Yellow Bullet Forums banner

1 - 20 of 47 Posts

·
Registered
Joined
·
6,968 Posts
Discussion Starter #1
With respect to a centrifugal blower, which uses more power?

Same blower turning same speed on a bigger motor making low boost vs. on a smaller motor making more boost?

Or are they the same?
 

·
Procharged SBC Enthusiast
Joined
·
5,150 Posts
The parasitic loss imop should be slightly less the less boost the engine is making . From a blower standpoint it is taking and compressing the same amount of air on either engine but the backup of boost in the plumbing you would think that you would use a little more hp to turn the blower with more boost upstream . JMOP
 

·
Registered
Joined
·
6,968 Posts
Discussion Starter #3
The parasitic loss imop should be slightly less the less boost the engine is making . From a blower standpoint it is taking and compressing the same amount of air on either engine but the backup of boost in the plumbing you would think that you would use a little more hp to turn the blower with more boost upstream . JMOP
That was my thought. I am curious about what others think.
 

·
Registered
Joined
·
20,079 Posts
just my .02, but wouldn't a bigger motor have more torq, so the power loss turning the SC would be less, plus the smaller motor making more boost would see the boost as more resistance, fighting against the comp. wheel
but then I only passed physics because I dated a girl who let me cheat off her work, lol
 

·
Registered
Joined
·
1,628 Posts
With respect to a centrifugal blower, which uses more power?

Same blower turning same speed on a bigger motor making low boost vs. on a smaller motor making more boost?

Or are they the same?

There is a paper on Vortec's web site on testing and efficiency that might be of interest.
 

·
Procharged SBC Enthusiast
Joined
·
5,150 Posts
IMOP, if there is enough restriction on the inlet side of the engine eventually the blower will start to see reversion which is another force the blower has to work against . I guess a lot would depend on how restrictive one engine is compared to the other. But with both engines spinning the blowers at the same speed the base Hp loss is the same wether it be driven by a BBC ,SBC or electric motor it takes x amount of HP to turn a blower compressing air at a given rpm with no restriction . Now when the blower is pumping against more resistance which is what boost essentially is the parasitic loss should go up . If it did not your power to parasitic loss on the dyno would be less drastic. It is very apparent when parasitic loss exceeds power being made on a dyno. My engine 2000 blower rpm was a wall . But if there was no extra parasitic drive loss from boost my engine should technically be able to make more power and overcome drive loss until the heads are lifting off the engine . Again JMOP.
 

·
Registered
Joined
·
6,968 Posts
Discussion Starter #10
In all examples impeller @ max RPM
Case 1: blower discharging to open air. Makes no boost, takes least power to drive.
Case 2: discharging into big deal motor. Makes low boost, takes a relatively little power to drive.
Case 3: small motor produces high boost and takes more power to drive.
Case 4: closed blower outlet. Max boost and max power to drive.

That's how I reason it. At any given RPM power to drive the blower is probably proportional to the boost.
 

·
Registered
Joined
·
25,667 Posts
I will take a low compression , long rod , short stroke, and 9500 rpm for the win.:p with a slightly oversize blower.:eek:
 

·
Registered
Joined
·
1,419 Posts
In all examples impeller @ max RPM
Case 1: blower discharging to open air. Makes no boost, takes least power to drive.
Case 2: discharging into big deal motor. Makes low boost, takes a relatively little power to drive.
Case 3: small motor produces high boost and takes more power to drive.
Case 4: closed blower outlet. Max boost and max power to drive.

That's how I reason it. At any given RPM power to drive the blower is probably proportional to the boost.
I know for fact #4 is wrong. With zero flow the blower goes into stall(might not be the right term) and drive loss goes way down.
 

·
Procharged SBC Enthusiast
Joined
·
5,150 Posts
Reversion is likely in#4 IMOP, the air likely starts exiting the inlet and therefore the blower cant compress much air.
 

·
Registered
Joined
·
331 Posts
Think it would have more to do with increased reversion and recycling of the same air due to increased boost - resulting in a reduction of mass flow through the engine - then the mechanical effect of the supercharger 'pushing' against a pressurized plenum. Takes 'x' amount of power to move 'x' amount of air...
 

·
Registered
Joined
·
4,570 Posts
Based on the Affinity laws the the power to drive the blower would be the same as long as the blower is operating within its curve on each motor regardless of the boost. Efficiency would be different :rolleyes:
 

·
Registered
Joined
·
775 Posts
I know for fact #4 is wrong. With zero flow the blower goes into stall(might not be the right term) and drive loss goes way down.
I remember u telling me with the discharge of the blower open it took a bunch of power to turn in testing. So that would be make #1 incorrect also
 

·
Registered
Joined
·
4,570 Posts
It seems like efficiency vs bhp is being confused. As I interpret the laws the bhp goes up/down with changes in volume(RPM) and impeller diameter.

The restriction effects efficiency. Even in surge or stall the power to drive the compressor at x rpm remains the same and the efficiency diminishes.
 

·
Registered
Joined
·
2,141 Posts
I know when I was back at Procharger that the BBC dyno motor wouldn't be able to spin an F3 to redline when blowing into atmosphere but as soon as you restricted the outlet of the blower it would spin right up to redline without a problem.
 

·
Registered
Joined
·
1,419 Posts
I know when I was back at Procharger that the BBC dyno motor wouldn't be able to spin an F3 to redline when blowing into atmosphere but as soon as you restricted the outlet of the blower it would spin right up to redline without a problem.
Shoot, we could barely get an F2 open to atmosphere to rev up when we tried it. I can't even imagine an F3
 

·
Registered
Joined
·
445 Posts
With respect to a centrifugal blower, which uses more power?

Same blower turning same speed on a bigger motor making low boost vs. on a smaller motor making more boost?

Or are they the same?
Refer to basic fan laws (probably several online calculators out there to plug numbers into and calculate different scenarios) to better understand the impact of pressure and volume on the flow of compressible gases.

Generally speaking, flowing a given mass of air at two different pressures (boost levels) the greater pressure will take more power (assuming the efficiency of the compressor does not change at the two different pressure levels)

Efficiency can come into play in some circumstances, but generally speaking if the compressor is well matched to the engine, efficiency is not a factor.
 
1 - 20 of 47 Posts
Top