Recirculating vs Venting
Aug 23, 2009, 04:19 PM
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Recirculating vs Venting
Hey guys, Im fairly new here but wanted to share some info i found on Import Tuner thought might be useful.
2008 Mitsubishi Lancer Ralliart - Fact Or Fiction
When searching for automotive-related debates or suspect products to test and expose for Fact or Fiction, it's easy to make the mistake of looking a little too hard, and forgetting about what's right in front of our faces. Like this month's subject: bypass valves (or blow-off valves) on turbocharged engines, and whether venting their charge to atmosphere can decrease performance as opposed to recirculating it.
When installed on a turbocharged engine, bypass valves use an engine's intake manifold vacuum at throttle let-off to open a diaphragm that vents excess boost pressure from its turbocharger's compressor. Without releasing that pressure, the turbocharger would otherwise force or "surge" boost pressure against a closed throttle plate, bringing it to a series of rapid stops that eliminate spool and damage the turbo. In most stock applications, the bypass valve recirculates boost pressure back into the turbo compressor's inlet, but in many modified instances, the bypass valve is made to vent directly to the atmosphere; some would argue, a move that decreases spool and slows throttle response.
The Test:
We knew testing this theory would be a little trickier than strapping the car to the dyno and testing peak power, so we enlisted the help of Mavrik Motorsports and their DynoLog chassis dynamometer, where lead tuner Teddy simultaneously logged boost pressure, throttle position, and time delay throughout a series of runs with our '08 Mitsubishi Lancer Ralliart test car, first with its factory bypass vlave recirculating boost, then again with it venting to atmosphere. Since this was a throttle response test and not one of peak power, we loaded the dyno to keep engine speed at a consistent 4,000 rpm in Fourth gear throughout testing, and tracked the amount of boost pressure our 4B11 engine produced at a series of wide-open-throttle jabs at specific intervals after throttle let-off from full boost, for each orientation of the bypass valve. And for kicks, we also tested peak power. Here's what we found:
The Verdict: Fact
After sifting through mounds of numbers, results were averaged for a few clean throttle tests for each variation of the bypass valve taken at different times, and the amount of boost our 4B11 produced after throttle let-off with its bypass valve recirculating boost was consistently higher than with it venting to atmosphere. But not by much-the benefits of recirculating will be more apparent with larger turbos, and larger, aftermarket replacement bypass or blow-off valves will likely offer improved results over original equipment, provided they offer the option to recirculate boost. Sure, recirculating boost may not sound as cool as blowing it off... but neither do First Place trophies, and we like those, too.
2008 Mitsubishi Lancer Ralliart - Fact Or Fiction
When searching for automotive-related debates or suspect products to test and expose for Fact or Fiction, it's easy to make the mistake of looking a little too hard, and forgetting about what's right in front of our faces. Like this month's subject: bypass valves (or blow-off valves) on turbocharged engines, and whether venting their charge to atmosphere can decrease performance as opposed to recirculating it.
When installed on a turbocharged engine, bypass valves use an engine's intake manifold vacuum at throttle let-off to open a diaphragm that vents excess boost pressure from its turbocharger's compressor. Without releasing that pressure, the turbocharger would otherwise force or "surge" boost pressure against a closed throttle plate, bringing it to a series of rapid stops that eliminate spool and damage the turbo. In most stock applications, the bypass valve recirculates boost pressure back into the turbo compressor's inlet, but in many modified instances, the bypass valve is made to vent directly to the atmosphere; some would argue, a move that decreases spool and slows throttle response.
The Test:
We knew testing this theory would be a little trickier than strapping the car to the dyno and testing peak power, so we enlisted the help of Mavrik Motorsports and their DynoLog chassis dynamometer, where lead tuner Teddy simultaneously logged boost pressure, throttle position, and time delay throughout a series of runs with our '08 Mitsubishi Lancer Ralliart test car, first with its factory bypass vlave recirculating boost, then again with it venting to atmosphere. Since this was a throttle response test and not one of peak power, we loaded the dyno to keep engine speed at a consistent 4,000 rpm in Fourth gear throughout testing, and tracked the amount of boost pressure our 4B11 engine produced at a series of wide-open-throttle jabs at specific intervals after throttle let-off from full boost, for each orientation of the bypass valve. And for kicks, we also tested peak power. Here's what we found:
After sifting through mounds of numbers, results were averaged for a few clean throttle tests for each variation of the bypass valve taken at different times, and the amount of boost our 4B11 produced after throttle let-off with its bypass valve recirculating boost was consistently higher than with it venting to atmosphere. But not by much-the benefits of recirculating will be more apparent with larger turbos, and larger, aftermarket replacement bypass or blow-off valves will likely offer improved results over original equipment, provided they offer the option to recirculate boost. Sure, recirculating boost may not sound as cool as blowing it off... but neither do First Place trophies, and we like those, too.
Aug 23, 2009, 05:03 PM
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The results are very marginal, not much of a difference at all like ppl make it out to be. I still prefer to recirc for right now though.
Aug 24, 2009, 08:43 AM
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Originally Posted by Mike W from RRE
The Holy Grail of anyone under 25 years old with a turbo car is to have this excess pressure release heard by other kids under 25 years old. High school boys are particularly impressed by this PH-Shhhhh sound. Word is that their high school girlfriends will leave them and come and jump into your car. Cools stuff indeed.
You can spend time and money trying to achieve this sound by taking off the factory BOV and replacing it with an aftermarket one. The aftermarket one will need to blow the air out so that it can be heard by the high school boys. You just cap off the hose where it was blowing back into the turbo inlet pipe.
On Mitsubishis this creates several issues. The ECU has seen all the air enter the system since it was measured by the air flow meter. The ECU gives you the right amount of fuel for all this air. If you blow a grip of air out for the high schools boys to hear, the ECU has no idea you blew it all out. It still gives you fuel for the air you let out. The car goes rich and almost stalls or bucks. The high school girls do indeed get wet though. It is a trade off like all things in life.
The answer is to tighten the aftermarket BOV so it does not blow off as much air so that the motor stalls. Now you hear this turkey gobble noise like “cha-chooo-chooo-chooo”. Think any HKS BOV you have heard. That is the sound of compressor surge destroying the turbo. Congratulations! ;-)
But sp4rkl3bunn3y on the forums says he runs his car blowing out and it does not stall. Well sp4rkl3bunn3y has a stock turbo running low boost and the little compressor surge he gets isn’t going to hurt much for now. He thinks the compressor surge sound he is hearing is a cool BOV noise. Higher boost and a real man sized turbo will make it undriveable.
Also on your RalliArts the way that the tranny is always up shifting and the ECU has more control over the throttle than you do I doubt you would hear much.
With the Mitsubishi drive by wire system there are a bunch more checks and balances with what air flow the air flow meter should be seeing at any given RPM and throttle position. I have seen so many EVO X guys fight SES lights and limp modes with various aftermarket BOVs. It is just another big mess to deal with. Even if you are recirculating the air back in, if the BOV is looser or tighter and allows different than expected air flow past the air flow meter, it is just misery.
You can spend time and money trying to achieve this sound by taking off the factory BOV and replacing it with an aftermarket one. The aftermarket one will need to blow the air out so that it can be heard by the high school boys. You just cap off the hose where it was blowing back into the turbo inlet pipe.
On Mitsubishis this creates several issues. The ECU has seen all the air enter the system since it was measured by the air flow meter. The ECU gives you the right amount of fuel for all this air. If you blow a grip of air out for the high schools boys to hear, the ECU has no idea you blew it all out. It still gives you fuel for the air you let out. The car goes rich and almost stalls or bucks. The high school girls do indeed get wet though. It is a trade off like all things in life.
The answer is to tighten the aftermarket BOV so it does not blow off as much air so that the motor stalls. Now you hear this turkey gobble noise like “cha-chooo-chooo-chooo”. Think any HKS BOV you have heard. That is the sound of compressor surge destroying the turbo. Congratulations! ;-)
But sp4rkl3bunn3y on the forums says he runs his car blowing out and it does not stall. Well sp4rkl3bunn3y has a stock turbo running low boost and the little compressor surge he gets isn’t going to hurt much for now. He thinks the compressor surge sound he is hearing is a cool BOV noise. Higher boost and a real man sized turbo will make it undriveable.
Also on your RalliArts the way that the tranny is always up shifting and the ECU has more control over the throttle than you do I doubt you would hear much.
With the Mitsubishi drive by wire system there are a bunch more checks and balances with what air flow the air flow meter should be seeing at any given RPM and throttle position. I have seen so many EVO X guys fight SES lights and limp modes with various aftermarket BOVs. It is just another big mess to deal with. Even if you are recirculating the air back in, if the BOV is looser or tighter and allows different than expected air flow past the air flow meter, it is just misery.
Aug 24, 2009, 09:45 AM
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For me, performance is not the concern/focus for "upgrading" my BPV. It's got more to do with practicality and functionality. I'm no expert, but aren't the Evo X guys having their vehicles run into Limp Mode since the ECU is not detecting the expected PSI it just recycled, using BOV's?
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Aug 24, 2009, 09:52 AM
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you can tune the car to run either.
on the stock map running vta will cause a rich mixture and may result in the engine pulsing.
with an intake like i have, you can hear a stock one very loud.
on the stock map running vta will cause a rich mixture and may result in the engine pulsing.
with an intake like i have, you can hear a stock one very loud.
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atmopshere, atmosphere, backing, blow, boost, bov, noise, recirc, recirculate, recirculating, stock, turbo, valve, vented, venting
