Why can't my boost taper like normal?
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Joined: Aug 2012
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From: jungle terrain, Malaysia
Why can't my boost taper like normal?
Hi newbie here, please bare with me.
As the title above, it may sound desirable but my 8 is completely stock. It used to peak at around 1.4bar (20psi) and tailing off to 1.1bar (16psi). Now it's PEAKING AND HOLDING at 1.4bar. Bit worried about long term effect on turbo. Anyone in the know?, curious to know what it is...
Great site!
As the title above, it may sound desirable but my 8 is completely stock. It used to peak at around 1.4bar (20psi) and tailing off to 1.1bar (16psi). Now it's PEAKING AND HOLDING at 1.4bar. Bit worried about long term effect on turbo. Anyone in the know?, curious to know what it is...
Great site!
What year and model of Evo is your VIII? What octane of pump gasoline do you run in your car? Is your car equipped with a catalytic convertor? How many miles/kilometers are there on the odometer? Do you have a factory boost gauge?
Last edited by sparky; Aug 27, 2012 at 06:59 PM.
So, do you think that the decat could have contributed to eliminating the boost taper, without any apparent increase in the boost pressure reading?....Of course it can. Here's why:
It seems funny but turbocharged cars are very sensitive beasts. Something as seemingly insignificant as removing the cat, for example, or even replacing a dirty air filter element with a new, and thus, better flowing, clean one, can have a significant impact on air flow into the turbocharger in the case of the filter example, or exhaust gas flow exiting out of the turbocharger(catalytic convertor removal).
When you change the air flow in or exhaust gas flow out, you in effect change the dynamic, by altering the pressure differential. This in turn spools the compressor wheel faster producing higher levels of boost at lower turbocharger shaft rotational velocity.....and yadayadayada.....
In your specific case, by removing the cat, you have changed turbocharger's efficiency. This improvement in efficiency did not result in a noticeable increase in a peak boost level, because your peak boost level and the rate of increase is controlled by the factory ECU/BCS/WGA loop.
On the other hand, if your car had been fitted with a manual boost controller(no ECU intervention)then you would have noted an increase in peak boost on your boost gauge. In which case you would have had to turn boost down via your controller knob.
In general, the 5 PSI decrease in boost taper(i.e., exhaust backpressure) should translate into a near equal increase in peak boost level( Actually, the rule of thumb for a stock car is that 2# of exhaust pressure produces roughly 1# of boost pressure. Note: this ratio is approximate depending on other variables). If your car had been equipped with a manual boost controller you would have had to adjust boost level downward with the knob.
Conversely, in your case, boost being controlled via ECU, you noticed the decrease in taper, but the "hidden hand" of the factory boost control circuit "automatically" reduced peak boost level to the factory set 20# limit via the BCS(boost control solenoid).
When you removed the cat you in effect reduced exhaust gas backpressure. This means that overall exhaust pressure throughout the turbine housing is reduced. Flow through the turbine is improved. Why? Because you have altered the pressure differential between the turbine inlet and the turbine exit. The back pressure reduction also means individually better exhaust flows out separately though the turbine exducer and concomitantly out through the wastegate bypass port passage(s).
Little did you realize that by removing your cat you effectively changed the pressure differential across your stock 16G turbocharger (That is the pressure differential between turbine/compressor). More specifically, you also altered the pressure differential across the turbine and out through the exducer and simultaneously the wastegate bypass port and also eliminated the boost taper and finally impacted the way in which the factory boost control circuit "sees" and controls boost.
Your ECU could probably benefit from a reflash. At least, it might be wise to install a digital air fuel ratio gauge with logging capability as a monitoring device.
P.S. In Malaysia, the giant Flying Fox bat(an herbivore) is an indigenous species of mammal. You wouldn't happen to have one as a pet at home, by any chance would you? If so, I think that Curt Brown might be interested in one of those critters. He happens to have a soft spot for funky jungle beasts, such as Capabari and Tapirs.
It seems funny but turbocharged cars are very sensitive beasts. Something as seemingly insignificant as removing the cat, for example, or even replacing a dirty air filter element with a new, and thus, better flowing, clean one, can have a significant impact on air flow into the turbocharger in the case of the filter example, or exhaust gas flow exiting out of the turbocharger(catalytic convertor removal).
When you change the air flow in or exhaust gas flow out, you in effect change the dynamic, by altering the pressure differential. This in turn spools the compressor wheel faster producing higher levels of boost at lower turbocharger shaft rotational velocity.....and yadayadayada.....
In your specific case, by removing the cat, you have changed turbocharger's efficiency. This improvement in efficiency did not result in a noticeable increase in a peak boost level, because your peak boost level and the rate of increase is controlled by the factory ECU/BCS/WGA loop.
On the other hand, if your car had been fitted with a manual boost controller(no ECU intervention)then you would have noted an increase in peak boost on your boost gauge. In which case you would have had to turn boost down via your controller knob.
In general, the 5 PSI decrease in boost taper(i.e., exhaust backpressure) should translate into a near equal increase in peak boost level( Actually, the rule of thumb for a stock car is that 2# of exhaust pressure produces roughly 1# of boost pressure. Note: this ratio is approximate depending on other variables). If your car had been equipped with a manual boost controller you would have had to adjust boost level downward with the knob.
Conversely, in your case, boost being controlled via ECU, you noticed the decrease in taper, but the "hidden hand" of the factory boost control circuit "automatically" reduced peak boost level to the factory set 20# limit via the BCS(boost control solenoid).
When you removed the cat you in effect reduced exhaust gas backpressure. This means that overall exhaust pressure throughout the turbine housing is reduced. Flow through the turbine is improved. Why? Because you have altered the pressure differential between the turbine inlet and the turbine exit. The back pressure reduction also means individually better exhaust flows out separately though the turbine exducer and concomitantly out through the wastegate bypass port passage(s).
Little did you realize that by removing your cat you effectively changed the pressure differential across your stock 16G turbocharger (That is the pressure differential between turbine/compressor). More specifically, you also altered the pressure differential across the turbine and out through the exducer and simultaneously the wastegate bypass port and also eliminated the boost taper and finally impacted the way in which the factory boost control circuit "sees" and controls boost.
Your ECU could probably benefit from a reflash. At least, it might be wise to install a digital air fuel ratio gauge with logging capability as a monitoring device.
P.S. In Malaysia, the giant Flying Fox bat(an herbivore) is an indigenous species of mammal. You wouldn't happen to have one as a pet at home, by any chance would you? If so, I think that Curt Brown might be interested in one of those critters. He happens to have a soft spot for funky jungle beasts, such as Capabari and Tapirs.
Last edited by sparky; Aug 28, 2012 at 09:34 AM.
So, do you think that the decat could have contributed to eliminating the boost taper, without any apparent increase in the boost pressure reading?....Of course it can. Here's why:
It seems funny but turbocharged cars are very sensitive beasts. Something as seemingly insignificant as removing the cat, for example, or even replacing a dirty air filter element with a new, and thus, better flowing, clean one, can have a significant impact on air flow into the turbocharger in the case of the filter example, or exhaust gas flow exiting out of the turbocharger(catalytic convertor removal).
When you change the air flow in or exhaust gas flow out, you in effect change the dynamic, by altering the pressure differential. This in turn spools the compressor wheel faster producing higher levels of boost at lower turbocharger shaft rotational velocity.....and yadayadayada.....
In your specific case, by removing the cat, you have changed turbocharger's efficiency. This improvement in efficiency did not result in a noticeable increase in a peak boost level, because your peak boost level and the rate of increase is controlled by the factory ECU/BCS/WGA loop.
On the other hand, if your car had been fitted with a manual boost controller(no ECU intervention)then you would have noted an increase in peak boost on your boost gauge. In which case you would have had to turn boost down via your controller knob.
In general, the 5 PSI decrease in boost taper(i.e., exhaust backpressure) should translate into a near equal increase in peak boost level( Actually, the rule of thumb for a stock car is that 2# of exhaust pressure produces roughly 1# of boost pressure. Note: this ratio is approximate depending on other variables). If your car had been equipped with a manual boost controller you would have had to adjust boost level downward with the knob.
Conversely, in your case, boost being controlled via ECU, you noticed the decrease in taper, but the "hidden hand" of the factory boost control circuit "automatically" reduced peak boost level to the factory set 20# limit via the BCS(boost control solenoid).
When you removed the cat you in effect reduced exhaust gas backpressure. This means that overall exhaust pressure throughout the turbine housing is reduced. Flow through the turbine is improved. Why? Because you have altered the pressure differential between the turbine inlet and the turbine exit. The back pressure reduction also means individually better exhaust flows out separately though the turbine exducer and concomitantly out through the wastegate bypass port passage(s).
Little did you realize that by removing your cat you effectively changed the pressure differential across your stock 16G turbocharger (That is the pressure differential between turbine/compressor). More specifically, you also altered the pressure differential across the turbine and out through the exducer and simultaneously the wastegate bypass port and also eliminated the boost taper and finally impacted the way in which the factory boost control circuit "sees" and controls boost.
Your ECU could probably benefit from a reflash. At least, it might be wise to install a digital air fuel ratio gauge with logging capability as a monitoring device.
P.S. In Malaysia, the giant Flying Fox bat(an herbivore) is an indigenous species of mammal. You wouldn't happen to have one as a pet at home, by any chance would you? If so, I think that Curt Brown might be interested in one of those critters. He happens to have a soft spot for funky jungle beasts, such as Capabari and Tapirs.
It seems funny but turbocharged cars are very sensitive beasts. Something as seemingly insignificant as removing the cat, for example, or even replacing a dirty air filter element with a new, and thus, better flowing, clean one, can have a significant impact on air flow into the turbocharger in the case of the filter example, or exhaust gas flow exiting out of the turbocharger(catalytic convertor removal).
When you change the air flow in or exhaust gas flow out, you in effect change the dynamic, by altering the pressure differential. This in turn spools the compressor wheel faster producing higher levels of boost at lower turbocharger shaft rotational velocity.....and yadayadayada.....
In your specific case, by removing the cat, you have changed turbocharger's efficiency. This improvement in efficiency did not result in a noticeable increase in a peak boost level, because your peak boost level and the rate of increase is controlled by the factory ECU/BCS/WGA loop.
On the other hand, if your car had been fitted with a manual boost controller(no ECU intervention)then you would have noted an increase in peak boost on your boost gauge. In which case you would have had to turn boost down via your controller knob.
In general, the 5 PSI decrease in boost taper(i.e., exhaust backpressure) should translate into a near equal increase in peak boost level( Actually, the rule of thumb for a stock car is that 2# of exhaust pressure produces roughly 1# of boost pressure. Note: this ratio is approximate depending on other variables). If your car had been equipped with a manual boost controller you would have had to adjust boost level downward with the knob.
Conversely, in your case, boost being controlled via ECU, you noticed the decrease in taper, but the "hidden hand" of the factory boost control circuit "automatically" reduced peak boost level to the factory set 20# limit via the BCS(boost control solenoid).
When you removed the cat you in effect reduced exhaust gas backpressure. This means that overall exhaust pressure throughout the turbine housing is reduced. Flow through the turbine is improved. Why? Because you have altered the pressure differential between the turbine inlet and the turbine exit. The back pressure reduction also means individually better exhaust flows out separately though the turbine exducer and concomitantly out through the wastegate bypass port passage(s).
Little did you realize that by removing your cat you effectively changed the pressure differential across your stock 16G turbocharger (That is the pressure differential between turbine/compressor). More specifically, you also altered the pressure differential across the turbine and out through the exducer and simultaneously the wastegate bypass port and also eliminated the boost taper and finally impacted the way in which the factory boost control circuit "sees" and controls boost.
Your ECU could probably benefit from a reflash. At least, it might be wise to install a digital air fuel ratio gauge with logging capability as a monitoring device.
P.S. In Malaysia, the giant Flying Fox bat(an herbivore) is an indigenous species of mammal. You wouldn't happen to have one as a pet at home, by any chance would you? If so, I think that Curt Brown might be interested in one of those critters. He happens to have a soft spot for funky jungle beasts, such as Capabari and Tapirs.
Yeah where the hell is my Capybara!!!!
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Thread Starter
Newbie
Joined: Aug 2012
Posts: 21
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From: jungle terrain, Malaysia
Thank you for the explaination sparky! Sounds very logical to me. But the thing is the decat has been there for quite sometime, almost 2 years IRRC and the tapering issue only popped up just recently about 2 weeks ago. Bit baffled...
P.S sparky, CBRE,
Yes you're right, the giant Flying Fox bat and other unique species of bats are local mammals, but no I don't have them i'm afraid. I think I would get fined if I were caught possesing them. You may want to pay them a visit in the next couple of months because I've heard it's their mating season and you might be able to observe their behaviour! You've been watching Animal Planets sparky?
P.S sparky, CBRE,
Yes you're right, the giant Flying Fox bat and other unique species of bats are local mammals, but no I don't have them i'm afraid. I think I would get fined if I were caught possesing them. You may want to pay them a visit in the next couple of months because I've heard it's their mating season and you might be able to observe their behaviour! You've been watching Animal Planets sparky?
Last edited by sparky; Aug 29, 2012 at 05:13 AM.
You do realize that a non-tapering turbo setup is desirable,right? Whereas before you were experiencing a boost taper issue, now, you have no boost taper issue. Whereas before, you did have a problem, now you don't.
Last edited by sparky; Aug 29, 2012 at 05:21 AM.
Of course, you seek a rational explanation as to why your turbo stopped tapering. That is the mystery.
First of all and as a practical matter you should perform a boost leak test on your vehicle. There are several how-to threads containing explanations on this forum. There you will find the simple instructions on how to build a basic tester and perform the test itself.
We can conjecture all day long and perhaps we'll never hit on the cause of the taper. The boost leak test is the logical first step to discovering the cause of the change in your boost control issue.
I would advise that you do a boost leak test and that you also install a wideband logging device. This way we can study comparative boost logs.
P.S. Watch out for those huge bats during mating season.
First of all and as a practical matter you should perform a boost leak test on your vehicle. There are several how-to threads containing explanations on this forum. There you will find the simple instructions on how to build a basic tester and perform the test itself.
We can conjecture all day long and perhaps we'll never hit on the cause of the taper. The boost leak test is the logical first step to discovering the cause of the change in your boost control issue.
I would advise that you do a boost leak test and that you also install a wideband logging device. This way we can study comparative boost logs.
P.S. Watch out for those huge bats during mating season.
Last edited by sparky; Aug 29, 2012 at 06:13 AM.
Thread Starter
Newbie
Joined: Aug 2012
Posts: 21
Likes: 0
From: jungle terrain, Malaysia
, but will it shorten the turbo lifespan do you think?
Thread Starter
Newbie
Joined: Aug 2012
Posts: 21
Likes: 0
From: jungle terrain, Malaysia
Of course, you seek a rational explanation as to why your turbo stopped tapering. That is the mystery.
First of all and as a practical matter you should perform a boost leak test on your vehicle. There are several how-to threads containing explanations on this forum. There you will find the simple instructions on how to build a basic tester and perform the test itself.
We can conjecture all day long and perhaps we'll never hit on the cause of the taper. The boost leak test is the logical first step to discovering the cause of the change in your boost control issue.
I would advise that you do a boost leak test and that you also install a wideband logging device. This way we can study comparative boost logs.
P.S. Watch out for those huge bats during mating season.
First of all and as a practical matter you should perform a boost leak test on your vehicle. There are several how-to threads containing explanations on this forum. There you will find the simple instructions on how to build a basic tester and perform the test itself.
We can conjecture all day long and perhaps we'll never hit on the cause of the taper. The boost leak test is the logical first step to discovering the cause of the change in your boost control issue.
I would advise that you do a boost leak test and that you also install a wideband logging device. This way we can study comparative boost logs.
P.S. Watch out for those huge bats during mating season.
I have AEM wideband ready to be installed. Still waiting for the 3 inch downpipe to arrive. (I should've bought the AEM Failsafe gauge tho...it has a boost logging capability if I'm not mistaken)
Thread Starter
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Joined: Aug 2012
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From: jungle terrain, Malaysia