Could this be the best exhaust setup?
Oct 8, 2004, 12:33 AM
#1
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Could this be the best exhaust setup?
Well, after trying to find an exhaust that is quiet, and has the best flow, I think I have found it.
I was going to keep my B&B downpipe, but put back a stock cat, and stock catback.
Next, I was going to buy a 3" stainless steel cutout, with a good smooth flow, and put the ATP Boost regulated cutout on it. Since it's built from wastegate material, it should be reliable... no mechanical pieces, and you can attach a boost controller to it to make it open when you want. The ATP cutout kit comes with a pipe, and another pipe welded on to it at a 90 deg angle. I do not think this is optimum. So instead of buying this kit:
http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
I would buy the unit:
http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
And the actuator:
http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
And set it to open at around 15 psi.
Instead of the 90 deg, it would be a smooth 45 or so like this:
http://www.installuniversity.com/ins...st_cutouts.jpg
Now, I'm not sure if this has the best flow, but by theory it should, unless if some of the exhaust gas goes into the stock catback, then yeah... but I figure with so much back pressure, most of the exhaust will flow out of the cutout.... path of least resistance, right?
So cruising around, quiet as stock... at WOT, basically an unrestricted open exhaust. And since it's adjustable, you can have it open at whatever boost level you want...
I could run the QTP electronic cutout, but with this setup, no electronics, no wires, only a vac line. Should be lots more reliable, and lighter.
What do you guys think?
I was going to keep my B&B downpipe, but put back a stock cat, and stock catback.
Next, I was going to buy a 3" stainless steel cutout, with a good smooth flow, and put the ATP Boost regulated cutout on it. Since it's built from wastegate material, it should be reliable... no mechanical pieces, and you can attach a boost controller to it to make it open when you want. The ATP cutout kit comes with a pipe, and another pipe welded on to it at a 90 deg angle. I do not think this is optimum. So instead of buying this kit:
http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
I would buy the unit:
http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
And the actuator:
http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
And set it to open at around 15 psi.
Instead of the 90 deg, it would be a smooth 45 or so like this:
http://www.installuniversity.com/ins...st_cutouts.jpg
Now, I'm not sure if this has the best flow, but by theory it should, unless if some of the exhaust gas goes into the stock catback, then yeah... but I figure with so much back pressure, most of the exhaust will flow out of the cutout.... path of least resistance, right?
So cruising around, quiet as stock... at WOT, basically an unrestricted open exhaust. And since it's adjustable, you can have it open at whatever boost level you want...
I could run the QTP electronic cutout, but with this setup, no electronics, no wires, only a vac line. Should be lots more reliable, and lighter.
What do you guys think?
Last edited by bo0oost; Oct 8, 2004 at 12:35 AM.
Oct 8, 2004, 07:32 AM
#2
Depends on who is correct about low end power and open exhaust 
Some people claim that a more restrictive exhaust gives you better spool up and more low end power. If that is correct then this would be the best setup you could possibly use.
Other people claim that the less restrictive your exhaust system the better and that an open downpipe gives you the best spool up and the most low end power. If they are correct then a setup that only opens up under boost would be crappy for low end power, but give great gains in the upper RPM range.
Later,
Keith
Some people claim that a more restrictive exhaust gives you better spool up and more low end power. If that is correct then this would be the best setup you could possibly use.
Other people claim that the less restrictive your exhaust system the better and that an open downpipe gives you the best spool up and the most low end power. If they are correct then a setup that only opens up under boost would be crappy for low end power, but give great gains in the upper RPM range.
Later,
Keith
Oct 8, 2004, 09:11 AM
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Well, either way, you can set the cutout to open at whatever boost... only thing is that it will be loud, but I've seen some people use cutouts as a side exit exhaust....
Oct 8, 2004, 12:24 PM
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Its pretty simple really. The amount of time that it takes the turbo to spool is directly related to the velocity of the exhaust air. So you don't want too much or too little back pressure. In general a larger exhaust (I wouldn't go much bigger than 3-4inches on a stock turbo or you will "go over the hump") will give increased velocity and thus your turbo will spool faster. Now, the other issue is low end power, especially prior to turbo spool. A little bit of back pressure is actually a good thing for your tourque numbers. So what is most common is that when you increase exhaust flow you increase peak hp and slightly decrease tourque. This is good and bad. Tourque is really what you want for acceleration, but once you get to a point where you have a large enough tourque to weight ratio that breaking the tires loose isn't a problem, then you can increase HP for higher top end accelleration and top speeds. Basiclly tourque gets you into 4th gear and HP is what does the rest of the quarter mile.
Oct 12, 2004, 09:49 PM
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Originally Posted by marksae
Have you considered the WORKS stealth muffler? I've heard it in person on the WORKS shop car and it's pretty quiet. They have a 3" downpipe, high flow cat, and 3" intermediate pipe along with it.
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Oct 12, 2004, 10:07 PM
#8
Originally Posted by Fourdoor
Some people claim that a more restrictive exhaust gives you better spool up and more low end power.
A smaller exhaust primary diameter at the exhaust manifold will increase the exhaust gas velocity (not backpressure) at lower engine speeds and should cause the turbo to spool quicker. The tradeoff is that at higher engine speeds and loads, the smaller pipe volume will be subject to a pressure increase due to its volumetric limitations and reduce the mechanical efficiency (power) of the engine.
Unlike a normally aspirated engine, once the gas has exited the hot side of the turbo, I believe the pressure wave is diminshed enough such that pulse tuning in the conventional sense is much less of an issue. The lower the residual pressure the hot side has working against it, the faster the gas should exit, and the better the turbo should perform.
In short, the cut out should improve power potential somewhat, but be advised that it almost certainly WILL necessitate recalibrating the fuel curve.
Oct 12, 2004, 10:58 PM
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Originally Posted by Ted B
In short, the cut out should improve power potential somewhat, but be advised that it almost certainly WILL necessitate recalibrating the fuel curve.
Oct 13, 2004, 05:22 AM
#10
Anything that significantly impacts the exhaust system characteristics will affect the A/F ratio. Figure that even if you already have a good aftermarket exhaust and have tuned the car, so much as swapping in a cat-delete pipe will typically require retuning for best performance. In this case, you are bypassing the entire exhaust system behind the valve.
Oct 14, 2004, 05:19 AM
#12
Essentially, yes.
In a sequentially injected engine with long overlap cams and an efficienct exhaust system, it should be expected that anything that changes exhaust gas velocity will have some impact on the A/F. The computer cannot compensate simply because the computer has no real means of mixture correction at WOT (wide open throttle). This is why it has to be told what adjustments to make by way of recalibrating the WOT A/F curve if best performance is going to be realized.
If the exhaust system is restrictive and some restriction is removed, the exhaust gas velocity may be increased, which may cause a leaning of the A/F. This is usually especially prevalent at low-midrange engine speeds - in the meat of the torque curve.
On the other hand, if the exhaust system already flows fairly well and we add a larger pipe section expecting to make a further improvement, we can actually decrease exhaust gas velocity. This being the case, bigger is not always better.
In any case, these basic concepts apply thoroughly to the exhausts of N/A engines. Where turbo engines are concerned, they apply more significantly to the exhaust path between the exhaust valve and the turbo. Nevertheless, if there is something to be gained by adding a low restriction exhaust on an otherwise stock EVO, it is because the exhaust relieves a buildup of pressure at the turbo exit. This apparently being the case, the exhaust cutout will greatly relieve pressure at the turbo exit, which should cause exhaust gases on the other side to move more quickly, and should be expected to have some impact on the A/F.
In a sequentially injected engine with long overlap cams and an efficienct exhaust system, it should be expected that anything that changes exhaust gas velocity will have some impact on the A/F. The computer cannot compensate simply because the computer has no real means of mixture correction at WOT (wide open throttle). This is why it has to be told what adjustments to make by way of recalibrating the WOT A/F curve if best performance is going to be realized.
If the exhaust system is restrictive and some restriction is removed, the exhaust gas velocity may be increased, which may cause a leaning of the A/F. This is usually especially prevalent at low-midrange engine speeds - in the meat of the torque curve.
On the other hand, if the exhaust system already flows fairly well and we add a larger pipe section expecting to make a further improvement, we can actually decrease exhaust gas velocity. This being the case, bigger is not always better.
In any case, these basic concepts apply thoroughly to the exhausts of N/A engines. Where turbo engines are concerned, they apply more significantly to the exhaust path between the exhaust valve and the turbo. Nevertheless, if there is something to be gained by adding a low restriction exhaust on an otherwise stock EVO, it is because the exhaust relieves a buildup of pressure at the turbo exit. This apparently being the case, the exhaust cutout will greatly relieve pressure at the turbo exit, which should cause exhaust gases on the other side to move more quickly, and should be expected to have some impact on the A/F.
Oct 14, 2004, 08:01 AM
#13
Originally Posted by Ted B
Essentially, yes.
In a sequentially injected engine with long overlap cams and an efficienct exhaust system, it should be expected that anything that changes exhaust gas velocity will have some impact on the A/F. The computer cannot compensate simply because the computer has no real means of mixture correction at WOT (wide open throttle). This is why it has to be told what adjustments to make by way of recalibrating the WOT A/F curve if best performance is going to be realized.
If the exhaust system is restrictive and some restriction is removed, the exhaust gas velocity may be increased, which may cause a leaning of the A/F. This is usually especially prevalent at low-midrange engine speeds - in the meat of the torque curve.
On the other hand, if the exhaust system already flows fairly well and we add a larger pipe section expecting to make a further improvement, we can actually decrease exhaust gas velocity. This being the case, bigger is not always better.
In any case, these basic concepts apply thoroughly to the exhausts of N/A engines. Where turbo engines are concerned, they apply more significantly to the exhaust path between the exhaust valve and the turbo. Nevertheless, if there is something to be gained by adding a low restriction exhaust on an otherwise stock EVO, it is because the exhaust relieves a buildup of pressure at the turbo exit. This apparently being the case, the exhaust cutout will greatly relieve pressure at the turbo exit, which should cause exhaust gases on the other side to move more quickly, and should be expected to have some impact on the A/F.
In a sequentially injected engine with long overlap cams and an efficienct exhaust system, it should be expected that anything that changes exhaust gas velocity will have some impact on the A/F. The computer cannot compensate simply because the computer has no real means of mixture correction at WOT (wide open throttle). This is why it has to be told what adjustments to make by way of recalibrating the WOT A/F curve if best performance is going to be realized.
If the exhaust system is restrictive and some restriction is removed, the exhaust gas velocity may be increased, which may cause a leaning of the A/F. This is usually especially prevalent at low-midrange engine speeds - in the meat of the torque curve.
On the other hand, if the exhaust system already flows fairly well and we add a larger pipe section expecting to make a further improvement, we can actually decrease exhaust gas velocity. This being the case, bigger is not always better.
In any case, these basic concepts apply thoroughly to the exhausts of N/A engines. Where turbo engines are concerned, they apply more significantly to the exhaust path between the exhaust valve and the turbo. Nevertheless, if there is something to be gained by adding a low restriction exhaust on an otherwise stock EVO, it is because the exhaust relieves a buildup of pressure at the turbo exit. This apparently being the case, the exhaust cutout will greatly relieve pressure at the turbo exit, which should cause exhaust gases on the other side to move more quickly, and should be expected to have some impact on the A/F.
By removing restrictions, more air is able to flow through the engine at higher speeds, which results in more power and may max out the stock fuel system, but that's a different topic.
Oct 14, 2004, 08:11 AM
#14
It would be great if it were that simple, but it isn't...
The ECU uses closed-loop operation to constantly monitor A/F at PT (part throttle). It makes a fuel calculation using the MAS and checks itself with the O2. When you go to WOT (wide open throttle) and the ECU goes into open loop mode, it uses only the MAS for its fuel calculation (no more O2), and extrapolates estimated fuel metering in accordance to the open loop fuel table using what it learned in closed loop.
Each injector flows one metered shot per intake stroke. If the exhaust suddenly flows easier, there will be increased cylinder scavenging, and more of the metered fuel charge will be drawn through the intake valve. The longer overlap in the cams, the more pronounced this effect will be.
The ECU has no means of monitoring this, and the actual A/F will become leaner.
The ECU uses closed-loop operation to constantly monitor A/F at PT (part throttle). It makes a fuel calculation using the MAS and checks itself with the O2. When you go to WOT (wide open throttle) and the ECU goes into open loop mode, it uses only the MAS for its fuel calculation (no more O2), and extrapolates estimated fuel metering in accordance to the open loop fuel table using what it learned in closed loop.
Each injector flows one metered shot per intake stroke. If the exhaust suddenly flows easier, there will be increased cylinder scavenging, and more of the metered fuel charge will be drawn through the intake valve. The longer overlap in the cams, the more pronounced this effect will be.
The ECU has no means of monitoring this, and the actual A/F will become leaner.
Oct 14, 2004, 11:21 PM
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thanks for the tech, Ted. I appreciate a response other than "'Cause the guy said so"
I've learned a lot from the eggheads on this forum. I don't want any of my tunes to fight each other.
I've learned a lot from the eggheads on this forum. I don't want any of my tunes to fight each other.