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 Mootori komponentide voolavuse testimine ehk flowbench
On see Eestimaal võimalik? Mõtlesin, et kui modimisega tegeleda, siis pole mõtet huupi panna - tulemused enne/pärast peaks ikka ära mõõtma. Kuna dynot meil pole ja "buttdyno" ei ole väga objektiivne, siis ehk on veel mingeid võimalusi?
Korraks lõi sellise mõtte pähe, et kui laseks nt sisselaske osale (õrufilter > toru > TB > plenum > runnerid > intake > kaaned, klapid lahti) mingi õhujoa sisse ja vaataks kompressori survet. Kui nüüd mingit osa portida, siis peaks voolavus paranema ja kompressori manomeeter väiksemat rõhku näitama, sest õhutakistus on väiksem. Kas see töötaks? |
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16.05.2002 at 18:08 |
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madis
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 Mootori komponentide voolavuse testimine ehk flowbench
Aga arvesta, et sul on vaja väga suurt mahtu, ning samas on rõhud väikesed, nii et vajad mingit eraldi manomeetrit millel oleks lai skaala madalal rõhul. Muidu on idee normaalne. |
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16.05.2002 at 19:08 |
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Erkki
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Mootori komponentide voolavuse testimine ehk flowbench
Eestis kahjuks flowbench'i ei leidu. Uurisin seda teemat eelmisel suvel, kui strokerit ehitasin, aga mida pole - seda pole. Lähim koht jällegi põhjanaabrite juures. Mul keerleb ka mõte selle ehitamise ümber  Uurisin väheke flowbench' tööpõhimõtet ja leidsin, et see on häbemata lihtne: mõõdetakse vee voolavust läbi plokikaanekanali klapi teatud avatuse korral. Voolavuse ühik on CFM ehk cubic feet per minut ehk eesti keeles kuuptolli ühe minuti jooksul. Et voolavusi oleks võimalik alati võrrelda, on kokku lepitud, et seda tehakse alati ühesuguse veesurvega, milleks on 28" H2O.
28 tolli veesammast on maakeeli 0,71 at survet. Nüüd tuleb valmistada plokikaane sisselaske kanalile flants külge, ühendada see veevärgiga, tagada ühtlane surve 0,71 kg/m2, avada sisselaskeklapp näiteks 0,4", lasta veel üks minut voolata läbi avatud sisselaskekanali lastes selle kuhugi anumasse, pärast mõõdad ära mitu cubic feet'i minuti jooksul kogunes ja saadki kanalite voolavuse teada. Usun, et üle keskmise nutikas eesti mees vooliks selle näppude vahel valmis. Kui ainult tahtmine piisavalt suur on.
Näiteks võin tuua, et stock chevy smallblocki sisselaskekanali voolavus klapi 0,4" tõusu korral on 190 CFM, agakorralikult porditud kaaned voolavad juba 230 CFM. Mida rohkem jõuab küttesegu ühes ajaühikus silindrisse voolata seda rohkem sealt powerit ka tuleb. Selle pärast ongi poweri võtmeküsimuseks plokikaaned. Kõik muu sh. nukk, headerid, sisselase, karpa kaotab mõtte kui ei ole korralikke plokikaasi.
____________________________
Chevrolet Camaro '71
Pontiac Firebird '71
Chevrolet Chevelle '69, 350 cid
El Camino '68
F150, 2011
Life begins at 1000 Hp... |
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16.05.2002 at 23:39 |
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urmas
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Mootori komponentide voolavuse testimine ehk flowbench
Erkki viimane lause on tõde vabalt hingava mootori kohta. Turbode ja jms. korral saavutatakse märgatav efekt ka stock kaantega.
Ok, aga miks peab reaalses elus õhu juhtimiseks tehtud torusüsteemi katsetama just veega? Veel on ju oluliselt teised näitajad, kui õhul: voolamise kiirus, turbulents, kokkusurutavus jne. |
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16.05.2002 at 23:52 |
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LaSa
 Moderator |
Mootori komponentide voolavuse testimine ehk flowbench
quote:
Mustang GT 94:Ok, aga miks peab reaalses elus õhu juhtimiseks tehtud torusüsteemi katsetama just veega? Veel on ju oluliselt teised näitajad, kui õhul: voolamise kiirus, turbulents, kokkusurutavus jne.
läbivoolanud vee hulka ju lihtsam mõõta  |
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17.05.2002 at 08:59 |
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newton
Moderator |
Mootori komponentide voolavuse testimine ehk flowbench
See, et rõhku veesamba kõrguses mõõdetakse, ei tähenda veel, et veega mõõdetaksegi.
http://www.superflow.com/support/support-flowbench-works-how.htm
Sealt nagu nähtub, et ikka õhku pumbatakse ja ma arvan, et see ikka ongi alati nii, tundub tõenäoline, et vee ja õhu käitumine võiks ikka kaunis erinev olla.
Ja ei mõõdeta õhu hulka, vaid rõhkude erinevusi enne ja pärsast porti-klappi. Surfates jäi silma ka igast linke kodukootud flowbenchide kohta.
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17.05.2002 at 09:25 |
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2koma8
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Mootori komponentide voolavuse testimine ehk flowbench
Hmm... flowbench sobiks ideaalselt kursaprojektiks! Kahjuks pole vaja projekti teha ja aega ka pole. Aga ajusid tasuks liigutada. |
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17.05.2002 at 10:06 |
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jyrki
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Mootori komponentide voolavuse testimine ehk flowbench
I have had two sets of heads flowed once myself, but the numbers we got there were confusing to say the least. I have debated this subject a lot, and some people "believe" in flow benches while some do not. Below is a wiev that I pretty much share. You need certain amount of flow to make power, but flow doens't necessarily mean power. Our local head shop HiCar does not use a flow bench, and despite of what many porters say they don't use either. They may measure the flow, but using the flow bench trying to get all out of the head si very time consuming and would be very expensive. I have debated this subject a lot, and some people "believe" in flow benches while some do not. Below is a view that I pretty much share. It's long but worth reading:
Our era is often referred as the Information Age, but not all of the available information is necessarily useful. I am beginning to think that flow benches should be labeled with a government warning: "Caution! Excessive reliance of flow benc numbers may be harmful to your engine!"
I'm kidding, of course. Used wisely, a flow bench can be a useful tool in engine development, just like a timing light or a dynamometer.Unfortunately some racers believe that a flow bench is the ultimate answer machine.
When the subject is cylinder heads the four words I dread to hear are "What do they flow?" Novice racers and magazine writers share a fixation about airflow. The mistaken belief that "more is better" is often the false assumption that produces an under performing engine.
A flow bench measures air movement in a very rudimentary way - steady-state flow at a constant depression (vacuum). Obviously the conditons that exists inside a running engine are quite different. The flow bench can't simulate the effects of the pistons going up and down, the reversion pulses as the valves open and close, the sonic waves that resonate inside the runner, the inertia of fuel droplets, and all of the other phenomena that influence engine performance in the real world. When you flow test a cylinder head, you are simply measuring how far you can move the liquid manometer.
The bigger you make the port, the more it flows. That's hardly shocking news. Bolt a sewer pipe onto a flow bench and it will generate terrific flow numbers. So should we use a port as big as sewer pipes on our race cars? The flow bench says we should - the time slip says something completely different.
If airflow were everything, we would all use the longest duration camshafts we could find - after all, more duratoin means more flow. In fact, we know that there is a finite limit to how long the valves can be open before performance suffers. That is because the valve events have to be in harmony with the rest of the engine.
The same principle applies to cylinder heads. simple airflow capacity should never be the first consideration in evaluating cylinder heads. Characterstics that are far more important include air speed, port cross section, port volume and shape, and the relationship between the size of the throat and the valve seat. If those attributes are wrong, you can work forever on the flowbench and not overcome the fundamental flaws.
Here is a do-it-yourself example: turn on a garden hose and the water will dribble out a couple of feet. Now put a nozzle on the hose and the water will spray across your backyard. The water pressure and volume haven't changed, but the velocity has increased dramatically. Now think about the air and fuel going into your cylinders. Which would you prefer: slow and lazy or fast and responsive?
An engineer will tell you that an engine requires a prescribed amount of air and fuel to produce "x" horsepower. In a perfect world that may be true - but we race with imperfect engines. The shape and cross-sectional area are absolutely critical to performance.
For example, I have two sets of Pro Stock cylinder heads that produce identical flow numbers, yet one pair produces nearly 150 more horsepower at 9200 rpm than the other. The flow bench can't tell the difference between them but the engine certainly can.
There are software programs that claim to be able to predict an enigne's performance based on airflow numbers. Unfortunately, a critical shortcoming of many of these programs is that they are based on inaccurate information or false assumptions. A computer is an excellent calculator, but it is not an experienced engine builder. The software doesn't know whether a port's short-turn radius is shaped properly, whether the flow is turbulent at critical valve lifts, or whether the flame speed is not fast enough. Racers have a tendency to believe that computers are infallible, so they accept the software's solutions as gospel when in fact they may be badly flawed.
Textbooks would lead you to believe that an exhaust to intake flow ratio of 80 % is ideal - yet a typical Pro stock head has exhaust ports that flow less than 60% of the intake runners. You can improve the exhaust flow tremendously with about 40 minutes of work with a hand grinder but the supposed improvements will just kill the engine's on track performance. I know because I've been there.
We also have learned that low lift flow (meaning anything under .400" in a Pro Stock engine) is relatively unimportant. Think about the valve events in a racing engine: From the point when the valve first moves off its seat until it reaches mid-lift, the piston is either going the wrong way or it's parked near the top dead center. The piston doesn't begin to move away from the combustion chamber with enough velocity to lower the pressure in the cylinder until the valve is nearly half way open. Consequently, it is high lift flow that really matters in a drag racing engine.
The shape of the combustion chamber also has a significant impact on performance. A conventional chamber with deep valve reliefs around the valve seats and a relatively flat valve seat angle can produce terrific flow to .200-.300" valve lift. Today, the state-of-the-art chamber typically as 55 degree valve seats and steep walls that guide the air/fuel mixture into the cylinder to enhance high lift flow.
This doesn't mean that every racer needs a state-of-the-art Pro Stock cylinder heads - along with the high maintenance they require. The heads have to match the application. Conventional combustion chambers and 45-degree valve seats are just fine for a dependable. low maintenance racing engine that will run a full season between overhauls.
The classic Hemi chamber is capable of producing impressive flow figures, but it's not going to make impressive power. Engine technology in all forms of motorsports is converging around smaller, high efficiency combustion chamber designs. You can see the result in lower brake specific fuel consumption numbers, which indicate improved engine efficiency. Twenty years ago, a racing engine with a .48 BSFC was considered very good; todays competition engines produce BSFC numbers in the neghbourhood of .35. This means that a given quantity of fuel is being atomized and burned more effectively to produce more power. A cylinder heads combustion efficiency can't be measured on a flow bench. Yet it has a huge impact on performance.
I am not against flow benches; in fact we use computerized flow benches daily. What I'm against is over reliance on flow numbers as the primary measurement of cylinder heads performance. A flow bench is a valuable tool that can help a racer fine tune a combination - but it is not the ultimate authority.
Yours, David Reher |
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17.05.2002 at 11:07 |
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partel
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Mootori komponentide voolavuse testimine ehk flowbench
I wish Bruce could do better in Pro Stock.. |
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17.05.2002 at 11:59 |
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Erkki
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Mootori komponentide voolavuse testimine ehk flowbench
To Jyrki: Missä päin see HICAR sijatsee Helsinkissa? Onko Sulla mitään tietoja tästa pajasta? Tai puhelinnumeroa?
____________________________
Chevrolet Camaro '71
Pontiac Firebird '71
Chevrolet Chevelle '69, 350 cid
El Camino '68
F150, 2011
Life begins at 1000 Hp... |
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19.05.2002 at 20:56 |
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jyrki
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Mootori komponentide voolavuse testimine ehk flowbench
Hernesaaressa, n. 250 m. Tallink terminaalista. +358-9-664808, myös sähköposti; hi.car@kolumbus.fi |
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19.05.2002 at 22:17 |
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Erkki
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 Mootori komponentide voolavuse testimine ehk flowbench
Thanks Jyrki!
____________________________
Chevrolet Camaro '71
Pontiac Firebird '71
Chevrolet Chevelle '69, 350 cid
El Camino '68
F150, 2011
Life begins at 1000 Hp... |
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19.05.2002 at 22:45 |
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camsist
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Mootori komponentide voolavuse testimine ehk flowbench
Mingi õpetuse leidsin siit http://www.govictory.com/How%20To/FLOWBENCH/FLOWBENCH.html#orifice , ehk on abi. |
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21.05.2002 at 15:12 |
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