Yet Another Exhaust Question

[SnowSurfLax]

Ok, I can't seem to find CARB legal headers for my QX. If I go ahead and get a 2.5" from the OE manifold to the cat and out the back, am I wasting money or will I get some performance increase?

 

I know it'll improve the flow some, I'm just not sure how much and if it's worth it.

[brenspath]

Hi, i tried 3 different set ups before finder the one that worked,

I found that a full 2 inch twin system, twin mufflers welded together and twin pipes out the back worked best,

i got 23kws at the wheels and a great sound.

Running big pipes makes less back pressure and on a standard motor you will lose bottom end and mid range power.

Mid range is where i was looking for more power and thats where i got mine, from 2000rpm - 4000rpm i have a 30% increase in torque.

A more open air box and pod filter helped here too.

In the dry i can spin the wheels out of corners and drift up to about 110kph(65mph approx)

In the wet its more that a hand full with the new tighter lsd i have.

[laxman0324]

Hi, i tried 3 different set ups before finder the one that worked,

I found that a full 2 inch twin system, twin mufflers welded together and twin pipes out the back worked best,

i got 23kws at the wheels and a great sound.

Running big pipes makes less back pressure and on a standard motor you will lose bottom end and mid range power.

Mid range is where i was looking for more power and thats where i got mine, from 2000rpm - 4000rpm i have a 30% increase in torque.

A more open air box and pod filter helped here too.

In the dry i can spin the wheels out of corners and drift up to about 110kph(65mph approx)

In the wet its more that a hand full with the new tighter lsd i have.

What was the price? What brand muffler and what model did you use? Is there any way you could post a sound clip? Im just nervous about it sounding like crap if i do it.

[02silverpathy]

Dude, it is crazy important to divulge what year and motor you're dealing with...I made the most expensive mistake with this rig yet by messing with my exhaust!! I have an 02 with the 3.5 and put a cat back 2.25" dual to a single GIANT magnaflow (x pipe inside) dual in dual out muffler and lost gobs of TQ...I had it hacked off my truck in less than 2 hrs and was welding the OEM back on minus the rear resonator.

 

On the flip...I want badly to put a Flowmaster 50 series SUV muffler (had this on my 3.3). I loved this muffler before and with 2.25 dual in and 3" out felt like I lost some tq then too. I am getting the impression that maybe the 1.75" OEM is best for torque and will swap my Flow 50 in and go with 3" out.....I did not mean to post jack, but please insert thoughts on this as well as more specifics to help solve this situation for SnowSurfLax....and maybe me too!!

[CDNBullrid]

In the wet its more that a hand full with the new tighter lsd i have.

 

 

what do you mean by the new tighter lsd? can you tighten the stock lsd or do you have to replace it? what did you do and where you get the stuff from?

[SnowSurfLax]

Ok, I can't seem to find CARB legal headers for my QX. If I go ahead and get a 2.5" from the OE manifold to the cat and out the back, am I wasting money or will I get some performance increase?

 

I know it'll improve the flow some, I'm just not sure how much and if it's worth it.

 

Ok, I had to answer my own question due to the lack of answers. So here's the best I got.

 

After MUCH research on exhaust principle (without delving directly into physics gas laws, thermodynamics, etc.) and to answer my own questions about what I can do with my exhaust system, I’ve made up a quick exhaust guide. I’ve included the links at the end if you want to get a little more in-depth knowledge. My only caveat is that I’m no physicist and I’m only giving the most basic explanation I can, so I’m not 100% correct on any of this. Also, keep in mind that forced induction changes some of the rules of the game, so you’d have to adjust for any kind of FI application.

To begin with, since exhaust system building and tuning is essentially an art, my suggestion is find someone who has mastered this art and pay him or her to do your exhaust system. Also, exhaust systems do not “produce power.” They reduce the power lost by the motor attempting to expel exhaust gases out through the exhaust pipes.

 

Here are the 3 main principles you have to take into consideration in regards to an exhaust system:

 

1. Exhaust Pulses

2. Restrictiveness

3. Exhaust Heat & Gas Expansion

 

Exhaust pulses are just how frequently the piston is pushing the exhaust gases out of the chamber. A 4 cyl. engine at 4000 rpms creates ~8,400 pulses a minute. Ideally you want each pulse to line up right behind each other. This is why headers are tuned to be the same length with minimal bends. If the pulse off cylinder 4 crashes into pulse off cylinder 1 (assuming they don’t cancel each other out), they don’t flow out of the pipe correctly and that creates a small amount of restriction and turbulence. Multiply that by the number of times it occurs in a minute and you can see the power loss.

 

Restrictiveness is the simplest to answer. The catalytic converter, a muffler, bends in the pipe and anything else that gets in the way of the flow of the gases all slow down the movement in the exhaust pipes and cause the engine to work harder to expel those gases out through the pipes. The ideal is to reduce the restrictions in the exhaust pipe to the minimal amount possible, but not without first taking into account for…

 

Gas Expansion. Exhaust gases are HOT and under high pressure. Exhaust gases cool as they work their way down the pipes. The problem occurs when the gases enter a larger area allowing them to expand which allows them to cool faster than the gases behind them. Cooler gases are denser and harder to move. This is how you can lose low-end torque by attaching larger pipes to your system. You suddenly have the hot, high pressure gases enter into a larger area allowing them to cool and expand and become denser and heavier. The hot, high pressure gases right behind them run into that denser air and can’t push it down the pipe as fast as they were going. Then the gases behind them can’t move those gases as fast, increasing the pressure back up the exhaust all the way to the piston, which must push harder to push the stream of exhaust gases out through the pipes and draining more power out of the engine. You see the power loss disappear at higher RPMs due to the increased speed at which the gases flow and the decreased rate at which the gases cool as they move down through the exhaust pipes.

 

So, all that being said, there are general rules for the size of pipe you want for the size of displacement you have. The following rules I stole from one of the links:

 

For NA engines:

100 – 150ci motor = 2” tubing

150 – 220ci motor = 2.25” tubing

220 – 350ci motor = 3” tubing

OR:

1639 – 2458cc motor = 5.08cm tubing

2458 – 3605cc motor = 5.72cm tubing

3605 – 5735cc motor = 7.62cm tubing

 

I’ve heard and read about the requirements of backpressure. For a 4 stroke engine, this technically shouldn’t be required, but due to valve timing (as valves are not perfectly timed for 99% of engines) there is usually a small period when both intake and exhaust valves are open and a small amount of backpressure would be required so that none of the air/fuel mixture is allowed to vent out through the exhaust valves. This would technically allow a varying degree of lean burn and hence power loss and increased emissions. So depending on the timing of your valves and the force with which the air/fuel mixture is entering the cylinder, you will want the optimal amount of back pressure to keep from venting it out. (On the contrary, too much back pressure can cause the exhaust gases to remain in the chamber causing lean burn and loss of power.) However, manufacturers design a tiny, specific amount of that into the engine in order to facilitate complete burning of the fuel and reduce noxious emissions.

 

So, in summary, a properly designed exhaust system improves the efficiency of an engine by reducing the power required by the engine to expel exhaust gases.

 

Hope I helped clear up a lot of peoples’ questions. I’ve come to the general conclusion that the best order of upgrades (in regards only to moving air in and out of the motor) for the VG33E engine goes something along the lines of Camshaft, Intake Upgrade and then Exhaust Upgrade. Not the easiest way to go, but given that they’re basically air pumps it makes the most sense to me. It does allow you to get the optimal flow, as the cam on a given displacement with a given head will set the maximum amounts possible for intake and exhaust, the intake will determine if the motor can pull all air it can handle, and then the exhaust just determines the efficiency of expelling the air that the cam allowed the motor to breathe through the intake. Head porting fits in there after the camshaft, but I’m trying to keep this simple.

 

All of you Nissan Techs please feel free to chime in for additional information.

 

I didn't get any specifics, but I at least figured out it's not worth changing much more than the muffler right now until I get a better cam, do some head porting and put in a proper cold air intake.

 

Here are the links:

http://www.physicsforums.com/s...54363

http://warnertechnology.com/Ca...shtml

http://auto.howstuffworks.com/question172.htm

http://www.miata.net/garage/Kn....html

http://member.rivernet.com.au/...p.htm

http://www.aaxel.com/tech_back_pressure.php

http://www.thrashercharged.com....shtm

http://www.uucmotorwerks.com/h...h.htm

[brenspath]

Ok, I had to answer my own question due to the lack of answers. So here's the best I got.

 

After MUCH research on exhaust principle (without delving directly into physics gas laws, thermodynamics, etc.) and to answer my own questions about what I can do with my exhaust system, I’ve made up a quick exhaust guide. I’ve included the links at the end if you want to get a little more in-depth knowledge. My only caveat is that I’m no physicist and I’m only giving the most basic explanation I can, so I’m not 100% correct on any of this. Also, keep in mind that forced induction changes some of the rules of the game, so you’d have to adjust for any kind of FI application.

To begin with, since exhaust system building and tuning is essentially an art, my suggestion is find someone who has mastered this art and pay him or her to do your exhaust system. Also, exhaust systems do not “produce power.” They reduce the power lost by the motor attempting to expel exhaust gases out through the exhaust pipes.

 

Here are the 3 main principles you have to take into consideration in regards to an exhaust system:

 

1. Exhaust Pulses

2. Restrictiveness

3. Exhaust Heat & Gas Expansion

 

Exhaust pulses are just how frequently the piston is pushing the exhaust gases out of the chamber. A 4 cyl. engine at 4000 rpms creates ~8,400 pulses a minute. Ideally you want each pulse to line up right behind each other. This is why headers are tuned to be the same length with minimal bends. If the pulse off cylinder 4 crashes into pulse off cylinder 1 (assuming they don’t cancel each other out), they don’t flow out of the pipe correctly and that creates a small amount of restriction and turbulence. Multiply that by the number of times it occurs in a minute and you can see the power loss.

 

Restrictiveness is the simplest to answer. The catalytic converter, a muffler, bends in the pipe and anything else that gets in the way of the flow of the gases all slow down the movement in the exhaust pipes and cause the engine to work harder to expel those gases out through the pipes. The ideal is to reduce the restrictions in the exhaust pipe to the minimal amount possible, but not without first taking into account for…

 

Gas Expansion. Exhaust gases are HOT and under high pressure. Exhaust gases cool as they work their way down the pipes. The problem occurs when the gases enter a larger area allowing them to expand which allows them to cool faster than the gases behind them. Cooler gases are denser and harder to move. This is how you can lose low-end torque by attaching larger pipes to your system. You suddenly have the hot, high pressure gases enter into a larger area allowing them to cool and expand and become denser and heavier. The hot, high pressure gases right behind them run into that denser air and can’t push it down the pipe as fast as they were going. Then the gases behind them can’t move those gases as fast, increasing the pressure back up the exhaust all the way to the piston, which must push harder to push the stream of exhaust gases out through the pipes and draining more power out of the engine. You see the power loss disappear at higher RPMs due to the increased speed at which the gases flow and the decreased rate at which the gases cool as they move down through the exhaust pipes.

 

So, all that being said, there are general rules for the size of pipe you want for the size of displacement you have. The following rules I stole from one of the links:

 

For NA engines:

100 – 150ci motor = 2” tubing

150 – 220ci motor = 2.25” tubing

220 – 350ci motor = 3” tubing

OR:

1639 – 2458cc motor = 5.08cm tubing

2458 – 3605cc motor = 5.72cm tubing

3605 – 5735cc motor = 7.62cm tubing

 

I’ve heard and read about the requirements of backpressure. For a 4 stroke engine, this technically shouldn’t be required, but due to valve timing (as valves are not perfectly timed for 99% of engines) there is usually a small period when both intake and exhaust valves are open and a small amount of backpressure would be required so that none of the air/fuel mixture is allowed to vent out through the exhaust valves. This would technically allow a varying degree of lean burn and hence power loss and increased emissions. So depending on the timing of your valves and the force with which the air/fuel mixture is entering the cylinder, you will want the optimal amount of back pressure to keep from venting it out. (On the contrary, too much back pressure can cause the exhaust gases to remain in the chamber causing lean burn and loss of power.) However, manufacturers design a tiny, specific amount of that into the engine in order to facilitate complete burning of the fuel and reduce noxious emissions.

 

So, in summary, a properly designed exhaust system improves the efficiency of an engine by reducing the power required by the engine to expel exhaust gases.

 

Hope I helped clear up a lot of peoples’ questions. I’ve come to the general conclusion that the best order of upgrades (in regards only to moving air in and out of the motor) for the VG33E engine goes something along the lines of Camshaft, Intake Upgrade and then Exhaust Upgrade. Not the easiest way to go, but given that they’re basically air pumps it makes the most sense to me. It does allow you to get the optimal flow, as the cam on a given displacement with a given head will set the maximum amounts possible for intake and exhaust, the intake will determine if the motor can pull all air it can handle, and then the exhaust just determines the efficiency of expelling the air that the cam allowed the motor to breathe through the intake. Head porting fits in there after the camshaft, but I’m trying to keep this simple.

 

All of you Nissan Techs please feel free to chime in for additional information.

 

I didn't get any specifics, but I at least figured out it's not worth changing much more than the muffler right now until I get a better cam, do some head porting and put in a proper cold air intake.

 

Here are the links:

http://www.physicsforums.com/s...54363

http://warnertechnology.com/Ca...shtml

http://auto.howstuffworks.com/question172.htm

http://www.miata.net/garage/Kn....html

http://member.rivernet.com.au/...p.htm

http://www.aaxel.com/tech_back_pressure.php

http://www.thrashercharged.com....shtm

http://www.uucmotorwerks.com/h...h.htm

 

 

 

 

 

 

Ok, we are working with 3.3lt in our 96 R50

The muffler is a walker(aust) muffler, it is a dual 2inch in and dual 2inch out muffler, it has an internal crossover in it that works to equalize the pipes.

As i said we did a few bit of changing and swapping to get the end result we wanted.

The total system cost me $400 aust, it isnt loud but does has a nice deep sound, when i get the pathy started i will try to record it and post it on youtube,

Just got to try to remember to do that before we start the engine swap,

[brenspath]

what do you mean by the new tighter lsd? can you tighten the stock lsd or do you have to replace it? what did you do and where you get the stuff from?

 

 

When i had my rear diff rebuilt i got the mechanic to tighten the clutch pack up about 25% more than standard.

It now reacts more like a ford detroit locker, just a little more flexible.

It still a has a bit of free drive in tight corners but when power is applied it drives both wheels without any slip at all.

Even on dry tar roads it will easily spin both wheels on take off, it is a necessity when you have more power and big rubber.

[SnowSurfLax]

Ok, we are working with 3.3lt in our 96 R50

The muffler is a walker(aust) muffler, it is a dual 2inch in and dual 2inch out muffler, it has an internal crossover in it that works to equalize the pipes.

As i said we did a few bit of changing and swapping to get the end result we wanted.

The total system cost me $400 aust, it isnt loud but does has a nice deep sound, when i get the pathy started i will try to record it and post it on youtube,

Just got to try to remember to do that before we start the engine swap,

 

What other engine modifications have you made? What you use is always dependent on what's on it before it hits that area.

 

And what are you swapping the engine to? Dont' say Turbo Diesel, I'll cry

[brenspath]

Turbo diesel, wash your mouth out my boy.

We are fitting a gen3 5.7lt, not into oil burners, to slow, got to have enough power to spin all 4 wheels on the tar.

280kws at the flywheel is so much more fun

[skrillz]

I'm in need of a new exhaust and was wondering if there is a mangaflow or flowmaster exhaust that fits a 3.3L '98 4x4? i think it's a dual inlet to single outlet? i really just want to replace the exaust since that's all that is wrong with it now. sorry to thread jack i didn't want to start a new one.

 

the shop wants 380 bucks to replace the stock exhaust and rear tail section. i thought that was a bit high, and buddy told me that a flowmaster wouldn't work b/c the inlets have to be in the right position to line up with the existing pipes.

[StockPathy]

I put a magnaflow muffler on mine and it sounds amazing, deep tone and even has a nice rumble in cold weather, wouldn't reccomend flowmasters on a V6 app. Not enough power (atleast that's what the shop told me) I paid around 350 at a local place and haven't regretted it since. Just make sure the resonator comes off, mine sounded terrible until it was removed

[rod_b]

StockPathy - Is it the one with 2.25" inlet, 2" dual outlet installed in reverse? This is the one I'm thinking about getting but don't know if the tubing sizes match up to stock. I don't want to lose any torque. I just wanna replace my rusty exhaust with all new stuff.

 

The one I'm thinking about getting is the 12148. Also looked at the 12258 but thought the tubing might be too large and lose too much low end.

Edited February 20, 2008 by rod_b