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Boost pressure vs air flow vs power

Old 06-09-2014, 03:17 PM
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Originally Posted by Braineack View Post
then at 30psi, your turbo is compressing a lot more air, into the same space, than a t25 would. So at the same pressure, you have almost twice the available oxygen to burn and that right there should equal tons more torque.
At 30psi a turbo can flow a range of volume, in case of EFR6758, anywhere between 30 and 53lb/min


The actual volume it will flow depends on the restriction.
Attached Thumbnails Boost pressure vs air flow vs power-30psi-range.png  
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Old 06-09-2014, 03:30 PM
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What i'd like to know is if there's actually a pressure point in which turbos become unhappy to the point that they consider and/or carry out suicide?

And yes, i need this data for a practical application.
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Old 06-09-2014, 03:34 PM
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I believe that point would be when you are spinning the turbo too high, which is going to be a combination of boost and flow.
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Old 06-09-2014, 03:37 PM
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Originally Posted by Full_Tilt_Boogie View Post
I believe that point would be when you are spinning the turbo too high, which is going to be a combination of boost and flow.


Well... i'm talking more like... take a BP, then cut the flow in half. In Soviet's case, i'd be spinning his same turbo to the point that it would be making 60psi and still only 460whp. (Bullshit maths, but you get the idea)

Is this bad? Would it actually be spinning too high? Or would it spin the same, just with more pressure because shitty motor?

I just want to know how to know at what pressure amount a turbo will become asploded.
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Old 06-09-2014, 03:44 PM
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Look at the compressor map



You may need compound turbos to get that kind of boost is something like a GTX cant do it.
Although, the turbo may survive going spinning above where its supposed to. I know DSM guys will push their little stock turbos way off of the compressor map. They like to set turbo records.
Attached Thumbnails Boost pressure vs air flow vs power-pjqvwh3.png  
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Old 06-09-2014, 03:47 PM
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But what makes it asplode, exactly? Would pressure alone do it?

I just need a turbo that will handle 60psi or so. Nothing crazy.
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Old 06-09-2014, 03:49 PM
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Turbo speed. Thats what those thick lines are with the numbers at the far right end.

If you take a 2560 beyond 143405 rpm, Garrett says it will die.
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Old 06-09-2014, 03:52 PM
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Nooooooooo . Damn backspace killed my description. I never use backspace to go back on my browser. I hate whoever invented that.

So anyway.. since I wrote a pretty technical section on this bare with me as i use the wrong words like bigger and smaller and whatever to describe turbos and things.

Basically the gist is. Smaller turbos spool quicker right? When they spool quicker it causes more heat. If gas is held at a constant pressure then it will expand to fill a larger volume. Since a smaller turbo will spool quicker it will constantly be applying more pressure to the molecules. Larger turbo will have more dense air.

Think about someone boosting in Colorado or in Florida. Which of the two states gets more power out of the same amount of boosties?
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Old 06-09-2014, 03:53 PM
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I understand speed, but speed doesn't have a direct relationship with pressure by itself without bringing a motor (restriction) into play.

If the 2560 is on a big block, it might only make 5psi before it hits 143406rpm and dies. If it's on an F2T, it might do almost 30psi before it hits 143406rpm and dies.

If the motor is shitty enough, you could go off the pressure end of the chart while staying in the "safe" zone in terms of RPM. Is this still bad, then? (And yes, i realize that we'd likely be walking on the nasty side of the surge line.)
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Old 06-09-2014, 03:55 PM
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Following on Soviet's map post:

It's not what a turbo can do, but what is the operating point. The question is, at the flow required at a given engine RPM and torque, will the large and small turbo end up operating at about the same pressure and flow. I think they will, less a little for efficiency, and a little for IC and charge piping. The latter variables go away if we look at MAP only.

Comparing (2) maps.
2554 @ 25 lbs/min and 2.0 P/R 69% efficiency
2871 @ 25 lbs/min and 2.0 P/R 75% efficiency.

So the 2871 is 75/69 = 9% more efficient so it has that much advantage on the compressor side. This does assume equal pressure drops in the IC and other intake areas.
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Old 06-09-2014, 03:56 PM
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Originally Posted by concealer404 View Post
I understand speed, but speed doesn't have a direct relationship with pressure by itself without bringing a motor (restriction) into play.

If the 2560 is on a big block, it might only make 5psi before it hits 143406rpm and dies. If it's on an F2T, it might do almost 30psi before it hits 143406rpm and dies.

If the motor is shitty enough, you could go off the pressure end of the chart while staying in the "safe" zone in terms of RPM. Is this still bad, then? (And yes, i realize that we'd likely be walking on the nasty side of the surge line.)
Err i re-read that. I don't think it would matter actually. If the car can't flow enough to over spool then it just gets hot and runs poorly... right?
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Old 06-09-2014, 04:00 PM
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Originally Posted by krissetsfire View Post
I'm guessing you'd just twist the **** out of the shaft and it would break?


That sounds awesome.

"Dear BW,

I'm writing to you to let you know that i've found a new and interesting way for your turbos to fail. I've been using an EFR with the turbo RPM logged so i know that it was not the RPMs that caused this particular example to fail.

I've attached a log showing what happens when you remove the wastegate from one of your EFRs and weld chains around your motor to keep the head attached to the block.

Yours Truly,

The Swanky One"
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Old 06-09-2014, 04:02 PM
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I edited it. I don't think It would get to that point. Since it can't flow you'd just end up with really hot exhaust gasses getting trapped and maybe some det? I don't think it's anything any of us will ever run into. Would be a humorous conversation though.
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Old 06-09-2014, 04:06 PM
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Originally Posted by krissetsfire View Post
I edited it. I don't think It would get to that point. Since it can't flow you'd just end up with really hot exhaust gasses getting trapped and maybe some det? I don't think it's anything any of us will ever run into. Would be a humorous conversation though.
I'm not sure. All i know is that i've run a Toyota CT26 to 25psi+, and this turbo is known to be pretty much put to death at 15psi eventually on the motor it came on originally. IATs were still well within "good" range.

Given the power goals i'm looking at and how little this motor flows (double digits on the bench awwwwwwww yiss) pressure may very well be something i need to look at, since the acceptable answer isn't "oversize the **** out of your turbo."
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Old 06-09-2014, 04:10 PM
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I am in no way a turbo engineer but I'd imagine that the factors that determine the life of the wheel would be things like lubrication and heat. If it can't be cooled properly it's most likely going to suffer some heat failure and warp or whatever... causing some sort of eventual or catastrophic failure.
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Old 06-09-2014, 04:15 PM
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I'm glad that this thread makes sense to some people. I'm not crazy, I guess.

My turbine wheel sheared off the shaft while mostly intact, then rattled in the downpipe. The force was not enough to go through the downpipe, unlike in some cases



Attached Thumbnails Boost pressure vs air flow vs power-10342395_720717917984979_5062727560167316481_n.jpg   Boost pressure vs air flow vs power-10306320_720725464650891_43740133116513653_n.jpg  
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Old 06-09-2014, 04:21 PM
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That's kind of awesome. What were the circumstances?

Not awesome from costing $$$ standpoint but intriguing.
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Old 06-09-2014, 04:35 PM
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Wow, I thought your turbine wheel failures were on Borg turbos. Did you have failures on Garretts and EFR's?
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Old 06-09-2014, 04:37 PM
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Actually... it looks like once you get into manly turbos, my question becomes a non-issue, since the pressure ratio scale goes square into "much testosterone" realm anyways.

Attached Thumbnails Boost pressure vs air flow vs power-s300-66-compressor-map.jpg  
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Old 06-09-2014, 04:43 PM
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Originally Posted by krissetsfire View Post
That's kind of awesome. What were the circumstances?

Not awesome from costing $$$ standpoint but intriguing.
thats not mine, thats a diesel drift mercedes wagon from finland
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