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Discussion Starter #1
Just wondering what the conversion would be to get from a flow value of mineral spirits to a flow value of gasoline

we use mineral spirits(with a touch of Marvels Mystrey Oil added as Lube) because its a good cleaner, and its not explosive like gasoline is

but we dont know the math to convert to a realistic flow rate for gasoline from this.


say we flow an injector, and we get 700cc/min in mineral spirits...

what should it equate to in gasoline?

we are in a room with the thermostat set to 72*, and the temperature of the Mineral Spirits in the tester from day to day is consistent within a degree or two either side of it.
 

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Did you ever figure this out? What did you come up with?

Here's my answer (yeah, better late than never right?). The difference would be in the mass of gasoline versus the mass of mineral spirits. You already know the volume of your example injector is 700 cc/min for mineral spirits, and you want to know the mass (lb per hour) for gasoline. The volume would remain 700cc for each fluid, as long as the viscosity of the fluid wasn't much different (for example, maple syrup versus water or 50w oil versus 20w).

We need to convert cc (volume) to lb (mass). Then, we need to convert from the mass of mineral spirits to the mass of gasoline.

It boils down to the specific gravity of each fluid. Pump gas probably has a specific gravity of .73 to .76, but you'll get a whole lot of different answers when you ask that question. Likewise, when I looked up the material safety data sheets of the first 3 mineral spirits I ran across, I got 3 very different answers for specific gravity also: .74, .78, and .81. At least with the mineral spirits, you can look up the specific MSDS for that brand. And with race gas, you can look up the specific gravity for that particular fuel/octane.

If you have a specific gravity that is the same for both fluids, there is no need for conversion. Usually, injector testing is done with n-Heptane (.681 specific gravity). And a conversion multiplier formula I found on the internet for n-Heptane to gasoline is 1.035x.

Test fluids like n-Heptane can be purchased from test fuel suppliers, and would come with an MSDS with specifics for that batch, I'm sure. The big variable would be the specific gravity of gasoline, which probably is different for every batch of pump gas, but should be more consistent for race fuels. There's testers for fuel to check that as well.
 

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Discussion Starter #3 (Edited)
it actually ends up being pretty close...
the mineral spirits we use are pretty close to the same specific gravity as gasoline most of the time

its close enough that a 600cc injector usually flows right at 600cc within a few cc's most of the time

and either way... the machine is mostly to clean, test, and flow injectors to make sure they all flow the same
 

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Viscosity has significant effect when comparing flow rates. Adding oil to the solvent will reduce the flow because of increasing the viscosity, so if you want your numbers to be consistent you need to take care to always use the exact same amount. You could make a simple viscosity checker with a small carb jet in the bottom of a liter or 2 liter bottle and use a stop watch to measure how long it takes it to run the same quantity through the container.

A pal of mine was just here with his weed whip because it wouldn't run. It is a new 4-cycle engine weed whip and he didn't notice this so he mixed oil with the gas like he did for his old 2-cycle whip. That may not have been much of a problem except he used too much oil, about enough for 2 gallons in about a quart of gas. It is a tiny engine, 27 cc or so I think, so the main jet is tiny enough the increased viscosity from the too-much oil made it so lean it wouldn't run at WOT at all, just died if you open the throttle, though it would idle. Just changing the gas to straight unleaded (like it says right next to the gas cap, LOL) and flushing the oil mix out of the carb and fuel filter made it run like new. Damn TCW oil is slimy stuff.
 

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That's an interesting observation, and a neat trick for comparing viscosity of two fluids. But I wonder if the specific gravity would also alter that viscosity test, since the weight of the fuel in the 2 liter would be different, applying more pressure to the fuel going thru the jet.

From what I've been told by the pros, the viscosity doesn't much matter, because we're generally all using a fluid similar to fuel. A situation something like you mentioned with using oil would certainly produce a much bigger effect.
 
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