I have a '96 Corolla with a 1.6L that has 1.75" tubing. My '11 Civic has a 1.8L with 2.25" tubing. All econobox's used to have sub 2" exhaust. Why the change? Isn't the smaller diameter better for torque? Curious what you guys think.
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exhaust diameter's
- Thread starter dwcopple
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I have noticed that Honda 4-cylinder engines seem to have rather large diameter exhaust, and I'm not sure why. I think my CR-V's exhaust is at least as large as the exhaust on our MDX, which has an additional 1.1L and 2 cylinders' worth of displacement. The MDX does split into two tailpipes and mufflers, but the main pipe is the same diameter I believe.
Lot of variables determine the resistance to gas flow in an exhaust pipe. Engine valve timing, number of cylinders, exhaust volume of each cyl, number of bends and angles of the bends, length of the pipe, muffler internal design and the list goes on. Some engines, due to valve timinga smaller dia pipe for best performance. I remember the Porsche 1500 Carrara had a small dia factory exhaust system. People put on a larger system and performance went way down. The reason was that the engine design benefited from some back pressure in order to get the best performance. Gads, I got carried away. Sorry. Ed
Remember the pea shooters on the old VW bugs??? Lots of "better looking" replacements were availible but few worked any better. Those that did were equal length pipes for each cylinder dumping into a collector and one common muffler. Exhaust design in a science, it's lucky that OBDII fuel injection systems can trim to cover a multitude of aftermarket sins. I do notice the "F Can" has gone out of style in older Civics. Of the new cars, I think Nissan has some of the best sounding V6 systems. It is difficult to get a true "dual" system on a transverse mounted engine. These "Y" pipe things are just for show.
No need or benefit in a non-turbo street car to have ex. dia > 150% of primary diameter, esp the further back you get. Exhaust tuning involves resonance tuning (like organ pipes) to scavenge on top of the inherent torque peak or flatten a peaky engine. I like peaky engine though.
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It's also interesting to note how the exhaust pipe diameter often decreases the further you get away from the engine. I think our Acura has a 2.5" head pipe, maybe 2.25" or 2" back to the resonator, and then 1.75" or 1.5" from the Y to each muffler in the back.
Originally Posted By: dwcopple
I have a '96 Corolla with a 1.6L that has 1.75" tubing. My '11 Civic has a 1.8L with 2.25" tubing. All econobox's used to have sub 2" exhaust. Why the change? Isn't the smaller diameter better for torque? Curious what you guys think.
Is that 2.25 all the way from front to back? My daughter has an 07 Civic EX - I will check hers. As others have mentioned, it is common and often beneficial to decrease size as gas flows. That said however, many exhaust tips are larger than the pipe ahead of the last muffler or resonator. Cosmetics is a factor.
I have a '96 Corolla with a 1.6L that has 1.75" tubing. My '11 Civic has a 1.8L with 2.25" tubing. All econobox's used to have sub 2" exhaust. Why the change? Isn't the smaller diameter better for torque? Curious what you guys think.
Is that 2.25 all the way from front to back? My daughter has an 07 Civic EX - I will check hers. As others have mentioned, it is common and often beneficial to decrease size as gas flows. That said however, many exhaust tips are larger than the pipe ahead of the last muffler or resonator. Cosmetics is a factor.
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As hinted at in my prev post, it's correct engineering that the tubing dia decreases. The gas is loosing heat energy, becoming less voluminous, and decreasing in velocity as a packet distances itself from the exhaust port.
Originally Posted By: ARCOgraphite
As hinted at in my prev post, it's correct engineering that the tubing dia decreases. The gas is loosing heat energy, becoming less voluminous, and decreasing in velocity as a packet distances itself from the exhaust port.
a couple of things:
The gas is becoming more dense as it cools, and should therefore have a larger pipe downstream. Kinda like a reverse funnel .
And except for some 2 strokes, no engine likes exhaust backpressure. Large pipes can INCREASE backpressure at low engine speeds because of the larger volume of gas in it that needs to be pumped [velocity is low and there is no ram tuning].
It can seem counter intuitive. This leads to the myth of an engine needing back pressure to run right [needing smaller pipes].
As hinted at in my prev post, it's correct engineering that the tubing dia decreases. The gas is loosing heat energy, becoming less voluminous, and decreasing in velocity as a packet distances itself from the exhaust port.
a couple of things:
The gas is becoming more dense as it cools, and should therefore have a larger pipe downstream. Kinda like a reverse funnel .
And except for some 2 strokes, no engine likes exhaust backpressure. Large pipes can INCREASE backpressure at low engine speeds because of the larger volume of gas in it that needs to be pumped [velocity is low and there is no ram tuning].
It can seem counter intuitive. This leads to the myth of an engine needing back pressure to run right [needing smaller pipes].
Originally Posted By: user52165
Is that 2.25 all the way from front to back? however, many exhaust tips are larger than the pipe ahead of the last muffler or resonator.
It is 2.25" the whole way. The tip is enlarged to maybe a hair under 2.5" for cosmetics.
I'd love to see how it drives with 1.75" tubing but I am sure not gonna do it.
Is that 2.25 all the way from front to back? however, many exhaust tips are larger than the pipe ahead of the last muffler or resonator.
It is 2.25" the whole way. The tip is enlarged to maybe a hair under 2.5" for cosmetics.
I'd love to see how it drives with 1.75" tubing but I am sure not gonna do it.
Originally Posted By: mechtech2
Originally Posted By: ARCOgraphite
As hinted at in my prev post, it's correct engineering that the tubing dia decreases. The gas is loosing heat energy, becoming less voluminous, and decreasing in velocity as a packet distances itself from the exhaust port.
a couple of things:
The gas is becoming more dense as it cools, and should therefore have a larger pipe downstream. Kinda like a reverse funnel .
And except for some 2 strokes, no engine likes exhaust backpressure. Large pipes can INCREASE backpressure at low engine speeds because of the larger volume of gas in it that needs to be pumped [velocity is low and there is no ram tuning].
It can seem counter intuitive. This leads to the myth of an engine needing back pressure to run right [needing smaller pipes].
I think that ARCO has it right. Pipe dia. will be larger closer to the engine. This is because they are moving at higher velocities and are expanding as they exit the engine. Once it (typically) passes through the muffler, the pipe diameter drops as the gasses have cooled and slowed.
Originally Posted By: ARCOgraphite
As hinted at in my prev post, it's correct engineering that the tubing dia decreases. The gas is loosing heat energy, becoming less voluminous, and decreasing in velocity as a packet distances itself from the exhaust port.
a couple of things:
The gas is becoming more dense as it cools, and should therefore have a larger pipe downstream. Kinda like a reverse funnel .
And except for some 2 strokes, no engine likes exhaust backpressure. Large pipes can INCREASE backpressure at low engine speeds because of the larger volume of gas in it that needs to be pumped [velocity is low and there is no ram tuning].
It can seem counter intuitive. This leads to the myth of an engine needing back pressure to run right [needing smaller pipes].
I think that ARCO has it right. Pipe dia. will be larger closer to the engine. This is because they are moving at higher velocities and are expanding as they exit the engine. Once it (typically) passes through the muffler, the pipe diameter drops as the gasses have cooled and slowed.
eric -
Actually, exhaust gas can be hotter after the cat, throwing your theory out the window.
Anyways, most cars use the same diameter pipe from the cat back to the large muffler.
I never saw one get narrower.
Actually, exhaust gas can be hotter after the cat, throwing your theory out the window.
Anyways, most cars use the same diameter pipe from the cat back to the large muffler.
I never saw one get narrower.
Originally Posted By: mechtech2
eric -
Actually, exhaust gas can be hotter after the cat, throwing your theory out the window.
Anyways, most cars use the same diameter pipe from the cat back to the large muffler.
I never saw one get narrower.
You are probably right too. I recall reading a tech article in a car magazine about this very subject which supports what I say... BUT, I'm sure it didn't take into account newer cars and cats.
I am still somewhat willing to bet that if a car had it's main muffler under the body somewhere, it would have a smaller pipe and I bet you're right in that it would be the same size to the muffler if is at the bumper.
eric -
Actually, exhaust gas can be hotter after the cat, throwing your theory out the window.
Anyways, most cars use the same diameter pipe from the cat back to the large muffler.
I never saw one get narrower.
You are probably right too. I recall reading a tech article in a car magazine about this very subject which supports what I say... BUT, I'm sure it didn't take into account newer cars and cats.
I am still somewhat willing to bet that if a car had it's main muffler under the body somewhere, it would have a smaller pipe and I bet you're right in that it would be the same size to the muffler if is at the bumper.
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