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Discussion Starter #1
Having shoveled snow my whole life, I figured it time to get a snowblower of my own now that I fix them.:D
Jan. 2009 we got ton's of snow so it was time to find a new machine.
I was a little late. Most dealers here were already out of stock, except Sears.
When I called, they said they only had one left! Oh no, will I get there in time to get it? As it turned out, they had only one "model" left.
This machine has a 28" cut path and a BIG engine, Briggs 1150 Snow Series.
6 forward and 2 reverse speeds and an electric start.
It has been absolutely the best throwing blower I have run for the past 2 years. And I've worked on over 300 machine now, testing each one.
The other day I was tuning up a friends machine (Craftsman) cause it would not idle and only ran on choke. No big deal, but I noticed it had a 5.5HP Briggs yet a 24" cut width. Then another customer brought in a Craftsman with a 9HP Briggs with a 26" width. The 2 machines were obviously from the same era as they sported the same paint scheme.
The big difference I noticed was the impeller diameter. The 5.5HP had a 12" diameter impeller and the 9HP had a 9" diameter impeller.
Both machines run close to the same RPM and 5.5HP throws snow about twice as far!
Here comes the cool part. My Craftsman has a 12" diameter impeller and out throws both machines with ease.

Being a retired engineer, I was curious about the designs and subsequent performance differences. Well it really is simple to understand now.
If we use the same RPM of the engines as a comparative, the biggest contributing factor for performance is the impeller diameter relative to the torque of the engine at operating RPM.
You can look at it as a change of diameter at the same RPM as an equation for surface speed of the impeller's outside diameter. SFM is short for surface speed in feet per minute.

SFM=.262 x diameter x RPM

Example:
9" diameter at 3600 RPM is roughly 8488 SFM(surface foot per minute)
12" diameter at 3600 RPM is roughly 11318 SFM
This results in a 25% increase in SFM for the 12" diameter impeller.
In other words, the 12" diameter impeller is traveling 25% faster at the outside diameter.
This is how a 5.5HP engine can throw snow better than the 9HP.

Now add the torque and HP of the 1150 series Briggs to the faster 12" impeller and you have a very high performance machine.

Not trying to say Craftsman is the end all to snowblowers at all. Simply stating that, by accident, the Craftsman I ended up buying turned out to have the engineering elements to make it the "BIG DOG" of my neighborhood. I honestly have not even looked into who the manufacturer is for this machine. But for these past 2 years, I'm very pleased.
Not to mention I got out the door, brand new, for only $800.

And no I have not felt the need to "tweak" it yet.;)
 

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This makes me wonder why manufactures would offer anything less than a 12" impeller on their machines? Especially those with wider augers and larger engines.
 

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I think the smaller impellers usually turn faster.

The engines are 3600 RPM, but the impellers are more like 1,000 - 1,400 rpm.
 

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Yes, they just might, it would depend upon the sizes of the pulleys. Butchf's explanation was calculated at a comparable engine rpm, so that doesn't factor those variables in. Still, it stands to reason that you could feed more snow into a 12" opening than a 9".
 

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Discussion Starter #5
I did some searching to find the impeller RPM and found nothing. Maybe that is how the industry is keeping the consumer in the dark.:rolleyes:
The greater volume is one factor, yet momentum and velocity can overcome the volume. Those kits they sell for the impeller count upon sealing off the clearance between the impeller and shroud creating a type of pressure vessel.
Look at single stage, rubber paddle type machines. If the rubber is worn it has a problem throwing snow. Single stage blowers count on the auger speed and clearance to the shroud to create pressure. The same effect as the impeller on a 2 stage machine. The biggest difference is the auger feeds the impeller at a relatively consistent volume on the 2 stage and the single stage counts upon the "walking" speed of the operator.. The faster one walks the larger the volume being fed. I've seen many single stage machines that work good when you feed them fast, but stink when you go slow. Usually those are the ones that need need blades.
I'll just keep looking for the science of these things just to occupy my mind.:D
 

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Impeller speed = engine speed x engine pulley diameter / impeller pulley diameter.

(3600 x 3 / 9 = 1200)

A larger diameter impeller can process more snow than a smaller diameter pulley at the same speed.

A faster moving impeller can process more snow than a slower moving impeller.

It is all a balancing act.
 

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So, there's an optimal operation that gets met when the amount of snow thrown matches the ability of the machine to throw it. The depth and consistency of the snow has to be mated to the speed and potential volume the machine can handle. Go too slow with a high volume machine in light snow, for instance, or too fast in wet heavy snow with almost any machine, and the results can be less than desired.

Is there such a thing as maximum impeller rpm?

All very interesting, but I think we agree, actually fun when you hear the machine hunker down, fill the chute and throw the snow a good distance.
 

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Discussion Starter #8
Impeller speed = engine speed x engine pulley diameter / impeller pulley diameter.

(3600 x 3 / 9 = 1200)

A larger diameter impeller can process more snow than a smaller diameter pulley at the same speed.

A faster moving impeller can process more snow than a slower moving impeller.

It is all a balancing act.
We agree....:D
 

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Impeller speed = engine speed x engine pulley diameter / impeller pulley diameter.

(3600 x 3 / 9 = 1200)

A larger diameter impeller can process more snow than a smaller diameter pulley at the same speed.

A faster moving impeller can process more snow than a slower moving impeller.

It is all a balancing act.
Its a lot easier to understand that way. I'm not too familiar with snowblower so this helps me out. This should help me out when I'm looking for a new one later this year. :D
 
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