Cutouts
01-13-10, 10:06 PM
#16
i had 3" piping while i was aquiring my 1j. i can tell you from expierence, 3" piping on my stock 2j actually lost power and torque, your engine needs back pressure. if you notice on v8/v6 true headers, not manifolds, are actually small. maybe 3/4 to 1 1/4 inches, they all 4 together in a collector. oem usually knows how to do it best, afterall they built the engine. look at the jdm type r header for the b18. the best headers of all, and often copied by dc sports, etc..
see headers make power on old chevys because they are primitive, not precise. they puddle fuel up behind the valves because the use a carburetor. top fuel cars have super tight tolerances, and are supercharged, and run on methanol. believe it or not those open headers are tuned to make power
i borrowed this from car craft
Header Basics
Think you know all there is to know about headers? Grab your favorite brain food and get ready to pay attention. We'll discuss all aspects of header design so you can accurately choose which set of pipes is best for your motor to exhale through.
February 24, 2009
By Jim McFarland
Photography by Car Craft Staff
Frankly, you'd think this subject would have been exhausted by now. After all, how much "borderless education" can you absorb about such common and oft-explained engine functions as getting rid of combustion by-products? Well, this story offers you a challenge. Our plan is to integrate various header functions, dispel a few myths about how headers work, and simplify matching parts to engine size and rpm.
Basics
Many stock exhaust systems are not capable of transferring sufficient exhaust gas at high engine speeds. Restrictions to this flow can include exhaust manifolds, catalytic converters, mufflers, and all connecting pipes routing combustion residue away from the engine. As power levels increase, proportionate amounts of exhaust can also increase, placing added demands on systems that may be flow deficient. Header manufacturers, among other objectives, attempt to build systems that fit (or should) and provide bigger pipes for high-rpm power gains. Knowing how and why a system needs to work helps in the selection process.
Combustion by-products won't burn a second time. Therefore, an exhaust system that cannot properly rid cylinders of exhaust gas can cause contamination of fresh air/fuel charges. Residual exhaust material occupies space in the cylinders that prevents maximum filling during inlet cycles. As a rule, this problem grows with rpm, potentially reducing the benefits that can be derived from other performance-enhancing parts.As you will see, exhaust-flow velocity is an important component in an efficient exhaust system. Simply stated, at low rpm, the flow rate tends to be slow.
As engine speed increases, so does flow rate. Then, as restrictions increase, velocity slows again, reducing power accordingly. Interestingly, camshaft design, compression ratio, ignition-spark timing, and piston displacement affect all this if an accompanying improvement in the exhaust system isn't included with such changes. In fact, these types of modifications can cause exhaust problems to occur sooner in the rpm range.On the other hand, exhaust systems can be too big for engine packages that don't produce sufficient exhaust-flow volume to necessitate size increase. So we're back to the flow-velocity issue. Sizing of system components, such as headers, can be keyed to engine speed and piston displacement. We'll show you how this is done later in the story.
Graph A illustrates how merely changing pipe diameter affects an engine's output. Note that the smallest diameter creates good midrange torque yet falls off at the top, while the larger primary header pipes add more high-rpm power at the expense of low-speed torque.
Primary pipe length can also skew an engine's power curve based on length changes. Primary-pipe diameter establishes the peak torque point, so changing the pipe length will rock the output curve by pivoting it around that peak torque point. Graph B shows how longer tubes tend to increase power below peak torque while hurting power above peak torque. Shorter tubes tend to affect the engine in exactly the opposite way, hurting midrange torque in favor of increasing top-end power.
What Primary Pipes Do
The main function of primary pipes is to set the initial rpm point (engine speed) at which a torque boost is created, as contributed by the headers. Keep in mind, exhaust and intake systems can be tuned to different engine speeds. By so doing, an overall torque curve can be broadened or narrowed by the separate dimensioning of intake and exhaust systems.
Several variables contribute to how headers affect engine performance, including the diameter and length of the primary-pipe and collector.In the case of headers, primary-pipe diameter determines flow rate (velocity). At peak torque (peak volumetric efficiency), the mean flow velocity is 240-260 feet per second (fps), depending upon which mathematical basis is used to do the calculation. But for sizing or matching primary pipes to specific engine sizes and rpm, 240 fps is a good number.
Changing the length of primary pipes generally affects the amount of torque produced above and below peak-torque rpm. For example, all else being equal, shortening primary pipes transfers torque from below to above the peak, not significantly shifting the rpm point at which peak torque occurs. Increasing primary-pipe length produces the opposite effect of shortening the length.
Primary-pipe diameter plays a big part in determining the torque curve. A pipe that is too small creates peak exhaust-gas velocity too early in the rpm curve and will limit top-end horsepower. Pipes that are too large create a very peaky output curve.What Do Collectors Do?
Essentially, collectors have an impact on torque below peak torque. While the gathering or merging of primary pipes does affect header tuning, it is the addition of collector volume (typically changes to pipe length once a diameter is chosen) that alters torque. Engines operated above peak torque, particularly in drag racing, do not derive any benefit from collectors. Those required to make power in a range that includes rpm below peak torque do benefit. And the further below peak torque they are required to run (from 2,500-7,500 rpm for example), the more improvement collectors provide.
Joining collectors, cross-pipe science notwithstanding, tends to further boost low-rpm torque by the increase in total collector volume. Generally, crossover pipes become less effective at higher rpm, as you might expect, although some manufacturers of the more scientific cross-pipes claim power gains as engine speed increases. The mere joining of collectors in a dual-collector system does not appear to produce this improvement.
Header Size
Consider this: It is the downward motion of a piston that creates cylinder pressure less than atmospheric. Intake flow velocity then becomes a function of piston displacement, engine speed, and the cross-section area of the inlet path. On the exhaust side, a similar set of conditions exists. In this case, exhaust-flow velocity depends on piston displacement, engine speed, the cross-sectional area of the exhaust path, and cylinder pressure during the exhaust cycle.
Of the similarities between the intake and exhaust process, piston displacement, engine speed, and flow-path cross section are common. Therefore, there must be a functional relationship among rpm, piston displacement, and flow-path section area, and there is (see the section on calculating pipe sizes).
Note how this shorty header minimizes the collector length. Generally, this is done to make it easy to fit the headers in the chassis. This mini-collector generally costs low-speed torque. If you have room to extend the collector length by 8 to 10 inches, this could improve torque.This suggests the possibility of sizing primary-pipe diameter to produce torque boosts (as contributed by the exhaust system) to an engine's net torque curve. The previously mentioned mean flow velocity (240-260 fps) found in primary pipes around peak torque rpm is a function of pipe diameter. So, selecting diameters that correspond with the rpm at which torque boosts are desired is one method of header selection or sizing.
Matching Headers to Objectives
If we know any two of the three previously mentioned variables (piston displacement, rpm, or primary-pipe diameter), we can apply some simple math to solve for the other. Here's how that works.
1. Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Given this relationship, we can perform some transposition to solve for the primary-pipe cross-section area.
2. Primary pipe area = peak-torque rpm / 88,200 x displacement of one cylinder. We can also determine the required displacement of one cylinder (multiplied by the number of cylinders for total engine size) by:
Out of all the variables to consider, one of the most important is that the headers fit the chassis without requiring significant surgery. There are also several different variations on the angle-plug concept for small-block Chevy engines that can cause difficulties if you haven't done your homework.3. Displacement of one cylinder = Primary pipe area x 88,200 / peak-torque rpm.
Equations 1 and 2 provide a method for determining peak-torque rpm (as contributed by the primary pipes) if you have already selected a set of headers and know the engine size. In equation 3, primary-pipe area can be determined if the desired peak-torque rpm and engine size are already known. It will also calculate engine size based on a known set of headers and rpm at which peak torque is desired.
Here's an example of how this approach can work. Suppose you have a 350ci small-block (43.75 cubic inches per cylinder). A primary-pipe torque boost around 4,000 rpm is your target engine speed. The choices for pipe size are 15⁄8 inches, 13⁄4 inches, and 17⁄8 inches. If we assume a tubing wall thickness of 0.040 inch, each of these od dimensions requires subtracting 0.080 inch when computing cross-section areas.
Using the formula, Area = (3.1416) x (id radius) x (id radius), we obtain the following cross sections: 15⁄8 inches = 2.07 square inches; 13⁄4 inches = 2.19 square inches; 17⁄8 inches = 2.53 square inches.
Remember that headers are just one part of the power equation. When trying to improve power, consider the headers as one part of the overall compression, cylinder-head, camshaft, and induction system.Plugging each of these values into equation 1, we find the selection of peak torque becomes (in the same order of pipe sizes), 4,173, 4,415 and 5,100 rpm. Based on an intention to provide a torque boost around 4,000 rpm, 15⁄8-inch-diameter primaries appears to work. In accord with our previous comments about primary-pipe length, extending these primaries will increase torque below 4,000 rpm at the expense of torque above this point, which is an additional tool to manipulate a torque curve about its peak (see "Torque Peaks").
While this method will not predict header-pipe area as precisely as some contemporary computer-modeling programs, it can be a valuable quick-and-dirty tool when making decisions about header choice or application of sets already on hand.
Conclusion
There is much more to the science of exhaust-system tuning and headers that space does not allow us to include. It's worth noting once again that the final combination of parts must take into account all the components as a system, rather than looking at the headers as a separate entity. Any engine will make its best overall power when treated as a complete system.
see headers make power on old chevys because they are primitive, not precise. they puddle fuel up behind the valves because the use a carburetor. top fuel cars have super tight tolerances, and are supercharged, and run on methanol. believe it or not those open headers are tuned to make power
i borrowed this from car craft
Header Basics
Think you know all there is to know about headers? Grab your favorite brain food and get ready to pay attention. We'll discuss all aspects of header design so you can accurately choose which set of pipes is best for your motor to exhale through.
February 24, 2009
By Jim McFarland
Photography by Car Craft Staff
Frankly, you'd think this subject would have been exhausted by now. After all, how much "borderless education" can you absorb about such common and oft-explained engine functions as getting rid of combustion by-products? Well, this story offers you a challenge. Our plan is to integrate various header functions, dispel a few myths about how headers work, and simplify matching parts to engine size and rpm.
Basics
Many stock exhaust systems are not capable of transferring sufficient exhaust gas at high engine speeds. Restrictions to this flow can include exhaust manifolds, catalytic converters, mufflers, and all connecting pipes routing combustion residue away from the engine. As power levels increase, proportionate amounts of exhaust can also increase, placing added demands on systems that may be flow deficient. Header manufacturers, among other objectives, attempt to build systems that fit (or should) and provide bigger pipes for high-rpm power gains. Knowing how and why a system needs to work helps in the selection process.
Combustion by-products won't burn a second time. Therefore, an exhaust system that cannot properly rid cylinders of exhaust gas can cause contamination of fresh air/fuel charges. Residual exhaust material occupies space in the cylinders that prevents maximum filling during inlet cycles. As a rule, this problem grows with rpm, potentially reducing the benefits that can be derived from other performance-enhancing parts.As you will see, exhaust-flow velocity is an important component in an efficient exhaust system. Simply stated, at low rpm, the flow rate tends to be slow.
As engine speed increases, so does flow rate. Then, as restrictions increase, velocity slows again, reducing power accordingly. Interestingly, camshaft design, compression ratio, ignition-spark timing, and piston displacement affect all this if an accompanying improvement in the exhaust system isn't included with such changes. In fact, these types of modifications can cause exhaust problems to occur sooner in the rpm range.On the other hand, exhaust systems can be too big for engine packages that don't produce sufficient exhaust-flow volume to necessitate size increase. So we're back to the flow-velocity issue. Sizing of system components, such as headers, can be keyed to engine speed and piston displacement. We'll show you how this is done later in the story.
Graph A illustrates how merely changing pipe diameter affects an engine's output. Note that the smallest diameter creates good midrange torque yet falls off at the top, while the larger primary header pipes add more high-rpm power at the expense of low-speed torque.
Primary pipe length can also skew an engine's power curve based on length changes. Primary-pipe diameter establishes the peak torque point, so changing the pipe length will rock the output curve by pivoting it around that peak torque point. Graph B shows how longer tubes tend to increase power below peak torque while hurting power above peak torque. Shorter tubes tend to affect the engine in exactly the opposite way, hurting midrange torque in favor of increasing top-end power.
What Primary Pipes Do
The main function of primary pipes is to set the initial rpm point (engine speed) at which a torque boost is created, as contributed by the headers. Keep in mind, exhaust and intake systems can be tuned to different engine speeds. By so doing, an overall torque curve can be broadened or narrowed by the separate dimensioning of intake and exhaust systems.
Several variables contribute to how headers affect engine performance, including the diameter and length of the primary-pipe and collector.In the case of headers, primary-pipe diameter determines flow rate (velocity). At peak torque (peak volumetric efficiency), the mean flow velocity is 240-260 feet per second (fps), depending upon which mathematical basis is used to do the calculation. But for sizing or matching primary pipes to specific engine sizes and rpm, 240 fps is a good number.
Changing the length of primary pipes generally affects the amount of torque produced above and below peak-torque rpm. For example, all else being equal, shortening primary pipes transfers torque from below to above the peak, not significantly shifting the rpm point at which peak torque occurs. Increasing primary-pipe length produces the opposite effect of shortening the length.
Primary-pipe diameter plays a big part in determining the torque curve. A pipe that is too small creates peak exhaust-gas velocity too early in the rpm curve and will limit top-end horsepower. Pipes that are too large create a very peaky output curve.What Do Collectors Do?
Essentially, collectors have an impact on torque below peak torque. While the gathering or merging of primary pipes does affect header tuning, it is the addition of collector volume (typically changes to pipe length once a diameter is chosen) that alters torque. Engines operated above peak torque, particularly in drag racing, do not derive any benefit from collectors. Those required to make power in a range that includes rpm below peak torque do benefit. And the further below peak torque they are required to run (from 2,500-7,500 rpm for example), the more improvement collectors provide.
Joining collectors, cross-pipe science notwithstanding, tends to further boost low-rpm torque by the increase in total collector volume. Generally, crossover pipes become less effective at higher rpm, as you might expect, although some manufacturers of the more scientific cross-pipes claim power gains as engine speed increases. The mere joining of collectors in a dual-collector system does not appear to produce this improvement.
Header Size
Consider this: It is the downward motion of a piston that creates cylinder pressure less than atmospheric. Intake flow velocity then becomes a function of piston displacement, engine speed, and the cross-section area of the inlet path. On the exhaust side, a similar set of conditions exists. In this case, exhaust-flow velocity depends on piston displacement, engine speed, the cross-sectional area of the exhaust path, and cylinder pressure during the exhaust cycle.
Of the similarities between the intake and exhaust process, piston displacement, engine speed, and flow-path cross section are common. Therefore, there must be a functional relationship among rpm, piston displacement, and flow-path section area, and there is (see the section on calculating pipe sizes).
Note how this shorty header minimizes the collector length. Generally, this is done to make it easy to fit the headers in the chassis. This mini-collector generally costs low-speed torque. If you have room to extend the collector length by 8 to 10 inches, this could improve torque.This suggests the possibility of sizing primary-pipe diameter to produce torque boosts (as contributed by the exhaust system) to an engine's net torque curve. The previously mentioned mean flow velocity (240-260 fps) found in primary pipes around peak torque rpm is a function of pipe diameter. So, selecting diameters that correspond with the rpm at which torque boosts are desired is one method of header selection or sizing.
Matching Headers to Objectives
If we know any two of the three previously mentioned variables (piston displacement, rpm, or primary-pipe diameter), we can apply some simple math to solve for the other. Here's how that works.
1. Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder. Given this relationship, we can perform some transposition to solve for the primary-pipe cross-section area.
2. Primary pipe area = peak-torque rpm / 88,200 x displacement of one cylinder. We can also determine the required displacement of one cylinder (multiplied by the number of cylinders for total engine size) by:
Out of all the variables to consider, one of the most important is that the headers fit the chassis without requiring significant surgery. There are also several different variations on the angle-plug concept for small-block Chevy engines that can cause difficulties if you haven't done your homework.3. Displacement of one cylinder = Primary pipe area x 88,200 / peak-torque rpm.
Equations 1 and 2 provide a method for determining peak-torque rpm (as contributed by the primary pipes) if you have already selected a set of headers and know the engine size. In equation 3, primary-pipe area can be determined if the desired peak-torque rpm and engine size are already known. It will also calculate engine size based on a known set of headers and rpm at which peak torque is desired.
Here's an example of how this approach can work. Suppose you have a 350ci small-block (43.75 cubic inches per cylinder). A primary-pipe torque boost around 4,000 rpm is your target engine speed. The choices for pipe size are 15⁄8 inches, 13⁄4 inches, and 17⁄8 inches. If we assume a tubing wall thickness of 0.040 inch, each of these od dimensions requires subtracting 0.080 inch when computing cross-section areas.
Using the formula, Area = (3.1416) x (id radius) x (id radius), we obtain the following cross sections: 15⁄8 inches = 2.07 square inches; 13⁄4 inches = 2.19 square inches; 17⁄8 inches = 2.53 square inches.
Remember that headers are just one part of the power equation. When trying to improve power, consider the headers as one part of the overall compression, cylinder-head, camshaft, and induction system.Plugging each of these values into equation 1, we find the selection of peak torque becomes (in the same order of pipe sizes), 4,173, 4,415 and 5,100 rpm. Based on an intention to provide a torque boost around 4,000 rpm, 15⁄8-inch-diameter primaries appears to work. In accord with our previous comments about primary-pipe length, extending these primaries will increase torque below 4,000 rpm at the expense of torque above this point, which is an additional tool to manipulate a torque curve about its peak (see "Torque Peaks").
While this method will not predict header-pipe area as precisely as some contemporary computer-modeling programs, it can be a valuable quick-and-dirty tool when making decisions about header choice or application of sets already on hand.
Conclusion
There is much more to the science of exhaust-system tuning and headers that space does not allow us to include. It's worth noting once again that the final combination of parts must take into account all the components as a system, rather than looking at the headers as a separate entity. Any engine will make its best overall power when treated as a complete system.
01-13-10, 10:12 PM
#17
As for the exhaust, your car has ODB II system and it has multiple air fuel ratio sensors.
if your downstream sensor gets no reading or a different reading than its supposed to get, you get a CEL, the computer cuts the power, to adjust the fuel ratio and cam timing to get where the engine is stable.
That kills power.
if your downstream sensor gets no reading or a different reading than its supposed to get, you get a CEL, the computer cuts the power, to adjust the fuel ratio and cam timing to get where the engine is stable.
That kills power.
01-13-10, 10:22 PM
#18
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although i don't know what any of you are talking about....i do know that kurtz and lobuxracer definitely know what they're talking about. not to gangbang you or anything gnode but i would just take their word for it and let this rest..
01-13-10, 10:49 PM
#20
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As I said before, good luck, and use a watch.
01-14-10, 04:18 AM
#21
Here's more people aware you're clueless:
http://www.superchevy.com/technical/...exh/index.html
If the pipes are too large a fair chunk of torque can be lost without actually gaining much in the way of top-end power.
Too large or too small of a pipe will push the scavenging bonuses out of the useable RPM range and will result in diminished overall performance
Pipe that is too large will loose low end torque as the gas starts moving slower.
If the exhaust pipe is too large, you will get reduced flow velocity of the exhaust gasses. The flow velocity of the exhaust gasses assists with the scavenging of the spent exhaust gasses as well as the amount of air/fuel mixture that can be drawn into the combustion chamber on the next intake stroke. This is because the flow velocity of the exhaust creates a low pressure immediately behind it that sucks more gasses out of the combustion chamber. The trick is thus to get the back pressure just right.
Too big of an exhaust pipe causes power loss, especially low-end torque. This is because a big pipe has less exhaust stream velocity than a smaller pipe.
If the exhaust pipe diameter is too large, the flow will be sluggish with low velocity and the scavenging with not be so good.
if you'd like to bet, literally, any amount of money on earth you're wrong let me know. Bet $50,000 if you like. Then get a 2.5" exhaust and a 5" exhaust and we'll dyno them on a few cars.
Be sure to have the $50,000 ready to pay me since you'll kill your exhaust velocity and lose power. Just like basic physics tells you, just like every source with a brain has told you.
YOU. HAVE. NO. CLUE. WHAT. YOU. ARE. SAYING.
Between myself, and especially Lobuxracer, I'd be even more willing to bet whatever amount you want you're wrong there too.
Your "full exhaust" math makes little sense as well, since you tried to use $300 as your total spent figure, but that clearly doesn't include headers. Taking headers out of the equation you're simply avoiding buying a from-the-header-back exhaust.
I already told you how for $500 to get 95% of the gain that would give you and be legal (and not risk the cutouts rusting shut or open some day too).
If you wanna save even more money, just remove the headers...after all, according to you removing restriction always adds power right? Can be any less restrictive than open exhaust ports on your heads!
What headers are you using BTW? I'm curious since I'm sure you're highly knowledgeable in all the various headers available designed for the 350, right? Can you, I dunno, name them all for us? Were they all designed to run open?
Anyway... good luck with your, err, "project"
Last edited by Kurtz; 01-14-10 at 05:41 AM.
01-14-10, 07:11 AM
#22
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As for the exhaust, your car has ODB II system and it has multiple air fuel ratio sensors.
if your downstream sensor gets no reading or a different reading than its supposed to get, you get a CEL, the computer cuts the power, to adjust the fuel ratio and cam timing to get where the engine is stable.
That kills power.
if your downstream sensor gets no reading or a different reading than its supposed to get, you get a CEL, the computer cuts the power, to adjust the fuel ratio and cam timing to get where the engine is stable.
That kills power.
Thanks for your input t0e. Do you have any 1/4 mile passes or dynos from before and after?
Most of the rest of you are blowing hot air and not really contributing here. The fact that aftermarket exhaust yields gains in IS350s is proof that there are bottlenecks in the stock system which can be reduced and improved on. A properly placed cut out will also eliminate those bottlenecks. The definition of properly placed being a location that does not interfere with sensors and also does not increase chaos/backpressure. I am concerned that t0e's setup probably disrupts flow by having the long tube before the cut out. However, his dual setup itself may make up for it.
Oh sweet: http://www.carcraft.com/techarticles...tallation.html
I will give this a shot and let you know what the chalk suggests. It looks like it should find the magic point where the stock exhaust system has served its beneficial purpose.
Last edited by gnode; 01-14-10 at 07:41 AM.
01-14-10, 10:28 AM
#24
just saying...why ask for advice if you're just going to tell everyone that tries to help you out that they're full of ****? If you know so much, you would have done this already because you should know exactly how it will affect your car, and not have to ask anybody.
But you knew that already, didn't you?
But you knew that already, didn't you?
01-14-10, 10:55 AM
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just saying...why ask for advice if you're just going to tell everyone that tries to help you out that they're full of ****? If you know so much, you would have done this already because you should know exactly how it will affect your car, and not have to ask anybody.
But you knew that already, didn't you?
But you knew that already, didn't you?
There are things that I do not know about IS350s specifically, such as how the computer might respond.
They aren't necessarily full of ****. However, they are speculating and theorizing after I specifically stated that I was not looking for speculation or theories, but actual results from someone who has done this already, especially to answer my specific questions about placement and computer response.
They did not answer either of those questions, and instead made naive guesses. If they really think a cutout can not yield a benefit, then they also should have the same opinion of any aftermarket cat back system. The limited gain we get from cat back systems does suggest the original exhaust is actually pretty good. I am not claiming the stock exhaust is "bad". On the contrary, for every day driving, I like it. That is why I don't really want to do a full exhaust system. Instead, I would rather flip a switch and go from comfortable cruising to a little meaner and faster, and then back to comfortable and quiet again.
Last edited by gnode; 01-14-10 at 10:58 AM.
01-14-10, 11:17 AM
#26
There are things that I do not know about IS350s specifically, such as how the computer might respond.
They aren't necessarily full of ****. However, they are speculating and theorizing after I specifically stated that I was not looking for speculation or theories, but actual results from someone who has done this already, especially to answer my specific questions about placement and computer response.
They did not answer either of those questions, and instead made naive guesses. If they really think a cutout can not yield a benefit, then they also should have the same opinion of any aftermarket cat back system. The limited gain we get from cat back systems does suggest the original exhaust is actually pretty good. I am not claiming the stock exhaust is "bad". On the contrary, for every day driving, I like it. That is why I don't really want to do a full exhaust system. Instead, I would rather flip a switch and go from comfortable cruising to a little meaner and faster, and then back to comfortable and quiet again.
"if you place the cutout AFTER the o2 sensors, you should not have a problem with the ECU."
Their intent is not to say it won't yield a benefit, rather that any benefit without a power adder will be negligible. Catback systems are a whole different animal. Regardless, you can't mod exhaust and expect power without modding intake...etc.
As for quiet, then flip a switch and loud, yes. Cutout will accomplish this. however, the limited gain you would see (MAYBE 5hp at the wheels, if?) would not make the car any faster. Trust me, my last vehicle was a 400hp supercharged mustang cobra. The power difference on that vehicle (relatively high displacement, low compression but supercharged) would be more than a stock IS350 (relatively low displacement, high compression).
Lowering backpressure too much in your exhaust is like lowering compression too much in your motor. sure, your Is350 makes 300hp and is quick at 11:1 compression; but thicken the headgasket or do internals to make that compression 9:1 and without a power adder, the car's a dog. See what I mean?
For the purposes you imply, I say do it. But might I caution you to not take personally the responses you get to a question, because people are only going to put up with attitude so many times when YOU ask THEM for help.
01-14-10, 11:45 AM
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however, you're doing the same speculating they are. I answered your question quite thoroughly in the other thread:
"if you place the cutout AFTER the o2 sensors, you should not have a problem with the ECU."
Their intent is not to say it won't yield a benefit, rather that any benefit without a power adder will be negligible. Catback systems are a whole different animal. Regardless, you can't mod exhaust and expect power without modding intake...etc.
As for quiet, then flip a switch and loud, yes. Cutout will accomplish this. however, the limited gain you would see (MAYBE 5hp at the wheels, if?) would not make the car any faster. Trust me, my last vehicle was a 400hp supercharged mustang cobra. The power difference on that vehicle (relatively high displacement, low compression but supercharged) would be more than a stock IS350 (relatively low displacement, high compression).
Lowering backpressure too much in your exhaust is like lowering compression too much in your motor. sure, your Is350 makes 300hp and is quick at 11:1 compression; but thicken the headgasket or do internals to make that compression 9:1 and without a power adder, the car's a dog. See what I mean?
For the purposes you imply, I say do it. But might I caution you to not take personally the responses you get to a question, because people are only going to put up with attitude so many times when YOU ask THEM for help.
"if you place the cutout AFTER the o2 sensors, you should not have a problem with the ECU."
Their intent is not to say it won't yield a benefit, rather that any benefit without a power adder will be negligible. Catback systems are a whole different animal. Regardless, you can't mod exhaust and expect power without modding intake...etc.
As for quiet, then flip a switch and loud, yes. Cutout will accomplish this. however, the limited gain you would see (MAYBE 5hp at the wheels, if?) would not make the car any faster. Trust me, my last vehicle was a 400hp supercharged mustang cobra. The power difference on that vehicle (relatively high displacement, low compression but supercharged) would be more than a stock IS350 (relatively low displacement, high compression).
Lowering backpressure too much in your exhaust is like lowering compression too much in your motor. sure, your Is350 makes 300hp and is quick at 11:1 compression; but thicken the headgasket or do internals to make that compression 9:1 and without a power adder, the car's a dog. See what I mean?
For the purposes you imply, I say do it. But might I caution you to not take personally the responses you get to a question, because people are only going to put up with attitude so many times when YOU ask THEM for help.
All engines output some certain amount of exhaust. You want your exhaust system to facilitate moving that volume of exhaust away as quickly as possible. Anything you do to help get more air in is going to increase the volume of exhaust that exits the engine, and you start to get further and further away from the optimal/original balance.
So if you supercharge a mustang or make changes on the turbo side of the MR2, you are increasing the volume of exhaust that needs to be moved by your exhaust system. What used to be freeish flowing is now insufficient, and requires bigger and/or piping to meet that need.
For my MR2, I replaced the stock system that had a 2.25" pipe, 90* bend, 180* bend, 2 cats, muffler, and dual outlets with a single pipe with ~90*ish curve, 3", 1 high flow cat. It lead to a significant gain in power.
Due to the reduction of backpressure, my turbo "spooled slower" based on RPM - it hit 17 psi further down the RPM range. However, the improved overall efficiency made the car much faster, more power, and freer revs. It would go through the RPM range much quicker.
I will probably do intake first, then cutout.
Regarding your original answer about placement related O2 sensor, I do still have a concern that if I place it too close to the O2 sensors, even though behind it, that there could be an issue of some back drafting throwing off the O2 sensor, especially during a deceleration or idle. But I am not sure at what distance that would start to become an issue.
01-14-10, 12:25 PM
#28
No, we're trying to explain fairly basic physics to you. So far without result.
it's like you saying "If you don't think switching from 13" wheels to 37" wheels will improve my handling then obviously switching to 17" wheels won't help either!"
There's a proper balance to be had.
You seem to have no understanding of exhaust whatsoever beyond the totally wrong notion that "less restriction is the only way to improve things" which I've already given you like 10 sources disproving. Scavenging and velocity are at least as important as volume.
that's why you were totally wrong when you claimed a 5" exhaust won't hurt a car that improves by switching to a 2.5" one. I notice you didn't take my bet there.
it's why you're wrong in claiming a car will always gain power slapping on cutouts versus a properly tuned exhaust system.
I am not claiming the stock exhaust is "bad". On the contrary, for every day driving, I like it. That is why I don't really want to do a full exhaust system. Instead, I would rather flip a switch and go from comfortable cruising to a little meaner and faster, and then back to comfortable and quiet again.
$400 for a used tanabe axle-back exhaust. 15 minutes to install. You've now gained 7 rwhp all the time without making the car obnoxiously loud, and without even needing to flip a switch... let alone hacking into your stock exhaust system in hopes you're putting cut-outs in the right place to maybe get the same range of gains a tiny part of the time and be painfully loud when doing it.
Last edited by Kurtz; 01-14-10 at 12:39 PM.
01-14-10, 12:26 PM
#29
You are absolutely right about how different setups yield different results. My last car was a 350whp MR2 turbo.
All engines output some certain amount of exhaust. You want your exhaust system to facilitate moving that volume of exhaust away as quickly as possible. Anything you do to help get more air in is going to increase the volume of exhaust that exits the engine, and you start to get further and further away from the optimal/original balance.
So if you supercharge a mustang or make changes on the turbo side of the MR2, you are increasing the volume of exhaust that needs to be moved by your exhaust system. What used to be freeish flowing is now insufficient, and requires bigger and/or piping to meet that need.
For my MR2, I replaced the stock system that had a 2.25" pipe, 90* bend, 180* bend, 2 cats, muffler, and dual outlets with a single pipe with ~90*ish curve, 3", 1 high flow cat. It lead to a significant gain in power.
Due to the reduction of backpressure, my turbo "spooled slower" based on RPM - it hit 17 psi further down the RPM range. However, the improved overall efficiency made the car much faster, more power, and freer revs. It would go through the RPM range much quicker.
I will probably do intake first, then cutout.
Regarding your original answer about placement related O2 sensor, I do still have a concern that if I place it too close to the O2 sensors, even though behind it, that there could be an issue of some back drafting throwing off the O2 sensor, especially during a deceleration or idle. But I am not sure at what distance that would start to become an issue.
All engines output some certain amount of exhaust. You want your exhaust system to facilitate moving that volume of exhaust away as quickly as possible. Anything you do to help get more air in is going to increase the volume of exhaust that exits the engine, and you start to get further and further away from the optimal/original balance.
So if you supercharge a mustang or make changes on the turbo side of the MR2, you are increasing the volume of exhaust that needs to be moved by your exhaust system. What used to be freeish flowing is now insufficient, and requires bigger and/or piping to meet that need.
For my MR2, I replaced the stock system that had a 2.25" pipe, 90* bend, 180* bend, 2 cats, muffler, and dual outlets with a single pipe with ~90*ish curve, 3", 1 high flow cat. It lead to a significant gain in power.
Due to the reduction of backpressure, my turbo "spooled slower" based on RPM - it hit 17 psi further down the RPM range. However, the improved overall efficiency made the car much faster, more power, and freer revs. It would go through the RPM range much quicker.
I will probably do intake first, then cutout.
Regarding your original answer about placement related O2 sensor, I do still have a concern that if I place it too close to the O2 sensors, even though behind it, that there could be an issue of some back drafting throwing off the O2 sensor, especially during a deceleration or idle. But I am not sure at what distance that would start to become an issue.
Or, you could just take the easy way out http://o2sim.com and put simulators in for the secondary o2's and not worry about it.
01-14-10, 12:39 PM
#30
i'd suggest having your exhaust installer move the cat further up or down the exhaust system, leaving you a few more inches of pipe to leave between the cutout and o2s.
Or, you could just take the easy way out http://o2sim.com and put simulators in for the secondary o2's and not worry about it.
Or, you could just take the easy way out http://o2sim.com and put simulators in for the secondary o2's and not worry about it.