Re: post turbo air velocity?
[Re: furious70]
#721178
06/18/10 01:26 PM
06/18/10 01:26 PM
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Joined: Mar 2010
Posts: 66 SRQ, FL
8valves
member
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member
Joined: Mar 2010
Posts: 66
SRQ, FL
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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.
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.
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)
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?
Aaron M
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Re: post turbo air velocity?
[Re: 8valves]
#721179
06/18/10 01:45 PM
06/18/10 01:45 PM
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Joined: Oct 2006
Posts: 365 Motor City
Shaker223
enthusiast
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enthusiast
Joined: Oct 2006
Posts: 365
Motor City
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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!
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!
That's the way I think!!
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Re: post turbo air velocity?
[Re: Shaker223]
#721180
06/18/10 03:09 PM
06/18/10 03:09 PM
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Joined: Nov 2006
Posts: 1,090 north cakalaky
instigator
super stock
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super stock
Joined: Nov 2006
Posts: 1,090
north cakalaky
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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.....
65 Barracuda All aluminum Indy HEMI with some boost! COMING TO A TRACK NEAR YOU!
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Re: post turbo air velocity?
[Re: instigator]
#721181
06/18/10 03:23 PM
06/18/10 03:23 PM
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Joined: Mar 2010
Posts: 66 SRQ, FL
8valves
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Posts: 66
SRQ, FL
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Should I ask what correction, smoothing, and dyno type your sig is based off of as well, then? Oh, and let's move to measuring in psia too! PS- Badass car, looking forward to seeing how the new setup responds. I would think quite well.
Aaron M
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Re: post turbo air velocity?
[Re: 8valves]
#721182
06/18/10 03:35 PM
06/18/10 03:35 PM
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Joined: Nov 2006
Posts: 1,090 north cakalaky
instigator
super stock
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super stock
Joined: Nov 2006
Posts: 1,090
north cakalaky
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Don't remember the details..was a dynojet....whatever it was it was enough to go 128mph in the 1/8th at 3500lbs!...
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.
65 Barracuda All aluminum Indy HEMI with some boost! COMING TO A TRACK NEAR YOU!
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Re: post turbo air velocity?
[Re: feets]
#721185
06/18/10 06:40 PM
06/18/10 06:40 PM
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Joined: Jan 2005
Posts: 2,540 Milwaukee WI
TRENDZ
master
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master
Joined: Jan 2005
Posts: 2,540
Milwaukee WI
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Technical shmechnical. My main point was to enlighten people to the fact that a turbo or supercharger does not have a positive effect (more speed) on velocity. I always think about an imaginary dyno room, where the atmosphere is 100% under my control. I could remove the throttle plate on the engine, and control idle speed by (my word) "de-densification", or max power by pressalizin. Think about what a throttle plate actually does. It changes the density in the manifold. An engine ran in my fantasy dyno room would have a very similar torque CURVE at all levels of pressure(including vacuum) just at different levels. This would indicate similar air speeds through the engine at similar rpms. Go ahead beat me up for living in a fantasy world
"use it 'till it breaks, replace as needed"
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Re: post turbo air velocity?
[Re: TRENDZ]
#721186
06/18/10 09:31 PM
06/18/10 09:31 PM
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Joined: Jan 2003
Posts: 28,068 Irving, TX
feets
OP
Senior Management
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OP
Senior Management
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Posts: 28,068
Irving, TX
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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.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: post turbo air velocity?
[Re: feets]
#721189
06/21/10 06:56 AM
06/21/10 06:56 AM
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Joined: May 2003
Posts: 6,566 Downtown Roebuck Ont
Twostick
Still wishing...
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Still wishing...
Joined: May 2003
Posts: 6,566
Downtown Roebuck Ont
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Quote:
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.
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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Re: post turbo air velocity?
[Re: instigator]
#721190
06/21/10 12:04 PM
06/21/10 12:04 PM
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Joined: Jan 2003
Posts: 3,336 Summit, NJ
whiplash
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Posts: 3,336
Summit, NJ
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Quote:
CFM don't mean squat..throw an A or an S before it and then we may be able to help out.....
Absolutely correct....
CFM is NOT a measure of Volume. It is a measure of FLOW....
This whole post is riddled with gray areas of physics.
It would be a lot easier if we all talked in terms of Mass flow. That's what auto engineers do. It takes a lot of the CFM SCFM ACFM PSI PSIG PSIA BS out of the equation. CFM is only "so" imporatnt because most people can't get their heads around grams/sec or lb/hour.
- 67 coronet 4dr, 383/727/GVOD, blown, EFI, daily driver
- 230/238, 114°LSA cam, 1.6 rollers, 9:1 comp, 8 psi boost
- NEW BEST ET - 12.40@110mph...
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