After Market BOV on a 1G?

[Oblivion02]

Hey guys,

Just wondering... Does installing an aftermarket BOV on a 1G Eclipse GS Turbo [basically stock] affect its performance? I was thinking of changing the BOV, but if it is going to affect how my car runs, then I'd rather not.

 

[MountainDew]

Spend your money on a hard UICP. (Upper Intercooler Pipe)

Ditch all the rubber crap.

 

[Oblivion02]

@ Kenamond -> Great post. Yeah I know what your saying. I "like" working on cars, but I do not know much. I basically just help my Dad out, he does everything. I guess the best thing is that I WANT to learn.

Anywayz, to the point. Searching around, found some instructions on building your own MBC, Im also gonna work on the BOV leak test. If I do get the MBC working properly, I wont put it over 15psi. At 15 psi the stock BOV shouldnt leak right? And I shouldnt have any problems with the rest of the engine?

 

[MountainDew]

You should be fine on 15psi just watch for boost creep (which is unlikely to happen on a bone stock car). Buy a boost gauge before you do ANYTHING though.

 

[Oblivion02]

boost creep? Not sure what that is. But any recommendations for a not EXPENSIVE, but good gauge?

 

[kenamond]

boost creep? Not sure what that is. But any recommendations for a not EXPENSIVE, but good gauge?

Okay, boost creep 101:

The turbocharger works as follows. The engine is more-or-less a self-powered pump. The exhaust stroke literally pumps the exhaust gasses out the valves as the piston goes up. On a turbocharged car, that exhaust stroke is indirectly part of the compression stroke. The piston forces the exhaust out of the motor and through the turbine. The turbine uses this energy to apply torque to the turbo shaft which is also connected on the other end to the compressor wheel. So the exhaust stroke requires the piston to compress air on the intake side of things. This isn't free of course. If the turbine wasn't there, the piston would have an easier time pushing the exhaust out of the motor. So the exhaust stroke on a turbocharged engine actuall subtracts torque at the crankshaft moreso than a normally aspirated engine. Some of that wasn't relevant to boost creep, but it's worth knowing if you don't already.

So normally, you want to limit how much you drive that turbine so that you limit how much you drive the compressor so that you limit how much air you force into the motor. That's the wastegate's one-and-only purpose in life. It lets some of the exhaust gas bypass the turbine wheel so that you can control boost.

So you have air being forced out of the motor by the pistons during the exhaust stroke, and it's heading through the exhaust manifold and into the turbine housing toward the turbine wheel. Our turbine housings have a "hole" in the side of the turbine housing that is upwind of the turbine wheel. That's the wastegate. This is closed when you want boost pressure to go up (this sends 100% of the exhaust gas to the turbine wheel so that you develop the most torque to drive the compressor wheel) and open to some degree when you want boost pressure to stay at a constant level ("just enough" exhaust gas goes on to the turbine wheel to generate exactly the correct torque to maintain the current boost level).

Most of the turbochargers used on our cars have this wastegate built into the turbine housing (called an "internal wastegate"). Other models put the wastegate on the exhaust manifold (called an "external wastegate"). The internal wastegates have a disc-shaped "door" called a flapper, and this is connected to a lever that is connected to a shaft that runs through the housing to the outside. On the end of the shaft is another lever. That connects to a rod called the actuator arm. That connects to the wastegate actuator or WGA. That's a "can" with a diaphragm inside. The arm is connected to the diaphragm, so that when the diaphragm moves, the arm moves, turns the external lever which opens the flapper inside the housing. The diaphragm is held in place by a spring so that the flapper will not move unless something pushes on the diaphragm "hard enough". The other side of the diaphragm is "fed" a boost pressure signal. So when boost gets high enough, the diaphragm moves against that spring's wishes, pushes the actuator arm, and ends up opening the wastegate inside the turbine housing, and this limits how much exhaust is fed to the turbine wheel, this limits how much torque the compressor wheel gets to compress intake air, and this limits the boost pressure.

The problem is that sometimes the exhaust gas that you're trying to divert away from the turbine wheel by sending it through the wastegate isn't actually getting diverted. The WGA is getting a nice, high boost pressure, it's pushing on the diaphragm, that's moving the actuator arm all the way, and that's opening the flapper as far as it can be moved, but still, not enough of the exhaust gas is choosing to go through the wastegate. As a result, you send too much exhaust to the turbine wheel, and it drives the compressor wheel a bit too much so that you get more boost than you wanted. That's boost creep. Usually, the boost level will reach a maximum value. At this point, you're flowing sooooo much exhaust gas through that turbine wheel that it's getting more restrictive, and the wastegate side-door is becoming a more attractive option for the exhaust gas, so you *finally* start to limit the boost level. Unfortunately, that's usually at such a high boost level that you can't add enough fuel to keep your air-fuel ratio sufficiently rich, or your small intercooler isn't cooling things enough and the super-hot intake temperatures cause premature detonation of the air-fuel mix (knock), or the compressor isn't designed to run that fast and it grenades or wears out...or you're lucky and your car just hauls ass and miraculously survives (unlikely).

There are several solutions to boost creep, and they usually involve improving the ability of your setup to divert exhaust gas around the turbine wheel (the one exception is to modify your setup (fuel system, front-mount intercooler, etc.) to be able to handle the larger boost pressure). This includes porting the inside of your turbine housing to make it easier for the exhaust gas to take that wastegate detour, modifying the WGA so that it opens that flapper more so that it's not in the way of the exhaust trying to get out the wastegate, etc. But the bottom line is that the exhaust isn't going out the wastegate as much as you want it to for whatever reason, the turbine gets too much flow as a result, and the boost continues to rise.

So now (hopefully) you know.

Oh, and by the way, you probably don't have any worries about boost creep at the moment and may never need to know. But something in my head makes me explain things that I understand but aren't necessarily necessary. You *did* ask, though!

 

[Oblivion02]

Kenamond -> Not sure if this forum has a reputation system, but you should definitly get props for posting such helpful/useful information. Thanks for taking the time out to explain it so well, since I am very new, and like to learn. Glad I do not have to worry about this though!

Any recommendations for a good gauge, but that isnt TOO expensive?

 

[MountainDew]

Okay, boost creep 101:

The turbocharger works as follows. The engine is more-or-less a self-powered pump. The exhaust stroke literally pumps the exhaust gasses out the valves as the piston goes up. On a turbocharged car, that exhaust stroke is indirectly part of the compression stroke. The piston forces the exhaust out of the motor and through the turbine. The turbine uses this energy to apply torque to the turbo shaft which is also connected on the other end to the compressor wheel. So the exhaust stroke requires the piston to compress air on the intake side of things. This isn't free of course. If the turbine wasn't there, the piston would have an easier time pushing the exhaust out of the motor. So the exhaust stroke on a turbocharged engine actuall subtracts torque at the crankshaft moreso than a normally aspirated engine. Some of that wasn't relevant to boost creep, but it's worth knowing if you don't already.

So normally, you want to limit how much you drive that turbine so that you limit how much you drive the compressor so that you limit how much air you force into the motor. That's the wastegate's one-and-only purpose in life. It lets some of the exhaust gas bypass the turbine wheel so that you can control boost.

So you have air being forced out of the motor by the pistons during the exhaust stroke, and it's heading through the exhaust manifold and into the turbine housing toward the turbine wheel. Our turbine housings have a "hole" in the side of the turbine housing that is upwind of the turbine wheel. That's the wastegate. This is closed when you want boost pressure to go up (this sends 100% of the exhaust gas to the turbine wheel so that you develop the most torque to drive the compressor wheel) and open to some degree when you want boost pressure to stay at a constant level ("just enough" exhaust gas goes on to the turbine wheel to generate exactly the correct torque to maintain the current boost level).

Most of the turbochargers used on our cars have this wastegate built into the turbine housing (called an "internal wastegate"). Other models put the wastegate on the exhaust manifold (called an "external wastegate"). The internal wastegates have a disc-shaped "door" called a flapper, and this is connected to a lever that is connected to a shaft that runs through the housing to the outside. On the end of the shaft is another lever. That connects to a rod called the actuator arm. That connects to the wastegate actuator or WGA. That's a "can" with a diaphragm inside. The arm is connected to the diaphragm, so that when the diaphragm moves, the arm moves, turns the external lever which opens the flapper inside the housing. The diaphragm is held in place by a spring so that the flapper will not move unless something pushes on the diaphragm "hard enough". The other side of the diaphragm is "fed" a boost pressure signal. So when boost gets high enough, the diaphragm moves against that spring's wishes, pushes the actuator arm, and ends up opening the wastegate inside the turbine housing, and this limits how much exhaust is fed to the turbine wheel, this limits how much torque the compressor wheel gets to compress intake air, and this limits the boost pressure.

The problem is that sometimes the exhaust gas that you're trying to divert away from the turbine wheel by sending it through the wastegate isn't actually getting diverted. The WGA is getting a nice, high boost pressure, it's pushing on the diaphragm, that's moving the actuator arm all the way, and that's opening the flapper as far as it can be moved, but still, not enough of the exhaust gas is choosing to go through the wastegate. As a result, you send too much exhaust to the turbine wheel, and it drives the compressor wheel a bit too much so that you get more boost than you wanted. That's boost creep. Usually, the boost level will reach a maximum value. At this point, you're flowing sooooo much exhaust gas through that turbine wheel that it's getting more restrictive, and the wastegate side-door is becoming a more attractive option for the exhaust gas, so you *finally* start to limit the boost level. Unfortunately, that's usually at such a high boost level that you can't add enough fuel to keep your air-fuel ratio sufficiently rich, or your small intercooler isn't cooling things enough and the super-hot intake temperatures cause premature detonation of the air-fuel mix (knock), or the compressor isn't designed to run that fast and it grenades or wears out...or you're lucky and your car just hauls ass and miraculously survives (unlikely).

There are several solutions to boost creep, and they usually involve improving the ability of your setup to divert exhaust gas around the turbine wheel (the one exception is to modify your setup (fuel system, front-mount intercooler, etc.) to be able to handle the larger boost pressure). This includes porting the inside of your turbine housing to make it easier for the exhaust gas to take that wastegate detour, modifying the WGA so that it opens that flapper more so that it's not in the way of the exhaust trying to get out the wastegate, etc. But the bottom line is that the exhaust isn't going out the wastegate as much as you want it to for whatever reason, the turbine gets too much flow as a result, and the boost continues to rise.

So now (hopefully) you know.

Oh, and by the way, you probably don't have any worries about boost creep at the moment and may never need to know. But something in my head makes me explain things that I understand but aren't necessarily necessary. You *did* ask, though!

Dude.... Copy and paste all your posts and make some Tech articles! That way you only explain it once and just give people the link!