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#14470 - 02/22/05 09:41 AM I was wrong. (Engine airflow vs flow bench flow.)
Jesse_Lackman Offline
super gas

Registered: 02/01/03
Posts: 752
Loc: North Dakota
A few months ago there was a thread about flow testing in which I said the flow in a running engine isn't even close to what it is on a flow bench. Using the example of a 360 engine running at 6000 rpm the calculated airflow (100% volumetric efficiency) is 624 cfm. 624 / 8 = 78 cfm per cylinder, this was the basis for me saying what I said.

Well I was wrong, no one corrected me, and now I must correct myself.

Up until now I always stopped at the 78 cfm (624 for eight cylinder four stroke 360 @ 6000 rpm). My mistake was not realizing the 78cfm/624 cfm is average flow and that the actual the intake flow is crammed into a much shorter time span. The port has to flow about 312cfm during the intake stroke to flow the average 78cfm.

If I did the math right a 45 cubic inch four stroke cylinder @ 6000 rpm will have around 332 ft/sec average intake velocity (average over 180 degrees crankshaft rotation) through a 2.25 sq in cross section at 100% volumetric efficiency.

78cfm average flow @6000 rpm

312cfm @ 6000 rpm ((720 / 180) *78 )) (average flow during 180 degrees of intake stroke)

312 * 1728 (1728 cubic inches in a cubic foot)

=539136 (cubic inches per minute)

/ 60 (seconds per minute)

= 9885.6 (cubic inches per second)

/ 2.25 (intake port cross section area, or volume @ 1" length)

= 3993.6 (average inches per second velocity)

/12 (inches per foot)

= 332. ft./sec average velocity during 180 degrees crankshaft rotation.

There is more about this at speedtalk;

http://www.speedtalk.com/forum/viewtopic.php?p=4774#4774

Quote:



maxracesoftware;


.50 Mach = 582.5 fps @ 105.5F = 77.4 Inches of Water
.60 Mach = 699.0 fps = 111.5 Inches of Water


700 Fps times .5 = 350 FPS , and 350 FPS = approx. 28" Inches of Water

Flow Testing at 28 Inches of Water is roughly "half" the Air Speed Velocity
in Live Engine conditions.




Note the velocity maxracesoftware is talking about easily believable since the calculations above show the average velocity in the 360 intake port to be 332ft/sec. The 332 ft.sec from above is an average velocity during 180 degrees intake stroke. The peak velocity is sure to be higher. I suppose someone somewhere has instrumented an intake port on a spintron or running engine and measured actual conditions.


Testing at high depressions never made sense to me before but it does now.



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#14471 - 02/22/05 10:33 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: Jesse_Lackman]
BradH Offline
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Registered: 01/30/03
Posts: 13635
Loc: Valhalla... eventually
I gotta start getting more than four or five hours of sleep a night... that just caused me a major brain cramp.
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#14472 - 02/22/05 10:33 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: Jesse_Lackman]
v8440 Offline
master

Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
Wow, great info! What I could follow of it, anyway. It makes sense-because a running engine has it's intake and exhaust flow as periodic events rather than continuous, the peak must necessarily be higher than the average. That being the case, designing stuff only for the average would not seem to be the best approach. I've wondered about this stuff off and on for years, and my basic theory is that (being very general and vague here) stuff like what you're talking about may help explain why chrysler engines seem to usually do better than ford and chevy under ACTUAL operating conditions. Perfect example-last night I'm reading a book about how to hotrod smallblock chryslers, and the author mentions something I hadn't paid attention to; the fact that an LA engine's valves open "on center" with the cylinder bore. Meaning, the valves aren't crammed toward the intake manifold OR the exhaust manifold side of the cylinder (as viewed from above). This shrouds them the least possible, which ford and chevy apparently do not. So, with a given bore size and valve size, an LA motor shrouds the valves less. The result-more flow UNDER ACTUAL OPERATING conditions. This is guaranteed to be missed by a flowbench, since they don't put a cylinder against the head in question.

Now that it seems like I rambled, let me try to tie it all together; What I just said has in common with your post the fact that there are things our simplistic models leave out. Flowbenches don't consider the relative centering (or lack thereof) of valves in a bore, and many theories and formulas neglect to consider that gas movement in an engine is a series of pulses instead of a continuous flow. It is this type of oversimplification that causes us to have an incomplete and flawed understanding of what's really going on in an engine. Hence, a well-prepped 340 will usually outrun an equally well-prepped 350 chevy, and many people will wonder why. Well, THIS IS WHY.
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#14473 - 02/22/05 10:39 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: Jesse_Lackman]
StrokedW7 Offline
top fuel

Registered: 01/20/03
Posts: 2333
Loc: Kalamazoo, MI
Yes... Larry Meaux is amazing. A bundle of knowledge.
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#14474 - 02/22/05 10:41 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: v8440]
BradH Offline
I Live Here

Registered: 01/30/03
Posts: 13635
Loc: Valhalla... eventually
Quote:

...Perfect example-last night I'm reading a book about how to hotrod smallblock chryslers, and the author mentions something I hadn't paid attention to; the fact that an LA engine's valves open "on center" with the cylinder bore. Meaning, the valves aren't crammed toward the intake manifold OR the exhaust manifold side of the cylinder (as viewed from above). This shrouds them the least possible, which ford and chevy apparently do not. So, with a given bore size and valve size, an LA motor shrouds the valves less. The result-more flow UNDER ACTUAL OPERATING conditions. This is guaranteed to be missed by a flowbench, since they don't put a cylinder against the head in question...





Better rethink your theory: A cylinder head tested on a flow bench is mounted on a bore adapter that replicates the effect of being mounted on a block. That's why it's important to know the bore size of the adapter used (e.g. 4.00", 4.25", etc.) during any particular flow test to be able to account for any increased / decreased shrouding effect compared to the bore size the head is actually used with.
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#14475 - 02/22/05 10:43 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: BradH]
v8440 Offline
master

Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
Ah, I didn't know that.
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Exactly 610 posts on old board, first whacked post in the history of this one! Funny moparts quote from Waginator: "*If you want your package lost, like bermuda triangle lost, use DHL (formerly airborne) *if you want it to get there but destroyed, use UPS."

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#14476 - 02/22/05 11:00 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: v8440]
aarcuda Offline
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Registered: 03/17/03
Posts: 15470
Loc: the boonies
i would think it would be more complicated than that. If you think aboutthe engine in its entirety, there is more than one intake valve open at any particular time. I dont have it charted out but the ol 18436572 tells me that when 1 is open, 2 and 8 may be open (either just closing or just opening) but is different amounts. so when i is flowing its max, part of the intake charge is going into other cylinders which may be just closing or just opening.

so the flow is proportional to the amoutn the valve is open and where the piston is.

so using differential equations to set up the dynamics of the engine would be required to determine the answer.

And what that answer is, I cant tell you because Im not about to go trying to figure it out.

I just thought Id add a little more difficutly to the problem.
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#14477 - 02/22/05 11:00 AM Re: I was wrong. (Engine airflow vs flow bench fl [Re: Jesse_Lackman]
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#14478 - 02/22/05 11:03 AM Re: I was wrong. (Engine airflow vs flow bench fl [Re: Jesse_Lackman]
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#14479 - 02/22/05 11:14 AM Re: I was wrong. (Engine airflow vs flow bench fl
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#14480 - 02/22/05 11:26 AM Re: I was wrong. (Engine airflow vs flow bench fl
v8440 Offline
master

Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
I may be completely off here, but it also seems that manifold plenum size (along with runner volume) would affect vacuum. As in, the smaller the plenum, the higher the vacuum (all else being equal). If I'm right, I guess this is at least part of the reason why excessively big intake plenums tend to give soggy response with carburetors.
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Exactly 610 posts on old board, first whacked post in the history of this one! Funny moparts quote from Waginator: "*If you want your package lost, like bermuda triangle lost, use DHL (formerly airborne) *if you want it to get there but destroyed, use UPS."

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#14481 - 02/22/05 12:23 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: v8440]
nomore65BelvJim Offline
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Registered: 12/28/03
Posts: 16827
Loc: Phoenix - surface of the sun
Reading this has me curious,just what are you all trying to figure out here? peak flow or peak vacuum/pressure? both? something else? couldnt max vac/press be figured by using piston speed at or near its highest point? wouldnt the vac/pressure level be controled by the most restrictive point in the flow path?
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#14482 - 02/22/05 12:36 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: v8440]
Anonymous
Unregistered


You guys are reading a lot into ejit's deleted post. He didn't actually SAY anything, other than somebody, somewhere, posted crap. That was interesting and informative.

As for people wanting stuff handed to them on a silver platter, what are you talking about? Why have this board at all if people are supposed to keep it a big secret and make everyone else go find out on their own?

"WAY TO GO EJIT you actually made some here think, now they may do the required work to get their questions answered..........and they will remember it."


No, that's NOT AT ALL what he did. He didn't provoke any thought on the actual subject of rod/stroke ratios, he spouted off. Have you seen anybody post thoughts on rod/stroke ratio as a result of ejit's post? I haven't. If you have, please point it out.

Again, vaguely referring to some "crap" in response to a technical question is not productive, as in "now they may do the required work to get their questions answered..."

If you know the answer, why not just say the answer? Streetwize seems to have survived the traumatic experience of simply ANSWERING THE QUESTION, why not ejit? The guy obviously has a huge wealth of technical information (I mean that seriously, not sarcastically). Why not share it? And if there's some reason to not share it, why even post at all? I'm not trying to say ejit should not be a member here-let me nip that **** in the bud before it starts. But I do wonder, if information must be earned the hard way, why be a member of a forum that's there to be an EASY way?

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#14483 - 02/22/05 12:41 PM Re: I was wrong. (Engine airflow vs flow bench fl
v8440 Offline
master

Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
Oh boy, here he goes, getting p#$$y because I busted him out a couple of weeks ago. Hence, he deletes useful posts. Ejit, as you well know, your posts in this thread are useful. As I've said before, you have all kinds of useful knowledge. However, that doesn't give you a free pass for when you decide to act like an @$$. So, I guess if you wanna take retribution for our last go-around, go ahead. There's nothing anyone can do to stop you.
_________________________
Exactly 610 posts on old board, first whacked post in the history of this one! Funny moparts quote from Waginator: "*If you want your package lost, like bermuda triangle lost, use DHL (formerly airborne) *if you want it to get there but destroyed, use UPS."

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#14484 - 02/22/05 12:46 PM Re: I was wrong. (Engine airflow vs flow bench fl
nomore65BelvJim Offline
I Live Here

Registered: 12/28/03
Posts: 16827
Loc: Phoenix - surface of the sun
do you take back things you say outloud as often as you delete posts here?
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#14485 - 02/22/05 12:49 PM Re: I was wrong. (Engine airflow vs flow bench fl
Jesse_Lackman Offline
super gas

Registered: 02/01/03
Posts: 752
Loc: North Dakota
Panic, would you repeat that bit about average flow being 6% of peak flow?

Is that average flow during the intake event?

And where did that figure come from?

------------------------------------------------

I wouldn't think velocity and pressure would be too hard to map in a running intake port - cylinder pressure has been recorded in running engines. I'd be willing to bet it's been done.

One thing to remember about flow bench depression is it on the cylinder side of the valve, not the port side, whatever that tidbit is worth.




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#14486 - 02/22/05 12:49 PM Re: I was wrong. (Engine airflow vs flow bench fl
BBR Offline
master

Registered: 01/19/03
Posts: 7117
Loc: Texas
Quote:

You guys are reading a lot into ejit's deleted post. He didn't actually SAY anything, other than somebody, somewhere, posted crap. That was interesting and informative.

As for people wanting stuff handed to them on a silver platter, what are you talking about? Why have this board at all if people are supposed to keep it a big secret and make everyone else go find out on their own?

"WAY TO GO EJIT you actually made some here think, now they may do the required work to get their questions answered..........and they will remember it."


No, that's NOT AT ALL what he did. He didn't provoke any thought on the actual subject of rod/stroke ratios, he spouted off. Have you seen anybody post thoughts on rod/stroke ratio as a result of ejit's post? I haven't. If you have, please point it out.

Again, vaguely referring to some "crap" in response to a technical question is not productive, as in "now they may do the required work to get their questions answered..."

If you know the answer, why not just say the answer? Streetwize seems to have survived the traumatic experience of simply ANSWERING THE QUESTION, why not ejit? The guy obviously has a huge wealth of technical information (I mean that seriously, not sarcastically). Why not share it? And if there's some reason to not share it, why even post at all? I'm not trying to say ejit should not be a member here-let me nip that **** in the bud before it starts. But I do wonder, if information must be earned the hard way, why be a member of a forum that's there to be an EASY way?





Where's that violin playin' smilie when you need him?

FYI - His post deletion is not limited to moparts.
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#14487 - 02/22/05 12:50 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: nomore65BelvJim]
v8440 Offline
master

Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
Oooh, that was rough! I know full well that I was hard on him in that other thread. It's just that what he said initially, and his attempts to defend it, were so indefensible as to be ludicrous. There's just no purpose in someone swooping in and saying something negative w/o adding anything useful. Negative with a point is an entirely different thing. I'm not immune to that sort of thing-I occasionally post stuff that I later regret, and see as an @$$hole kind of post on my part. When I do see that, I try to make amends.

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Exactly 610 posts on old board, first whacked post in the history of this one! Funny moparts quote from Waginator: "*If you want your package lost, like bermuda triangle lost, use DHL (formerly airborne) *if you want it to get there but destroyed, use UPS."

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#14488 - 02/22/05 12:56 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: Jesse_Lackman]
v8440 Offline
master

Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
Yeah, I bet a restrictive valve could kill velocity down quite a bit, as well as change the TIMING of the pressure variations on the intake manifold side of the valve. I'm gonna theorize that a restrictive intake valve would somewhat attenuate and delay the vacuum/pressure effects on the intake-side of the port, as it would limit the cylinder's ability to affect anything past the valve. Sort of a smoothing effect, in other words.


Edited by v8440 (02/22/05 12:57 PM)
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Exactly 610 posts on old board, first whacked post in the history of this one! Funny moparts quote from Waginator: "*If you want your package lost, like bermuda triangle lost, use DHL (formerly airborne) *if you want it to get there but destroyed, use UPS."

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#14489 - 02/22/05 01:03 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: v8440]
v8440 Offline
master

Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
Jesse, I'm sorry that my posting here caused him to pack up and go home. I'm guessing that once he realized that I was the same guy who busted him in the other thread, he decided to pull all his posts, and instead post what I said to him that made him mad. Anyway, I have emails from the board with the contents of what he posted. If you want, I can cut/paste them into a pm for you. I could just repost them under my own name, but even I'm not that cold. Just lemme know if you want them.
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Exactly 610 posts on old board, first whacked post in the history of this one! Funny moparts quote from Waginator: "*If you want your package lost, like bermuda triangle lost, use DHL (formerly airborne) *if you want it to get there but destroyed, use UPS."

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