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#14490 - 02/22/05 01:07 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: nomore65BelvJim]
Anonymous
Unregistered


Another thing to consider is that there will be pressure differences at every lift of the valve.A pressure of 40" might exist at .400 lift and then drop to 30" at .500 lift all in the same stroke.That would mean that the terminal velocity of a port at some lift in the same stroke would precede what the terminal velocity would be at some other lift.So in actuality even if a head were to flow some maximum flow on the bench at so and so lift it may never see that potential in real engine performance.Ejit touched on the idea that rod ratio may be something to consider in designing a cam. I believe that to be totally something to consider.This has been brought up before and is something i'm incorporating into the design of my next flow bench.When we see flow charts for ports we usually see every lift of the valve flowed at the same test pressure(28"....25"....etc.)But the same pressure for each lift in a real engine doesn't see the same pressure at the same engine speed.The pressure varies with each lift.Possibly a properly designed cam lifting just the right amount to avoid that terminal velocity at every lift until much later might be the way to go.I believe one way to determine that would be to have a flow curve not based on flow at every lift at some same depression but a flow curve that shows the flow at every lift within the same rpm range in actual conditions.I've thought about this somewhat and how to measure this.I've got a good idea on how this can be done.

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#14491 - 02/22/05 01:09 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: v8440]
aarcuda Offline
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Registered: 03/17/03
Posts: 15475
Loc: the boonies
thats it. im deleting my post too!
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#14492 - 02/22/05 01:15 PM Re: I was wrong. (Engine airflow vs flow bench fl
v8440 Offline
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Registered: 01/19/03
Posts: 4415
Loc: Montgomery, AL
Bad ace, good thought. All this stuff is tied together, and tied to "tuning" an intake and exhaust system. Your idea leads me to think that maybe more than rpm affects the tuning range of an intake system. As in, different valve opening RATES will tend to change the peak velocity of the intake charge, which in turn would change the time/space between vacuum pulses, independant of the rpm. I'd be willing to bet that rpm would have a much greater effect than lobe steepness though.
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#14493 - 02/22/05 02:04 PM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: Jesse_Lackman]
earlybee Offline
master

Registered: 01/19/03
Posts: 8064
Loc: Arlington, Texas
is this program any good? http://www.bgsoflex.com/intakeln.html

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#14494 - 02/22/05 02:04 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: v8440]
nomore65BelvJim Offline
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Registered: 12/28/03
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wouldnt peak velocity(intake or exhaust)come as the piston reaches its max speed as the valve is fully opened at that point, or am I missing something?
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#14495 - 02/22/05 03:17 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: v8440]
Anonymous
Unregistered


A comment was made on another board about taking a small port head and flowing it at 28" with some valve lift.Then taking that head off the bench and placing another bigger port head on the bench with the same valve lift.Don't change a thing but the heads.Turn on the same number of vacuum motors used to test the other head and do nothing to change the test pressure.What will likely happen?The test pressure will differentiate i'm sure.The bigger port head will more than likely show a smaller pressure and possibly less flow than the other head.If this is the case then it goes to show why the smaller port may indeed outflow the bigger port at the same engine speed.Simply because there is more pressure drop at the same rpm.Now take that same idea and apply it to flowing one port at different lifts on the bench. Of course it's no secret to head porters that at every difference of lift the test pressure has to be readjusted.I'm definitely no expert so I'll leave it up to whomever...what if we just test the port without adjusting the test pressure?This should very closely simulate the flow of each lift of the valve at the same engine speed. May this in fact give us a better way to design cams? Heck I don't know but i'm going to research it more.Maybe they're already doing it somewhere i'm sure if it does in fact work.Another thing that concerns me is the initial opening of the valve.Does that create an initial vacuum pulse. If so what affect does that have?Maybe the experts will chime in later.

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#14496 - 02/22/05 03:34 PM Re: I was wrong. (Engine airflow vs flow bench fl
BradH Offline
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Registered: 01/30/03
Posts: 13919
Loc: Valhalla... eventually
Quote:

...what if we just test the port without adjusting the test pressure?This should very closely simulate the flow of each lift of the valve at the same engine speed...




I don't think so. If you've even seen graphically the pressure variations that an engine experiences in the intake & exhaust tracts as it runs through the complete 4-cycle series, you'd see there's a whole lot more going on there.

Unfortunately, using the same standard test pressure for each lift is the simplest way to capture comparative data from one head / port to another. Does it accurately reflect exactly what's going on with a running engine? Not really...

EDIT: Go check out http://www.audietech.com and look at the page for the Dynomation 4 Stroke program. Scroll down to see the "pressure graph screen" showing intake & exhaust port velocities vs. crankshaft rotation to get an idea of what I'm referring to.


Edited by Brad_Hawk (02/22/05 04:01 PM)

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#14497 - 02/22/05 04:26 PM Re: I was wrong. (Engine airflow vs flow bench fl [Re: BradH]
Anonymous
Unregistered


Yeah I know it's not going to actually simulate true engine conditions. But if the port flows say 200 cfm at .300 lift with 28" of test pressure and say 300 cfm at .500 lift with 28" test pressure then it doesn't tell us anything about what engine speed that 28" of pressure will occur for both lifts.By the time 28" is reached at .300 lift then what will the pressure be at .500 lift during the same stroke?You're right there is too many differentials to generalize.I'm only guessing that by not changing the test pressure on the bench and using the same number of vacuum motors with the air valve opened at the same point....it would more closely represent the true vacuum at the same engine speed for both lifts.Thanks for the input.

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#14498 - 02/22/05 10:11 PM Re: I was wrong. (Engine airflow vs flow bench fl
Demon340GSS Offline
member

Registered: 01/01/04
Posts: 167
Loc: orange city,FL
Ok, alot of info here... My question is this. How do you decide what amount to flow a combination at? Is there an industry standard that says I have to flow it at say 28# manifold pressure ? just trying to get some more info, before I ask more questions. So what happens when you add boost to the flow instead of vacume? (is this not done on a bench somwhere??)I'm curious because my heads flowed 335 @ 28# , but my Supercharger is pumping 22 lbs boost WOT, with a mild 620 lift solid roller in a 496.(based on a 440) What does that take my flow number too?... How much does humidity affect volumetric efficiency on a flow bench? what about Altitude?... 28# here in Colorado Springs, Colorado is NOT the same as 28# in Miami, FLA.(desinty altitude affects my race car just like in my Cessna 180. most of Us know what it does in the "real world" but is it even factored into the equation? What about temperatures of the air being flowed? AKA...Density. I know that most lift/flow improvements are made to produce gains in a naturally aspirated engines. Most of this technology does not apply to supercharged engines.(beyond the basics) It was mentioned in one of the posts on this topic, the effects of overlap ( the period when the intake valve has already opened, and the exhaust valve is not yet closed.) in a blown motor this is power lost and heat gained to some degree, yet a naturally aspirated motor tolerates this. as Air needs time to get "moving". I'm not trying to change the subject here. just trying to get some better understanding before I build my next motor. I have the use of a Superflow brand bench test stand whenever I want it... Just waiting to build a Larger Air/fuel Pumper!!!! Thankyou.... Grant Eaton 719-330-0468 best time in street legal trim to date 8.03@172 mph at our MILE HIGH ALTITUDE. yup, :Licence plates, ET street tires and no traction!!!!


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#14499 - 02/22/05 11:01 PM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: Jesse_Lackman]
RyanJ Offline
moparts member

Registered: 01/19/03
Posts: 8547
Loc: State College, PA
We are building a new flow bench that is capeable of pulling 400 cfm @ 40" of vacuum. I have known for quite some time the importance of flowing at higher depressions, but COST is reason most of us don't. More inches = more blower motor which = more $. I will be able to pull "normal" SB heads that flow in the under 300 range to easy 50+ inches, and exhaust ports well over 60". Dwyer 120" vertical manometer should allow room to grow in future if I ever saw need for more airspeed. I just want to be able to test a W8 style head at over 28 inches and figured 40 would be good place to stop $ wise on the blower motors and complexity of the bench.

Biggest thing is just being able to generate enough airspeed for BIG ports to see what the short turn REALLY does. What may be stable at 10 or 20" may not be at 28 or 35"+ Or sometimes it's other way around, port can be unstable at 10" but crank airspeed up and air can actually hang onto the ST better.

Some of the Formula 1 type guys are testing now over 100 inches because they have measured presure spikes in oprating engines of similar outputs. Jim McFarland who used to design intakes for Edelbrock used sensors in between intake and head to measure airspeed in running engines. If have never heard his auido interview on SpeedTalk I'd highly recommend it. It's 98% about inatke manifold science not heads, but is best interview I have ever heard. That is one sharp dude, I learned more about intakes in hour and half than I had in my whole life.
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#14500 - 02/23/05 11:14 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: RyanJ]
Jesse_Lackman Offline
super gas

Registered: 02/01/03
Posts: 752
Loc: North Dakota
What I got out of churning that speedtalk thread is that the port velocity during testing is very important and should be matched with what it is in an actual running engine. Of course it takes high depression/high pressure to get the velocity that high on a flow bench. It's pretty obvious that flow bench test depression/pressure needs to be much higher than I previously thought to get the port velocity even somewhat close to the levels it is in running engines.

If the exhaust port average flow is only 6% of the peak flow (from a book Panic is reading) it would take a tremndous amount of test pressure to get the flow bench port velocity close to what it is in a running engine. You would have to start measuring test pressure in HG or psi.

No wonder some head porters say they are barely scratching the surface.

What are you going to use for a blower in your new bench?

Have you thought about computerizing your new bench?

That would eliminate the 120" manometer - you would need a tall shop for that thing.

What is the suction limit of centrifugal blowers anyway?

We have some "exhausters" where I work that will pull 26" hg, and lots of CFM. These are a centrifugal design not a roots type blower, they would be very smooth.

I wonder how a big diesel turbocharger would work if you spun it with an electric motor? Probably fine for pressure but how good for vacuum?

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#14501 - 02/23/05 11:16 AM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: v8440]
Anonymous
Unregistered


Quote:

Hence, a well-prepped 340 will usually outrun an equally well-prepped 350 chevy, and many people will wonder why. Well, THIS IS WHY.




I would think that the overall design (Chamber and port design) of the cylinder head itself would also play a major role in this equation (V8440's quote above.). It would be interesting to put both classes of motor together at the same ci. of displacement and best iron oem production head design and see where each stood. Of course I think that keeping the intake, carb and camshaft duration the same would help with a true comparison; no? For example 355 ci., 9.5:1, Vortec heads (for Chevy) and Magnum (Chysler), hyd. flat tappit 230@.050, dual plane intake, 750 cfm vac. sec carb., standard oem ratio rockers. It would be a neat comparison. With that being said I am not convinced that I would want to put my money either way. Let the flaming begin. Cheers !!!

Big Jimmy

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#14502 - 02/23/05 12:49 PM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: RyanJ]
69_Swinger Offline


Registered: 01/21/03
Posts: 708
Loc: Citrus Heights, CA
OK- silly question from someone who doesn't know a thing about flow bench measurements. If someone were to assemble a complete motor and hook up a drive motor with enough umph to turn the crankshaft, could actual flow in the test engine be simulated accurately by turning the it at various RPM?

Of course, there would be some differences between the test setup and reality, but seems it would be closer than a flow bench. The trick would be how to measure pulsed flow vs. the continuous flow on a bench.
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#14503 - 02/23/05 05:40 PM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: 69_Swinger]
Anonymous
Unregistered


Quote:

OK- silly question from someone who doesn't know a thing about flow bench measurements. If someone were to assemble a complete motor and hook up a drive motor with enough umph to turn the crankshaft, could actual flow in the test engine be simulated accurately by turning the it at various RPM?

Of course, there would be some differences between the test setup and reality, but seems it would be closer than a flow bench. The trick would be how to measure pulsed flow vs. the continuous flow on a bench.




Your statement above got me to thinking. Having experience in Industrial Automation I was thinking about this. What if someone were to make a flowbench and was hooked to a pump source for both vacuum and pressure yet used solonoids controled by a PLC (Programmable Logic Controler) that actuated the valves according to the specified cam specs that could be programmed into the PLC. The programming tell it how long and how far to open each valve. I would think that the PLC could be interfaced to control the velocity of the pump which would simulate the VE of the motor. would it not? Would it work? Any Thoughts? Cheers !!!

Big Jimmy

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#14504 - 02/23/05 07:11 PM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: Jesse_Lackman]
RyanJ Offline
moparts member

Registered: 01/19/03
Posts: 8547
Loc: State College, PA
Quote:



What are you going to use for a blower in your new bench?

Have you thought about computerizing your new bench?

That would eliminate the 120" manometer - you would need a tall shop for that thing.
\




It's a U stlye Manometer so 60" tall.

Amatech Blower Motors, same as used in SF's

Don't plan on computerizing it.
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#14505 - 02/23/05 08:16 PM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: RyanJ]
quickd100 Offline
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Registered: 01/20/03
Posts: 6188
Loc: nielsville, minn.
Ryan; Please excuse my ignorance but what size are these blower motors on your bench and what type of fan do they run? Coming from a farming background we use some pretty big fans on grain storage. Such as 7-1/2 hp motors and larger on large squirrel cage type fans. They move a tremendous amount of air. Dave
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#14506 - 02/23/05 09:42 PM Re: I was wrong. (Engine airflow vs flow bench fl
69_Swinger Offline


Registered: 01/21/03
Posts: 708
Loc: Citrus Heights, CA
That sounds like a FUN project

The only thing I would wonder about is how quickly the "switching" affect could be accomplished. You figure that for an engine turning at 6k RPM, the intakes are going at 3k RPM = 50 cycles per second! That might exceed the mechanical capability of most pneumatic valves

It kind of touches off another thought though. At that high a pulse rate, I wonder if the inertia of the air flow mass exceeds the force required to cause a change in it's velocity (which makes a flow bench a more plausible approximation of reality). Guess I should dust of my Fluid Dynamics books!
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#14507 - 02/23/05 09:56 PM Re: I was wrong. (Engine airflow vs flow bench flow.) [Re: RyanJ]
Jesse_Lackman Offline
super gas

Registered: 02/01/03
Posts: 752
Loc: North Dakota
Quote:


Amatech Blower Motors, same as used in SF's






I might have some Ametek 115923 vacuum motors for sale in a couple weeks.

D100,

I don't think those single stage blowers have enough pressure/vacuum for flow testing. These vacuum motors will pull 28" H20 while flowing about 100 cfm. They are two stage vacuum motors similar to what's used in a central vacuum system.

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