D.I.Y. really simple flowbench

Competition engines and 'live' projects only. Good photos to illustrate your post are expected.
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NOSferatu
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Joined: October 22nd, 2006, 9:43 am
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D.I.Y. really simple flowbench

Post by NOSferatu »

I am considerin to make a flowbench as easy and cheap as possible. No cmf or any numeric output, but only vacuum indicator, for comparison between four cylinders, checking vacuum level at combustion chamber one by one, that those are on same level, and also to check frequently changes in vacuum, while doing experimental porting.

I have very simple plan, but only thing I need to know, how much vacuum and how much flow the fan must develope, that those comparison tests correlate at least "somewhat close" to flow and vacuum levels in real situation? At first I am thinking of doing it to simulate flowrates on maximum torque area, but with different valve lifts.

Could you give any advice on this? I have one radial fan that is not more than 100watts, but it produces quite big flow (everybody hold on your hats) :) low power although means low pressure capability :(
How about Vacuum cleaner motor? Which is better?

Br, Sami
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TomLouwrier
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Re: D.I.Y. really simple flowbench

Post by TomLouwrier »

hi Sami,

If you look around at flow results on this site you see that almost all measurements are done at 10" water, that's 254mm H2O or better: 249kPa or 0.0249 bar.
Flow ranges are from something like 20CFM to about 130CFM and then some if you have a large 4-valve.
Most commercial flow benches that can do these sort of numbers have electric power around 1200 to 1600W. A motor from a vacuum cleaner will do quite well. In fact many DIY kits use a workshop vac as power source.

In the USA people tend to use 28" as standard testing pressure. Also their heads flow enough air to fill up to 7 litres on 8 cylinders (cylinder heads that is ;-), so their benches are often much bigger. They may use banks of up to 16 (yes, sixteen!) vacuum motors. Mind you that's on 110 volts, so imagine the amps for such an installation... not something to connect with a household plug!

I've been working a very low budget concept myself, but due to way too much work it's been waiting for more than half a year now. All calcs and drawings done, most parts for the base casing made. Need to fabricate parts of the valves, assemble and calibrate. (Unfortunately Guy just sold his rig, so that means finding another place to get a reference orifice plate measured.)
Will try to get this little project going again, have already written enough about it to make several long posts here once it's finished and proven.

Good luck with your set up, I'm interested in the method you intend to use.

regards
Tom
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Guy Croft
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Re: D.I.Y. really simple flowbench

Post by Guy Croft »

If you test on a Superflow (eg) at 10" depression the inlet port of a 16v head capable of 280bhp is going to need to be around 148-150cfm. It might only flow 120cfm @ 10" in standard trim and the bench is used to improve the flowrate at a defined test depression.

The lower the depression the lower the cfm reading. You just don't have to test a high depression to pick up loss and measure gain, ie: if you have a less powerful motor than a Superflow. On the kind of heads (European/Japanese) you're likley to be testing anything from 5-10" is going to be fine for you. A lot of folk (errononeously) think the higher the depression the more valid their results will be. They won't. I am sure there are some in the world who said, 'Oh, he (me) only tests at 10", his results aren't representative'. Nonsense - I have the power results to disprove that.

Sure if the head is off a very big engine it's going to swallow up your bench capacity very quickly. I've tested stuff on my Superflow SF120 which comfortably outflowed the rig and from that I could deduced readily that the items (head or inlet manifold) were certainly not going to be an impediment to power. That is all I need to know. How the engine was built and with what parts is another matter.

What cfm your bench tells you is immaterial really because you are looking (during dev) for are gain/loss trends from reshaping. You're testing with air which has extremely low viscosity and these will show up at very low test levels. The absolute values of flow from your rig are only useful for comparative purposes against other data and to archive against dyno so you know what to produce next time.

Do be aware that 'working' the air thru the head and rig heats it up and temperature correction is important.

Hope that makes some sense, maybe helps a bit.

G
NOSferatu
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Joined: October 22nd, 2006, 9:43 am
Location: Finland
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Re: D.I.Y. really simple flowbench

Post by NOSferatu »

Thanks! This was useful info. I also found one blog where is quite detailed explanation with pictures, of his homemade flowbench with vac motors.

Vacuum cleaners have accumulated to our house... Relatives every now and then buy vacs as gifts, and those are usually cheap and small. We have Dyson DC19 that we have self bought, and those other cheap vacs can't compare... are just good for different projects ;) One motor I used on 30 litre oilcan. It sucks through wall connecting piece and I clean my lathe with that. :) Two could be used for flowbench. I probably don't need more, as I am mostly using it for 132 based 2.0TC (8valve). or some as old motorcycle heads.

If interested, I could report later, what I have got put together :)

Br, Sami
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Guy Croft
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Re: D.I.Y. really simple flowbench

Post by Guy Croft »

Report?!

Of course you must!!

G
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