Re: I was wrong. (Engine airflow vs flow bench fl
[Re: nomore65BelvJim]
#14490
02/22/05 04:07 PM
02/22/05 04:07 PM
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Anonymous
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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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Re: I was wrong. (Engine airflow vs flow bench fl
[Re: v8440]
#14491
02/22/05 04:09 PM
02/22/05 04:09 PM
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Joined: Mar 2003
Posts: 15,493 the boonies
aarcuda
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I Live Here
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thats it. im deleting my post too!
It's got a cop motor, a 440 cubic inch plant, it's got cop tires, cop suspensions, cop shocks. It's a model made before catalytic converters so it'll run good on regular gas.
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Re: I was wrong. (Engine airflow vs flow bench fl
#14492
02/22/05 04:15 PM
02/22/05 04:15 PM
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Joined: Jan 2003
Posts: 4,424 Montgomery, AL
v8440
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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.
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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Re: I was wrong. (Engine airflow vs flow bench fl
[Re: v8440]
#14495
02/22/05 06:17 PM
02/22/05 06:17 PM
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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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Re: I was wrong. (Engine airflow vs flow bench fl
[Re: BradH]
#14497
02/22/05 07:26 PM
02/22/05 07:26 PM
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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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Re: I was wrong. (Engine airflow vs flow bench fl
#14498
02/23/05 01:11 AM
02/23/05 01:11 AM
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Joined: Jan 2004
Posts: 169 orange city,FL
Demon340GSS
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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!!!!
Owner of Original collector and restored original mopars from Mr Norms Grand Spaulding Dodge.
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Re: I was wrong. (Engine airflow vs flow bench flow.)
[Re: v8440]
#14501
02/23/05 02:16 PM
02/23/05 02:16 PM
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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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Re: I was wrong. (Engine airflow vs flow bench flow.)
[Re: RyanJ]
#14502
02/23/05 03:49 PM
02/23/05 03:49 PM
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Joined: Jan 2003
Posts: 741 Citrus Heights, CA
69_Swinger
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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.
67 Valiant /6 2-door (Father/Daughter project)
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Re: I was wrong. (Engine airflow vs flow bench flow.)
[Re: 69_Swinger]
#14503
02/23/05 08:40 PM
02/23/05 08:40 PM
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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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Re: I was wrong. (Engine airflow vs flow bench flow.)
[Re: Jesse_Lackman]
#14504
02/23/05 10:11 PM
02/23/05 10:11 PM
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Joined: Jan 2003
Posts: 8,547 State College, PA
RyanJ
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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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Re: I was wrong. (Engine airflow vs flow bench fl
#14506
02/24/05 12:42 AM
02/24/05 12:42 AM
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Joined: Jan 2003
Posts: 741 Citrus Heights, CA
69_Swinger
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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!
67 Valiant /6 2-door (Father/Daughter project)
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Re: I was wrong. (Engine airflow vs flow bench flow.)
[Re: RyanJ]
#14507
02/24/05 12:56 AM
02/24/05 12:56 AM
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Joined: Feb 2003
Posts: 752 North Dakota
Jesse_Lackman
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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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