Dondo's Second Supercharger Build
08-12-2012, 03:41 PM
#77
Really?
Why does a twin screw supercharger pull through system need a blow off valve that is vented to the atmosphere, when it has a by pass valve? As far as I know pull through superchargers dont have a problem with excess boost when the butterfly closes.
Now you know I am stuck in the backwoods of Ga --so i never hear nuthing! Is this something new?
Tell me more....
Why does a twin screw supercharger pull through system need a blow off valve that is vented to the atmosphere, when it has a by pass valve? As far as I know pull through superchargers dont have a problem with excess boost when the butterfly closes.
Now you know I am stuck in the backwoods of Ga --so i never hear nuthing! Is this something new?
Tell me more....
08-13-2012, 04:09 PM
#81
blower out -> bypass -> blower in
........................|
....................blowoff
ignore the periods, they're for spacing
so the bypass unit is plumbed the same expect it has a blowoff feature built in.
08-13-2012, 08:22 PM
#82
I am getting freaking dizzy trying to wrap my head around this!
here is how I understand it: someone else wrote this but it explains it like what I know:
"Both Turbo and Centrifugal SC use Centrifugal Forces to build boost pressure. They are what are called non-Fixed Displacement compressors. This means, they do not pump a fixed volume of air per revolution. Rather they "fling" the air down the pipe faster than the engine can breath in, resulting in boost. These are the only types of compressors that will allow pressure build up to be pushed back through it's compressor blades. I can't for the life of me recall the term to describe this though.
Both Roots and TwinScrew Supechargers are Fixed Displacement compressors. This means that for every revolution, they pump a fixed volume of air. These "force" or "push" volumes of air down the pipe faster than the engine can breath, resulting in boost. These types can NOT allow pressure buildup to be pushed back through their compressors. Not without risk of serious damage
BOV
I think that most of us know what a BOV is and how it works. So, I'm not going to stress this one. The Primary purpose is to release the build up of pressure behind the Throttle Body as a result of a still compressing turbo or Centrifugal Supercharger. Most have a vacuum line used to assist in opening the valve on throttle lift, and also during high-vac cruise situations.
Most Typical BOVs (like that of the WRX or STi) use a diaphragm or a piston for the actual valve. The benefit of this is that even without the vacuum line pulling open the valve, too much pressure build up will still result in the valve opening. Because it just pushes it harder than the spring can hold it. You could argue that a BOV is also a fancy Pop-Off-Valve. A sort of safety release valve.
It's actually possible to have a turbo system without a BOV. Sure, it's not really good for the turbo, but it's possible. That said, I can't imagine anybody wanting to skip using a BOV.
In a Typical Turbo or Centrifugal Supercharger system, the order of components is the same.
Filter -> Compressor -> BOV -> Throttle Body -> Intake
With a BOV put between the Compressor and the TB.
Because, it's going to be releasing the pressure build up due to the TB being slammed shut on throttle lift.
CBV
Now for the reason for this thread, CBV (Compressor Bypass Valve).
While you might think it's just a BOV with a different name, it actually isn't. It's intended purpose is not to release a buildup of pressure in front of the TB. Rather, it's designed to reduce the load on the supercharger belt during high vacuum (Cruise) situation. This is a very important distinction to understand. Especialy when you consider that a CBV is almost never used on a Centrifugal Supercharger. It's pretty much just used on Fixed Displacement (Roots or Twin Screw) superchargers. Also, a typical CBV is not a Diaphram or Piston sytle of valve. It's almost always a Butterfly Valve with a Vacuum Actuator. Very similar to an Turbo Wastegate, except that Boost closes a CBV, and vacuum opens it.
A typical Roots/TwinScrew Supercharger Setup
Filter -> Throttle Body -> CBV -> Compressor -> Intake
Or
Filter -> Throttle Body -> Compressor -> Intake
Notice the location of the Compressor and the Throttle Body. They are basically swapped compared to a Turbo system. This is not just Typical, it's Normal! To do it any other way is NOT normal. Also note that the use of a CBV is totally optional! When a CBV is used, it's only to reduce the slight load on the SC belt during high-vacuum cruise and idle situation. But, that's the point, it's a very light load. It's hard to imagine, but during idle without a CBV, your SC would be actually building "boost" in Vacuum. It tries to go from -25inHg of vac right after the TB, to about -20inHg after the SC. This is the ONLY reason for a CBV. On high-rpm Throttle Lift, the compressor won't slam air against the TB because... well... Duh! The TB is in front of the SC.
Another very important note is that a CBV typically will start to open with as little as 2inHg of vacuum. While a typical BOV takes >10inHg of vacuum to start top open. The reason for this is because for a proper CBV to do it's job, it needs to be closed by 0inHg, but works best when it's open the whole time under vacuum. If it isn't, then there is almost no point in even using it.
The key is that Throttle Body is in front of the whole system. So, the amount of air let into the system is controlled completely by it. Thus, there is no way to create a boost buildup in front of it like a Turbo System. So... no need for a BOV. Clearly you can see now why a BOV is useless in a proper Fixed Displacement SC system"
This really has my interest up.......
Now a by pass valve can become a blow of valve by venting to the atmosphere instead of back into the intake side--but you will loose some throttle response while off boost.
Maybe I am about to learn something--i need too.
here is how I understand it: someone else wrote this but it explains it like what I know:
"Both Turbo and Centrifugal SC use Centrifugal Forces to build boost pressure. They are what are called non-Fixed Displacement compressors. This means, they do not pump a fixed volume of air per revolution. Rather they "fling" the air down the pipe faster than the engine can breath in, resulting in boost. These are the only types of compressors that will allow pressure build up to be pushed back through it's compressor blades. I can't for the life of me recall the term to describe this though.
Both Roots and TwinScrew Supechargers are Fixed Displacement compressors. This means that for every revolution, they pump a fixed volume of air. These "force" or "push" volumes of air down the pipe faster than the engine can breath, resulting in boost. These types can NOT allow pressure buildup to be pushed back through their compressors. Not without risk of serious damage
BOV
I think that most of us know what a BOV is and how it works. So, I'm not going to stress this one. The Primary purpose is to release the build up of pressure behind the Throttle Body as a result of a still compressing turbo or Centrifugal Supercharger. Most have a vacuum line used to assist in opening the valve on throttle lift, and also during high-vac cruise situations.
Most Typical BOVs (like that of the WRX or STi) use a diaphragm or a piston for the actual valve. The benefit of this is that even without the vacuum line pulling open the valve, too much pressure build up will still result in the valve opening. Because it just pushes it harder than the spring can hold it. You could argue that a BOV is also a fancy Pop-Off-Valve. A sort of safety release valve.
It's actually possible to have a turbo system without a BOV. Sure, it's not really good for the turbo, but it's possible. That said, I can't imagine anybody wanting to skip using a BOV.
In a Typical Turbo or Centrifugal Supercharger system, the order of components is the same.
Filter -> Compressor -> BOV -> Throttle Body -> Intake
With a BOV put between the Compressor and the TB.
Because, it's going to be releasing the pressure build up due to the TB being slammed shut on throttle lift.
CBV
Now for the reason for this thread, CBV (Compressor Bypass Valve).
While you might think it's just a BOV with a different name, it actually isn't. It's intended purpose is not to release a buildup of pressure in front of the TB. Rather, it's designed to reduce the load on the supercharger belt during high vacuum (Cruise) situation. This is a very important distinction to understand. Especialy when you consider that a CBV is almost never used on a Centrifugal Supercharger. It's pretty much just used on Fixed Displacement (Roots or Twin Screw) superchargers. Also, a typical CBV is not a Diaphram or Piston sytle of valve. It's almost always a Butterfly Valve with a Vacuum Actuator. Very similar to an Turbo Wastegate, except that Boost closes a CBV, and vacuum opens it.
A typical Roots/TwinScrew Supercharger Setup
Filter -> Throttle Body -> CBV -> Compressor -> Intake
Or
Filter -> Throttle Body -> Compressor -> Intake
Notice the location of the Compressor and the Throttle Body. They are basically swapped compared to a Turbo system. This is not just Typical, it's Normal! To do it any other way is NOT normal. Also note that the use of a CBV is totally optional! When a CBV is used, it's only to reduce the slight load on the SC belt during high-vacuum cruise and idle situation. But, that's the point, it's a very light load. It's hard to imagine, but during idle without a CBV, your SC would be actually building "boost" in Vacuum. It tries to go from -25inHg of vac right after the TB, to about -20inHg after the SC. This is the ONLY reason for a CBV. On high-rpm Throttle Lift, the compressor won't slam air against the TB because... well... Duh! The TB is in front of the SC.
Another very important note is that a CBV typically will start to open with as little as 2inHg of vacuum. While a typical BOV takes >10inHg of vacuum to start top open. The reason for this is because for a proper CBV to do it's job, it needs to be closed by 0inHg, but works best when it's open the whole time under vacuum. If it isn't, then there is almost no point in even using it.
The key is that Throttle Body is in front of the whole system. So, the amount of air let into the system is controlled completely by it. Thus, there is no way to create a boost buildup in front of it like a Turbo System. So... no need for a BOV. Clearly you can see now why a BOV is useless in a proper Fixed Displacement SC system"
This really has my interest up.......
Now a by pass valve can become a blow of valve by venting to the atmosphere instead of back into the intake side--but you will loose some throttle response while off boost.
Maybe I am about to learn something--i need too.
08-13-2012, 10:46 PM
#84
rev it up
The compression on a blower is limited by the pulley size. This means you will not be over boosting so your tune should be controlled all the way to maximum boost.
Therefore, I do not understand why a BOV is required. As OD mentioned the bypass valve allows the car to run without FI and only go into boost when required.
Therefore, I do not understand why a BOV is required. As OD mentioned the bypass valve allows the car to run without FI and only go into boost when required.
08-14-2012, 08:05 PM
#85
orifii? Lol I like it...T shirt word for sure!!
Now anyone feel free to blow holes in whatever I post on this subject--- I dont claim to be an expert.... I dont want to be an expert either--its costs too much money.
Ray I kinda understand what you are referring too, but wouldnt a bov positioned after the maf cause a rich afr when it lets the air out? Does that matter.
If MM is thinking reversion of the air flow, i guess he is seeing maf fluctuations when they shouldnt be? If so wouldnt that be better handled with a better bypass outlet design?
This is interesting.
I have done some work on the Pettit outlet design--it points toward the twin screws but its at approx 120 degree angle ( best guess, didnt measure). The orifice and the bypass valve outlet is on the small size imho, but I have nothing to back that up?
Following with interest.
Now anyone feel free to blow holes in whatever I post on this subject--- I dont claim to be an expert.... I dont want to be an expert either--its costs too much money.
Ray I kinda understand what you are referring too, but wouldnt a bov positioned after the maf cause a rich afr when it lets the air out? Does that matter.
If MM is thinking reversion of the air flow, i guess he is seeing maf fluctuations when they shouldnt be? If so wouldnt that be better handled with a better bypass outlet design?
This is interesting.
I have done some work on the Pettit outlet design--it points toward the twin screws but its at approx 120 degree angle ( best guess, didnt measure). The orifice and the bypass valve outlet is on the small size imho, but I have nothing to back that up?
Following with interest.
08-14-2012, 10:13 PM
#86
ok so the bypass/blowoff is installed although it's a little ghetto until I have time to make it pretty.
The boost gauge is installed and it seems to be holding better now. I hit 9lbs on a short 2nd pull so I think we'll be in good shape when it's loaded on the dyno. Also, I think the dyno will be the best way to see the bypass opening and adjusting the spring rates accordingly. Unfortunately I only have two spring sizes right now although the bypass only valve I have may have a third so I'll check that out tomorrow. I think this is a really interesting idea so it'll be good to see how it goes when Jeff gets a chance to look at it again.
The boost gauge is installed and it seems to be holding better now. I hit 9lbs on a short 2nd pull so I think we'll be in good shape when it's loaded on the dyno. Also, I think the dyno will be the best way to see the bypass opening and adjusting the spring rates accordingly. Unfortunately I only have two spring sizes right now although the bypass only valve I have may have a third so I'll check that out tomorrow. I think this is a really interesting idea so it'll be good to see how it goes when Jeff gets a chance to look at it again.
08-15-2012, 10:45 AM
#87
i dont run a spring in my by pass valve. On my car --it does better without one. Even at idle. I guess it is like some cars like maf screens and some are fine without them? IDK.
I wish we could plumb this type of bypass valve in
http://t1.gstatic.com/images?q=tbn:A...bUdGv_61oaPFxQ
there is a group of people out there that swear up and down that the piston type bypass is not the best to have--but they also say if you are running less than 12 psi of boost --it doesnt matter. Again IDK
I have ran several types of by pass valves and the best one so far for me has been Pettis aluminum one. Maybe you are on to something better?
Anyway at what psi does the bov actuate?
I only have the 7-8 lb pulley on so if you are getting to 9psi i am assuming you have the bigger pulley?
I wish we could plumb this type of bypass valve in
http://t1.gstatic.com/images?q=tbn:A...bUdGv_61oaPFxQ
there is a group of people out there that swear up and down that the piston type bypass is not the best to have--but they also say if you are running less than 12 psi of boost --it doesnt matter. Again IDK
I have ran several types of by pass valves and the best one so far for me has been Pettis aluminum one. Maybe you are on to something better?
Anyway at what psi does the bov actuate?
I only have the 7-8 lb pulley on so if you are getting to 9psi i am assuming you have the bigger pulley?
08-17-2012, 02:09 PM
#90
hmm who makes em? I'm happy to experiment with these.
most recent update:
there are only two spring sizes, red (softer) and yellow (harder) for the TurboSmart gear.
Exhaust is installed though so we're ready to roll on the dyno once I nail Jeff down again.
most recent update:
there are only two spring sizes, red (softer) and yellow (harder) for the TurboSmart gear.
Exhaust is installed though so we're ready to roll on the dyno once I nail Jeff down again.
08-18-2012, 08:52 AM
#91
Kenne Bell makes them
After thinking about this--what yall are trying to do is to relieve the boost in the manifold in a faster manner. Jeff must have seen some evidence of reversion--like Ray was referring too also.
Significant reversion will show on your maf readings---if it varies during acceleration for example, or decell. But, if you set the engine up so it can breath better then you shouldnt see this at this boost level. Then again if the bypass return spot is poorly designed--or the by pass is overwhelmed due to being to small etc --then it can also be seen. Air is going to go somewhere.......
After thinking about this--what yall are trying to do is to relieve the boost in the manifold in a faster manner. Jeff must have seen some evidence of reversion--like Ray was referring too also.
Significant reversion will show on your maf readings---if it varies during acceleration for example, or decell. But, if you set the engine up so it can breath better then you shouldnt see this at this boost level. Then again if the bypass return spot is poorly designed--or the by pass is overwhelmed due to being to small etc --then it can also be seen. Air is going to go somewhere.......
)
09-18-2012, 10:31 PM
#96
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I'm pretty sure K&N RU-3130 (4.625"x7") will work but its 7" and oiled. As people have mentioned its not ideal.
K&N RE-0920 is 6"x9" which is the same size as the AEM filter which comes on the AEM cold air intake. I have this and most definitely does not fit.
AEM 21-2047BF is 5.25"x7" which maybe just small enough to fit and its a dry filter. Space it tight down there though. I may mock up the dimensions to see if it will work.
AEM 21-2047BF - AEM DryFlow Air Filter - AEM Online Store
Dondo - if you get a bigger filter you're going to have to tuck it behind the crash bar a little. You'll have to snugg the front most portion of the intake up to the front engine bay wall or whatever you want to call it. FYI.
09-18-2012, 10:56 PM
#97
I just ordered this filter: 21-2047DK - AEM Universal Air Filters, AEM DryFlow Air Filter
which is the same dimensions as the Brute Force Version you posted so I should know if it fits for sure in a week or two when I receive it.
which is the same dimensions as the Brute Force Version you posted so I should know if it fits for sure in a week or two when I receive it.
09-19-2012, 12:04 AM
#98
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i just mocked it up. The base outside diameter is the killer. Even 5.25 is going to be a squeeze.
I have a feeling the filter will fit but you'll have to tuck it so far inboard you wont be able to connect the intake pipe.
Let us know how it goes
I have a feeling the filter will fit but you'll have to tuck it so far inboard you wont be able to connect the intake pipe.
Let us know how it goes
09-19-2012, 12:27 AM
#100
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K&N RU-1785 seems like it may be a better fit and its longer. Not sure how i feel about K&N though.
RU-1785 - K&N Universal Air Filters, Universal Rubber Filter direct from K&N
RU-1785 - K&N Universal Air Filters, Universal Rubber Filter direct from K&N