Excellent Document Regarding Supercharger Technology From the Man who Designed both
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Excellent Document Regarding Supercharger Technology From the Man who Designed both
This document was sent to a potential client in another forum when he posed a question directly to Vortech Engineering, the company that supplies RIPP with the V3 Centrifugal supercharger. The document was the response he got in relation to his question. It is written by Jim Middlebrook, owner designer and chief-engineer at Vortech. Vortech designs and manufactures what is considered the best centrifugal supercharger on the market and owns Lysholm, the best Twin Screw on the market as per the SAEJ1723 testing. The question, regarding boost levels and subsequent heat in relation to non-intercooled supercharger kits like the ones recently proposed to this community by another manufacture. This document outlines the pros and cons between different types of superchargers and why OEM's pick one over the other. It also outlines the loss is power at the crank between the two as well at the heat. The supercharge used to test against V3 is the newer Kenny-Bell which is one of the most efficient positive displacement (Roots, Whipple or Twin Screw's) on the market. We would be more thorough in posting comparisons charts to demonstrate the difference, but we cannot find any reasonable compressor maps on the net to compare to the V3. Vortech makes all their documents viable on their website for any and all to see.
Please keep in mind, we do sell a non-intercooled supercharger kit and it is safe to run, but there is a definitive power-loss throughout the power-band as a result. Hence, we sell 100 to 1 (intercooled/non-intercooled)
RIPPTECH
COMPARING TWO STATE OF THE ART AUTOMOTIVE SUPERCHARGERS
ROOTS TYPE verses CENTRIFUGAL
Jim Middlebrook 15 February 2012
The question always arises: why do the auto manufacturers (OEs) nearly always choose a roots type supercharger? The one word answer is price. Sure, there may be other influences such as the supplier’s requirement for tier-one status, or the extreme marketing efforts that no centrifugal manufacturer can match. But cheap pricing to the OEM’s is compelling enough to make up for all the deficiencies associated with the roots type supercharger. Please note that the roots type can be called a supercharger, but not a compressor, because it is not; it’s an air mover.
One misconception is about the airflow path for these Roots superchargers: the air does not flow through or between the rotors but rather around, on the housing sides within the voids of the rotors. The roots supercharger traps air in a chamber between the rotor and the housing, in the void between the rotor’s lobes, and transports this trapped air to the outlet side, at the engine’s intake manifold. By virtue of moving air into the manifold at a rate higher than the engine consumes it, pressure is built. Every time the chamber of trapped air opens to the manifold, the previously pressurized manifold air reverse flows into the chamber until pressure is normalized, then the chamber is closed and exhausted as the rotors mesh together. This “reversion”, plus the internal leakage between each rotor as well as the housing, combined with the tortuous flow path the air must follow, is why the roots type supercharger is the least efficient of the types available. Additionally, this pulsed delivery results in a loud and unpleasant shriek at higher speeds. While the aforementioned process can offer reasonable performance at low pressures, say 5 to 6psig, operation at one atmosphere (14.7 psig) and above, clearly shows the limitations of the device. When operating a Roots supercharger at higher pressures, it is probable that half of the input power is consumed to make heat rather than pressure. This would roughly indicate a very low adiabatic efficiency of 50%, or below. It is possible for a centrifugal to operate this inefficiently also, but it would be due to an exceptionally poorly designed and sized installation and certainly not typical.
When we use the term supercharger efficiency, we mean adiabatic efficiency as an expression of how well the supercharging process works. All of this supercharging process is about increasing air density (pressurizing or compressing air) and an inefficient supercharger will put more heat into the air during process, and thus reduce density, than an efficient one. Further, that heat isn’t free, it was bought by a parasitic power drain on the engine.
Some manufacturers will attempt to mislead or confuse shoppers by using the term volumetric efficiency instead of adiabatic, so they can display a very favorable number, usually in the ninety percent range. The term volumetric efficiency only refers to how well the chambers are being filled and has little to do with how well the supercharger is working; this term only applies to positive displacement devices and not to centrifugals. Others, even large OEM suppliers, will sometimes offer sales materials or compressor maps showing unlikely performance and/or supercharger efficiencies. They definitely have a straw in the Kool-Aid.
Some are eager to point out that the roots type supercharger will make boost [pressure] at very low engine RPM. This is true; they make more boost than a centrifugal at low speed and less at high speed, but this feature is much less helpful than it would first appear. First, excessive boost cannot be utilized at these low speeds. On most engines the ignition timing must be significantly retarded to avoid destructive detonation that it is very probable that no net increase in power is realized especially considering the parasitic drive losses. Second, the newer high performance engines with variable valve timing and inlet runners have more than enough low speed power to exceed the tire traction available. Third, low engine speed is not where power is made. Fourth, when roots advocates point out the “area under the curve” they usually refer to a huge misrepresentation of what the curve should look like; no one can explain the mathematical significance of this phantom area! Further they ignore the heat soak and inherent “nosing over” performance of the roots type at higher engine speed, right when a high performance vehicle should pull the hardest.
For similar output, a roots type supercharger will out weigh a centrifugal by about eight times, and will generally require a larger, heavier charge cooling system. Also it is necessarily placed in the worst possible place: way up high and forward, right on top of all the other weight. A competent circuit driver can feel the unwelcome weight.
Adding a roots type supercharger to an engine that has a tuned runner, or variable runner, intake system will usually require the removal of the tuned system and the loss in those free benefits. A centrifugal does not require this removal and all the engineered-in tuning can still be appreciated.
The rotating mass of a typical roots type supercharger for a V8 is large, with very high inertia compared to most centrifugal compressors. The power it takes to accelerate that inertia, to speed it up or slow it down can be huge and this is independent of actually doing any useful work.
So, with a roots type supercharger you get:
A noisy, heavy, high inertia, poorly placed, air-moving device that makes too much boost when you can’t use it and not enough when you can, that is as good a heater as it is a supercharger, that shows even lower performance after a full warm up. And when the profilers on flash that big horsepower number on You tube, you can bet two things, it was a first “pull” with a cooled engine and they won’t show a second “pull” because it will be much lower and a third even more so. Centrifugal compressors are in a different league.
THE NUMBERS
Test point:
Flow: 25 M/min (883 CFM)
Pressure: 2.0 PR (~14.7 psig.)
70°F
Best Selling Positive Displacement Supercharger
Vortech V3 (used in all RIPP Supercharger kits)
Please keep in mind that RIPP runs its JK kits at 8psi peak boost - Vortech has calculated our crank Drive Train power to be 11-15peak HP to deliver 120peak rear wheel HP...
Please keep in mind, we do sell a non-intercooled supercharger kit and it is safe to run, but there is a definitive power-loss throughout the power-band as a result. Hence, we sell 100 to 1 (intercooled/non-intercooled)
RIPPTECH
COMPARING TWO STATE OF THE ART AUTOMOTIVE SUPERCHARGERS
ROOTS TYPE verses CENTRIFUGAL
Jim Middlebrook 15 February 2012
The question always arises: why do the auto manufacturers (OEs) nearly always choose a roots type supercharger? The one word answer is price. Sure, there may be other influences such as the supplier’s requirement for tier-one status, or the extreme marketing efforts that no centrifugal manufacturer can match. But cheap pricing to the OEM’s is compelling enough to make up for all the deficiencies associated with the roots type supercharger. Please note that the roots type can be called a supercharger, but not a compressor, because it is not; it’s an air mover.
One misconception is about the airflow path for these Roots superchargers: the air does not flow through or between the rotors but rather around, on the housing sides within the voids of the rotors. The roots supercharger traps air in a chamber between the rotor and the housing, in the void between the rotor’s lobes, and transports this trapped air to the outlet side, at the engine’s intake manifold. By virtue of moving air into the manifold at a rate higher than the engine consumes it, pressure is built. Every time the chamber of trapped air opens to the manifold, the previously pressurized manifold air reverse flows into the chamber until pressure is normalized, then the chamber is closed and exhausted as the rotors mesh together. This “reversion”, plus the internal leakage between each rotor as well as the housing, combined with the tortuous flow path the air must follow, is why the roots type supercharger is the least efficient of the types available. Additionally, this pulsed delivery results in a loud and unpleasant shriek at higher speeds. While the aforementioned process can offer reasonable performance at low pressures, say 5 to 6psig, operation at one atmosphere (14.7 psig) and above, clearly shows the limitations of the device. When operating a Roots supercharger at higher pressures, it is probable that half of the input power is consumed to make heat rather than pressure. This would roughly indicate a very low adiabatic efficiency of 50%, or below. It is possible for a centrifugal to operate this inefficiently also, but it would be due to an exceptionally poorly designed and sized installation and certainly not typical.
When we use the term supercharger efficiency, we mean adiabatic efficiency as an expression of how well the supercharging process works. All of this supercharging process is about increasing air density (pressurizing or compressing air) and an inefficient supercharger will put more heat into the air during process, and thus reduce density, than an efficient one. Further, that heat isn’t free, it was bought by a parasitic power drain on the engine.
Some manufacturers will attempt to mislead or confuse shoppers by using the term volumetric efficiency instead of adiabatic, so they can display a very favorable number, usually in the ninety percent range. The term volumetric efficiency only refers to how well the chambers are being filled and has little to do with how well the supercharger is working; this term only applies to positive displacement devices and not to centrifugals. Others, even large OEM suppliers, will sometimes offer sales materials or compressor maps showing unlikely performance and/or supercharger efficiencies. They definitely have a straw in the Kool-Aid.
Some are eager to point out that the roots type supercharger will make boost [pressure] at very low engine RPM. This is true; they make more boost than a centrifugal at low speed and less at high speed, but this feature is much less helpful than it would first appear. First, excessive boost cannot be utilized at these low speeds. On most engines the ignition timing must be significantly retarded to avoid destructive detonation that it is very probable that no net increase in power is realized especially considering the parasitic drive losses. Second, the newer high performance engines with variable valve timing and inlet runners have more than enough low speed power to exceed the tire traction available. Third, low engine speed is not where power is made. Fourth, when roots advocates point out the “area under the curve” they usually refer to a huge misrepresentation of what the curve should look like; no one can explain the mathematical significance of this phantom area! Further they ignore the heat soak and inherent “nosing over” performance of the roots type at higher engine speed, right when a high performance vehicle should pull the hardest.
For similar output, a roots type supercharger will out weigh a centrifugal by about eight times, and will generally require a larger, heavier charge cooling system. Also it is necessarily placed in the worst possible place: way up high and forward, right on top of all the other weight. A competent circuit driver can feel the unwelcome weight.
Adding a roots type supercharger to an engine that has a tuned runner, or variable runner, intake system will usually require the removal of the tuned system and the loss in those free benefits. A centrifugal does not require this removal and all the engineered-in tuning can still be appreciated.
The rotating mass of a typical roots type supercharger for a V8 is large, with very high inertia compared to most centrifugal compressors. The power it takes to accelerate that inertia, to speed it up or slow it down can be huge and this is independent of actually doing any useful work.
So, with a roots type supercharger you get:
A noisy, heavy, high inertia, poorly placed, air-moving device that makes too much boost when you can’t use it and not enough when you can, that is as good a heater as it is a supercharger, that shows even lower performance after a full warm up. And when the profilers on flash that big horsepower number on You tube, you can bet two things, it was a first “pull” with a cooled engine and they won’t show a second “pull” because it will be much lower and a third even more so. Centrifugal compressors are in a different league.
THE NUMBERS
Test point:
Flow: 25 M/min (883 CFM)
Pressure: 2.0 PR (~14.7 psig.)
70°F
Best Selling Positive Displacement Supercharger
- Volumetric efficiency 84%
- Adiabatic efficiency 55%
- Discharge temp. 114°C (237°F)
- Drive power (81hp)
- Hot soak effects devastating
Vortech V3 (used in all RIPP Supercharger kits)
- Volumetric efficiency N/A
- Adiabatic efficiency 78%
- Discharge temp. 83°C (182°F)
- Drive power (40hp)
- Hot soak effects incidental and stable
Please keep in mind that RIPP runs its JK kits at 8psi peak boost - Vortech has calculated our crank Drive Train power to be 11-15peak HP to deliver 120peak rear wheel HP...
JK Newbie
Joined: Dec 2010
Posts: 56
Likes: 0
From: Edmonton
Pretty much in toe with what the staff has championed all along. Proof in the pudding, as they say.
Too bad a properly built PR44 is so damn expensive or I'd be sneezing my way around the city in a few weeks. Oh well; 11 months isn't so long!
Too bad a properly built PR44 is so damn expensive or I'd be sneezing my way around the city in a few weeks. Oh well; 11 months isn't so long!
so confused.