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Old 12-07-2017, 05:59 AM   #1
MonkeyMD
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It's not turbo lag

So all this time I've been using the term turbo lag to refer to boost threshold. Hmmm. Learn something new everyday.

https://jalopnik.com/boost-threshold...ing-1821055465

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Old 12-07-2017, 06:20 AM   #2
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I always new they were different, but I never had a name for boost threshold so I ended up just referring to it as turbo lag as well. I always thought the term lag didn't really define how the engine isn't capable of spinning up the turbo at low rpm very well.
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Old 12-07-2017, 07:03 AM   #3
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Yeah that's a few minutes I'll never get back. Boost threshold isn't mistaken for turbo lag...just nobody talks about it because you'd never be WOT or expecting boost in that situation.

Yeah no, ah!t you're not gonna make boost in 6th gear at 1,100 Rpm...
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Old 12-07-2017, 09:06 AM   #4
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I think Jason has the problem that a lot of experts in their field have, where they view most things regardless of complexity as super obvious and basic, and have a hard time differentiating what the average person will find obvious or not. Half the time I watch his videos and think that everyone and their mother's pets could figure that out, but then the other half of the time I come out of it having actually learned something that could change my perspective on how a thing works.
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Old 12-07-2017, 12:49 PM   #5
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Another good topic is pressure vs flow.

Boost pressure is the most pointless and irrelevant number that people love to talk about.

Quote:
Originally Posted by Gti jake View Post
Boost threshold isn't mistaken for turbo lag...
It's constantly mistaken for turbo lag.

Not everyone has a stock turbo, either. Do you hear people describe big turbo cars as laggy, or having a high boost threshold?
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Old 12-07-2017, 11:42 PM   #6
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He didn't address throttle angle during these events.
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(Mostly) Posted by Josh/AWE. Flapper valves are open at idle, close after 1100 RPM during part throttle. Full throttle 1st-4th gear the valves open until throttle let off. 4th gear, 1500 RPM to full throttle closed, closed until 3500 RPM, then open until lift off throttle.
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Old 12-08-2017, 12:15 AM   #7
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This statement is believable "Boost Threshold And Turbo Lag Aren't The Same Thing"

This statement is not "Turbo lag is the additional time delay above boost threshold, when the engine’s throttle valve is open and the turbocharger needs to accelerate to deliver positive pressure to the engine."

Think about this statement "Basically, boost threshold is the engine speed at which you have enough exhaust gas flow in order to create boost."

If the engine is at the boost threshold, the point where it can create boost because there's enough exhaust gas flowing through the turbine, then there is no lag, because the turbo is already in a condition where it can produce boost.

Plus the definition of turbo lag is inadequate, it cannot be measured. It sounds like it is supposed to start at boost threshold (time delay), but when does it end?
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Old 12-08-2017, 08:38 AM   #8
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Nobody's ever been driving along in 6th gear with their buddies in the car and said "alright I'm gonna do a pull" and just floor it without down shifting...that's the kinda situation where someone would incorrectly say "man this turbo is laggy"

Nope...you'd down shift to second or third to bring the rpm up (now you're above boost threshold) and lay into it. If someone then said man this turbo is laggy they'd be exactly correct.

I also don't get the "not everyone has a stock turbo" comment above either. Not only would the above still apply exactly the same, it would be even less likely that you wouldn't brake boost and skip Boost Threshold and lag (for the most part) all together.
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Old 12-08-2017, 09:31 AM   #9
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Quote:
Originally Posted by Gti jake View Post
Nobody's ever been driving along in 6th gear with their buddies in the car and said "alright I'm gonna do a pull" and just floor it without down shifting...that's the kinda situation where someone would incorrectly say "man this turbo is laggy"

Nope...you'd down shift to second or third to bring the rpm up (now you're above boost threshold) and lay into it. If someone then said man this turbo is laggy they'd be exactly correct.

I also don't get the "not everyone has a stock turbo" comment above either. Not only would the above still apply exactly the same, it would be even less likely that you wouldn't brake boost and skip Boost Threshold and lag (for the most part) all together.
I do however experience some lag when I wanna do pull from 50 mph in 3 gear. My rpm are around 3700 and it takes a solid second for it to built up boost. Would brake boosting be beneficial sense the stock is20 still relativley small?
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Old 12-08-2017, 11:52 AM   #10
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Brake boosting works really well, you can leave from 30ish mph in 2nd or 50ish in 3rd at almost full boost.
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Old 12-09-2017, 05:34 PM   #11
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Video doesn't address load either. If you go by the video alone you would think our threshold is between idle and 1800 RPM since we can make max torque at 1800 RPM, and there wouldn't be any lag.
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(Mostly) Posted by Josh/AWE. Flapper valves are open at idle, close after 1100 RPM during part throttle. Full throttle 1st-4th gear the valves open until throttle let off. 4th gear, 1500 RPM to full throttle closed, closed until 3500 RPM, then open until lift off throttle.
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