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Discussion Starter #1
This is an older article, but it's still relevent for those who want to plug that boost leak but still have a fully functioning CEL free evap system.

I think it's time to explain the boost leak fix, also knows as the free power mod. I'll go over various versions of the mod and argue that some are better than others.

This in not intended to be a commercial post. This will be primarily a DIY post. I first posted this mod over three years and to date there has not been a single CEL or other issue with the mod.

One of the problems with writing something technical is deciding just how much detail to go into. I am going to have to risk boring some of you with some pretty basic stuff you already know in order to insure there is enough information to people who are new to this mod.
If you are reading this thread, you probably know that the 1.4 multiair turbo engine as installed in the Abarth and various other cars has a built in boost leak. Why does this matter? It matters because it costs us a small amount of horsepower and torque while increasing boost lag and boost threshold.

No I am going to tell you right now, it's a very minor leak. Dyno testing, and careful analysis has show that on a stock engine it costs at the MOST 2 horsepower. Of course some people really want that 2hp, plus on modified engines it could be more! For many of us less lag, and a lower threshold are desirable so for some it's a worthwhile mod.

Now a little history on this. The first people to try and fix this leak were some in the Dodge Dart 1.4T and Abarth community. They immediately found out that simply plugging the leak will normally result in a check engine light as a result of the effect on the evaporative emissions system. Before we go any farther we are going to have to discuss basic evap systems in modern cars.

I'll try and list sources as we go along so anyone wanting to read more about some relatively boring topics will be easily able to do so.

The Evap system is an emission control system which prevents gasoline vapors from escaping directly into the atmosphere. Before we get into the 1.4T's system lets discuss the system on a normally aspirated car. Here is Toyota's description of such a system:

"The EVAP system is a fully closed system designed to maintain stable fuel tank pressures
without allowing fuel vapors to escape to the atmosphere. Fuel vapor is normally created in the
fuel tank as a result of evaporation. It is then transferred to the EVAP system charcoal canister
when tank vapor pressures become excessive. When operating conditions can tolerate
additional enrichment, these stored fuel vapors are purged into the intake manifold and added
to the incoming air/fuel mixture."1

Notice is says the vapors are purged into the intake manifold. That's going to matter later on in this discussion.

Now lets look at a couple diagrams of modern evap systems on normally aspirated cars. Trust, me I am getting to the Fiat's system soon enough, but it's really important to understand this part first.

MR2Evap.gif

HyundaiEvap.jpg

Notice both of these systems pictured above purge into the intake system AFTER the throttle. I could post pictures of dozens of modern evap systems on non turbo cars and they would all show essentially the same thing. It's very rare to find one on a normally aspirated car that purges into an area before the throttle.

So why do we need an evap system? The answer is simple, gasoline evaporates, and evaporates very easily. Anyone who has ever spilled a little bit of gasoline in their shop knows that it evaporates fast and soon the whole shop smells like gas. We also need to regulate pressure in the tank, although that aspect is outside the scope of this discussion.

In your car's fuel tank the gas tends to evaporate, the hotter it is, or the lower the atmospheric pressure the faster it evaporates. There are actually engineering standards for measuring just how fast it evaporates and not surprisingly the epa has allowable specifications for this. Gasoline evaporating into the air can be a large source of pollution so it makes sense that it's regulated. Plus it just smells bad and gives people headaches.

Now take a look at the diagrams I posted. No they are not Abarths, but the basics are the same. From the fuel tank there is a line going to the charcoal canister. There are other lines from the fuel tank going to sensors, vents, all sorts of things, but on modern cars there is ALWAYS a line going to the charcoal canister.

The charcoal canister, really does contain charcoal and this is where the vapors are stored until the engine is ready to draw them in. So far this is all just how the system works in your Abarth or 500T.

Fuel that has evaporated into the charcoal canister has to be purged back into the engine. The flow of vapors back into the engine is regulated by a valve, often called a purge control solenoid valve (PCSV). When the ecu decides it's time for vapors to return to the engine it opens this valve. However something has to push or pull the vapors there. There is no pump (normally) to do that. We will have to rely on differential air pressure. Remember, pressure flows from high to low so we need the vapor to go somewhere with relatively low pressure.

Under certain conditions, there may be enough pressure in the lines to sort of self purge as soon as the valve opens, of course in that case the pressure would drop quickly so this isn't something we can rely on. (it's true that the fuel tank is often under slight positive pressure) What the manufactures do is purge into an area of reliably low pressure. In the case of a normally aspirated car, that's easy, they simply connect a line to the intake manifold after the throttle so after startup and during all normal driving engine vacuum can be used to create that pressure differential in the evap system and draw out the vapors. Now at full throttle pressure in the manifold will rise reducing or even eliminating the differential pressure, but that's not really a problem because it's such a small percentage of the vehicle's operation.

The engine vacuum not only helps pull the vapors through, they help keep the fuel in a vaporized form. At lower pressures, fuel evaporates at a lower temperature, or evaporates faster at a given temperature. The exact pressure it starts to evaporate at has a lot to do with the exact blend of gasoline you are using. At 100F the pressure varies from 13.8psi to 7.4psi with lower numbers at lower temperatures. Now the problem here is that this barely works so if the canister becomes saturated it may be impossible for the emissions system to pull all the fuel out. (2)

So far it's pretty simple right? Fuel evaporates from the tank, gets stored in the charcoal canister, and when the ecu decides it's ok, it opens a valve allowing the vapors to get sucked into the engine. Simple right? Other than all the sensors that are in the system for OBD2 diagnostic purposes, it actually is quite simple.

Of course, there has to be a problem, and it's the turbocharger If we simply purge into the intake manifold, then as soon as the car goes into boost, pressure will start pushing the other way, trying to pressurize the evap system. Not only would that prevent flow, it would cause all sorts of other problems so we can't do that. I will explain how Fiat does this in the next post.

Cont:
 

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Discussion Starter #2 (Edited)
On a typical naturally aspirated engine, intake manifold vacuum is used to draw in the evap vapors. Before we go any farther, let's see exactly what Fiat says about that. Now this is the FACTORY talking, Not me.

"Subsequently, when engine operating conditions are conducive, a purge valve located between the intake manifold of the engine and the canister opens and vacuum from the intake manifold draws the vapor to the engine's combustion chamber. Thereafter, the purge canister is regenerated with newly formed fuel vapor, and the cycle continues."

I think that's very clear. "intake manifold vacuum draws the vapor". It's not simply connected anywhere upstream of the intake valves, it's connected where there is vacuum.

Ok, Ok, so what about on a Turbo Fiat. Do we still need vacuum? If so, how does Fiat generate it? Let's see what the FACTORY says about that:

"As opposed to vacuum in naturally aspirated applications, at higher throttle levels a turbocharged/supercharged engine's intake manifold can see relatively high boost pressures generated by forced induction. Under this condition, a one-way check valve can be used to prevent backflow through the EVAP system and furthermore a vacuum ejector tee can be used to provide vacuum for purge flow."

If that's not clear enough, they go on to say "This creates a pressure differential in vacuum ejector tee 42 and causes a vacuum to be drawn across port 46 due to a Venturi effect. Due to this vacuum, vapor flows from canister"

That last sentence, DUE TO THIS VACUUM, VAPOR FLOWS FROM CANISTER is very telling.

So, what is an "ejector tee" and how does it generate vacuum? An ejector tee is often called an ejector pump, jet pump, vacuum ejector, and a lot of other names. It's simply a venturi tube. When air accelerates through it, the Bernoulli effect causes a pressure drop. This pressure drop can be used to pull in vapors.

Here is a generic video showing an ejector pump in action, fast forward to about 30 seconds where the action starts:


The following diagram is a factory Dodge Dart 1.4T diagram. It uses the same system as our Abarths and 500 Turbos. I added the colored arrows to show the direction of flow. This should be pretty clear. Air flows from the high pressure pipe located between the throttle body and the intercooler through the "bypass hose to ejector tee". From there it goes to the turbo's intake.

PressureDrop2.JPG

There has been some confusion on the direction of flow here, but there really shouldn't be. Air pressure flows from high to low. As the throttle is after the bypass hose's connection point, that section is never under vacuum and pressure there is essentially never lower than in the intake system on the other side of the motor. (there is a transient condition when it's possible for pressure to be higher on the intake side, but it's very slight, and could be measured in hundredths of a second and isn't really a factor for this discussion.)

So far so good. The factory system uses an ejector tee which has no moving parts to wear out or fail. It really shouldn't have any problems. Ironically the factory installed some ejector tees backwards in some early cars causing check engine lights and P1CEA codes. There have also been a few cases of leaks which can also cause this code. That said, with the exception of some early cars, all of which should have been straightened out by now, the evap system is essentially trouble free.

So then, what's the problem? The problem is that boost leak needed to make the ejector tee work costs us a small amount of power. Some of us want that power back! The boost leak is also blamed for some anomalies, which I will touch on later. Right now we are talking about power.

Common Fixes:

In the early days, meaning about 12-18 months ago, quite a few people tried simply plugging the leak. This will work in terms of power, however it will also seriously comprises the evap system's operation. What happened next was interesting. Some people reported, "works great, no problems". Then others would try it and get a check engine light and a P1CEA code almost immediately. Some people could go for several tanks of fuel, but nearly all would eventually get a CEL. I don't think anyone who said it works was lying, they were just crying success a little too early. Now, under certain conditions, it is possible to plug the leak and not get a code. At the end of this article I will explain some of the variables involved. These variables make it possible to have one car throw a code after 50 miles and another identical car throw it in 500 miles.

There have been quite a few other mods, and some people have put an incredible effort into finding a boost leak fix that won't cause a cel. In my opinion most of these are fatally flawed because they do not purge into a low pressure area, which will inhibit proper purging and lead to canister saturation.

When every auto manufacture on the planet purges into a vacuum/low pressure area, including Fiat, you need to ask why? It's certainly not because I told them too. It's because their engineers studied the issue and they all came to the same conclusion. Purge into vacuum. I will talk about how to do that in the next installment.
 

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Discussion Starter #3 (Edited)
Before I get to the next phase of this article, here are a couple of fun things, only sort of relevant. This video shows how fast water can change state from liquid to gas at room temperature by applying vacuum and dropping the pressure. Of course water requires a massive pressure drop, but gasoline doesn't.


Here is an Alfa Romeo Giulietta Sportiva with a 1.4 Multiair Turbo. Why? Because it's Europe's Dart, and I really like the car :)

AlfaTurbo.jpg


So, we know we cant just block the boost leak all the time because that would prevent the ejector tee from functioning. We also want to purge into a low pressure area, and the only area with low enough pressure during boost is in the ejector tee, which is why the system is designed the way it is in the first place.

The solution is to use a controllable valve that will allow purging at the right times, but also close and shut off the leak when it matters most. Early on in our work on this project, we at HPSI settled on an electric valve to do the job. The valve can be triggered a number of ways. It's possible to control the valve with a computer which we could do very easily. It's also possible to go super low tech here and control it with a simple on/off switch. This would be OK for a car which does autocross or track events. Simply throw the switch on and close the valve during track time. I think for most the best solution is to use a switching mechanism that closes the valve based on boost or throttle position, which is what we do.

Before we get too deep into the switching mechanism, let's look at the location of the valve.The valve MUST be located in the bypass hose BEFORE the ejector tee, meaning upstream. Under no conditions should it ever be installed on the other side of the tee. Other than that it doesn't really matter exactly where it goes.
 

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Discussion Starter #4 (Edited)
Attaching the valve is actually pretty easy. I suggest getting some length of hose that will tightly slip fit over the bypass hose. For this 8mm id silicone hose will work perfectly. If lubed up it will slip fit over the hose but be very tight and not leak. Now simply cut the bypass hose with a razor blade. That one cut is all you need. No need to hack up the system or remove anything. Now using your silicone hose (or whatever you bought) route the hose from the boost pipe to the IN port on the valve and the other from the OUT port to the hose going to the ejector tee. I generally use a few feet of hose so I can mount the valve up at the front of the engine just forward of the battery. The extra length makes absolutely no functional difference.

The actual valve you use is up to you. There are cheap plastic valves which will probably do the job. I think it's better to spend more and go with a brass or stainless steel valve, but it's really up to you. Once you get the valve, head to Ace, or your favorite hardware store and pick up some threaded fittings with 3/8" barbed ends you can use to connect to the silicone hose. You could buy those on ebay, but I prefer to get the fittings locally.

When searching for a valve, I suggest using this phrase in evil bay's search engine "1/2" 12V normally open solenoid valve" . The phrase normally open is important, we want a valve that's open all the time and closes when it gets power. Here are a couple of choices for valve, first the cheapo:

Plasticsolenoid.JPG


Now, I haven't used the plastic valve, but at $16 I can see it might be tempting, and it's specs look OK. However, I personally go with a higher end metal valve because I know they will tend to outlast just about everything else on the car. The best metal ones in the correct specs, (1/2" normally open 12V) will run from $50-$75, If you scour the auction sites you can sometimes get them for as little as $35.

stainlessvalve.JPG


The stainless steel valve shown above is currently on ebay for $73.99, so it's pretty expensive.
 

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Discussion Starter #5 (Edited)
Now that we have the valve, we need to think about controlling it. When do we want it to close? Well, the main reason we are doing this is to get more power, so it makes sense that we would want to close it at or near full throttle. After all, if we were just cruising along at light throttle and wanted more power we would simply push the accelerator down more. However connecting an electrical switch to the throttle or gas pedal assembly would be a pain, and it would be tricky to come up with an adjustment mechanism. A much easier way is to connect it to a pressure switch. That will enable is to close the valve at the boost level of our choice.

As an alternative to a pressure switch, I mentioned we could control it with a computer. In the case of our Unichip tune we could easily do that. However one vendor has a tuner box on the market right now that can control it, and that's Road Race Motorsports. They sell an excellent tuner box which can trigger just about whatever you want including one of these valves. It triggers at 17psi.

I prefer to use a pressure switch and trigger it at 12psi for a street driven car. Why 12psi? Before we show OBD2 data, let's just think about this logically. We obviously don't need to trigger it when not on boost. If we are not on boost and need more power, we can simply push the pedal down farther. Ahh, but what about purging? Some say the system does most or all of it's purging at medium and high boost levels. Hmm, really? That's simply not true. Think of this, in NON sport mode, or in a 500Turbo, the engine rarely sees above 12psi. Yet they they purge just fine. You don't get a cel if you drive your Abarth like a grandma and never go about 5 pounds of boost. When you do go above 12 pounds of boost it's usually when you are at full throttle and you certainly can't do it for long because you will run out of rpm and have to shift, causing boost to drop again for a moment. If you keep going, you run out of road or quickly achieve unsafe speeds. There is just no way on a street car to stay above 12psi for very long.

Pressure switches are adjustable. I suggest 12psi and promise that at that level you will not have a problem. Nobody every has. However if you are really worried about it you could select a higher level. Boost switches are available in all sorts of ranges. I personally like the "2-10psi" switches because the upper end is actually about 12, so it's super easy to set up, just dial it to the end and it's set. However a "6-30" psi switch is available.

Here is the pressure switch I like to use:

BrassSwitch.jpg

These brass switches are very rugged and reliable. I have been using them for over 10 years without a single failure. I also like the thumb wheel adjustment making setting it easy. That said, they are pricey, typically about $30. For me that's money well spent. However as with everything there is a lower cost option. Plastic switches can be found which do the same thing. They usually require a tiny allen wrench to adjust and have no printed scale on them, so adjusting them is a pain. However they can often be found for around $15.

Plasticswitch.JPG
 

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Discussion Starter #6 (Edited)
To find pressure switches simply search evil bay for "boost pressure switch" or "adjustable pressure switch" and just scroll until you find one that matches the pictures I showed.

Once the valve and switch are mounted, all that's left is to wire this thing up. It's going to be really easy. There are a lot of ways to do it, I will cover three of them.

1. If you have the Road Race Motorsports Ultimate ECU, it's going to be very easy to hook this up. If using the RRM ECU for switching you DO NOT need a boost pressure switch which helps drive down the cost of this.

Understand this, the RRM ECU simply connects the two wires it has to each other at 17psi. It should only be used for grounding, so we will need to switch the valve on and off by switching the ground. This is not a problem, it's the way many things in cars are switched on and off.

At the time of this writing the two wires are black and orange. However that could change so read the documentation that came with it the RRM ECU. The documentation will tell you to connect one of those wires to ground. Connect the other to the grounding terminal on the valve. The other terminal on the valve (the positive terminal) needs to be connected to switched power, meaning power that's only on when the ignition switch is on. These valves typically draw less that 1.6 amps, so just about any circuit you want to use is fine. I suggest finding a wire in the bundle forward of the battery. There are some good ones in there, and you don't even need to cut one, Use a "Posi-Tap" to connect it to the positive side of the valve. I like Posi-Taps, they don't damage a single strand of the original wire.

posi-tap_n2_a2-b.jpg

That's it. So with the RRM ECU you simply use a Posi-Tap to connect the positive side of the valve to a wire that has power only when the ignition is on. Then connect the negative side to the RRM module, and the Modules last remaining wire will connect to a ground. Done, your valve will now trigger everytime you hit 17psi.

2. If your car has water injection it's going to be easy to hook this up, provided you don't mind slaving the valve closing with the water injection system turning on. To do this, connect the valve's ground wire to a good ground on the chassis. Next, using a Posi-Tap, connect the valves positive wire to the wire that sends power to the water injection pump. Simple, now whenever the water injection turns on, the valve will close. This is actually the way I do it. In this case we are switching it on with power, not with a ground like in example 1, but either will work.

3. If you don't have an RRM Ultimate ECU, or a water injection system, it's still going to be pretty easy. Now you can choose to control it by switching either power or ground. For this example I will be switching it via ground. So, using a Posi-Tap connect the positive terminal on the valve to a wire that has power only when the ignition is on. Again, there are some good wires for this forward of the battery box.

Now, the pressure switch will need to be connected. It will typically have three terminals on it labeled, "COM", "NO", and "NC". The last two look almost the same so make sure you know what your are looking at. That "C" and "O" can look a lot a like. Anyway...you will only be using the COM and NO terminals. Connect one to a good chassis ground, and the other the the valve's ground wire. It doesn't matter which of the two terminals connects to the valve and which connects to a chassis ground. What does matter is that you DO NOT use NC.

Switch.JPG
 

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Discussion Starter #7
A few more notes on electrical stuff.

It's possible but not required to switch this thing on with a relay and or add in extra fuse protection. In fact, option #2 as described above does that, because most water injection pumps are relay controlled and their main power wire is normally fused prior to the relay. Road Race also includes instructions for connecting things to their box via a relay, and it's certainly not a bad idea. In the examples I gave I did not use a relay, or extra fuse protection, but you certainly can. My logic is this. The whole point of a relay is to use a very small amount of current to control a large current. The valve just doesn't draw much current anyway,most draw less than 1.6 amps. The power wire you tap into will most likely already have fuse protection on it, in fact you would be hard pressed to find one in that location big enough to tap into that didn't, so it's not a problem.

The next thing I want to mention is the switching positive vs switching negative (power vs ground switching). I want to start off by saying there are actual electrical gurus here on this forum that know a lot more on this subject than I do (I am looking at you Trevor). I have seen electrical gurus with knowledge far greater than mine have rather heated debates on this subject. I am sure you can find arguments about it on electrical forums. The proponents of switching via ground claim that it extends the life of the switch and of the components. I have NO idea if that's true or not. What I do know is that electrical systems in cars do it both ways, and the only logic I can see is they seem to do whatever is going to use the least wiring. For example, I have not yet seen headlights that were switched on by ground switching. That would require running a ground wire from the headlights to a switch near the driver and then to a chassis ground. It's a lot easier to ground the headlights right were they are. Fuel injectors, which cycle a gazillion times are almost always switched via ground. Bottom line is I don't know which is best, but I do know this valve will work fine either way.

Now, when do we want to switch on the valve and cause it to close? I strongly suggest setting it for 12psi for the reasons I outlined earlier. In the case of the "2-10" switch just roll the thumb wheel all the way to maximum. We do have some customers who have been setting it lower, but at some point it will probably trigger a cel.

If you are intent on setting it lower, at least understand the variables involved. When the boost retainer valve is closed purging is NOT blocked, the vapors can still work their way out of the canister, but they won't be helped by the ejector tee. They will only purge if there is some differential pressure between the evap system and the intake pipe. Sometimes you may have enough differential pressure, sometimes you won't.

Under some conditions pressure in the evap system can be relatively high, much the way pressure in the fuel tank can rise. Conversely pressure in the intake tube can be a little low. Normally it's at ambient thus normally there is no vacuum or low pressure in the intake tube. However under some conditions it can drop a little, not much and not during normal driving, but at high boost and high rpm the intake system doesn't feed the turbo quite fast enough and pressure in that pipe drops. I have measured it, and with a stock intake it drops under these conditions over 1psi. Thus, if you are driving like a banshee, and have consistently high pressure in your evap system, you might be able to get away with relatively low settings as there will be a minor pressure differential helping us out.
Another variable is the type of fuel you are using. Some fuel evaporates at much higher pressures and lower temperatures than others. Depending on where you live an your gasoline formula, you may be able to sneak by with less threat of canister saturation than others.

These variables help explain why some people who eliminate the ejector tee with the various "re-routes" don't get check engine lights and some do.

Is there any advantage to setting it lower? Not really. When you hit the gas, boost shoots from 2-12 psi so fast that it would be impossible to measure or notice any performance difference. What about off boost drive-ability? Nope, again this portion of the evap system does essentially nothing off boost anyway because the ejector tee isn't functioning during these conditions. It needs boost to do anything. OK, what about drive-ability between 0 and 12psi? I have experimented with this quite a bit, and I don't notice any measurable or even repeatably difference in drive-ability. I have tried it with the re-route, plugging the leak and various settings on the boost retainer valve. Drive-ability is such a non-quantifiable, nebulous term that it's very difficult to really debate in terms of improvements.
 

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Very happy with my HPSI BRV system. The turbo spools noticeably quicker above the set point of the switch.

This is a really good explanation and summary of how the evap system works and how we can improve on it. The information is out there in various places here on the forum, but it is all hard to find and piece together. This is a good consolidation that I can point people towards.








 

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[email protected] Can we disconnect the evap system all together and write a tune to eliminate the check engine light?
 

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Discussion Starter #17
Thank you for a fantastic write-up and explanation.

I noticed the boost leak repair from HPSI is no longer available for purchase on the website or on the EC site - are you no longer offering this item? @[email protected]
We don't really offer that kit anymore. This is strictly an economic/business issue. We can't get the parts at a reduced cost by purchasing them in bulk, so it's less expensive for the end user to simply follow our guide and source the parts independently. It doesn't take a lot of parts, so it's pretty easy. That said, we do have lots of valves in stock, as well as hose. If you want one, shoot Jordan an email, then get the switch and wire on your own.

Greg
 

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Discussion Starter #18 (Edited)
[email protected] Can we disconnect the evap system all together and write a tune to eliminate the check engine light?
Mr. Miller, that's a decent question, but the answer is that I simply don't want to. I am not over here drinking the green Kool-Aid that's so common in society today. I'll be the first to say that a lot of emission components in the past were pure B.S. Anyone remember the "smog pumps" in the 70's, or the "NOX Device" that California required everyone to install on their older cars at one time? Those items were pure B.S. they hurt fuel consumption, performance, and emissions.

On the other hand, the Evap system is a good system. It actually does reduce emissions, it reduces them a lot, and has NO adverse effect on performance (once the boost leak is plugged). For that reason, I just can't see getting rid of it. Even if you leave the boost leak in place, the loss of performance is minor and the improvement in emissions is significant. Without an evap system under some conditions you will actually be able to smell the fuel evaporating out of your car.

Greg
 

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Mr. Miller, that's a decent question, but the answer is that I simply don't want to. I am not over here drinking the green Kool-Aid that's so common in society today. I'll be the first to say that a lot of emission components in the past were pure B.S. Anyone remember the "smog pumps" in the 70's, or the "NOX Device" that California required everyone to install on their older cars at one time? Those items were pure B.S. they hurt fuel consumption, performance, and emissions.

On the other hand, the Evap system is a good system. It actually does reduce emissions, it reduces them a lot, and has NO adverse effect on performance (once the boost leak is plugged). For that reason, I just can't see getting rid of it. Even if you leave the boost leak in place, the loss of performance is minor and the improvement in emissions is significant. Without an evap system under some conditions you will actually be able to smell the fuel evaporating out of your car.

Greg
The main reason is that I have a leak in the system and if you just turn it off there would be no more worries from future problems or components going bad. I already removed the cat so emissions are not a concern to me. By they way any idea on when phase 2 will come out? Thanks
 
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