Bigger blower = more power?

LT1Porsche

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So I poked around and didn't see exactly what I was looking for so just thought I'd ask.

So a couple people were standing around having a convo about upgrading blowers and turbos and I made a comment that a bigger displacement blower will make more power at a given PSI than a smaller displacement blower. It was at that point another guy chimed in and stated that PSI is PSI and it doesn't matter the blower size. He said that if a smaller and larger blower were compared at the same peak PSI they would make the same HP. Now I have personally seen a comparison that disproves his theory. Now in the past I have been taught that the turbine efficiency of a turbo increases velocity which helps move air fast therefor allowing the engine to take in more air which in turn makes more power but that's making a change that effects exhaust backpressure and the recycle of exhaust gas. How does this change in efficiency occur with a bigger blower when the exhaust side of the engine remains unchanged. I know a bigger blower works harder to create the same pressure so is the gain in HP directly related to heat or is the bigger blower also moving more air at the same time and even though both engines are seeing 15psi (lets say) the larger blower is making that same pressure with a higher volume of air.

My belief was the larger blower is moving more volume at a more efficient level therefor also creating less heat and making more power.

His argument was if both blowers were pushing the same PSI and had the same IAT they would make the same power. Which I disagreed with.

Thanks
 

SID297

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Bigger doesn't necessarily make it more efficient. A 1.9L TVS is more efficient as a a street blower than a 2.3, but guess which one sells better?
 

Catmonkey

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I believe efficiency does indeed impact usable power under the curve. You're ignoring the characteristics of a bigger blower by isolating a single data point at the peak power output. I've seen a whole lot of dynos that show reduced boost with bigger blowers in the lower rpm range which also reduces torque. You might make more power at the peak with a bigger blower, but if it's too big, it acts just like a centrifugal blower and tends to make boost in a progressive fashion, not linear like a proportionately sized blower would make.

So in your example let's say a smaller blower is making 15 psi of boost through the pull and your bigger blower is making 10 psi at the hit because it's out of it's efficiency range below 5,500 rpm. Will the resultant parasitic loss in spinning slower make up for the reduced torque and horsepower? Only the track will tell? I tend to look at average horsepower and torque, not just what it makes at the peak. There are a lot of trade offs in the bigger vs smaller debate. Just remember, we can't just drive at the peak.
 

LT1Porsche

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I know a smaller blower will make more power under the curve and be more usable daily driving. This wasn’t started to ask which blower is more suitable for usable power. The question is at a given pressure (15 psi vs 15 psi) will a bigger blower make more power than a smaller blower? If so, why? Is it because it’s moving a larger volume of air at the given pressure while at a lower charge temp? Or is the increase in power specifically coming from the lower charge temp because the blower is working more efficiently at the peak pressure? Thanks
 

fullboogie

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You also need to consider how much HP it takes to drive each of those blowers to achieve the 15 psi you are talking about.
 

Black Cobra '99

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The other guy is mistaken, PSI is a measure of restriction. It seems to me he thinks its a measure of power and thats why he thinks a small blower and a bigger one will be equal.
Everything else equal, the bigger blower will produce more power because it moves more air at the same restriction (PSI) level. So yeah, you are right.
 

Weather Man

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It depends on efficiency of blower and parasitic loss from the particular blower. A 2.6 Kenne Bell will make more power than a 3.4 whipple at 19 PSI. The whipple consumes way more power and is not in its efficiency zone. Push both blowers to 28 PSI and it reverses, the 2.6 is out of the zone producing tremendous heat and the whipple is dancing.
 

Handlebar Moustache

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upload_2018-7-4_15-24-46.png


KB has a lot of info on that topic on their website. How much of it is marketing hype...that I don't know. Here's some peak dyno numbers comparing the 2.8L KB to the 3.2L KB at various boost levels. Sort of apples to apples, since they both use the same basic design; one is just larger.
 

Robert M

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I wonder why Ford didn't just spin the smaller 2007-2012 Eaton a little faster for the 2013/14 if larger really doesn't matter at the street PSI levels that most of our cars are driven and/or raced?.........if smaller is more efficient?



R
 

merkyworks

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I wonder why Ford didn't just spin the smaller 2007-2012 Eaton a little faster for the 2013/14 if larger really doesn't matter at the street PSI levels that most of our cars are driven and/or raced?.........if smaller is more efficient?

Not sure what you are implying.

2007-2012 had a 2.3L Eaton 3 lobe rotor pack
2013-2014 had a 2.3L TVS 4 lobe rotor pack

Ford didn't change the size of the SC, they just moved to a more efficient rotor pack.
 

LT1Porsche

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Not sure what you are implying.

2007-2012 had a 2.3L Eaton 3 lobe rotor pack
2013-2014 had a 2.3L TVS 4 lobe rotor pack

Ford didn't change the size of the SC, they just moved to a more efficient rotor pack.

The 07-12 blowers are 2.0L blowers not 2.3L. 07-12 gt500 are 5.4L engine with 2.0L blower. 13-14 gt500 are 5.8L engine with 2.3L blower.
 

Weather Man

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Here is a chart with 2 3V 2.6 Kenne Bells against my 3.4 whipple. All cars 4.6L. It is a pretty dramatic demonstration of the whipple not being efficient and consuming LOTS of HP. By the time the Whipple catches up, the race would be over. Now the Kenne Bells were pretty much maxed for their setups and my Whipple had tons of room for power growth.

PVumO6T.png
 

Klaus

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Here is a chart with 2 3V 2.6 Kenne Bells against my 3.4 whipple. All cars 4.6L. It is a pretty dramatic demonstration of the whipple not being efficient and consuming LOTS of HP. By the time the Whipple catches up, the race would be over. Now the Kenne Bells were pretty much maxed for their setups and my Whipple had tons of room for power growth.

View attachment 1499827

Is light blue 3.4?
 

Weather Man

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Is light blue 3.4?

It is the bottom trace that doesn't catch up until way up there. It is amazing how badly they kick sand in the 3.4's face. It could be argued that 3.4 on a 4.6 is just to much blower unless an all out race effort.
 

Catmonkey

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All blowers have a sweet spot and it's a narrow window of where it's at in terms of peak efficiency, albeit it is a tapered peak. If that sweet spot is too low in the power band, it's going to run out of steam on the top end. If that sweet spot is in the middle of the power band, you have usable power above and below it. If the sweet spot is too high in the power band, the blower is going to be down on power in the lower to mid range.

If you look at the bottom part of Weather Man's chart, the only place you sort of see boost points coming close to the same point in terms of rpm it's just before 6 grand. I don't see that's it's leading that pack at that stage.
 

Klaus

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It is the bottom trace that doesn't catch up until way up there. It is amazing how badly they kick sand in the 3.4's face. It could be argued that 3.4 on a 4.6 is just to much blower unless an all out race effort.

Boost pressure of red and dark blue are goofy to me, especially >6k. They look like turbos that have waste gate issues.
 

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