2 pipes or 1?

So my good friend has a 2004 Nissan Altima SE-R with 330 hp v6. It came with dual exhaust, but he says he wants to get more torque, so he may switch to single. I believe his exhaust goes 2-1-2 now, and he wants 2-1.
1. will this give him more low end torque?
2. how much?
3. will it even be noticeable?

If it goes Y in Y out and he switches to Y in I out or just drops a dual outlet muffler, there will likely be little noticeable change one way or the other.

If it has an X or H pipe like the Mustangs, then he will loose power.

If he wants more torque he needs a stroker kit.

First thing to know is that no 4-stroke engine runs better with back pressure.
This bit of information has been known since the 1890's, the first 4-stroke engines

So a few vehicle manufacturers have picked up on it in the last 128 years

On V6 or V8 engine you have the option of Dual or Single exhaust.
Neither changes the power output of the engine
You can add "H" or "X" pipes to dual exhaust to gain some Scavenged power

Scavenged power is used in all factory exhaust manifolds or headers, since the 1970's
It uses the Velocity of the exhaust leaving a cylinder to DROP the pressure at the other exhaust ports on that bank/side of the engine.

This drop in pressure means when the exhaust valve opens exhaust is PULLED from the cylinder which leaves more power on the crank, so more power for rear wheels.
This lower pressure can only be generated in one of 3 RPM ranges
Low-band
Mid-band
High-band

Rangers come with mid-band

From the exhaust manifold back as long as you don't restrict the exhaust flow there will be no change in the power.
Cats and mufflers don't effect power unless they are blocked, or the wrong size
Larger pipes from Cat back sound better, to some, but also won't effect power

Larger pipes on the heads will lose power

The "H" or "X" pipes on dual exhaust uses opposing Pulses to create a lower pressure in each pipe which PULLS exhaust out better, leaving more power on the crank
This ain't much but ain't 0 either, lol

Single exhaust is cheaper, thats why it is used
Dual exhaust can sound better and is good for advertising, but if it improves power then something was wrong with single exhaust system

If your friend wants more low end power then get headers tuned for low RPM band

RonD said:

First thing to know is that no 4-stroke engine runs better with back pressure.
This bit of information has been known since the 1890's, the first 4-stroke engines

So a few vehicle manufacturers have picked up on it in the last 128 years

On V6 or V8 engine you have the option of Dual or Single exhaust.
Neither changes the power output of the engine
You can add "H" or "X" pipes to dual exhaust to gain some Scavenged power

Scavenged power is used in all factory exhaust manifolds or headers, since the 1970's
It uses the Velocity of the exhaust leaving a cylinder to DROP the pressure at the other exhaust ports on that bank/side of the engine.

This drop in pressure means when the exhaust valve opens exhaust is PULLED from the cylinder which leaves more power on the crank, so more power for rear wheels.
This lower pressure can only be generated in one of 3 RPM ranges
Low-band
Mid-band
High-band

Rangers come with mid-band

From the exhaust manifold back as long as you don't restrict the exhaust flow there will be no change in the power.
Cats and mufflers don't effect power unless they are blocked, or the wrong size
Larger pipes from Cat back sound better, to some, but also won't effect power

Larger pipes on the heads will lose power

The "H" or "X" pipes on dual exhaust uses opposing Pulses to create a lower pressure in each pipe which PULLS exhaust out better, leaving more power on the crank
This ain't much but ain't 0 either, lol

Single exhaust is cheaper, thats why it is used
Dual exhaust can sound better and is good for advertising, but if it improves power then something was wrong with single exhaust system

If your friend wants more low end power then get headers tuned for low RPM band

Click to expand...

Well, that kills anything I had to contribute! Ha Ha! Good job.


Sent from my iPhone using Tapatalk

He already got the headers, and other stuff. The car is pretty freaking fast.I think he's trying to squeeze every little bit out of that car. Says he wants to be quicker off the start

Shorter tires will do it...

Agree with what is said above, but I'll add that true dual exhaust on a V6 sounds terrible! We sell 300hp 4.3L V6's at work for jet boats which are generally dual exhaust, very whiny and kinda annoying...

that was at the wheels tuned on a dyno? that is pre vvt so theres limits...but if it is at the tire.... thats impressive power over stock...those things stock hit the traps at a 100 mph back in the day. impressive cars. and they were only 250 hp or so...

the money it may take figuring out exhaust i cant see being worth it at this power level. dyno time alone would be more then one change. if he can build his own stuff and quickly change it on the dyno i know i would love to see the results.

exhaust has been something that has bit me in the ass many times going by the book...so i am open to dyno results. i have sized systems wrong causing all kinds of tuning issues going by the book.

RonD said:

First thing to know is that no 4-stroke engine runs better with back pressure.
This bit of information has been known since the 1890's, the first 4-stroke engines

So a few vehicle manufacturers have picked up on it in the last 128 years

On V6 or V8 engine you have the option of Dual or Single exhaust.
Neither changes the power output of the engine
You can add "H" or "X" pipes to dual exhaust to gain some Scavenged power

Scavenged power is used in all factory exhaust manifolds or headers, since the 1970's
It uses the Velocity of the exhaust leaving a cylinder to DROP the pressure at the other exhaust ports on that bank/side of the engine.

This drop in pressure means when the exhaust valve opens exhaust is PULLED from the cylinder which leaves more power on the crank, so more power for rear wheels.
This lower pressure can only be generated in one of 3 RPM ranges
Low-band
Mid-band
High-band

Rangers come with mid-band

From the exhaust manifold back as long as you don't restrict the exhaust flow there will be no change in the power.
Cats and mufflers don't effect power unless they are blocked, or the wrong size
Larger pipes from Cat back sound better, to some, but also won't effect power

Larger pipes on the heads will lose power

The "H" or "X" pipes on dual exhaust uses opposing Pulses to create a lower pressure in each pipe which PULLS exhaust out better, leaving more power on the crank
This ain't much but ain't 0 either, lol

Single exhaust is cheaper, thats why it is used
Dual exhaust can sound better and is good for advertising, but if it improves power then something was wrong with single exhaust system

If your friend wants more low end power then get headers tuned for low RPM band

Click to expand...

so defining back pressure verse pressure waves seems to be the misconception for most..


this reads like the oem kicks out the best possible available power and exhaust scavenging scenario. nnnnnnnnoooo. it does not. on the best days before vvt.... compromise is being polite. 15-20 hp across the range is pretty easy to do for a typical v8.

this is too technical of an issue without knowns. especially with that particular nissan v6 he is working with. its a monster.

the basis of all this is correct. pipes/manifolding dont necessarily mean restriction/reduction of power.

but what are these theories starting with? stock as delivered? because all vehicles are delivered with compromise due to nvh perceptions to its complete customer base and emissions laws...noise and combustion..

for sure it depends on actual application. and for sure changing the exhaust system changes useable power output from an oem given. you can shift not only the measured out put...but the power band and operating temperatures of an engine with exhaust changes. just the way it is.


there are two ends to the pump that is a 4 stroke engine. tuning of the flow on one side or the other will usually cause power change. whether it is a measurable loss or gain depends on the whole package...valve events...being fixed or variable really changes the outcomes..

if the intake is tuned together with the exhaust side from a no manifolds on either side condition.... on a typical engine you can increase flow...or what ends up being power.

if one reads this they would be tempted to think that an engine...say... lets work with a stock 302 from an 89 efi pick up...as results are known...

in theory, removing its exaust system would allow maximum power and power would increase. because any manifold restricts power and there is no benefit from restriction on a 4 stroke..

doing so would be a noisy disappointment for most. sure, it can increase max power at some new peak...but usable range falls on its face..especially with that engine.

it is actually one that a 2 into one will make better bottom end. getting to that combination goldilocks zone is not always easy either. but it sure as fawk is more then seat of the pants when done right. getting it right is the problem...




generally, say the iron head 302 engines with the least and simplest intake and exhaust manifolding run at 90 or less(usually much less) percent ve at max points where ever they fall in rpm..depending on cam/valve events.. tuning the exhaust and intake can allow over 110 percent v/e. same unit.

your not necessarily adding power reducing restriction with the right pipes on the intake and exhaust..as the rule. with certain early oem cats you can have issues...but modern cats, if your running efi and o2 sensors can actually help.










naturally aspirated verse forced induction radically changes the issue.


forced induction changes all of that. with a blower no exhaust wont matter looking at it from a pump standpoint..

RonD said:

First thing to know is that no 4-stroke engine runs better with back pressure.
This bit of information has been known since the 1890's, the first 4-stroke engines

So a few vehicle manufacturers have picked up on it in the last 128 years

On V6 or V8 engine you have the option of Dual or Single exhaust.
Neither changes the power output of the engine
You can add "H" or "X" pipes to dual exhaust to gain some Scavenged power

Scavenged power is used in all factory exhaust manifolds or headers, since the 1970's
It uses the Velocity of the exhaust leaving a cylinder to DROP the pressure at the other exhaust ports on that bank/side of the engine.

This drop in pressure means when the exhaust valve opens exhaust is PULLED from the cylinder which leaves more power on the crank, so more power for rear wheels.
This lower pressure can only be generated in one of 3 RPM ranges
Low-band
Mid-band
High-band

Rangers come with mid-band

From the exhaust manifold back as long as you don't restrict the exhaust flow there will be no change in the power.
Cats and mufflers don't effect power unless they are blocked, or the wrong size
Larger pipes from Cat back sound better, to some, but also won't effect power

Larger pipes on the heads will lose power

The "H" or "X" pipes on dual exhaust uses opposing Pulses to create a lower pressure in each pipe which PULLS exhaust out better, leaving more power on the crank
This ain't much but ain't 0 either, lol

Single exhaust is cheaper, thats why it is used
Dual exhaust can sound better and is good for advertising, but if it improves power then something was wrong with single exhaust system

If your friend wants more low end power then get headers tuned for low RPM band

Click to expand...

OK, but where's the part about the low pressure at the exhaust valve instigating some flow from the intake valve during overlap? the piston is at/near TDC, so it isn't doing diddly squat to get the intake charge moving into the cylinder. talking naturally asperated, not forced induction.

Bobbywalter, 330 at the motor. This thing is tricked out and fast as f*^k. You are pretty on point. He says it's all he can do now to get where he wants it to be aside from adding an all wheel drive setup. I don't think that was an option.

My post wasn't meant to be in depth report on exhaust scavenging, lol

OPs question was would there be better torque by switching to single exhaust from a dual exhaust
I don't think there would be any change as long as flow wasn't restricted from headers back.
If he had working "H" or "X" crossovers now with the Dual setup then he may lose a bit

RonD said:

My post wasn't meant to be in depth report on exhaust scavenging, lol

OPs question was would there be better torque by switching to single exhaust from a dual exhaust
I don't think there would be any change as long as flow wasn't restricted from headers back.
If he had working "H" or "X" crossovers now with the Dual setup then he may lose a bit

Click to expand...

just trying to keep you on your toes.

IIRC he's willing/knows he will lose some hp to gain the torque. He's going for quicker take offs for street racing also his daily driver. Also it sits in the driveway a lot with something broke.