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ej8
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Discussion Starter #1
So my friend was asking me some questions about turbos and how there size and power is different.
I was explaining to him that psi doesnt mean much without a turbob size reference.
Kinda like saying or its 10 long. 10 what inch, feet, miles..
He understood.

Explain to him a turbo doesnt add the amount its made for.
I.e. if a turbo can flow 300hp thats the max hp a car will output with that turbo.
The turbo isnt adding 300hp to the 100hp base the car alreadys has (400hp in total).
This is correct right?
Long time ago its how i was total. And it was the reason v8 dont run 350hp turbos. The motor would out flow the turbo and what not.


Now to his question.
If 2 cars run the same turbo but have different base hp. Will they need the same psi to equal the same amount of hp?

I know if 2 cars same build and same tuner will net around the same hp. Different tuners can net different hp.

But lets say car A has 100hp base and runs 10psi on X turbo and makes 200hp.
Now car B has 150hp base and runs the same 10psi on the same turbo.
Will car B net more then 200hp?

I read over the compressor map reading stuff and i know different cars need and output different cfm at different rpms. Giving the spool time, and seeing if the turbo is to big or small but trying to understand this hp output.
 

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97 EJ6 boosted D16Z6
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the turbo on car b only needs to be 51% as effective to exceed 200hp.
so probably yes. but many variables apply.....
 

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ej8
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Discussion Starter #3
the turbo on car b only needs to be 51% as effective to exceed 200hp.
so probably yes. but many variables apply.....
Yea, thats what i am trying to find is a for sure answer.
Car B flows more exhaust into the turbo. Spooling it up faster. But when it runs the same psi as car A is the power output going to be the same.
Would it choke the motor causing the power output to be around the same.


And whats what im trying to wrap my head away. What if 10psi is the max the turbo can run and that will be 200hp.

I know if you put a k04 turbo on a big motor it will have instant boost but choke the motor and not let it breath to make power.
 

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97 EJ6 boosted D16Z6
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Yea, thats what i am trying to find is a for sure answer.
Car B flows more exhaust into the turbo. Spooling it up faster. But when it runs the same psi as car A is the power output going to be the same.
Would it choke the motor causing the power output to be around the same.


And whats what im trying to wrap my head away. What if 10psi is the max the turbo can run and that will be 200hp.

I know if you put a k04 turbo on a big motor it will have instant boost but choke the motor and not let it breath to make power.
yes, depending on the displacement difference and flow of the heads.
for example a from a d16 to a b20...
the small turbo will probably still get you to 200 hp, but 'run out of puff' thereabouts.
on a sbc, probably not, but you might already be past 200 hp without the turbo....

you're just trying to get more oxygen in the cc so you can release energy from MORE fuel at a time....
 

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ej8
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Discussion Starter #5
But as for power output from the same turbo but two different base hp.

Do they make the same hp per lb or does the higher base power motor, need less lbs of boost to make the same amount out hp.

And if that is true. Then do both cars max out the turbo at the same hp?

Just trying to get a better understanding of same size turbos and different cars.
 

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Classic Man
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Think of it as compounding two compressors. The turbo and the engine. Its really hard to break it down into solid numbers like you ask above. There are soooo many variables.
 

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If you have two of the same engines let's say 1.6. One makes 100 hp the second one has a ported head and makes 150. If you put the same turbo at the same psi the 150 hp base engine will still make more power because it is a more efficient system with the better flowing heads.

Think of it this way if turbo psi and flow where the only things that mattered, then no one would ever bother with turbo cams or better manifolds.
 

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98 Civic LX
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Like stated there are too many variables.

The turbo, at 10psi at given rpm it flows a given amount of air. Hp is basised off air flow.

The engines, with different power levels, the engines flow different amounts of air.

So, If you make each engine flow the same amount of air, you will spin the turbo at the same speed, the one with more starting power will spool the turbo quicker (lower RPM)

Thats my stab at it trying to keep it simple and all veriables aside
 

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2005 Legacy GT
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Think of it in pressure ratios instead of PSI.

100 hp engine need 2x the air (pressurized air is more air) to double it's power. So you need a turbo running a pressure ratio of 2 to get to 200 hp.

150 hp engine only needs a pressure ratio of 1.3ish to get to that same 200 hp.

You don't need to compress the air as much for engine number 2 because you don't need to add as much more fuel to get to the power goal.

Yes super over simplified ... I know.

A turbo is like a "precompressor" or if you are into music a pre amp.
 

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ej8
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Discussion Starter #10
Thank you guys for all the info.
It was just something that had me a bit confused.
Since i was thinking about if a turbo is only good for X amount of hp, how that would relate to different cars and what not.

But i believe i got a understanding of it.
 

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CL9 and ED7
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let's say I have an engine making 130hp at 6800 rpm. let it's volumetric efficiency will be equal to 103%. Also, I have the engine making 103hp at 6800 rpm. Its volumetric efficiency is 82%. Volumetric efficiency depends on porting the head, camshaft, compression ratio, etc. I got Garrett gtx2860r and goal 200hp. I must use 7.8psi boost for 200hp at 6800 rpm with the first engine and for the same power at the same rpm with second engine I need 13.5psi. Power depends on the amount consumed air by the engine. So I think the choice of the turbocharger is directly dependent on the which zone of turbocharger efficiency will be air consumption of a given engine for a given power.
If I'm wrong please correct me.
Unfortunately I can not show a picture of a compressor map and my calculations, because of post count must be greater.
 

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you cannot go car A has 100hp, and car B has 200hp, and expect a turbo that flows enough for 350hp to do better on car B

What if that carB is a 1.0L 3cylinder metro banging out 200hp on a GT25 and car A is a lazy GM 2.2L 4cyl making 100hp?

That turbo on the 2.2 will spool way faster, make more power at the same internal wastegate spring, and all around destroy that 1L 3cyl.

Like posted, the shear number of variables makes it near impossible to tell what will actually happen unless math is done, or there are very relative examples already built around.
 

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CL9 and ED7
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you cannot go car A has 100hp, and car B has 200hp, and expect a turbo that flows enough for 350hp to do better on car B

What if that carB is a 1.0L 3cylinder metro banging out 200hp on a GT25 and car A is a lazy GM 2.2L 4cyl making 100hp?

That turbo on the 2.2 will spool way faster, make more power at the same internal wastegate spring, and all around destroy that 1L 3cyl.

Like posted, the shear number of variables makes it near impossible to tell what will actually happen unless math is done, or there are very relative examples already built around.
Oh yes, yes, of course displacement is important thing. I forgot to mention in my example, let dispacement of both engines will be 1.5L.
 
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