to make the exhaust air "want" to flow out of the car to the low pressure area. 

Now a bigger diameter piping would do this...BUT! Hell the velocity in that thing is slow! The air would reach there eventually but at a slower rate. Think of a house hose, make it a very big diameter now. What happens? The water in the hose will come out a lot slower! And if you held it out to water the plants, the water would most likely drop on your foot instead

A smaller diameter piping creates faster velocity in fluid flow as well as lower pressure...BUT!!! The pressure in it would be extremely small. This means that the Force/Area of the air flow would be small, meaning the acceleration(not velocity) of the gas would be slow! This makes sense, because gas would want to leave a low pressure zone more slower than a high pressure zone! Also, if you decrease the diameter of the piping, it would be like your car breathing through a straw!

Ok so for the exact diameter of the piping we need something that balances the pressure of the exhaust gas as well as the velocity of flow of the exhaust gas! We need a correct diameter that balances out both! This is why you can't have a too big diameter piping or a too small diameter piping!


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## Guest (May 21, 2003)

My opinion is that this "law" has nothing to do with this issue. The issue is one of obtaining minimum backpressure as seen by the engine. I'm not disagreeing with Bernoulli's's Principle, just with how you are applying it. It seems some folks here are trying to tell me that if you keep increasing the size of the pipes... you will hit a point of diminishing returns as far as flow volume. I think this is nonsense in an auto exhaust system...



UNISH25 said:


> *WOW! This post is really heating up!
> 
> Hmmm...4 years of engineering school..Thinks of gas flow as liquid flow. It's both the same thing really! Except gas is a less dense material than liquid.
> 
> ...


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## zeno (Sep 17, 2002)

WHO GIVES A SHIT!  

GA16
Smaller than 2"----bad
Larger than 2"----bad

SR20DE
Smaller than 2"----bad
Larger than 2.5"----bad

Turbo
Smaller than 3"----bad
Larger than 3"----the peasants rejoice

I think 1997 GA16 is right on track. He may not know every single little precise law of physics but it works. None of us have Ph.D in physics, all this physic law crap is getting out of hand. You cannot simply throw out one single law and explain how a car exhaust works. There are hundreds of variables all operating on different physical laws. If it was that easy to say x physical law is what causes exhaust gases to behave in a certain way then auto engineers would of mastered this long ago....but they haven't! It's getting kind of lame to argue such minor specifics.


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## se7enty7 (Jun 18, 2002)

it's for the sake of argument.

I understand it using the siphon explanation.. the gases are actually 'pulling' themselves out


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## Guest (May 21, 2003)

It's nice that you understand "siphoning"... but it doesn't have much to do with exhaust systems on cars. You see... siphoning is a function of gravity. The system we are talking about here is a pressurized system. Any siphoning effect in this application is insignificant.


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## Ninety-Nine SE-L (May 5, 2002)

You know, this is getting pretty dumb, there's no better explainations that can be added. Believe us, we're not lying. if you want the maximum amount of power:
GA16DE = 2"
SR20DE = 2"-2.25"
QG18DE = 2"
QR25DE = 2.25"-2.5"

Nitrous app = add .25"
Turbo app = add .5" or more


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## Guest (May 22, 2003)

In other words... I'm just supposed to take your word for it... you have no good scientific explanation. You are merely repeating what you have heard.
That's what I thought... lol



1997 GA16DE said:


> *You know, this is getting pretty dumb, there's no better explainations that can be added. Believe us, we're not lying. if you want the maximum amount of power:
> GA16DE = 2"
> SR20DE = 2"-2.25"
> QG18DE = 2"
> ...


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## sethwas (Apr 30, 2002)

Hmm,
As fun as this is (and it is fairly fun since its ll been clean so far, no flaming) maybe there is a misunderstanding.
I don't think bgriffy wants to know which size tube is best. He, as do all of you, knows. What he wants to know is why. And up to now no-one has brought anything other than hearsay, or a less than perfect answer. Majority being the latter. Still keep it going, just remember whats the point.

Seth


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## Guest (May 22, 2003)

Not exactly... I just want some proof of these rumors on pipe size. I don't believe them right now and I see no logical explanation for these statements that claim there is an optimum pipe size. Don't want to get anybody worked-up... just want a plausible explanation instead of just repeating "hear say"...



sethwas said:


> *Hmm,
> As fun as this is (and it is fairly fun since its ll been clean so far, no flaming) maybe there is a misunderstanding.
> I don't think bgriffy wants to know which size tube is best. He, as do all of you, knows. What he wants to know is why. And up to now no-one has brought anything other than hearsay, or a less than perfect answer. Majority being the latter. Still keep it going, just remember whats the point.
> *


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## zeno (Sep 17, 2002)

> I just want some proof of these rumors on pipe size. I don't believe them right now and I see no logical explanation for these statements that claim there is an optimum pipe size. Don't want to get anybody worked-up... just want a plausible explanation instead of just repeating "hear say"...


You are right, I do not have any first-hand evidence concerning pipe size. However; there are numerous authorities on this subject who know a whole lot more than me, have done the testing, and their recommendations have held true. These pipe sizes are coming straight from se-r.net, sentra.net, Mike Kojima, Mike Young, and NPM (I posted numerous quotes by them on another similar thread). Now if you want to bring this issue up w/ them, fine....but for now, I certainly trust their authority on the subject.


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## go4broke44 (Jan 14, 2003)

well as nissan performance mag reported, they tested different size piping, and for the GA16DE, 2" was the best performance gain. as far as im concerned, i dont need physics to prove why, but since they already tried it, its obvious 2" is your best bet


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## Ninety-Nine SE-L (May 5, 2002)

Stromung exhaust makes cat-back exhaust for most popular Nissan models now and also alot with Suburu. Before they introduce a new product, they test fit it to a test car and they dyno it and tune it for optimal performance. By tuning it, they test the best amount of bends, the compatability of he flanges, the fitment (no rattling), and PIPE SIZE. Everytime they change something, it is re-dynoed. Once all the testing is done, they will finally release the new system to the market. After testing the GA16DE's exhaust, is it just a coincidence that the 2" system came out on top? If you want proof, y don't you ask Mike kojima personally? Nissan performance magazine has proven it, sentra.net has done it, Stromung has done it, mike kojima has done it, if you want to do it too, I'll tell you what. I got dynos on my webpage (it will say dyno at the top), I gained 10.4hp with the 2" exhaust. If you are so interested to see for yourself, find youself a GA16DE, slap on a 3" pipe, and get a before and after dyno. Even so, if you happened to gain 1 (topend)hp over mine, I gurantee the car will launch worse than a honda.


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## sathid (May 22, 2003)

a couple of things- the straw analogy...ever tried sucking water thru anything that big? the longer the straw, the harder it will be, because you wont be able to remove enough air to bring the water level up high enough to drink. lol.
but thats another story.
what would have been a better analogy, is spitting water OUT of a straw.
teensy little straw, and u put huge pressure on the side of your mouth, trying to get the water thru the hole.
go to say, a straw thats the size of your little finger, and it's much easier, yet the fluid still comes out fast.
try and spit it out of something the size of your wrist....and you'll get a little trickle down the end.

it's pointless trying to compare gas movement and fluid movement because they are NOT the same.
gas compression and the way it responds to friction and pressure have a major effect on how it flows.
think about it, if you go from a 4" pipe, flowing into a 2" pipe, u will still be able to get the gas through as fast, but it will have to be pushed harder, so that it compresses to fit through the space of the 2" pipe. 
take liquid flowing through the same point. the difference in flow, would be equal to the difference in the cross sectional area of the pipe, provided that the first pipe, was filled by the water completely.

also, i vaugley remember hearing at uni once that gases move fastest over a surface (in an example to do with cooling the body by sweating) which is the opposite to water. for example in a river, the middle flows faster than the outside.
this is probably why mandrel bent pipes flow better.
my 2c


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## Rama (Mar 8, 2003)

Why don't you believe them did you read the articles that 97 posted It goes through explaining why you don't want too big of an exhaust. If you think bigger is better than why not open up a 7 inch pipe on a 91whp vehicle shouldnt that get you better gains than say a 2 or 3 in exhaust? You say we provide no explanation for it yet you haven't proven that we aren't right. What exactly makes you think otherwise?


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## Guest (May 23, 2003)

First of all 97 people saying something doesn't make it fact.
They have to provide some viable proof when making statements about exhaust size/efficiency... not repeating like a parrot. Yeah, yeah they did the dyno tests. Well, how do we know they did them right? What was the margin of error on those tests? What was the repeatability of those tests? What other factors might have impacted those tests? I'm not disputing the tests... just looking for a reasonable scientific exploanation to support to their findings...



Rama said:


> *Why don't you believe them did you read the articles that 97 posted It goes through explaining why you don't want too big of an exhaust. If you think bigger is better than why not open up a 7 inch pipe on a 91whp vehicle shouldnt that get you better gains than say a 2 or 3 in exhaust? You say we provide no explanation for it yet you haven't proven that we aren't right. What exactly makes you think otherwise? *


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## sethwas (Apr 30, 2002)

But if all your friends jumped off the empire state building, woudln't you want to as well?

Seth


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## Guest (May 23, 2003)

It seems most of this group would... lol



sethwas said:


> *But if all your friends jumped off the empire state building, woudln't you want to as well?
> *


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## PatScottAKA99XE (Apr 30, 2002)

bgriffey,
I have not read all of this thread so I may end up repeating something here, but here is my take on this.
Lets talk about the GA16DE for now. We have all been told and its been proven to us(Dyno) that 2" is the best performer. The dyno results should be telling you something.

Why too big is possible:
Scavaging(sic?) When you get to a certain diameter you reach your best scavaging. Yes it is possible for an exhaust system to have vaccum. I cant remember if its IRL cars, CART cars or F1, but one of them has an exhaust that its tuned to create vaccum at certain RPM ranges. You need high velocity to create this scavaging/vaccum affect. Going too big decreases this velocity. Now I highly doubt anyone can build a system like this for a GA, but the princible still applies. Built for the best possible scavaging you wont see a vaccum in a GA exh, but you will end up with lower absolute pressure than an exh that is too big for best scavaging. I saw somewhere that the point of open headers was brought up. Thats because the open headers will cause a lower absolute pressure. Why try to tune 6-8 feet of pipe for the low pressure benifits of scavaging when you can just eliminate the pipe all together. Lets jump back a bit. Remember when I said those race systems do create vaccum at certain rpm ranges? On a GA the affect of 2" exhaust is best for "overall" performance. It is quite possible that a different, maybe even bigger pipe would be better if you were trying to make power in one certain range. Since the system was designed for "overall" performance, its built to be best for a wide range of rpms. 
Thats my take on it, but I could be wrong. Im not an engineer by any means.

I also like the fact that someone brought up HP output and exhaust. I also tend to lean to the fact that a any two 400hp motors need about the same exhaust because it takes the same amount of air and fuel to make 400hp no matter the engines displacement.

To answer the original question in this thread:
If you own/drive a street car powered by a GA get 2" mandrel bent and your set. The dyno doesnt lie.


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## Guest (May 23, 2003)

OK, I did some research and found that in fact there were several legitimate sources that acknowledges exhuast tuning for 4 cycle engines. However, they all made a point of stressing that the gains realized were only in a very narrow RPM range... So I don't know how valuable this would be to a car engine. Anyway, here is an article I found on the net from an aircraft exhaust manufacturer that I thought was interesting:


"Tuning an exhaust system is critical for an aircraft engine. It is more practical to tune an aircraft engine than a car or motorbike, because the range of RPM used is much narrower. The major obstacle is that space inside the cowl tends to be very scarce!

Although motorcycle and automobile racers have been tuning their exhausts for over forty years, until the late 90's, there were no tuned exhausts on certified aircraft. In order to work, a tuned exhaust must reduce the pressure at the exhaust port just before it closes, to below the pressure in the intake manifold at that time... called the overlap phase. At that moment, fresh mixture can be drawn into the cylinder and simultaneously spent gases removed from it. In an untuned exhaust, the pressure in the exhaust at that moment will be greater than that of the intake, and spent gases will remain in the cylinder or even flow backwards into the intake manifold.

The power developed by a stroke in which fresh cool gas is being compressed will be much greater than the same stroke in which the cylinder is partly filled with spent hot gases.

But before we get into scavenging, let's review what is happening inside the cylinders of your engine. Your engine goes through four "strokes" during the combustion process. The Intake, Compression, Combustion, and Exhaust strokes.

An "intake" valve is located at the top of the cylinder. During the intake stroke, the piston moves down the cylinder, sucking a new fuel/air mixture through the open intake valve. The intake valve closes, and the piston moves back up the cylinder, compressing the fuel air mixture, at which point a spark from the spark plug ignites and explodes the compressed mixture. This explosion forces the piston back down the cylinder, producing the necessary power to turn your prop. Next, the exhaust valve opens as the piston pushes out most of the spent fuel air mixture, and the cycle starts all over.

Having said that, here is what is happening when you have your original exhaust system.

As the spent fuel air mixture leaves the cylinder, it is routed through a set of headers, into a common collector area, and pushed out the tail pipe by the remaining pressure. Like a garden hose with a kink in it, pressure builds up through out the exhaust system, making it more difficult for the spent gas mixture from the next cycle to leave. So now, the exhaust isn't flowing as freely as it should, leaving some exhaust in the cylinder, taking up space better used for a clean fuel/air charge.

Our Tuned Exhaust System is totally different. When you break down our exhaust system, you have two "sets" of pipes; the primary (header/collector combination) and the secondary (pipe after the collector). The primary contains four independent tubes that all join at the "4-1 Collector" (see below). As each "exhaust puff" of spent fuel travels through the primaries, it leaves a vacuum behind. In our tuned exhaust system, we have adjusted the length of each tube so that the vacuum reaches the collector just in time to "suck out" the exhaust from the next cylinder. The exhaust gases are not only being pushed out by the cylinder, but "extracted" by the vacuum, so a bigger, fresher charge will enter the cylinder during the next cycle. A tuned exhaust system really promotes a smoother, cooler, and finally more powerful running engine."


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## dono200sx (May 2, 2002)

bgriffey said:


> *First of all 97 people saying something doesn't make it fact.
> They have to provide some viable proof when making statements about exhaust size/efficiency... not repeating like a parrot. Yeah, yeah they did the dyno tests. Well, how do we know they did them right? What was the margin of error on those tests? What was the repeatability of those tests? What other factors might have impacted those tests? I'm not disputing the tests... just looking for a reasonable scientific exploanation to support to their findings... *


Think of it this way. You are running a business that depends on word of mouth. What happens if your work is found out to be crap, or that what you are telling your customers if found to be untrue? Your business goes in the toilet because no one is going to go back to you. This is basically what happens with NPM, sentra.net, se-r.net, Mike Young, Mike Kojima, and the rest of them. Over time, these guys (and gals) have proved their trustworthiness. People here on the forums have tried what the Mikes have said, and see exactly what they said would happen. 

I completely agree with wanting to make sure that it is not just hear-say. I was pretty edgey when I first came onto the forums. What I did was study what I found online, then I went and talked with a couple trusted mechanics. They confirmed for me whatI was learning. I would suggest you do the same. We here on the forum may not know the principles by names, but we do know the effects pretty well, and for most of us that seems to be fine.


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## zeno (Sep 17, 2002)

> First of all 97 people saying something doesn't make it fact.


No one ever said it did, but a large group of Nissan and car experts all coming to the same conclusion through tests and experience is probably pretty close. Is there a better system? Maybe....but this is best we have at the moment.



> They have to provide some viable proof when making statements about exhaust size/efficiency... not repeating like a parrot. Yeah, yeah they did the dyno tests. Well, how do we know they did them right? What was the margin of error on those tests? What was the repeatability of those tests? What other factors might have impacted those tests? I'm not disputing the tests... just looking for a reasonable scientific exploanation to support to their findings...


What do you think we have been doing, do you think we have a random quote generator? Concerning errors in testing, yes this is a valid point, people need to be able to duplicate their findings (like any scientist). This is why you will find the same results from many different people and sources that 2" is the best size.

I really don't know what you need in order to be convinced. You asked for proof; we gave you sources, dynos, physics law, etc. and you still aren't convinced. What do you want? Do you want Mike Kojima to publish and articles in engineering articles!? This is ridiculous, I think you are arguing simply for the sake of arguing and you don't want to admit your mistake.


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## Ninety-Nine SE-L (May 5, 2002)

bgriffey said:


> *First of all 97 people saying something doesn't make it fact.
> *


 when he said 97, he was referring to me (my username)


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## Rama (Mar 8, 2003)

Yeah that's exactly what I was doing maybe if I said GA16DE it would have been clearer but then again GA16DE people saying something doesnt make it fact either.


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## sathid (May 22, 2003)

take out the word "people" and they both make sense.


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## shift_of_legend (Jun 2, 2004)

I can't find dyno of a 2" vs 2.25" and 2.5" for a GA16de motor.


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## psuLemon (Apr 23, 2003)

check your PM... it has been tested by stromung and other companies.


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## chubsmagee44 (Jun 24, 2004)

just a point, the original analogy of the engine having to push out more like sipping through na giant straw or pvc, in that case, isnt your foe actually gravity, and our sucking power is limited also by lungs and mouth size


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## B13boy (Dec 16, 2004)

Why is everybody talking about sucking? aren't we blowing the exhaust out? I understand the *anal*ogy and the argumentation here. I wonder if the Nissan techs that designed the exhaust for this car argued this much, the 2" is proven through application. If you want a scientific explanation goto school and learn sciences. Let this argument die... :balls: Some of us just accept the fact that there are people since the day this car hit the market have been modifying their cars. So I am sure that people have wasted countless hours and lots of money testing this exhaust theory out, if a company like stromung makes a decent 2" exhaust and all of the "fast" people have 2" just use the 2" and be happy or just sell the car and buy something already fast. This much argumentation about stupid exhaust is just.... :banhump:


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