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I see some honda guys running liek GT35R's and like 8psi. And some gas trucks running huge turbos but only like 5psi of boost. I thought these turbos dont even unleash till like say 20+ psi. So why dont they just get a cheaper and smaller turbo, is it just cause the big mothers might flow more at lower boost or?? Sorry If I sound like an idiot:wall: .

I was getting flamed from a buddy cause my 50trim was too big for 12's:rolleyes:
 

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They flow same air at low boost as small ones at high. I also think that at high boost smaller turbos blow hotter air than smaller ones, but i could be wrong. I prefferably would go for smaller fast spooling if i was turboing something for low boost only, but who keeps their boost down once they get it?
 

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I will try to give an educated, and opinionated guess, I my self have the capability to run 8psi on my car, Now while this is hardly making the power that it can make, it does help with traction issues. Also what I intend to do is varie the boost for say when i want to go into the mountain's and such, sometimes less is more, if you catch the point.

I guess I will put it like this I would rather be powering through a corner with 8psi max, then having to fight the cars control over hitting 20+.
 

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White91TalonTsi said:
I see some honda guys running liek GT35R's and like 8psi. And some gas trucks running huge turbos but only like 5psi of boost. I thought these turbos dont even unleash till like say 20+ psi. So why dont they just get a cheaper and smaller turbo, is it just cause the big mothers might flow more at lower boost or?? Sorry If I sound like an idiot:wall: .

I was getting flamed from a buddy cause my 50trim was too big for 12's:rolleyes:
i hated when this comes up. if i was to run a sc61 on my stock 6bolt, dsmers will say that that turbo is way too big and too much lag but its okay for a honda to run it with a stock motor doing 5-6psi. and its a perfect size turbo for their honda.
 

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A larger turbo flows more cfm at lower psi. Think of it like a ballon, a smaller one may have the same psi as a bigger one but the bigger one still has more air. Sorry its kind of hard to explain, but I hope that helps.
 

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my favourite annolgoy is,

imagine being squirted by a garden hose turned on full, you'd get wet.

now imagine being squirted by a fire hose turned on to the same pressure the garden hose was on, i bet you'd get blown over.

same basic prinicpal applies for turbo sizes, for a large turbo to flow as much air as a smaller turbo on say "20psi", you turn the "boost" pressure down on the large turbo to say "10psi". and they both push the same amount of air volume.

its a lot more complicted than that, but i like the garden hose explaination :)
 

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Your engine can only eat so much air at a given RPM. Whether you stick a "garden hose" or a "fire hose" into it - makes no difference. If you have 8 psi or whatever, big turbo/small turbo does not matter.

However

- With a smaller turbo, you'll spool faster, but at higher RPMs turbo won't provide enough air, so your boost will drop.

- With a bigger turbo, you'll spool slower, but it will hold boost at higher RPMs.

So it's a trade off. Generally you want to have all the boost in your engine's power band, which's usually the high RPM. Which's why they usually put the bigger turbos on.

Once you're boosting, it doesn't matter. You can put a jet sized turbo or a lawnmower one - if it's holding boost, it'll be the same - your engine can only eat so much.
 

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T25 is a pretty good turbo for a stocker DSM, because it holds boost up to what, 5500 RPMs, which's about the end of a stock 4g63 powerband. This is the reason why if you slap a 50 trim on a stocker without tuning it, you'll only hurt yourself.

However, on "racing" dsms, they can put huge turbos on those, because they tune the engine to run with a powerband being like 5-8k rpm, which's a blessing for a 50-trim sized turbo. Just make sure you're in the right gear ;)
 

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Only2InFront said:
Your engine can only eat so much air at a given RPM. Whether you stick a "garden hose" or a "fire hose" into it - makes no difference. If you have 8 psi or whatever, big turbo/small turbo does not matter.

However

- With a smaller turbo, you'll spool faster, but at higher RPMs turbo won't provide enough air, so your boost will drop.

- With a bigger turbo, you'll spool slower, but it will hold boost at higher RPMs.

So it's a trade off. Generally you want to have all the boost in your engine's power band, which's usually the high RPM. Which's why they usually put the bigger turbos on.

Once you're boosting, it doesn't matter. You can put a jet sized turbo or a lawnmower one - if it's holding boost, it'll be the same - your engine can only eat so much.
Umm no, you are absolutely incorrect, in what you just said an engine can only eat so much as in NA yes, but we are talking forced induction here.

psi = psi is one thing however what you are really wanting to compare is air volume.
A t25 will not flow nearly the same amount of air as say a 16g, nor will it be as efficient. That is why you see some people who are running 15psi losing to others who have 9-10psi
It’s all a matter of chemistry,
Another example: at 5500rpm on a 16g at say 18psi, now take a say 57trim to4e at the same psi same rpm, put them head to head who will when? Now why? It sure isn’t because the engine can only ingest so much air :rolleyes:
Its because the 57trim has a better compressor then the 16g and compresses the air more efficiently charge temps for the 57trim will be 20+ cooler then the 16g, which there for = colder charge= more oxygen dense = more power.
Please do not give out information when you do not know what you are talking about.
 

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to4garret said:
my favourite annolgoy is,

imagine being squirted by a garden hose turned on full, you'd get wet.

now imagine being squirted by a fire hose turned on to the same pressure the garden hose was on, i bet you'd get blown over.

same basic prinicpal applies for turbo sizes, for a large turbo to flow as much air as a smaller turbo on say "20psi", you turn the "boost" pressure down on the large turbo to say "10psi". and they both push the same amount of air volume.

its a lot more complicted than that, but i like the garden hose explaination :)
I like that analogy.
 

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Its because the 57trim has a better compressor then the 16g and compresses the air more efficiently charge temps for the 57trim will be 20+ cooler then the 16g, which there for = colder charge= more oxygen dense = more power.
You are right, but so am I. Turbo isn't chosen based on how cold the resulting air will be. A turbo is chosen based on where you want the boost to be.

I guess TECHNICALLY I was wrong when I said that at 10 psi a T25 will not be pushing any different amount of air than a 50 trim, because the 50 trim air will be a bit colder, so there will be more of it. But you exhaggerated with the 20 degrees, it's not that much, 5 degrees tops. In reality that difference will be overshadowed by the supporting mods of the car.

However, according to your logic, the bigger the turbo, the better, which we all know isn't the case.

T25 is there for a reason - you have boost avable in very low RPMs, which's good for daily driving. King Kahuna is there also for a reason - your car will be a monster with your shift points tickiling 8000 RPM with the proper tune, but in daily driving you'll feel like you're rolling in a civic.

Let's just say we're both right in our own way and kiss. A girl who knows about cars makes me hot.
 

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Doesnt Compression Ratio have a big role in it also? Like for the honda's and such?

Since they are running higher compression it is alot safer to run smaller amounts of boost but still produce around the same amount of power, compared to lower compression with higher boost?

Correct me if i'm wrong please. Just trying to learn a little bit more. :)
 

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1990 Dsm Gsx said:
Doesnt Compression Ratio have a big role in it also? Like for the honda's and such?

Since they are running higher compression it is alot safer to run smaller amounts of boost but still produce around the same amount of power, compared to lower compression with higher boost?

Correct me if i'm wrong please. Just trying to learn a little bit more. :)

What your talking about are cylinder pressures in relation to compression and boost. And yes, flowing the same amount of air at a lower pressure level = safer. Provided you have enough fuel to cover the air.

And... when we are talking about newer turbo's... there is a compromise between the small = fast & less topend. And big = slow and more big power and top end.

Ball bearing turbo's spool sooner, even large ones. And new wheel and cartridge designs, light weight alloys... etc allow for bigger turbo's to act like smaller ones. Taking the superb efficiency of say the "50 trim" with a BB center... you can make alot of power early, and over a broad powerband.

Its not all black and white.
:cool:
 

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Asmodeus said:
What your talking about are cylinder pressures in relation to compression and boost. And yes, flowing the same amount of air at a lower pressure level = safer. Provided you have enough fuel to cover the air.
Ok nice. I knew i was "SORTA" in the ballpark but not totally. Thanks for clearing that up.
 

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comparing, a t3/to4e 57 trim, to a 16g , at like 20 psi , , not only is the bigger turbo in a higher efficiency area, but its exhaust side, is more free flowing, and thats going to help the engine breath better, increasing the ve on the top end. Ide say the decrease in backpressure(PRE TURBO), is big part in making more power at the same boost level, on the same motor...
 

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To add to this, actually the engine is just a big air pump, and it all comes down to the engines volumetric efficiency at a given rpm/throttle openings as far as how much air is required for maximum power at certain points, and smaller turbos wont cut it once the engines ve changes due to bigger cams, porting, bigger valves etc.
 

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to4garret said:
my favourite annolgoy is,

imagine being squirted by a garden hose turned on full, you'd get wet.

now imagine being squirted by a fire hose turned on to the same pressure the garden hose was on, i bet you'd get blown over.

same basic prinicpal applies for turbo sizes, for a large turbo to flow as much air as a smaller turbo on say "20psi", you turn the "boost" pressure down on the large turbo to say "10psi". and they both push the same amount of air volume.

its a lot more complicted than that, but i like the garden hose explaination :)

I've read through countless explanations of CFM meanings and PSI meanings, and I still fail to understand how any of you make any sense.

PSI IS PSI. The only difference between a garden hose and a fire hose is the volume that is occupies. The fire hose has a stronger force because force is a direct representation of pressure over area. So obviously a big balloon will have more force due to its increase in area. Obviously a bigger hose will have more force due to its increase in volume.

My point is this: A 4663t combustion chamber is the same size no matter what turbo you are running. It has the same surface area, and is therefore subject to the same force when introduced to the same PSI. It is simple physics. :wall:

I think you all are very mislead in your thinking. Although this is just a hypothesis, I have yet to find an explanation that proves it wrong.

- A turbo is run using the exhaust energy of an engine. A bigger turbo is able to run the same PSI as a smaller turbo while converting less of that exhaust energy into direct heat loss. A bigger turbo becomes more efficient, therefore creating more power. This is the only explanation that makes any sense to me. Everyone's ability to pull the letters CFM out of their asses does not help me. It defies physics, and makes no sense. PLEASE SOMEONE SHED SOME EDUCATED LIGHT FOR ME!!!!!!!! I need this explained.

Edit: To put it another way, if you were to tell me what volume of air you had, and at what PSI the air was at - I could tell you exactly the amount of air you had. And since the volume of air in a combustion chamber is constant, a given PSI is going to be a constant mass of air! The only other variable that can control the amount of air present is temperature, which again leads me to my above conclusion that a bigger turbo makes more power at the same PSI soley due to a change in energy loss as heat. :)
 

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CFM is CFM; at one and the same RPM the same displacement will draw the same air at the same PSI; but then there's VE (Volumetric Efficiency) which is altered by cams, manifolds etc etc. VE has a big effect on power.

And then, a small turbo will have much harder time sustaining xx psi at high rpm than a larger turbo.
 

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T_K said:
CFM is CFM; at one and the same RPM the same displacement will draw the same air at the same PSI; but then there's VE (Volumetric Efficiency) which is altered by cams, manifolds etc etc. VE has a big effect on power.

And then, a small turbo will have much harder time sustaining xx psi at high rpm than a larger turbo.
This volumetric efficiency is something I have not heard of. Perhaps I'll go read up.

I do understand the larger turbo's ability to sustain higher PSI levels at higher RPMs. Hypothetically speaking that a small and big turbo are holding the same PSI, I'm just trying to learn why a bigger turbo makes more power.
 
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