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Discussion Starter · #1 ·
Okay, dont really know how to word this so bear with me.

Basically I know a compressor map shows where a turbo works best. But isnt it missing the engine effeciency factor?

for instance a highly efficient/good flowing engine will require higher turbo rpms to make a givin boost pressure. Resulting in higher IAT's and overspinning of the turbo for higher boost ranges.

So isnt it like anything else where the restriction against flow creates the pressure??

So what if the engine is a known poorly flowing setup? How do you plot that against a compressor map to know what boost is okay to run?
 

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Discussion Starter · #2 ·
So I guess Im asking if boost pressure is TRUELY relevant to turbo rpms?

Since my engine flows so poorly, cant I safely run higher boost on a given turbo without overspeeding it?
 

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Discussion Starter · #3 · (Edited)
How do I figure out what my turbo's limit is?

How do I choose a properly matched turbo for my setup based on a horsepower goal? I understand it comes down to the actual air the turbo can flow but at what boost?

For instance, a buddy can run a turbo on his car on pump gas @ 17psi before he starts to see high IAT's but with good HP results. Whereas I can take the same turbo and use the same fuel and run into the 20psi range with still no unfavorable symptoms (high IAT,knock,etc) other than a lower HP figure.

So who is overspeeding the turbo?
 

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Compressor maps show pressure ratio versus mass flow. Mass flow, multiplied by an engine efficiency factor etc, can give you an idea of horsepower. Compessor maps are for the compressor only, it could go to an engine or into thin air and would not change.

your badly flowing engine 'could' run more boost but you could end up going out of the 'sweet spot' on the map and see higher iat's.

Probably neither of you, but the higher iat's of your bud could indicate going out of the sweet sopt on the map and running into lower efficiencys.

Then again, I could be wrong lol.
 

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How do I figure out what my turbo's limit is?

How do I choose a properly matched turbo for my setup based on a horsepower goal? I understand it comes down to the actual air the turbo can flow but at what boost?

For instance, a buddy can run a turbo on his car on pump gas @ 17psi before he starts to see high IAT's but with good HP results. Whereas I can take the same turbo and use the same fuel and run into the 20psi range with still no unfavorable symptoms (high IAT,knock,etc) other than a lower HP figure.

So who is overspeeding the turbo?
Below is a link to BorgWarner’s online matching tool. Start off by watching the instructional videos and then go from there. If you have any specific questions send me a PM.

Thanks, Seth

http://www.turbodriven.com/performanceturbos/matchbot/index.html



Instructional videos
Part 1
http://www.youtube.com/watch?v=qIGDnbaBcJI

Part 2
http://www.youtube.com/watch?v=6I79sUKGXyE

Part 3
http://www.youtube.com/watch?v=lHKMsYZDrn0

Part 4
http://www.youtube.com/watch?v=kpkvwe8qRMI
 

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Discussion Starter · #6 ·
Thats an awesome program but not exactly what I was looking for. (plus even following along the videos I was totally lost being that alot of it was guessing?)

Engine VE. Its a total guess. How do I get in the ballpark for that? Basically Ive been going off results people are having with engines close in displacement. Then if they are efficient designs I subtract an amount of HP (guess) to get an idea what I might make. Or I find guys with similar poor flowing engines and go off of their numbers and maybe add a bit.

Problem is my engine is not a very popular setup for good reason. So little research has been done.

The only other info I have to use is my own results between the 2 different turbos I have ran. But I dont wanna GUESS buy another turbo. I dont even want another turbo, I just want to know if the one I have now will fulfill my HP goals.
 

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For VE, you know the maximum theoretical air flow from the displaement and rpm. For actual values, you need a mass airflow sensor that's properly calibrated and has enough range for your setup.
 

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Discussion Starter · #8 ·
Yeah, Im on speed density MAP only. So with the MAP id just calculate the actual values to see how much air Im actually flowing. Then refer to my compressor map to see theoretical RPM's and where this turbo stands?
 

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Okay, dont really know how to word this so bear with me.

Basically I know a compressor map shows where a turbo works best. But isnt it missing the engine effeciency factor?

for instance a highly efficient/good flowing engine will require higher turbo rpms to make a givin boost pressure. Resulting in higher IAT's and overspinning of the turbo for higher boost ranges.

So isnt it like anything else where the restriction against flow creates the pressure??

So what if the engine is a known poorly flowing setup? How do you plot that against a compressor map to know what boost is okay to run?
Compressor maps are generated in test cells under ideal conditions. They are application specific. I sometimes use them as a tool to see if I'm "in the hunt" or "out in the ding weeds".

Boost pressure equals shaft speed. Volumetric efficiency should be addressed as "the system as a whole".

If the engine has a poor VE and the the compressor is too large it will reach a point where the engine can no longer use the air the compressor is trying to move at a given load and throttle position. This will cause the air to back up and act as a brake on the compressor limiting boost/shaft speed. This will slow the turbine back pressure will rise and VE will drop. If the compressor is too small the engine will run away from the compressor the boost and VE will drop.

The bottom line, application is everything! Hope this helps.
 

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Discussion Starter · #11 ·
my overall goal is to figure out why the turbo Im running now is making overall better power than my previous larger setup.

The way the dynographs show my power is real strange with only a change in turbo's. Im real confused about it. Was hoping a better understand of the whole thing could help.
 
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