good god you all bitch alot.
7-10psi depending on turbo size/fuel to air mixture.
wheel size can be a factory too when boosting.
...
450whp DSM
Sould be approx 550engine hp
205 stock eng hp @ ?10?psi and 345 more hp from boost
@10/psi would be running 44.5psi of boost
@7/psi would be 59.2psi of boost
My car's faster w/o boost and AWD.
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yes i am stupid as hell to make the hp that i do. generally speaking 7-10hp per psi is the norm. Sry if u think i'm a dsm ass. Take a look at it this way Imagine you have a box that holds 550 CF. You can pack 550 cubic feet of air in it and it's nothing special. Or you can pack 1650 cubic feet in it and now you have boost (3psi if I am thinking straight). Sure you can do it, but your box will weigh more (mass) with 3x the air inside it. I think this can illustrate the difference in CFM and lb/min ratings. CFM is the physical size of your box. Lb/min is how much air you are cramming in it at a specifc rate.
95 Talon Tsi AWD 450whp.....can't do that jbodies
Think of it this way, the engine at a given rpm draw a certain amount of air (this volume is fix and the formula is given on the page since we know the rpm and the capacity of the engine) so if the pressure in the system is constant at 15psi, how can one turbo flow more than the other? It doesnt. What's different is a t25 spin more rpm to push the air to maintain 15psi compared to a 16g. This makes the 16g compressor wheel more efficiency than the t25 because it pushing cooler air out. With these information (engine capacity, rpm, boost, temperature), you should be able to plot out a graph on the comp map of the turbo you wish to run and see how well it work.
Let's take for instance the T25 and a 16G both have the same TD05H wheel (which is not true but just for comparison purposes), then the only advantage the 16G has over the T25 is the better efficiency comp wheel. However, this is not the case, the 16G has a larger TW which allow more flow. So, remember the hot side plays an important role when picking a turbo because what you want is the most flow through the whole system.
95 Talon Tsi AWD 450whp.....can't do that jbodies
If you run through the math, you find that while an increase in compression efficiency does lower the compressor outlet temperature, its not that big of a gain.
The outlet temperature is only dependant on two things: the efficiency and the pressure ratio (or the outlet pressure/inlet pressure). And if we keep the boost level constant, we only have the efficiency to deal with.
At 15 psi boost the pressure ratio will be about 2.25. With a 60% compression efficiency and a 80F inlet temperature, the outlet temperature should be about 315F. Suppose you put some new turbo on and it has a compression efficiency of 70%. The new outlet temperature is about 280F. 35F drop is pretty good, but is it really worth? Turns out the colder outlet temp increases the air density by 4.5% If you had a nonintercooled car, that should mean (all else being equal) a 4.5% increase in mass air flow, and a 4.5% increase in power. Think about that, 10% better efficiency leads to a 35F drop in temperature, but that by itself is only worth 4.5% more air flow on a nonIC car.
But toss the IC into the equation. An air/air IC can at best get the air down to ambient temperature. If you study heat exchanger theory, you find that dropping the inlet temperature by 35F doesn't mean the outlet temperature also drops by 35F. The IC kind of dampens things, on the one hand it doesn't have as much heat to transfer with the colder inlet, but on the other hand the closer you get to ambient air temperature the harder it is to get there. Net effect, if you drop the inlet temperature by 35F then the outlet may only drop by 20F. And what is that worth? A 20F drop in the IC outlet only increases the charge air density (and therefore mass air flow and therefore power) by a little over 3%.
To sum all that up, on an intercooled car, an increase in compressor wheel efficiency from 60% to 70% (a pretty big jump) will only net a 3-4% gain in air flow *from temperature effects alone*.
When you changed the charge air temperature from 165 F to 120 F you cheated. That is why you got the big air flow increase. In reality it will be a lot less.
But still, people put on bigger turbos and do see more power at the same boost level. If its not air temperature, then what is it? I think it's two things (and this is my opinion, remember my qualifications, so take it for what its worth), and they are both on the exhaust side.
As you so correctly mentioned, when you swap turbos you swap turbine sides as well as compressor sides. A better flowing turbine side will reduce exhaust backpressure. Less backpressure means less exhaust left in the cylinder after the exhaust valve closes, which means more room for fresh air on the intake stroke. This means increased volumetric efficiency, or more air flow at the same charge air temperature and boost level. It's like adding more cubic inches! I believe that if you kept the compressor side exactly the same and changed the turbine side to something more freely flowing, you will see a power increase. And you do. Bigger turbine housings give a power increase, even though you haven't changed the compressor side at all. Might add some lag and such, but ultimately power is improved. It's similar in concept to getting rid of a cat converter or a restrictive muffler. Lower backpressure = improved VE = more air flow = more power. So thats one thing.
The other thing I think does come from improved compressor efficiency, but it isn't a temperature thing. It takes power to turn that compressor wheel, hp that is extracted from the exhaust by the turbine. If you improve the compression efficiency from 60% to 70% you need something like 20% less hp to drive the compressor wheel. Power to drive that wheel comes from exhaust temperature, exhaust flow, and exhaust pressure. If you reduce the power required by the compressor, then the exhaust flow that the turbine wheel needs goes down (ie more exhaust through the wastegate) and the exhaust pressure required goes down. And again, the lower backpressure means improved VE, more air flow, and more power.
Sorry this has been such a long book, but to sum up: IMO, a bigger turbo at the same boost level makes more power, but not due to temperature effects, but mostly due to improved VE. If you change compressor sides and don't change the turbine side, I don't think you'll see nearly the gains that someone who gets a whole new unit sees.
95 Talon Tsi AWD 450whp.....can't do that jbodies
well you just proved me right...nobody can type that much in 2 minutes...nice cut and paste
Thanks for cut and pasting that - part of it was from our own faq.... way to go.
You still didn't answer the question. WHERE does your magical 7-10 hp/psi number come from?
And how does it apply to your car? Remember, your own theory proved your car isn't making 450 whp.
-Chris-
-Sweetness-
-Turbocharged-
Slowly but surely may some day win this race...
speaking of tools /\ /\ /\
