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Old 11-16-2016, 09:08 AM   #1
Mitchrod1
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Lightbulb Turbo Size matters for motor life???

Ok so last night i was in bed thinking about my build. I was thinking about turbos and the way they take our normal car and make it ....WOW fast. but then a question came to me...

this is example numbers to get my point and hopefully make sense of the question:

SO if i say use a PTE6262 at 24psi and get 500wph,would it be more SAFE to say use a PTE6666 at 19psi to get 500whp (all other factors are the same)..


My thought to this is that 19psi @ 500whp would be better for the motor then say 24psi @ 500whp, being less motor pressure, or am i thinking this wrong???
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Old 11-16-2016, 09:34 AM   #2
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so two completely different motors you mean?

how would you get 500hp from 19psi or 24psi?

Of course more boost is going to put more stress on the motor.
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Old 11-16-2016, 09:53 AM   #3
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Originally Posted by rtv900 View Post
so two completely different motors you mean?

how would you get 500hp from 19psi or 24psi?

Of course more boost is going to put more stress on the motor.
1. no same motor
2. small turbo vs bigger turbo (example pte 6262 vs pte 6666) the smaller turbo will need more pis to make the same power as the bigger turbo.

So that is why I ask is a bigger turbo safer for the motor at same power say 500hp being it takes less pis to get that power then a smaller turbo witch needs more psi to make that power?

example pte6262 smaller so 24psi to get 500hp vs bigger turbo pte6666 say 19psi gives you 500hp.. these numbers are off im sure but that is just the example so maybe people understand what im trying to say.
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Old 11-16-2016, 10:02 AM   #4
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Yes there is a difference between pressure and volume.

So if you could make 600 at 10 psi versus 600 at 30 psi the lower boost pressure setup will be less stress. However it's always a toss up between good spool characteristics and not working the turbo to death!
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Old 11-16-2016, 10:23 AM   #5
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Originally Posted by stretchedk7 View Post
Yes there is a difference between pressure and volume.

So if you could make 600 at 10 psi versus 600 at 30 psi the lower boost pressure setup will be less stress. However it's always a toss up between good spool characteristics and not working the turbo to death!
that is what i was thinking that lag would be more pron. but life of motor would be alot better with let pressure.

now lets say this too... just thought of it... say at 30 psi small turbo makes the 600hp and the big turbo at 30psi makes 700hp (same motor same everything) would life be the same or less on the setup with the bigger turbo at same psi with more power?????
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Old 11-16-2016, 10:38 AM   #6
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Your method of thinking is correct. A larger turbo is going to have a lower outlet temp for a given mass flow than a smaller turbo in general. This reduction in outlet temp allows you to move more air (by mass) for a given boost pressure.
The big kicker comes with the hot side as well. A larger turbo will also have a bigger hot side. This will translate into lower back pressure than a smaller turbo setup at an equivalent horsepower. the reduction in back pressure raises the VE of the motor and further allows it to make better power for a given boost pressure (raises BSFC).
The reduction in back pressure also will pay dividends in safety. The reduction in back pressure/ boost required for a given power output will make the motor less prone to knock.
The only downside to running a larger turbo for a given power level is the additional lag you will incur.
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Old 11-16-2016, 11:15 AM   #7
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Your method of thinking is correct. A larger turbo is going to have a lower outlet temp for a given mass flow than a smaller turbo in general. This reduction in outlet temp allows you to move more air (by mass) for a given boost pressure.
The big kicker comes with the hot side as well. A larger turbo will also have a bigger hot side. This will translate into lower back pressure than a smaller turbo setup at an equivalent horsepower. the reduction in back pressure raises the VE of the motor and further allows it to make better power for a given boost pressure (raises BSFC).
The reduction in back pressure also will pay dividends in safety. The reduction in back pressure/ boost required for a given power output will make the motor less prone to knock.
The only downside to running a larger turbo for a given power level is the additional lag you will incur.
awesome that is what i was thinking. so my build im doing for a DD i am using a pte6262 Jbearing would like to be around the 500whp mark. would it be a safer choice to go to a bigger turbo to get that same power with less PSI or will lag be to much and my power will be way high in the revs. Say i do go bigger turbo would say just going about 2 sizes up be the best way to go or would it not be worth it really? Again my end game goal is 500whp SAFELY with as smooth power delivery that i can get.
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Old 11-16-2016, 11:29 AM   #8
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Ideally, a safe by would be if you could make your goals at like 19-20 psi on 93 you'd be doing great or 23-25 psi on e85
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Old 11-16-2016, 11:32 AM   #9
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Safe bet**
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Old 11-16-2016, 11:42 AM   #10
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Quote:
Originally Posted by stretchedk7 View Post
Ideally, a safe by would be if you could make your goals at like 19-20 psi on 93 you'd be doing great or 23-25 psi on e85
I will be running 93. where i live 85 is not easy to get. what PTE turbo would get me around the 19-20 psi and get me the 500whp that im looking for?? now that we are talking about this its seeming my 6262 maybe just a little small. any thought?
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Old 11-16-2016, 11:43 AM   #11
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im running a fully built EJ20 closed deck.
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Old 11-16-2016, 12:09 PM   #12
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Quote:
Originally Posted by MartinSTi05 View Post
Your method of thinking is correct. A larger turbo is going to have a lower outlet temp for a given mass flow than a smaller turbo in general. This reduction in outlet temp allows you to move more air (by mass) for a given boost pressure.
I wouldn't make any decisions for your build based on this. This is horribly inaccurate information.
For one, a turbo is NOT a positive displacement compressor, which would be the only case where the above statement would even remotely apply.
A turbo builds pressure by nature of backpressure within a fixed volume, your intake, which I'm guessing will be the same regardless right? But even if not it still does not make a difference.
So the idea that 19psi from turbo A can make the same power as 24psi from turbo B is absolutely crazy. Your boost is in your intake manifold waiting under pressure until a valve opens to let it in a cylinder. That cylinder doesn't give a f-ing hoot whether you have turbo A or B, it cares what psi is waiting in there for it.

You need to make your decision about a bigger turbo or a smaller one based on the standard facts about turbo size and the pros and cons associated with it, all documented on this site.
DO NOT make your decision based on the theory quoted above. You'd consider the things like that if you were using a positive displacement supercharger and wanted to size for engine displacement and rpm range. Not a turbo which is nothing more than a fan that forces air into a fixed volume and pushes so hard it compresses it.
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Old 11-16-2016, 12:38 PM   #13
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your intake, which I'm guessing will be the same regardless right? But even if not it still does not make a difference.
So the idea that 19psi from turbo A can make the same power as 24psi from turbo B is absolutely crazy. Your boost is in your intake manifold waiting under pressure until a valve opens to let it in a cylinder. That cylinder doesn't give a f-ing hoot whether you have turbo A or B, it cares what psi is waiting in there for it.


I will be using the OEM JDM EJ205 intake. im not sure how the idea is crazy when say a OEM turbo at around 19-20PSI gets you no where close to 500whp, maybe close to the 300-350whp. when say a big pte 6266 at 19-20psi on the same motor is going to be way more power closer to the 500whp then said oem turbo big time. please tell me if im wrong. so that is why i am asking is a bigger turbo saver at less PSI to get said goal then a smaller turbo?? Pluse a big turbo at same PSI giving you more power what is safer?
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Old 11-16-2016, 01:31 PM   #14
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I'm just going to...
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Old 11-16-2016, 01:58 PM   #15
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Originally Posted by Mitchrod1 View Post
SO if i say use a PTE6262 at 24psi and get 500wph,would it be more SAFE to say use a PTE6666 at 19psi to get 500whp (all other factors are the same)..
Am I misunderstanding something about this^

Aren't you asking (and someone confirmed somehow) that 19 psi from one turbo will make the same power as 24 psi from another turbo. . . . .all other factors being the same.

And somehow one is 'safer' than another, yet they make the same power with significantly different boost levels???????

How does that work? Maybe KillerB can explain it rather than just attach an emoticon.
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Old 11-16-2016, 02:40 PM   #16
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It works because the larger turbo at lower psi is putting out cooler air, which has a higher density, so the mass flow rate can actually be the same. plus the colder charge would allow more power from more timing advance.
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Old 11-16-2016, 03:45 PM   #17
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It works because the larger turbo at lower psi is putting out cooler air, which has a higher density, so the mass flow rate can actually be the same. plus the colder charge would allow more power from more timing advance.
The air DOES NOT compress in the turbo dude, it is a FAN, that's all.
It compresses in the fixed volume that is the piping to the intake and the intake itself.
A turbo is not a compressor.
The temp will be affected by compression the same way at whatever level of compression it is taken to.
If that's 19 then it's 19 no matter what size fan is forcing it into your intake.
The bigger one will of course have a much higher top end capability, but it doesn't seem like that is the question at all for whatever reason.
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Old 11-16-2016, 11:28 PM   #18
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Your motor will feel looser when you go from a big turbo to a smaller turbo, like your fat friend returning your sweater, or a girl who's been with a bla... yeah
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Old 11-16-2016, 11:30 PM   #19
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Default Turbo Size matters for motor life???

Volume and pressure are not the same. I think that's basically what is being talked about with his post. 20 psi from a 49lb/min turbo is not the same amount of air as 20 psi from a 110 lb/min turbo.


Also it should be noted the bigger snail will create less heat generally as well as not fall off up top!
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Old 11-16-2016, 11:31 PM   #20
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Your motor will feel looser when you go from a big turbo to a smaller turbo, like your fat friend returning your sweater, or a girl who's been with a bla... yeah

LOL nice
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Old 11-17-2016, 12:07 AM   #21
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rtv900 is an engineer so don't argue with him because you will lose since he knows everything and built a hotdog with his own two hands.

edit: Maybe he said hotrod.
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Old 11-17-2016, 12:15 AM   #22
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rtv900 is an engineer so don't argue with him because you will lose since he knows everything and built a hotdog with his own two hands.

edit: Maybe he said hotrod.

Yeah I see that!!
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Old 11-17-2016, 06:30 AM   #23
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rtv900 is an engineer so don't argue with him because you will lose since he knows everything and built a hotdog with his own two hands.

edit: Maybe he said hotrod.
man if you're gonna trash talk you should really be sure you know what you are talking about.

So volume and pressure are not the same? Gee, thanks for clearing that one up Mr Newton. And what is your point? Don't tell me you are suggesting the bigger turbo is outputting more volume into the same space, at the same load level, but somehow that ends up as LESS pressure, but cooler. . blah blah where on earth are you going with that one?

I got news dude, the turbo is throttled. That is the thing connected to the pedal you actuate with your foot to meet intake demand. Nobody is debating whether a bigger turbo can supply more volume for higher demand level. Did you think it was a coincidence that the bigger the engine, the bigger the turbo?
You are pulling air from a plenum wise guy. 19 psi in a plenum IS 19 psi, the space has no idea how 19 psi got in there, it was pushed in, PERIOD. It does NOT matter how it was pushed in when we are talking about one fan vs another fan that is throttled to meet demand. You guys sound ridiculous trying to trash talk me by taking the position that 19 psi from one turbo is the same amount of air as 24 psi in THE SAME plenum from a different turbo. The plenum is what compresses it! Come on, how do you think it works?
I can't believe somebody is spending the money to build a motor custom and THIS is what he's going to base his choices on.

Funny our resident expert KillerB hasn't corrected me yet. You know why? He SELLS these things and they are a vendor, so he has to appease the group and not make waves by jumping in and saying sorry guys, he's completely right. I don't make money off the 'subaru' community, so I have no incentive to upsell people on turbos.
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Old 11-17-2016, 10:48 AM   #24
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this was not the base of witch I was picking my turbo.. to be a fact I have a PTE6262 ready to bolt on right now... but what I don't understand is if what I'm asking all depends upon the intake then how does a oem turbo make 300-350whp at about 20psi it's been said all over the place that stock tubes will get you to around that number..... when there is a guy in my area running 20pis out of a PTE 6266 and is around the 500whp.(seen the papers to prove that too).... same psi same 2.5 same 2.5 intake... it happens and I'm just trying to figure out how and why. and if this makes the build safer so to say by being able to us less pressure to yield the same hp amount. I get your an engineer.. but there has to be a cause and effect somewhere that can be explained and that is what I'm looking for.... I may be saying this wrong but volume and pressure I believe are different and this is the CAUSE is that 19psi out of a 10mm tube is going to have less volume coming out of say a 12mm tube... the EFFECT more air coming out of the 12mm tube still at 19psi creating more air volume for the fact more air can pass throw the tube easier .( so in thoughts it would take less psi to equal the same volume of air out of 10mm tube) the cause and effect should be the same on a turbo or am I thinking wrong and why???
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Old 11-17-2016, 11:11 AM   #25
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This is gold. Killer B send that popcorn over, I trade you for some of my Mike & Ike.
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