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It's all over my head.....
I'm just going to put a bigger spring in the wastegate and let it ruin all of my velocity while I keep my volume the same but increase the pressure.

Velocity. We don' need no stinking velocity. We gots boostage!

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Funny, but lots of people would be far better off if they ignored math that may or may not be fully understood and go with that method!

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Haha! No, not needed at all, but I will certainly try to make it simpler yet for you.



That's how a boosted engine makes power. That's why I've put together several 122 CID setups that make more power than your car, or any of mine for that matter. The cylinder pressure increases exponentially, yet the 1200 HP 122 CID motor is still moving X CFM, just like the 1200 HP 500 CID motor. Same CFM. Just a different pressure to get it.

Once more: CFM is a measurement of volume. It IS DIRECTLY effected by pressure.

This still has nothing to do with your original post/question, but I figure someone ought to stand up in a thread where people are discussing calculating airflow velocity theories and ideas, when this basic principal was jumped right over.

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I'm not sure why anyone coming across as a self appointed turbo expert would be talking in terms of volume instead of mass???

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Once more: CFM is a measurement of volume. It IS DIRECTLY effected by pressure.

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While not untrue, this is a very confusing statement to make as the formula for cfm has no ability to describe this effect.

lbs/min makes a lot more sense than cfm to me when trying to accurately describe the air being consumed by an engine with a turbo on it. I would like to see your math laid out that shows the 2 engines you describe above consume the same cfm (in order to do so I believe you are going to have to make a whole host of assumptions- the very crux of the problem here- trying to use a unit of volume measure when a unit of mass measure is required)

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Does an engine use mass efficiency, or volumetric efficiency?

As I said above half kidding, if people thought outside of the math that can become quite overwhelming they often get alogn pretty well just on logic alone.

But, here.

V(cu.ft./min) = n(lbs/min) x 10.73 x T(deg R)/(29 x P(psia))


That is why I'm speaking in CFM. Because it's a function of lb/min. I was trying to make this as simple as possible. Since most engine builds calculate in CFM (head flow, for instance) instead of turbo guys calculating compressor flow in lb/min.

Furthermore, Feets, if math is all we're going to argue with here then the proof is there for you. Pressure is directly involved in the equation to find volume.

What more can I offer?

I'm not getting riled or mad or anything, just trying to point out some things since people around here respect your opinion and look to it as truth. To make the statement "pressure has NOTHING to do with volume" is wrong, however you want to argue it.

This isn't a d*ck measuring contest either. The small engine comparison was for demonstration purposes. No braggign needed, I'm not looking for a pick-me-up. If anything this should be a good read for some.

And as a final note to ponder, lets make this very simple, once more.

A throttle body flows 600 CFM at 28" depression on a flowbench. Does it change how much it flows if it is done at 10" depression. How about 10 psi? 30?

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It's all over my head.....
I'm just going to put a bigger spring in the wastegate and let it ruin all of my velocity while I keep my volume the same but increase the pressure.

Velocity. We don' need no stinking velocity. We gots boostage!

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Funny, but lots of people would be far better off if they ignored math that may or may not be fully understood and go with that method!

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A throttle body flows 600 CFM at 28" depression on a flowbench. Does it change how much it flows if it is done at 10" depression. How about 10 psi? 30?

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will the friction loss stay the same with a proportional increas of mass due to a proportional increase of pressure as long as temp stays the same????this is the question.

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My original question was about air velocity between the turbo and engine. The size of the intake tube will determine velocity. Is there a point where the air is moving too fast?

We kinda got sidetracked on semantics.

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My original question was about air velocity between the turbo and engine. The size of the intake tube will determine velocity. Is there a point where the air is moving too fast?

We kinda got sidetracked on semantics.

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According to a friend of mine who is way smarter about this stuff than I am, and if I understand him correctly, once it goes supersonic, flow will stall, that is it wont flow anymore CFM no matter what pressure is behind it.

I think a turbo map (hieroglyphics to me ) kind of explains that theory ie once the compressor wheel reaches a certain speed efficiency drops off a cliff. I'm pretty sure that speed equals or approaches supersonic. Or not .

Kevin

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CFM don't mean squat..throw an A or an S before it and then we may be able to help out.....

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