Performance Exhaust System Basics
06-07-2007, 06:19 AM
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Performance Exhaust System Basics
Here's a nice tech article I found on exhaust. It should maybe even be a sticky. I also found another one with pixz and stuff and it's really detailed.
http://www.lcengineering.com/TechNotes/TechNote68.htm <=extra detailed
http://www.isuzuperformance.com/isup...h/exhaust.html <=shown below
[ul]Header Design
[ul]Torque is determined by header design and all of the power band tuning is done between the head and the final collector, where the last of the primary or secondary pipes is joined to a single exhaust pipe.
4-1 headers typically loose a lot of low end and mid range torque by their design. The 4-1 design will show a single peak in power improvement with a sharp decrease in power both above and below the single peak, when compared to the stock power level. Most header makers using this design will tune for peak horsepower at or above the engine's maximum speed, loosing power throught he lower half of the power curve for a very small gain at maximum engine speed. However, the exact point in the RPM range at which that peak occurs is determined by the diameter and length of the primary pipes, and some makers will use longer and smaller diameter primary pipes which will result in a small peak in power in the mid to low RPM range with power loss at both very low RPM and across the upper half of the range of engine opperating speed.
Tri-Y headers produce even power across the entire RPM range with very noticeable improvement in mid and low range torque. This is because the Tri-Y design produces two seperate peaks in power gain which taper off more gradually below the first peak and above the second peak, most often not showing any dip below the stock power level. Where those peaks occur in the range of engine speed is determined by the diameter and length of both the primary pipes and also the secondary pipes. Most makers of headers with this design will tune for the first peak in power in the lower half of the engine's opperating speed and the second peak in the upper half of the engine's opperating speed, for an even and consistent improvement in power across the entire range of engine speed which will in all cases out perform the 4-1 design for both street and race use.
The main reason that 4-1 headers are so common is the fact that they are less difficult and less expensive to manufacture and, therefore, provide greater profit margins for the manufacturer and the retailer.
[/ul]
Pipe Diameter and Bend Type
[ul]For non-turbo engines under 2.4 liter in displacement and turbocharged engines under 2.2 liter displacement and producing less than 400 HP, 2 1/2 inch mandrel bent exhaust pipe size is optimum for high performance. 2 1/4 inch pipe can limit air flow once the engine buildup gets serious and the owner has bolted on more than header, intake, and pulley.
Many people will claim that 2 1/2 looses torque, but this is not true.
As discussed earlier, all of the tuning for torque is done between the head and the final collector, in the header. After the final collector, the only thing determined by pipe diameter is how much work the engine has to do to push the exhaust gas to the back end of the car and out the tail pipe, and the less work the engine has to do, the more power it can produce.
The people advocating 2 1/4 inch diameter exhaust systems and complaining about low end power loss are also using 4-1 headers. This isn't unique to Storms, it is a serious misconception among the Cavalier/Sunfire crowd as well. These people are compensating for poor header design by strangling down the exhaust pipe diameter at the expense of mid and upper RPM engine performance.
All of this has been specific to mandrel bent pipe. Squeeze bent pipe looses 1/3 of its interior cross sectional area in a right angle bend. There are three right angle bends in the exhaust system of both the Storm and the I-Mark.
Mandrel pipe bending keeps a consistent inside diameter of the pipe through right angle and even U bends.
2 1/2 inch diameter squeeze bent pipe will flow the equivalent of 1.6 inch diameter pipe at each of those squeeze bends. The entire exhaust system will flow only as much as the tightest constriction in flow, meaning that all of the 2 1/2 inch pipe has been a waste, the total system will flow the same as a 1.6 inch diameter mandrel bent exhaust system.
To build a 2 1/2 inch diameter system using squeeze bent pipe, every bend would have to be made using 3 1/2 inch diameter pipe to compensate for the inside space lost from the squeeze bend. This means that the straight sections of pipe would be 2 1/2 inch pipe, then expanded to 3 1/2 inch bends for each and every curve, and then turned back down to 2 1/2 inch pipe for the straight pipe until the next bend.
[/ul]
Muffler Types
[ul]For maximum flow, a straight through muffler works best.
Conventional reflection mufflers use U bends within the muffler to reflect the flow and sound back and forth in a S curve through the body of the muffler. This is the most restrictive muffler design, but provide the most sound volume reduction.
Chambered mufflers have angled walls within the muffler body to reflect the sound and flow from side to side. These are less restrictive, but not optimum and provide less sound volume reduction than the conventional reflection muffler type. It is easy to see the restrictions within these mufflers as there will be areas of heat discoloration on the side of the muffler anywhere there is a restriction in flow. This is usually at the first V wall separating flow and the first reflection back toward the middle of the muffler.
Straight through mufflers offer the highest flow, because they have no restriction or impediment to flow through the muffler, but they offer the least reduction in sound volume. These are usually made up of a perforated core, wrapped with steel cloth, and packed with a sound absorbent material. The idea is that the sound is absorbed and deadened by passing through the perforations into the deadening material. Avoid designs with louvers, they stick out into the air flow and inhibit flow through the muffler. One important advantage of the straight through muffler is that they produce little or no back pressure to reduce performance and, because of this, two of this type muffler can be used in series to reduce sound volume more without sacrificing any measurable amount of performance. This is discussed further under the heading of Resonators.
[/ul]
Resonators
[ul]Resonators are designed to reduce harshness and volume of the exhaust sound prior to the muffler. These are typically an additional muffler which is placed directly behind the catalytic converter. For maximum flow and performance, these should be eliminated. In most cases, resonators are the same restrictive design as conventional reflection type mufflers. From a performance perspective, they serve one purpose, to cause back pressure and decrease power output. The drawback to this is increased exhaust sound volume. As described earlier, straight through mufflers cause little or no back pressure and adding an additional straight through muffler to an exhaust system will not decrease performance measurably. However, adding a straight through muffler will help reduce exhaust sound volume. This is a very effective use for a straight through muffler without sacrificing performance.
[/ul]
Catalytic Converters
[ul]Hollowing out a catalytic converter or replacing it with a test pipe or straight section of pipe is a violation of Federal Law punishable by fines in excess of $25,000 and/or jail time for both the vehicle owner and the person doing the work.
Removing a catalytic converter will result, at mos
http://www.lcengineering.com/TechNotes/TechNote68.htm <=extra detailed
http://www.isuzuperformance.com/isup...h/exhaust.html <=shown below
[ul]Header Design
[ul]Torque is determined by header design and all of the power band tuning is done between the head and the final collector, where the last of the primary or secondary pipes is joined to a single exhaust pipe.
4-1 headers typically loose a lot of low end and mid range torque by their design. The 4-1 design will show a single peak in power improvement with a sharp decrease in power both above and below the single peak, when compared to the stock power level. Most header makers using this design will tune for peak horsepower at or above the engine's maximum speed, loosing power throught he lower half of the power curve for a very small gain at maximum engine speed. However, the exact point in the RPM range at which that peak occurs is determined by the diameter and length of the primary pipes, and some makers will use longer and smaller diameter primary pipes which will result in a small peak in power in the mid to low RPM range with power loss at both very low RPM and across the upper half of the range of engine opperating speed.
Tri-Y headers produce even power across the entire RPM range with very noticeable improvement in mid and low range torque. This is because the Tri-Y design produces two seperate peaks in power gain which taper off more gradually below the first peak and above the second peak, most often not showing any dip below the stock power level. Where those peaks occur in the range of engine speed is determined by the diameter and length of both the primary pipes and also the secondary pipes. Most makers of headers with this design will tune for the first peak in power in the lower half of the engine's opperating speed and the second peak in the upper half of the engine's opperating speed, for an even and consistent improvement in power across the entire range of engine speed which will in all cases out perform the 4-1 design for both street and race use.
The main reason that 4-1 headers are so common is the fact that they are less difficult and less expensive to manufacture and, therefore, provide greater profit margins for the manufacturer and the retailer.
[/ul]
Pipe Diameter and Bend Type
[ul]For non-turbo engines under 2.4 liter in displacement and turbocharged engines under 2.2 liter displacement and producing less than 400 HP, 2 1/2 inch mandrel bent exhaust pipe size is optimum for high performance. 2 1/4 inch pipe can limit air flow once the engine buildup gets serious and the owner has bolted on more than header, intake, and pulley.
Many people will claim that 2 1/2 looses torque, but this is not true.
As discussed earlier, all of the tuning for torque is done between the head and the final collector, in the header. After the final collector, the only thing determined by pipe diameter is how much work the engine has to do to push the exhaust gas to the back end of the car and out the tail pipe, and the less work the engine has to do, the more power it can produce.
The people advocating 2 1/4 inch diameter exhaust systems and complaining about low end power loss are also using 4-1 headers. This isn't unique to Storms, it is a serious misconception among the Cavalier/Sunfire crowd as well. These people are compensating for poor header design by strangling down the exhaust pipe diameter at the expense of mid and upper RPM engine performance.
All of this has been specific to mandrel bent pipe. Squeeze bent pipe looses 1/3 of its interior cross sectional area in a right angle bend. There are three right angle bends in the exhaust system of both the Storm and the I-Mark.
Mandrel pipe bending keeps a consistent inside diameter of the pipe through right angle and even U bends.
2 1/2 inch diameter squeeze bent pipe will flow the equivalent of 1.6 inch diameter pipe at each of those squeeze bends. The entire exhaust system will flow only as much as the tightest constriction in flow, meaning that all of the 2 1/2 inch pipe has been a waste, the total system will flow the same as a 1.6 inch diameter mandrel bent exhaust system.
To build a 2 1/2 inch diameter system using squeeze bent pipe, every bend would have to be made using 3 1/2 inch diameter pipe to compensate for the inside space lost from the squeeze bend. This means that the straight sections of pipe would be 2 1/2 inch pipe, then expanded to 3 1/2 inch bends for each and every curve, and then turned back down to 2 1/2 inch pipe for the straight pipe until the next bend.
[/ul]
Muffler Types
[ul]For maximum flow, a straight through muffler works best.
Conventional reflection mufflers use U bends within the muffler to reflect the flow and sound back and forth in a S curve through the body of the muffler. This is the most restrictive muffler design, but provide the most sound volume reduction.
Chambered mufflers have angled walls within the muffler body to reflect the sound and flow from side to side. These are less restrictive, but not optimum and provide less sound volume reduction than the conventional reflection muffler type. It is easy to see the restrictions within these mufflers as there will be areas of heat discoloration on the side of the muffler anywhere there is a restriction in flow. This is usually at the first V wall separating flow and the first reflection back toward the middle of the muffler.
Straight through mufflers offer the highest flow, because they have no restriction or impediment to flow through the muffler, but they offer the least reduction in sound volume. These are usually made up of a perforated core, wrapped with steel cloth, and packed with a sound absorbent material. The idea is that the sound is absorbed and deadened by passing through the perforations into the deadening material. Avoid designs with louvers, they stick out into the air flow and inhibit flow through the muffler. One important advantage of the straight through muffler is that they produce little or no back pressure to reduce performance and, because of this, two of this type muffler can be used in series to reduce sound volume more without sacrificing any measurable amount of performance. This is discussed further under the heading of Resonators.
[/ul]
Resonators
[ul]Resonators are designed to reduce harshness and volume of the exhaust sound prior to the muffler. These are typically an additional muffler which is placed directly behind the catalytic converter. For maximum flow and performance, these should be eliminated. In most cases, resonators are the same restrictive design as conventional reflection type mufflers. From a performance perspective, they serve one purpose, to cause back pressure and decrease power output. The drawback to this is increased exhaust sound volume. As described earlier, straight through mufflers cause little or no back pressure and adding an additional straight through muffler to an exhaust system will not decrease performance measurably. However, adding a straight through muffler will help reduce exhaust sound volume. This is a very effective use for a straight through muffler without sacrificing performance.
[/ul]
Catalytic Converters
[ul]Hollowing out a catalytic converter or replacing it with a test pipe or straight section of pipe is a violation of Federal Law punishable by fines in excess of $25,000 and/or jail time for both the vehicle owner and the person doing the work.
Removing a catalytic converter will result, at mos
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