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Old 06-09-2014, 05:44 PM   #41
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Originally Posted by concealer404 View Post
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.
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Old 06-09-2014, 05:46 PM   #42
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My boost gauge. True story.

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Old 06-09-2014, 05:46 PM   #43
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BLOW'ER
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Old 06-09-2014, 05:47 PM   #44
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Pretty sure i got it from a parted out M45 car.
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Old 06-09-2014, 05:53 PM   #45
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Originally Posted by concealer404 View Post
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.
WHAT DOES THE ******* COMPRESSOR MAP SAY? It has the turbo speed lines on it, go too much past the turbo's redline in any direction and kiss your shaft and/or bearings goodbye.
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Old 06-09-2014, 06:13 PM   #46
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WHAT DOES THE ******* COMPRESSOR MAP SAY? It has the turbo speed lines on it, go too much past the turbo's redline in any direction and kiss your shaft and/or bearings goodbye.

Just to clarify... you're saying that it doesn't matter if the turbo is pushing against a brick wall, it's going to take that S366 exactly 117119rpm to make 55psi?

And yes, i know that PSI doesn't matter, i know the bigger picture is RPM. I'm just wondering if there IS an actual pressure limit to turbos. That's all.
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Old 06-09-2014, 06:14 PM   #47
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Just to clarify... you're saying that it doesn't matter if the turbo is pushing against a brick wall, it's going to take that S366 exactly 117119rpm to make 55psi?

And yes, i know that PSI doesn't matter, i know the bigger picture is RPM. I'm just wondering if there IS an actual pressure limit to turbos. That's all.
If its pushing against a brick wall you're going to have compressor surge and destroy the thrust bearing faster than over reving it.
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Old 06-09-2014, 06:17 PM   #48
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Originally Posted by Leafy View Post
If its pushing against a brick wall you're going to have compressor surge and destroy the thrust bearing faster than over reving it.

These are the sort of answers i'm looking for.

So basically: Going to the left of the entire map = surge = hilarious noises = turbo sadness.
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Old 06-09-2014, 06:19 PM   #49
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I'm glad that this thread makes sense to some people. I'm not crazy, I guess.
Those few are just crazy like you, that's all.
You're wrong, very very wrong.
Either that or I'm completely misunderstanding you or you're explaining it wrong.

Among other reasons, I'll give you a practical one from my experience: I remove a td04 from a subaru, and bolt in a vf39. Both turbos have the same inlet and outlet size on both compressor and hotside. The 39 just has slightly bigger wheels. I run 10psi on both. Literally all other variables are identical. With the 39 car picks up at least 30-40hp

Please don't go full retard and go down the path of that one moron n00b trying to explain to us that you can't "overfill the cylinders", cause it seriously looks like you're headed that way.

By your logic I can remove a gt2554 from a miata, bolt up a 3076r and as long as I don't exceed 10psi on both, they will both make 180hp.
That's not even close to true
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Old 06-09-2014, 06:21 PM   #50
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Originally Posted by concealer404 View Post
These are the sort of answers i'm looking for.

So basically: Going to the left of the entire map = surge = hilarious noises = turbo sadness.
Yes. And going off the top of the map without going off to either side is normally really hard to do, because thermodynamics and time and ****. But way over speeding it by going up and right isnt too hard, but there's no power there and most IWGs wont let you get over there anyways so again, it doesnt happen often. Because once you're over there EMP goes through the mother ******* roof.
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Old 06-09-2014, 06:22 PM   #51
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I can't really Fathom any motor having a pressure ratio of say 2ish and flowing less than 5 lbs/min... You would have to be a complete retard to pair a turbo that badly. I'm pretty sure like 99% of turbo failure from going outside that range is not from being on the left side.
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Old 06-09-2014, 06:22 PM   #52
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Originally Posted by Leafy View Post
WHAT DOES THE ******* COMPRESSOR MAP SAY? It has the turbo speed lines on it, go too much past the turbo's redline in any direction and kiss your shaft and/or bearings goodbye.
Haha, my thoughts exactly. I would like to add that I'm not sure you can fail a turbo by boost pressure alone. Flow wise, the turbo would end up being destroyed by other things first. Keep in mind, taking most compressors into the 60psi range(Pressure Ratio > 5) will either be far into the turbo killing surge region, or wayyy beyond the designed maximum turbo speed. Either way, it's not going to be pretty.

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Originally Posted by krissetsfire View Post
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.
I don't mean to come across as rude, but this is nowhere close to reality.

The small turbo in and of itself will not cause more heat because of better spool. In theory, a small turbo could spool very quickly into its highest efficiency island, and therefore produce less heat.

Heat comes from inefficiency in the compressor. If a compressor was 100% efficient, all of the energy would go to the compression of the gas, and no energy would be lost due to heat.

I'm also confused at what you are referring to when you are talking about the smaller turbo constantly applying more force to the molecules. Your mixing and matching terms and principles from fluid dynamics, thermodynamics, and chemistry. Not in a good way, either.
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Old 06-09-2014, 06:24 PM   #53
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Originally Posted by Leafy View Post
Yes. And going off the top of the map without going off to either side is normally really hard to do, because thermodynamics and time and ****. But way over speeding it by going up and right isnt too hard, but there's no power there and most IWGs wont let you get over there anyways so again, it doesnt happen often. Because once you're over there EMP goes through the mother ******* roof.
beat me to it. well said.
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Old 06-09-2014, 06:30 PM   #54
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Originally Posted by krissetsfire View Post
I can't really Fathom any motor having a pressure ratio of say 2ish and flowing less than 5 lbs/min... You would have to be a complete retard to pair a turbo that badly. I'm pretty sure like 99% of turbo failure from going outside that range is not from being on the left side.
The best video of turbo destroying spool up surge you can find on the internet is an RB26 with a GT35R on it, I think they're doing terrible things to it with a mustang dyno though to make it make the sound. I've also heard of people pushing 16gs on 2.5 subarus across the surge line on cold days.
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Old 06-09-2014, 06:45 PM   #55
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Quote:
Originally Posted by krissetsfire View Post
I can't really Fathom any motor having a pressure ratio of say 2ish and flowing less than 5 lbs/min... You would have to be a complete retard to pair a turbo that badly. I'm pretty sure like 99% of turbo failure from going outside that range is not from being on the left side.

It's rhetorical when we're talking extremes like that. And it would surge first.
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Old 06-09-2014, 07:11 PM   #56
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Originally Posted by soviet View Post

Boost pressure is a function of air flow vs restriction of the engine's intake path. The more restriction, the higher the pressure differential (boost pressure) needs to be to overcome the restriction.[/b]
In most cases boost pressure is a function of the exhaust path and not the intake path.
In regular turbo set ups the significant flow restriction in the system will be the hotside wheel. The exhaust manifold will be see about the same pressure as the throttle body and the exhaust gases are pumped out of the engine by the crank. If a larger hotside wheel is fitted then it will allow more flow to pass through it for a given boost level.

If you have a huge turbo or a really restrictive intake then boost pressure becomes a function of the engines intake path.
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Old 06-09-2014, 07:51 PM   #57
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Originally Posted by Dustin1824 View Post
I don't mean to come across as rude, but this is nowhere close to reality.

The small turbo in and of itself will not cause more heat because of better spool. In theory, a small turbo could spool very quickly into its highest efficiency island, and therefore produce less heat.

Heat comes from inefficiency in the compressor. If a compressor was 100% efficient, all of the energy would go to the compression of the gas, and no energy would be lost due to heat.

I'm also confused at what you are referring to when you are talking about the smaller turbo constantly applying more force to the molecules. Your mixing and matching terms and principles from fluid dynamics, thermodynamics, and chemistry. Not in a good way, either.
I did a bad job of breaking it down and I jumped all over the place.

Really in frustration from me losing my bit i typed about about turbo efficiency and temperature.

If you take your in temp at say 100degree cause you live in southern arizona and apply some vacuum lets say -1 then some discharge pressure at say 15 and your turbo is 75% efficient you will end up with....

~268 degree discharge temp. Lets say your motor is PERFECTLY paired and you have a sweet spot that your turbo is 100% efficient it would be running at ~226 with the same environment. That's a 50degree difference in temp. That's a HUGE difference in air density.

So as you can see the efficiency of the turbo plays a large roll in the intake temps. Now the amount of air the motor can flow also plays a nice roll in here. Based on your restrictions and motor size. The amount of air you can flow is the volumetric efficiency.

Because turbo compressor maps are simply the compressor maps they don't take into account the turbine side. Having the right turbine can change the efficiency of the compressor as well.

Edit: Anyway the idea is it isn't always about psi. Based on many variables you could get more power with a "larger" setup (same psi as "smaller" turbo).

Last edited by krissetsfire; 06-09-2014 at 08:29 PM.
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Old 06-09-2014, 08:03 PM   #58
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Originally Posted by krissetsfire View Post
I did a bad job of breaking it down and I jumped all over the place.

Really in frustration from me losing my bit i typed about about turbo efficiency and temperature.

If you take your in temp at say 100degree cause you live in southern arizona and apply some vacuum lets say -1 then some discharge pressure at say 15 and your turbo is 75% efficient you will end up with....

~268 degree discharge temp. Lets say your motor is PERFECTLY paired and you have a sweet spot that your turbo is 100% efficient it would be running at ~226 with the same environment. That's a 50degree difference in temp. That's a HUGE difference in air density.

So as you can see the efficiency of the turbo plays a large roll in the intake temps. Now the amount of air the motor can flow also plays a nice roll in here. Based on your restrictions and motor size. The amount of air you can flow is the volumetric efficiency.

Because turbo compressor maps are simply the compressor maps they don't take into account the turbine side. Having the right turbine can change the efficiency of the compressor as well.

Anyway the idea is it isn't always about psi. Based on many variables you could get more power with a "larger" setup.
Yep, I totally agree with what you said in this post. In general, you will probably make more power with the larger turbo, even if the boost is the same. I was just making sure that post was qualified. You guys reply so fast, my last post was probably unneeded due to what Leafy said.

Great discussion starter though. Soviet and 18psi you both have valid points, but your just looking at it from different perspectives.
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Old 06-09-2014, 08:38 PM   #59
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So I guess nobody really defined efficiency. What makes a turbo efficient? Anybody have a good definition or explanation on turbo efficiency calculation?
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Old 06-09-2014, 08:53 PM   #60
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Thread too long, didnt read.

Turbos pose a restriction on both the intake and exhaust side. Also bigger wheels move air easier.

End of story.

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