Small Engine Carb/Head Flowbench

[LWhitson2]

Recently decided I was going to take the plunge and build my own flowbench. I have been looking around on the forums the last couple months and figured that now was as good of a time as any. What I am looking at is using the flowbench to test one-cylinder small engine carburetors and heads, a Honda GX-390K1 to be exact. We use these motors in the minicup racing series and I figure I might be able to find a little bit of horsepower this way.

I plan on purchasing the flowbench plans from this site, but I would like to get some initial information to make sure I can successfully do what I want to do. The plan is to have a single bench that I can bolt either the head or carburetor to. My biggest fear is that I won't be able to to run them both with the same motor or something of that nature which would make it pain to switch. The carburetor has a maximum bore of 0.925" and the valves on the engine measure approximately 1.0" in diameter.

With that being said, what size motor would I need to purchase in order to run this setup? My goal is to put the bench in my garage which only has standard 120V electric. I believe I have a 20 Amp breaker, but I don't know that for sure. I'll have to check on that. Ideally though, I would like to run it on a standard 15 Amp breaker so I can locate the bench anywhere I want.

Thoughts, comments, suggestions???

[jfholm]

If your valve is only 1 inch in diameter then You may not need a lot of airflow 1 in.² of perfect area Would flow 147 ft.³ a minute so you may be able to get away with just two vacuum motors I would make the flow bench capable of more than that but I would still Just start with two motors Look under the thread for air movers there should be a link there for the vacuum cleaner Motors called lighthouse vacuum cleaner motors and they have some specials on there for the flow bench people

[Tony]

Welcome to the forum.

A 120 volt supply with only 15 amps available is not a lot of power.
About the best you may be able to achieve will be perhaps about 150 CFM, but only with the most efficient motors available.
Some less than wonderful motors may only be able to reach half that airflow, which isn't going to be enough.
That should be sufficient to do what you want to do, but spend some time to do some research before you buy the motors.

The figures you need to be looking at will be CFM per amp at around 45 inches of back pressure.
Motor size has nothing to do with efficiency, but fit enough motors to take you comfortably above 15 amps flat out.
You can always reduce motor speed to lower the current drawn, but if you are flat out with less current and less airflow than is needed for the particular job, you will be cheating yourself.
So don't under power the bench, you need to be limited only by the available mains amps.

If you fit an amp meter to the bench, experience will quickly tell you where the main fuse usually pops, and you can stay just below that, without having to constantly fix blown fuses.

[Malvin]

Tony Wrote

You can always reduce motor speed to lower the current drawn, but if you are flat out with less current and less airflow than is needed for the particular job, you will be cheating yourself.
So don't under power the bench, you need to be limited only by the available mains amps.

That is really good solid Advise

You can always build your PTS flow bench like the 8 or 10 or 12 Vacuum motors & just put 4 vacuum motors in it & block off the rest of the openings
for the other vacuum motors that way in the future you can add motors &
not have to build a new flow bench.

[Heph]

Are you working on 2 or 4 valves per cylinder head ?

I work on 4 valves per cylinder heads and the intake valves are about 1"1/4 diam.
I built a PTS bench as per the drawings but fitted 4 engine instead of 8. This is about 5200W (4x1200) and that's fine for my needs with a fair safety margin.
Later on if I need to I'll be able to upgrade.

I'm in Europe so we have 240V and my setup "only" draws 22 Amps. So with 110V / 15A you might struggle to reach 28" depression if your cylinder heads are 4 valves.

But unless you're space limited, you should allow for later upgrade, you never know what you'll be working on next

[LWhitson2]

The engine is a single cylinder with two valves (one intake, one exhaust). I wish I had a 220V drop in my garage but the people who owned it before me did not see that as being necessary. I looked into installing one but all the electricians I talked with said it would be too expensive because of the distance between the garage and the house.

Thanks for the advice so far as it has given me a few things to consider. I checkout out the Lighthouse motors and it looks like a couple of the high-power/high-efficiency 120V motors may cover my needs. One other quick question, one person said that I need to look at the 48" vacuum numbers but everyone else is talking about 28" of vacuum. Was the 48 a typo or am I missing something here...

[Heph]

Yes you’re missing something : the measuring device.

To mesure airflow, you have an orifice plate and measure the pressure difference across it. So the motors needs to pull the 28” for the test piece plus the 16” (maximum) across the orifice plate.
That’s 44” total.

So on lighthouse chart you need to look for +/- 45” to get the usefull flow of the motors.

[Tony]

See how you go sourcing some really efficient motors, but I still feel 110 volts and 15 amps is going to be a major restriction.
And 45 inches back pressure was not a typo, it is the pressure the motors have to work against which is 28 inches test pressure, plus typically 16 inches across the flow measurement system, (rounded to 45 inches).

One alternative might be to run as many motors as you possibly can from the power that is already available, which may be sufficient for some useful testing.

If you run out of air, how about running a big extension cable back to the house, and plug it into another completely different circuit, maybe even 220 volts ?
That could enable you to run a whole bunch of additional motors, which may not be needed all that often.
And it is something you can do yourself at minimum cost quite legally.
And it would be landlord friendly.

[LWhitson2]

It's not a landlord issue, it's just a "too cheap to run a 220V line to my garage" issue. Most of the quotes were on the order of $400-$500. I could probably just run it off of a couple different breakers out there. I think there are four different breakers for the garage alone.

[Bambi4010]

So you have a sub panel in the garage? Can you explain exactly what you have or post pics? There are some electricians on here that may be able to help you out.