Bigger blower = more power?

Catmonkey

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M112 was used as the production supercharger in the Lightning and Harley Davidson F-150s. It's got a very small inlet, unlike the M122 and was top feed. It was never used on the GT500.
 

69b302

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Bigger Blower=more peak HP. Yes some smaller blowers are more efficient down low. Know your application before purchasing.
 

LT1Porsche

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So the start of the thread wasn’t to determine which blower would work better where. It’s a question about the relation of PSI and Volume. So the statement was a bigger blower and smaller blower with make the hp at the same psi. If you were able to remove parasitic loss as a factor and keep Charge temp the same would they make similar power?
 

Catmonkey

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I have to think so assuming both are capable of making the same amount of boost at the same rpm and identical timing. I think parasitic loss and charge temps probably play the bigger role in influencing a different outcome. But it's a given you will have to spin a smaller blower faster to generate the same amount of boost as a bigger blower. It may or may not consume more power to spin the rotors depending on the extremes of the different combinations used in a comparison. A smaller, or I should say an undersized, blower is generally way outside its adiabatic efficiency, if the measurement occurs at or closer to peak power output where the bigger blower should be closer to it's peak adiabatic efficiency. That will generally requiring spinning the little blower even faster and generate higher charge temperatures. I guess the real answer is "it depends".
 
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69b302

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So the start of the thread wasn’t to determine which blower would work better where. It’s a question about the relation of PSI and Volume. So the statement was a bigger blower and smaller blower with make the hp at the same psi. If you were able to remove parasitic loss as a factor and keep Charge temp the same would they make similar power?

If you remove the parasitic loss differences and heat differences, at the same boost and engine rpm, then they would make the same power IMO. At the same boost/psi the airlflow is the same, since that is dependent on engine restrictions(heads, cams, exhaust, etc), and not the blower on top.
 
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fullboogie

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So the start of the thread wasn’t to determine which blower would work better where. It’s a question about the relation of PSI and Volume. So the statement was a bigger blower and smaller blower with make the hp at the same psi. If you were able to remove parasitic loss as a factor and keep Charge temp the same would they make similar power?

If you remove parasitic losses and heat, you disregard the differences between the blowers - which just makes it an academic exercise. So with those assumptions, the answer would be yes, but it's not a real world scenario.
 

LT1Porsche

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If you remove parasitic losses and heat, you disregard the differences between the blowers - which just makes it an academic exercise. So with those assumptions, the answer would be yes, but it's not a real world scenario.
So I guess that’s the actual question. What is the relation to boost pressure and volume? Can a bigger blower move a large volume of air at a given pressure when compared to a smaller blower? So is a 4.0L blower moving more air at 15psi than a 2.0L blower at 15psi?
 

sono

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I think it's 2 fold
1st and most important is blower efficiency. Better design, 3 lobes vs 4, twists etc, also how much hp to spin the blower. Best case they were completely efficient and weighed nothing vs a gun safe that's hard to spin.

2nd Bigger is better.
I say look at a 2.3 boost curve vs 4.0 liter boost curve. All things being equal the bigger blowers makes desired boost quicker due to slower rpms, and the boost never peaks or dips because you are at half it's limits in most scenarios. Using the same blower designs.
I refer to 2 engines that both make 400hp/tq and spin to 7000rpm, but one makes the power much earlier in the rpm range.
 

StrayBullitt

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Could we all wrap our head around the idea that a bigger blower could make equal or more power on a dyno at less psi ? If so, then how would it not out perform at equal psi.

A bigger blower with more volume needs more air volume compressed inside of it to create the same pressure. Think of it as filling up a small tire vs a large tire to a certain pressure, more air is needed.

You can search this topic in the Turbo world, it's been discussed same principal of compressing air, large turbo vs small at the same boost pressure.
 

StrayBullitt

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So I guess that’s the actual question. What is the relation to boost pressure and volume? Can a bigger blower move a large volume of air at a given pressure when compared to a smaller blower? So is a 4.0L blower moving more air at 15psi than a 2.0L blower at 15psi?

Yes, there is more air volume inside a 4.0 L blower vs a 2.3 L at a given psi.

I just went back and watched VMP's Gen 3 video on Justin's GT500. At the 5:40 mark of the video he shows a dyno graph, gen 3 vs gen 2 R. After 4500 rpm, boost pressure is nearly Identical at around 18psi, power is up around +30 over the curve on the Gen 3. Under 4500 rpm, Gen 3 is lagging slightly in boost pressure, power is still up slightly on the whole pull, I would be curious about the charge air temps, though at 18 psi I would think they may be comparable through both blowers.
 

69b302

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What is the relation to boost pressure and volume?

OK, so if you use one air pump to inflate a tire to 35 psi, and then use another air pump to inflate the same tire to 35 psi, do you think the volume of compressed air is different based upon the pump you used? The volume of air is the same at a given rpm and boost. Heat does impact the density(not volume). Colder air is better as it contains more O2 than hot air, at the same volume, in addition to helping avoid knock. My 0.02.
 

LT1Porsche

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OK, so if you use one air pump to inflate a tire to 35 psi, and then use another air pump to inflate the same tire to 35 psi, do you think the volume of compressed air is different based upon the pump you used? The volume of air is the same at a given rpm and boost. Heat does impact the density(not volume). Colder air is better as it contains more O2 than hot air, at the same volume, in addition to helping avoid knock. My 0.02.

Using this theory your HP gains with a bigger blower at equal or less pressure would be a result that could only explained by temps and the HP gains would mostly be seen at higher boost pressures. That’s the side of the argument I’m not agreeing with. 15psi from one blower is not equal to 15psi from every blower as far as volume because that would leave your HP gains only to thermodynamics and efficiency characteristics of each blower. Totally ignoring CFM capability. I’ve seen bigger blowers make more power on less PSI. Those gains cannot only be from temp and parasitic loss. Has to be a volume. With turbos there is a scanvenging effect caused which increases velocity through the ports which is said to be where most of the increase in HP comes from in that area. Now taking that out of the equation bc we aren’t dealing with turbos.
 

fullboogie

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Porsche, don't overlook the hp needed to drive the blowers. Kenne Bell has a few really good articles about this topic and if I recall, the numbers are quite significant. All this boils down to net hp, so you have to take into account hp losses to drive a small blower at 15 psi vs. hp losses to drive big blower at 15 psi, right? Seems that a larger blower that doesn't work as hard to achieve the 15 psi takes less hp to drive, which may be the difference you are looking for. Just an idea. I'm no engineer, just going on what *might* make sense.

Isn't this the same reason the TF and Alcohol guys switched to the high helix twin screws years ago? Same psi, less hp to drive the blower, so more net hp.
 
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Weather Man

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Go back and look at my dyno chart. The 3.4 is at 19 psi and the 2.6 blowers are 3-4 psi less and kicking the 3.4's ass. I have been on here a while and noticed a guy pick up a 3.4 for a 4.6 and then a month later it's for sale. GT500 guys with more displacement and a better intercooler have better results.

Parasitic power loss is real and substantial and 4.6 guys (especially) should take careful note. It is ironic that since I don't have that wall of torque hitting the tires, my car is a hoot to drive on the street and very controllable.
 

Robert M

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This is an interesting discussion. So how would a blower be chosen as the "sweet spot " in size for a specific CID application? At some point the blower would be too small and at some point a blower could be too large. I would guess that spinning the blower slower would generate less heat, heat is something we all fight, heat robs power.

And on the 2007-2012 Eatons, I had always understood that they were the same size M122, but with a color change only in 2011?


R
 
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fullboogie

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This is an interesting discussion. So how would a blower be chosen as the "sweet spot " in size for a specific CID application? At some point the blower would be too small and at some point a blower could be too large. I would guess that spinning the blower slower would generate less heat, heat is something we all fight, heat robs power.

And on the 2007-2012 Eatons, I had always understood that they were the same size M122, but with a color change only in 2011?


R

Gotta look at the compressor maps, which are on Eaton's website. Check this out for the TVS: TVS® Supercharger, Twin Vortices Series® Superchargers - Vehicle - Eaton

It's the same for sizing turbos and centrifugals. And yes, all these years later, it's amazing there is still confusion as to our stock blowers.
 
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Klaus

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I have about as like for like comparison as there is. Today I switched from VMP gen2 to gen3. The designs are very similar, with one being larger than the other. Cannot speak to differences in case dimensions or flow, but the similarity is definitely closer among these two than any other comps.

Motor is 2012 5.4 set up was exactly the same for both: ID 1000s, VMP twin 67 TB, 128 CAI, VMP BAP, kooks long tubes and full exhaust. I ran a 2.4 pulley on the gen 2 and a 2.8 pulley on the gen 3.

I do not have jpeg of graph, but peak HP was 662 on the gen 2 and 681 on the gen 3. I lost a tiny bit of torque going to the bigger blower, but the butt dyno gives indication that gen 3 is definitely stronger. It is more responsive and boost comes on faster.

Both were at 17 lbs of boost. I do not have data log in front of me but we did have to pull timing on the gen 3. Air temp was 14 degrees hotter when I ran the gen 3 although air temp at blower inlet was only 6 degrees warmer. While I had 147 CAI, I could not run it because we could not get the big KB TB to fit onto the gen3. It was clearly choking with the smaller TB and CAI and would have responded very nicely with larger of each.

So, conclusions on as like for like comparison as I can think of? Larger blower at same boost does = more power. The curve was smoother and it is clearly running more efficiently. Not by much though. Honestly not by enough to matter with current set up. That said, the potential with the larger blower with larger CAI + TB + E85 is FAR greater than it is with smaller. Nevertheless, the data is what it is and larger blower was +20 WHP.
 

Weather Man

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For your engine size and the blowers used, pretty much what you would expect.
 

StrayBullitt

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@Klaus. Interesting, and that is a pretty good testament with higher charge air temps, less ignition timing and still made more power at the same Boost. Not too bad also considering only about 21 ?more ci from the Gen 3


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