The Basics of How A Turbo System Works.
Ok, air comes in through the filter, then through the AFM (which measures the amount of air coming in so the ECU can calculate the amount of fuel required).
The air is then sucked into the turbo, where the compressor wheel increases its pressure and sends it to the engine. On the way there's an intercooler to lower the air temp, because a by product of the turbo is quite a lot of heat.
Before the air gets into the engine it passes through the throttle body, which is what your accelerator pedal is connected to.
The throttle valve restricts airflow into the engine so that you can vary the power it makes.
When it's open the engine tries to produce maximum power, and when it's closed (almost closed) the engine will be at idle.
So the path of air is: filter -> AFM -> compresor (turbo) -> intercooler -> throttle -> engine.
The exhaust gas flow from the engine is roughly proportional to the amount of power it's making, and that flow is what spins the turbo's turbine, which in turn drives the compressor.
So, the more air going in, the more power, and hence more exhaust coming out, which means more boost, which means more air, hence even more power. It's a feedback loop which is kept under control by the throttle input from the driver.
To keep the maximum boost at a safe level there's the wastegate, which is just a valve allowing exhaust to bypass the turbo, and therefore not spin the turbine any faster, or create more boost.
It works in a very simple way. The valve is held closed (all gas goes through the turbine) by a spring, until it is forced open by a diaphragm driven by boost pressure.
When the appropriate boost is reached the wastegate starts to open, and the turbo will stay at the set boost level while the exhaust flow can still increase as the engine revs rise.
All of this works quite simply under constant acceleration:
Air comes in, is compressed to the set boost level, intercooled, used by the engine, and the exhaust keeps the turbo spinning.
It becomes more complex when you start changing throttle settings.
If the throttle is wide open, and you're at full boost accelerating, then close the throttle (for a gear change, or back off) suddenly the turbo is pushing against a closed throttle, and at the same time the engine has stopped producing exhaust gas, so the turbo starts to slow down.
Now that there's a whole intake system full of compressed air with nowhere to go, and the compressor is not being driven by the turbine - so it can't hold the same air pressure that it did while spinning flat out. The air will start to flow the other way, which means going backwards through the still spinning compressor.
This is where compressor surge comes into play. The compressor is still trying to pump air, but at the speed it's going it can't provide as much pressure as there already is in the pipe.
This causes the compressor to "stall". Stall is a misleading turn used here, because it doesn't mean stall as in to stop spinning. It's the aerodynamic stall, like a plane that's tried to climb too steeply, or has slowed down too much to maintain lift.
The smooth air flow through the compressor blades is broken up, and some of the air will flow back out through the compressor, making a hissing noise.
Centrifugal compressors work on a "squared" relationship for speed vs flow / pressure, so if the turbo slows down to half speed it will only be able to hold a quarter of the boost pressure.
The "chopping" or "fluttering" sound is caused by the accoustic effects in the intake system, determined by the size and length of the piping / cooler.
Rather than air constantly flowing back out of the turbo it tends to come out in bursts, triggered by pressure waves in the piping hitting the compressor.
Generally though the flutter is the sound of the pressure wave cause by the throttle closing bouncing back and forth between the turbo and the throttle plate (the longer the pipes the slower the flutter).
Every time the wave hits the turbo it causes the compressor to cavitate, which makes the noise.
It's not the blades chopping the air making the flutter. Since the blades are spinning at 80000+rpm you wouldn't be able to hear the individual "chops"
If you listen closely you'll actually hear a more constant hiss sound at higher boost levels and rpm when backing off. (ie, a "whooosh" rather than a "chop chop chop")
The loudest flutter tends to occur at lower rpm and boost levels of only slightly above atmospheric pressure (0psi). This is partly because the sound is "chopped" up more noticeably, and partly because the rest of the car is making less noise at lower speeds. This is also where it's least damaging.
Car manufacturers don't like weird noises from the intake system, so they use restrictive airboxes designed to muffle the sound, and more recently (SR20 onwards) used a Blow Off Valve.
The blow off valve provides a new path for air to get out past the compressor. Instead of forcing its way back through the spinning blades it is piped out of the intercooler piping and back into the intake piping before the turbo.
Obviously it could be vented straight out to the atmosphere, but the AFM has already measured that air coming in, and if it doesn't reach the engine the ECU will be injecting too much fuel in its absence.
(Also, venting to atmosphere makes a bit much noise for conservative owners and manufacturers)
The BOV works a bit like the wastegate, in that it's held closed by a spring, and controlled by a pressure operated diaphragm.
This time though the boost pressure helps keep it shut rather than open it.
The control air pressure for the BOV comes from the plenum, which is the chamber between the throttle and the engine.
When the throttle closes the engine creates a vacuum (negative pressure) in the manifold / plenum as it tries to suck air past the closed throttle.
The vacuum is used to "pull" open the BOV, to vent the excess air in the intake system, preventing "flutter" and other noises.
A BOV is a compromise device because, to eliminate all fluttering it will have to open at very low boost levels, and very quickly - which means that it must have a very weak spring. This can cause some leaking of boost due to the valve not staying sealed properly, and also means that every time you back off the throttle, all the pressure in the intake system is vented. When you open the throttle again the turbo will have to build up all that pressure again, whereas if there was no BOV there'd be more pressure remaining as it's a lot harder to get out through the compressor.
Most aftermarket BOVs won't open until you reach 6psi or so of boost (because with an atmo venting BOV if it leaks boost you'll have major problems - whereas a slightly leaking plumb back type won't cause bad running, just a very slight loss of power)
When you start running well over stock boost, and have larger intercoolers / intake piping obviously there's a lot more air in the intake system, and it will be at higher pressure - so when you back off the throttle there's a lot of air trying to escape through the compressor. This means it will be slowed down quite quickly and violently, which puts large loads on the turbo bearings, wheels, and shaft. Repeated hammering by high boost backoffs can harm the turbo, and the amount of slowing each time causes a lag when the turbo spools back up after each backoff / gearchange.
The best compromise setup is to have a BOV which will open when you back off at over say 6 psi, and vent back into the intake to prevent the rich running problems of atmo BOVs. If it's too loose you'll lose boost response due to too much presure being lost on gearchanges, and if it's too tight you'll lose response due to the turbo being slowed down too much - and potentially damaged by the rapid deceleration.
Why does it flutter when my gauge isnt reading any boost?
The reason it flutters even when you can't see boost on the guage is that you're looking at the pressure in the plenum (after the throttle), but the turbo can actually be producing a bit of boost in the cooler and intake piping.
Full Version: How A Turbo System Works For Newbies
That was an awesome description mate 
It explained all those things about turbos i never quite got. It's always good to learn that bit extra about car engines for future reference. Keep up the good work 
TRD Rolla
Mate, even though it was an awesome explanation, heres a diagram so that people can visualise whats happening
TRD Rolla
TRD Rolla
This is the most informative thread I have read in a long time. Thanks
You're about 4 months too late 
this is way easier than reading Street Machiones technical acrticles which are designed for 34 year olds, and being 14 understanding is kinda hard. But i knew most of that stuff anyway ,
Roy
this is way easier than reading Street Machiones technical acrticles which are designed for 34 year olds, and being 14 understanding is kinda hard. But i knew most of that stuff anyway ,Roy
That was an EXCELLENT description dude thanks heaps for that
thanks heaps for that
| QUOTE |
| A BOV is a compromise device because, to eliminate all fluttering it will have to open at very low boost levels, and very quickly - which means that it must have a very weak spring. This can cause some leaking of boost due to the valve not staying sealed properly, and also means that every time you back off the throttle, all the pressure in the intake system is vented. When you open the throttle again the turbo will have to build up all that pressure again, whereas if there was no BOV there'd be more pressure remaining as it's a lot harder to get out through the compressor. |
That applies, except when you use a Super Sequential Valve (SSQV) like I do. Doesn't leak under boost and vents even the smallest pressures on throttle close
Other than that, very informative
without a BOV doesn't the compressor slow down considerably due to the air trying to force its way back the way it came?
yeah very good information there. Also you should mention at the start how a turbo spools up.
A turbo spools and creates boost by flowing wasted exhaust gas from the engine through the exhaust housing side of the turbo (the back of a turbosystem, similar in design to the compressor side of the turbo see the diagram its the brown rusty looking part on the turbo). This exhaust gas makes the turbine blades spin, which are connected to the compressors side turbine wheel by a small rod.
This flow makes both turbines spin, and this creates the induction (the turbo is sucking in air through the AFM and filter). The forced induction part is where the air is compressed (pressurised) and flows through your intercooler piping through your throttlebody and into your engine providing you with positive pressure and a big grin.
A turbo spools and creates boost by flowing wasted exhaust gas from the engine through the exhaust housing side of the turbo (the back of a turbosystem, similar in design to the compressor side of the turbo see the diagram its the brown rusty looking part on the turbo). This exhaust gas makes the turbine blades spin, which are connected to the compressors side turbine wheel by a small rod.
This flow makes both turbines spin, and this creates the induction (the turbo is sucking in air through the AFM and filter). The forced induction part is where the air is compressed (pressurised) and flows through your intercooler piping through your throttlebody and into your engine providing you with positive pressure and a big grin.
mabey this should be made a sicky to help out beginners
| QUOTE (Ni_Slo @ Jul 30 2004, 10:11 PM) |
| That applies, except when you use a Super Sequential Valve (SSQV) like I do. Doesn't leak under boost and vents even the smallest pressures on throttle close Other than that, very informative |
how the hell does that work? anyone care to explain how the ssqv can achieve this mighty feat?
| QUOTE (Bitsaremissin' @ Jul 30 2004, 10:19 PM) |
| without a BOV doesn't the compressor slow down considerably due to the air trying to force its way back the way it came? |
i throught without a BOV the compressed air goes back into the turbo and slows it down i think thats wat i read in the web site
AWESOME piece of work. amazing that you managed to offer only facts. no "maybe a bov is good i don't know". just the cold hard facts. refreshing reading
| QUOTE |
| how the hell does that work? anyone care to explain how the ssqv can achieve this mighty feat? |
its a pull type valve, i dunno the specifics but on a normal bov the compressed air pushes the piston up and releases. the hks and monza (imitation) ssqv's work in the opposite way. ill find an article in a second and edit this post.
"As you know, HKS is the #1 choice overall for performance between shifts. The reason is the reverse design of the BOV that allows the boost to push the valve closed, eliminating any chance of leakage. This is called a pull type BOV. Boost is pressing on the back of the valve, holding it closed, until the BOV sees vacuum (when you let off the throttle) which pulls the small valve up letting the air out. The larger valve opens as well, depending on the spring tension. Also, with twin valves, you can be sure that you are releasing pressure under low boost and high boost."
http://www.935motorsports.com/hksbov.htm#hksfaq
| QUOTE |
| without a BOV doesn't the compressor slow down considerably due to the air trying to force its way back the way it came? |
depends on your shifting time. if your being a granny then yes you may be off boost in the next gear but if you can shift fairly quickly then you'll still be boosting. probably also gotta factor in turbo size as larger compressor wheel would have more resistence but also more momentum so would take longer to slow down.
Nice work dude heaped out heaps 
that article is fantastic -- i remember reading it AGES ago and always refer back to it in FLUTTER arguments with people -- but could never remember the linkn
NOW I HAVE IT!!!
awesome article -thanku!
NOW I HAVE IT!!!
awesome article -thanku!
Yeah dude i learnt heaps from your post...thanks heaps 
| QUOTE (Pie @ Jul 31 2004, 03:18 PM) |
| The reason is the reverse design of the BOV that allows the boost to push the valve closed, eliminating any chance of leakage. This is called a pull type BOV. Boost is pressing on the back of the valve, holding it closed, until the BOV sees vacuum (when you let off the throttle) which pulls the small valve up letting the air out. The larger valve opens as well, depending on the spring tension. Also, with twin valves, you can be sure that you are releasing pressure under low boost and high boost. |
when you say"until the BOV sees vacuum (when you let off the throttle) which pulls the small valve up letting the air out." do you mean vacume from the plenum? which means on the ssq style bov you would need to have a hose runnng from the plenum to bov to operate the pressure release valve? is that right???
sory if it sounds like a noob question, just trying to understand corectly.... great article by the way!
So if you want the fluttering sound then you want a wastegate not a bov? and say running at about 8-12 pounds of boost would u still get the fluttering sound or not? personally i rekon it sounds better than a bov but.... others would probably disagree. THNX 
| QUOTE (wrx_sti_01 @ Jul 30 2004, 05:47 PM) |
| The Basics of How A Turbo System Works. Ok, air comes in through the filter, then through the AFM (which measures the amount of air coming in so the ECU can calculate the amount of fuel required). The air is then sucked into the turbo, where the compressor wheel increases its pressure and sends it to the engine. On the way there's an intercooler to lower the air temp, because a by product of the turbo is quite a lot of heat. Before the air gets into the engine it passes through the throttle body, which is what your accelerator pedal is connected to. The throttle valve restricts airflow into the engine so that you can vary the power it makes. When it's open the engine tries to produce maximum power, and when it's closed (almost closed) the engine will be at idle. So the path of air is: filter -> AFM -> compresor (turbo) -> intercooler -> throttle -> engine. The exhaust gas flow from the engine is roughly proportional to the amount of power it's making, and that flow is what spins the turbo's turbine, which in turn drives the compressor. So, the more air going in, the more power, and hence more exhaust coming out, which means more boost, which means more air, hence even more power. It's a feedback loop which is kept under control by the throttle input from the driver. To keep the maximum boost at a safe level there's the wastegate, which is just a valve allowing exhaust to bypass the turbo, and therefore not spin the turbine any faster, or create more boost. It works in a very simple way. The valve is held closed (all gas goes through the turbine) by a spring, until it is forced open by a diaphragm driven by boost pressure. When the appropriate boost is reached the wastegate starts to open, and the turbo will stay at the set boost level while the exhaust flow can still increase as the engine revs rise. All of this works quite simply under constant acceleration: Air comes in, is compressed to the set boost level, intercooled, used by the engine, and the exhaust keeps the turbo spinning. It becomes more complex when you start changing throttle settings. If the throttle is wide open, and you're at full boost accelerating, then close the throttle (for a gear change, or back off) suddenly the turbo is pushing against a closed throttle, and at the same time the engine has stopped producing exhaust gas, so the turbo starts to slow down. Now that there's a whole intake system full of compressed air with nowhere to go, and the compressor is not being driven by the turbine - so it can't hold the same air pressure that it did while spinning flat out. The air will start to flow the other way, which means going backwards through the still spinning compressor. This is where compressor surge comes into play. The compressor is still trying to pump air, but at the speed it's going it can't provide as much pressure as there already is in the pipe. This causes the compressor to "stall". Stall is a misleading turn used here, because it doesn't mean stall as in to stop spinning. It's the aerodynamic stall, like a plane that's tried to climb too steeply, or has slowed down too much to maintain lift. The smooth air flow through the compressor blades is broken up, and some of the air will flow back out through the compressor, making a hissing noise. Centrifugal compressors work on a "squared" relationship for speed vs flow / pressure, so if the turbo slows down to half speed it will only be able to hold a quarter of the boost pressure. The "chopping" or "fluttering" sound is caused by the accoustic effects in the intake system, determined by the size and length of the piping / cooler. Rather than air constantly flowing back out of the turbo it tends to come out in bursts, triggered by pressure waves in the piping hitting the compressor. Generally though the flutter is the sound of the pressure wave cause by the throttle closing bouncing back and forth between the turbo and the throttle plate (the longer the pipes the slower the flutter). Every time the wave hits the turbo it causes the compressor to cavitate, which makes the noise. It's not the blades chopping the air making the flutter. Since the blades are spinning at 80000+rpm you wouldn't be able to hear the individual "chops" If you listen closely you'll actually hear a more constant hiss sound at higher boost levels and rpm when backing off. (ie, a "whooosh" rather than a "chop chop chop") The loudest flutter tends to occur at lower rpm and boost levels of only slightly above atmospheric pressure (0psi). This is partly because the sound is "chopped" up more noticeably, and partly because the rest of the car is making less noise at lower speeds. This is also where it's least damaging. Car manufacturers don't like weird noises from the intake system, so they use restrictive airboxes designed to muffle the sound, and more recently (SR20 onwards) used a Blow Off Valve. The blow off valve provides a new path for air to get out past the compressor. Instead of forcing its way back through the spinning blades it is piped out of the intercooler piping and back into the intake piping before the turbo. Obviously it could be vented straight out to the atmosphere, but the AFM has already measured that air coming in, and if it doesn't reach the engine the ECU will be injecting too much fuel in its absence. (Also, venting to atmosphere makes a bit much noise for conservative owners and manufacturers) The BOV works a bit like the wastegate, in that it's held closed by a spring, and controlled by a pressure operated diaphragm. This time though the boost pressure helps keep it shut rather than open it. The control air pressure for the BOV comes from the plenum, which is the chamber between the throttle and the engine. When the throttle closes the engine creates a vacuum (negative pressure) in the manifold / plenum as it tries to suck air past the closed throttle. The vacuum is used to "pull" open the BOV, to vent the excess air in the intake system, preventing "flutter" and other noises. A BOV is a compromise device because, to eliminate all fluttering it will have to open at very low boost levels, and very quickly - which means that it must have a very weak spring. This can cause some leaking of boost due to the valve not staying sealed properly, and also means that every time you back off the throttle, all the pressure in the intake system is vented. When you open the throttle again the turbo will have to build up all that pressure again, whereas if there was no BOV there'd be more pressure remaining as it's a lot harder to get out through the compressor. Most aftermarket BOVs won't open until you reach 6psi or so of boost (because with an atmo venting BOV if it leaks boost you'll have major problems - whereas a slightly leaking plumb back type won't cause bad running, just a very slight loss of power) When you start running well over stock boost, and have larger intercoolers / intake piping obviously there's a lot more air in the intake system, and it will be at higher pressure - so when you back off the throttle there's a lot of air trying to escape through the compressor. This means it will be slowed down quite quickly and violently, which puts large loads on the turbo bearings, wheels, and shaft. Repeated hammering by high boost backoffs can harm the turbo, and the amount of slowing each time causes a lag when the turbo spools back up after each backoff / gearchange. The best compromise setup is to have a BOV which will open when you back off at over say 6 psi, and vent back into the intake to prevent the rich running problems of atmo BOVs. If it's too loose you'll lose boost response due to too much presure being lost on gearchanges, and if it's too tight you'll lose response due to the turbo being slowed down too much - and potentially damaged by the rapid deceleration. Why does it flutter when my gauge isnt reading any boost? The reason it flutters even when you can't see boost on the guage is that you're looking at the pressure in the plenum (after the throttle), but the turbo can actually be producing a bit of boost in the cooler and intake piping. |
Wow thats awesome!
FINALLY.....
a post thats longer than those of KOTCJ, took ages but well done mate.
So really its the same as a supercharger
Yep, except its driven from the exhaust gasses, where as a supercharger is driven from the crank.
informative.. well done.
| QUOTE (wrx_sti_01 @ Jul 30 2004, 05:47 PM) |
| So the path of air is: filter -> AFM -> compresor (turbo) -> intercooler -> throttle -> engine. |
Unless it's MAP sensed...
QUOTE(mattysaidso @ Dec 31 2004, 09:20 AM)
when you say"until the BOV sees vacuum (when you let off the throttle) which pulls the small valve up letting the air out." do you mean vacume from the plenum? which means on the ssq style bov you would need to have a hose runnng from the plenum to bov to operate the pressure release valve? is that right?
[right][snapback]4884191[/snapback][/right]
[right][snapback]4884191[/snapback][/right]
That's what the original post says
WOW that was awsome 
QUOTE(infamous_69 @ Jan 8 2005, 05:49 AM)
So if you want the fluttering sound then you want a wastegate not a bov? and say running at about 8-12 pounds of boost would u still get the fluttering sound or not? personally i rekon it sounds better than a bov but.... others would probably disagree. THNX 
[right][snapback]4895863[/snapback][/right]
[right][snapback]4895863[/snapback][/right]
no way infamous
nothing sound better then a wategate slammin hard
informative and not dumbed down, i mayb a newbie but im not stupid and this was a great piece of informative literature. keep up the great reads choice! 
nice one manu really know ur shit on turbos
that was great
u a teacher or something
could you help me out about lag then please
u a teacher or something
could you help me out about lag then please
well i learned something, nice description 
awsum analogy... www.howstuffworks.com is where i learned the basics of engines n turbo systems etc... they have everythin easily xplained with simple diograms and discriptions for a beginer.
wow,
how in depth was that? lol
I'm actually an ex holden owner(Written off in november) and will be making my first leap into a turbo car some time in febuary should things go to plan. considering my freshmen status with in the turbo community this has been a great insight and very educational.
Thanx man
-R337
how in depth was that? lol
I'm actually an ex holden owner(Written off in november) and will be making my first leap into a turbo car some time in febuary should things go to plan. considering my freshmen status with in the turbo community this has been a great insight and very educational.
Thanx man
-R337
Pies on the right track with the compressor fact, that why prople make living knowing the ins and outs of compressor and turbine sizes, hence the growing popularity of hyrbrid turbos.
QUOTE
Obviously it could be vented straight out to the atmosphere, but the AFM has already measured that air coming in, and if it doesn't reach the engine the ECU will be injecting too much fuel in its absence.
Just a thought, what if venting boost to atmo could be a good thing.
Your in second, throttle off, throttle plate closed, boost vents, clutch in, excess fuel dumped in abscence of vented boost, overfueling leaves fuel unburnt, unburnt fuel expelled into exhaust, unburnt fuel into turbo 900'C+, fuel combusts and expands accelerating turbo, 3rd cog selected, clutch out, throttle on... off-throttle spooling.
So your turbo has been spooling while your shifting then you put on the gas n the boost is there or more accuratly the turbo acceleration has begun already.
After thoughts: The vacuum in manifold would be keepin the Bov open while the turbo is producing boost from excess fuel. THOUGH.. this happens as fast as you can shift and it takes time to build up boost. If the bov is right before the throttle plate then compressed air (boost) created from excess fuel would rush along towards the bov from the compressor outlet. As it heading there your shifting, your find 3rd, clutch up, then you put the throttle down, throttle plate opens, vacuum goes, Bov closes and the charging boost would keep on going straight into your engine. sounds good aye
The greater the volume of your intake(piping, intercooler) the longer the boost has to travel to vent through the open Bov before you put on the throttle. Although the duration of the fuel dump is interesting. Thinking about it the turbo is spooling drawing air through the AFM telling the ecu to put in more fuel therefore creating a cycle. Youd have to consider how long all these processes take.
Also if the timing was retarded then less fuel would be burnt in the motor and more in the turbo giving greater force pusing the turbine around aswell as greater heat.
This type of anti-lag was used in F1 like in the 80s to help them rocket out of corners on boost with relatively no lag. Ferrari had a valve connecting the intake to the exhaust manifold so when the throttle plate shut the excess boost went into the turbine (exhaust housing) aswell as the fuel (with retarded timing) and just went nuts. Too higher temps and lack of turbo technology destroyed alot of their turbos by this method.
Anything you think of about this idea of off-throttle spooling or anti lag methods i want to hear, tell me if iam wrong with anything! The effect would be only minimal with a street car although it could be enhanced with a compromise between fuel efficiency and heat. what are your thoughts.
the compressor flutter or surge is about the worst thing that you can do to a turbo, it can bend the shaft,
damaging the bearings, leading to metal to metal contact between housing and wheel, destroying the turbo.
ALWAYS run a BOV, on both maf and map systems, but not diesels or suck-through turbos, there's no need
damaging the bearings, leading to metal to metal contact between housing and wheel, destroying the turbo.
ALWAYS run a BOV, on both maf and map systems, but not diesels or suck-through turbos, there's no need
anti-lag: some rally drivers get on brakes and accelerator at some time to build boost, works because engine is under load, load + rpm = boost
another way is that in some *special* DOHC turbo engines, ecu can retard the exhaust cam timing, or manually holding the exhaust valves open, building boost.
another way is that in some *special* DOHC turbo engines, ecu can retard the exhaust cam timing, or manually holding the exhaust valves open, building boost.
yea good 4 u guys there is still stuff i dont get ARGH
i read it and it makes sense but the next day ill come bac and i will have forgotten most of it
i read it and it makes sense but the next day ill come bac and i will have forgotten most of it
that was incredibly informative, i had a basic idea but that told me everything i needed 2 know in-depth
so the fact that i've got a BOV and i still get the "flutter" sound which seems to come from the air filter would mean???
I'm guessing the BOV is either siezed or not connected properly
I'm guessing the BOV is either siezed or not connected properly
So if you run a turbo less than 6psi there is no point for a bov?
No that is not the case.
The bov is there to protect the bearings in the turbo.
If your bov doesnt work at low boost then you have a too hard spring in it.
The bov is there to protect the bearings in the turbo.
If your bov doesnt work at low boost then you have a too hard spring in it.
I'm only running 6psi without a BOV and I'm still getting the flutter at 2500-3000rpm. I don't even need to take the revs high. (And yes I know I should have a BOV on but I lost it when I got my new piping and no workshops are open to put my new one on yet)
QUOTE(wrx_sti_01 @ Jul 30 2004, 05:47 PM) [snapback]4641052[/snapback]
So the path of air is: filter -> AFM -> compresor (turbo) -> intercooler -> throttle -> engine.
where abouts can a BOV be placed? for example, does it HAVE to go be4 the turbo or HAVE to go after turbo and does it make any difference? hope that makes sence
It has to go after the turbo or there would be no build up of air pressure, but it makes no difference going before or after the intercooler.
Actually you are wrong.
The bov is best placed as close to the turbo as practical.
Its job is to take the pressure away from the inlet wheel, hence saving the bearings.
The bov is best placed as close to the turbo as practical.
Its job is to take the pressure away from the inlet wheel, hence saving the bearings.
QUOTE(TwinCam16 @ Jan 6 2007, 12:20 AM) [snapback]1280640518[/snapback]
The bov is best placed as close to the turbo as practical.
Its job is to take the pressure away from the inlet wheel, hence saving the bearings.
Sort of like saying the sky is not red. True, but doesn't quite give the full picture.
The BOV also keeps up the rpm of the turbo (while changing gear) so you'll have less lag as you accelerate after sliding in the next gear.
From this, if you take a while to change gears, (ie. typical street driving) then BOV closer to the turbo is a good thing, however all the air in the plumbing and intercooler must reverse direction to head back to the BOV and change direction again when you accelerate, each time you accelerate the air it is using up HP.
If you change gears quickly (but not flat shifting where you don't take your foot off the throttle to change gear) then you don't want this direction changing.
If the BOV is closer to the throttle body, this direction change of the air doesn't have to happen and you conserve the momentum of the air, however the turbo is now working against the pressure drop of the intercooler before it gets to the BOV, which will slow down the compressor a little more, but now you don't have to reaccelerate the air in the plumbing/intercooler when you stamp on the throttle again.
Then, just to make things ugly, you can't have it right at the throttle plate either, as doing this can miss the intial pressure wave sent back from the throttle plate as it closes both delaying the BOV opening and sending an unwanted pressure wave to the turbo. Bareing in mind at this point this is all to find that 0.1% gain and the fluidic modelling to find the ideal point is just goind to send most people
QUOTE(TwinCam16 @ Jan 6 2007, 12:20 AM) [snapback]1280640518[/snapback]
Actually you are wrong.
The bov is best placed as close to the turbo as practical.
Its job is to take the pressure away from the inlet wheel, hence saving the bearings.
it was actually ure pic that got me confused TwinCam16. thanks for the info anyway guys. http://www.boostcruising.com/forums/index....showtopic=45275
(3rd pic)
Ahhh ok.
the valve was there to hide it.
It should have gone on the other side of the cooler, but since that was before i could weld, i had to get someone else to make the pipework up for me, hence, not being where it was meant to be.
Sort of like saying the sky is not red. True, but doesn't quite give the full picture.
The BOV also keeps up the rpm of the turbo (while changing gear) so you'll have less lag as you accelerate after sliding in the next gear.
From this, if you take a while to change gears, (ie. typical street driving) then BOV closer to the turbo is a good thing, however all the air in the plumbing and intercooler must reverse direction to head back to the BOV and change direction again when you accelerate, each time you accelerate the air it is using up HP.
If you change gears quickly (but not flat shifting where you don't take your foot off the throttle to change gear) then you don't want this direction changing.
If the BOV is closer to the throttle body, this direction change of the air doesn't have to happen and you conserve the momentum of the air, however the turbo is now working against the pressure drop of the intercooler before it gets to the BOV, which will slow down the compressor a little more, but now you don't have to reaccelerate the air in the plumbing/intercooler when you stamp on the throttle again.
Then, just to make things ugly, you can't have it right at the throttle plate either, as doing this can miss the intial pressure wave sent back from the throttle plate as it closes both delaying the BOV opening and sending an unwanted pressure wave to the turbo. Bareing in mind at this point this is all to find that 0.1% gain and the fluidic modelling to find the ideal point is just goind to send most people
Faircall!
the valve was there to hide it.
It should have gone on the other side of the cooler, but since that was before i could weld, i had to get someone else to make the pipework up for me, hence, not being where it was meant to be.
QUOTE(Aiko @ Jan 6 2007, 09:04 AM) [snapback]1280640792[/snapback]
Sort of like saying the sky is not red. True, but doesn't quite give the full picture.
The BOV also keeps up the rpm of the turbo (while changing gear) so you'll have less lag as you accelerate after sliding in the next gear.
From this, if you take a while to change gears, (ie. typical street driving) then BOV closer to the turbo is a good thing, however all the air in the plumbing and intercooler must reverse direction to head back to the BOV and change direction again when you accelerate, each time you accelerate the air it is using up HP.
If you change gears quickly (but not flat shifting where you don't take your foot off the throttle to change gear) then you don't want this direction changing.
If the BOV is closer to the throttle body, this direction change of the air doesn't have to happen and you conserve the momentum of the air, however the turbo is now working against the pressure drop of the intercooler before it gets to the BOV, which will slow down the compressor a little more, but now you don't have to reaccelerate the air in the plumbing/intercooler when you stamp on the throttle again.
Then, just to make things ugly, you can't have it right at the throttle plate either, as doing this can miss the intial pressure wave sent back from the throttle plate as it closes both delaying the BOV opening and sending an unwanted pressure wave to the turbo. Bareing in mind at this point this is all to find that 0.1% gain and the fluidic modelling to find the ideal point is just goind to send most people
Faircall!
is ther any reason why you couldent have 2?
one close to the turbo and one close to the trottla body?
or would that not have a big enough effect to worry about doing it?
one close to the turbo and one close to the trottla body?
or would that not have a big enough effect to worry about doing it?
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