Rotrex Supercharger thread
10-01-2012, 08:27 AM
#151
Define a ton of timing? How many degrees? This is right in line, maybe a bit light for 7 psi. At 6 psi I made identical numbers but different dyno different day. I have -3 progressively taken out and up to an additional -3 taken out depending on my IAT sensor reading.
10-01-2012, 08:47 AM
#152
Rennlist Member
You would expect to take out about 1 deg of ignition advance for each lb of boost. If intake temps rise due to inadequte charge cooling, them more will be taken out, as Colin commented.
10-01-2012, 09:49 AM
#153
When I read your post, my first reaction was " Wow! That sounds really high." So I googled it and lo and behold, I came up with this chart. It sure is alot higher than I would have expected. I found it on this website, http://fepower.net/
Horsepower Consumed by Centrifugal Supercharger
Superchargers require power to run, and we thought it would be an interesting experiment to try to determine just how much power was required at various boost levels. To start this test we removed the supercharger belt from the 489" supercharged engine and ran it on the dyno naturally aspirated, to get a baseline horsepower curve. Then, we re-installed the belt and put an adjustable restrictor on the outlet of the supercharger, with a pressure sensor at the outlet to measure the boost. After some experimentation we were able to adjust the restrictor so that at 6000 RPM we got boost levels of 7, 13, and 17 pounds. We also monitored the airflow through the supercharger at these different levels. Boost and airflow at 6000 RPM are plotted on the graph at right, along with the horsepower loss for each pull, as compared to the baseline run. From the graph it is clear that it definitely costs some power to run the centrifugal supercharger
Horsepower Consumed by Centrifugal Supercharger
Superchargers require power to run, and we thought it would be an interesting experiment to try to determine just how much power was required at various boost levels. To start this test we removed the supercharger belt from the 489" supercharged engine and ran it on the dyno naturally aspirated, to get a baseline horsepower curve. Then, we re-installed the belt and put an adjustable restrictor on the outlet of the supercharger, with a pressure sensor at the outlet to measure the boost. After some experimentation we were able to adjust the restrictor so that at 6000 RPM we got boost levels of 7, 13, and 17 pounds. We also monitored the airflow through the supercharger at these different levels. Boost and airflow at 6000 RPM are plotted on the graph at right, along with the horsepower loss for each pull, as compared to the baseline run. From the graph it is clear that it definitely costs some power to run the centrifugal supercharger
10-01-2012, 10:33 AM
#154
Man of many SIGs
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Of course you wouldn't but that wouldn't be a proper test since the SC'er isn't blowing "into the wind" during normal use. If it didn't have any restrictions to it's flow during normal use you would never build any boost pressure.
10-01-2012, 10:52 AM
#155
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here is what I have read.
"The Rotrex supercharger’s unique traction drive also has the highest drive efficiency of any other blower with 98.4% efficiency which means less parasitic losses than traditional gear driven blowers allowing for better fuel economy when your foot isn’t buried in the throttle."
"A typical centrifugal supercharger is about 60-65 percent efficient, but according to Rotrex, the higher impeller speeds its units generate elevate them into turbocharger efficiency ranges of up to 80 percent or higher.
I will contact Rotrex and find out the exact numbers
"The Rotrex supercharger’s unique traction drive also has the highest drive efficiency of any other blower with 98.4% efficiency which means less parasitic losses than traditional gear driven blowers allowing for better fuel economy when your foot isn’t buried in the throttle."
"A typical centrifugal supercharger is about 60-65 percent efficient, but according to Rotrex, the higher impeller speeds its units generate elevate them into turbocharger efficiency ranges of up to 80 percent or higher.
I will contact Rotrex and find out the exact numbers
Last edited by victor25; 10-01-2012 at 11:13 AM.
10-01-2012, 11:08 AM
#156
Victor: Here is an article from Hod Rod Magazine regarding Rotrex. I like the mention of the dual supercharger setups like the ones they mentioned. That would look awesome with boost pipes on each side going to an intercooler at the back. Perhaps your next project?? 
http://www.hotrod.com/techfaq/hrdp_0...r/viewall.html
http://www.hotrod.com/techfaq/hrdp_0...r/viewall.html
10-01-2012, 12:48 PM
#157
Rennlist Member
Those numbers are exactly what I was expecting.
Plumb the IC with a proper water system and you will gain more power and be able to put down more ponies!
The fact you have to pull tons of timing up top says the air is too hot. This also means that your AFR will have to be readjusted as colder air is much more dense.
Plumb the IC with a proper water system and you will gain more power and be able to put down more ponies!
The fact you have to pull tons of timing up top says the air is too hot. This also means that your AFR will have to be readjusted as colder air is much more dense.
?
10-01-2012, 12:51 PM
#158
Rennlist Member
Define a ton of timing? How many degrees? This is right in line, maybe a bit light for 7 psi. At 6 psi I made identical numbers but different dyno different day. I have -3 progressively taken out and up to an additional -3 taken out depending on my IAT sensor reading.
10-01-2012, 12:53 PM
#159
Man of many SIGs
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The advertised efficiency of a supercharger or turbo has nothing to do with how much HP it takes to drive it. It refers to how much the charge air is heated.
10-01-2012, 01:00 PM
#161
Man of many SIGs
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I'm not sure what that means but...OK. 
Here are a few paragraphs from the article that Cosmo Kramer posted regarding the efficiency of compressors and specifically the Rotrex.
Here are a few paragraphs from the article that Cosmo Kramer posted regarding the efficiency of compressors and specifically the Rotrex.
The key to this combination is its patented traction-drive system that connects the unit's beltdriven pulley to a turbocharger housing and impeller through a set of roller bearings that produce an extremely high step-up ratio compared to typical geardriven centrifugal superchargers. Where a typical geardriven blower can spin its impeller up to about 5 times faster than the pulley (a 5.0:1 step-up ratio), Rotrex superchargers are capable of step-up ratios ranging from 7.5:1 to as high as 13.0:1, which puts the supercharger into the range of turbocharger efficiency with impeller speeds in the 90,000-125,000-rpm range compared to a suggested high of about 50,000-60,000 rpm for a geardriven blower.
These high impeller speeds produce adiabatic efficiency levels similar to an exhaust-driven turbocharger. Adiabatic efficiency describes an air compressor's ability to compress air without increasing air-charge temperature. The higher the efficiency, the lower the intake-charge temperature and the higher the density of the compressed air-cooler, denser air makes more power. In a perfect world, a compressor would be 100 percent adiabatic efficient, but in the real world, adiabatic efficiencies range from a low of about 40-50 percent for a Roots-type supercharger to slightly above 80 percent for the most efficient turbochargers. A typical centrifugal supercharger is about 60-65 percent efficient, but according to Rotrex, the higher impeller speeds its units generate elevate them into turbocharger efficiency ranges of up to 80 percent or higher.
"The machining tolerances required to produce a conventional gearset capable of operating at rpm levels that high are prohibitively expensive," says Rotrex Technical Sales Manager Bruce Harris, noting its primary advantage over geardriven competitors. The roller bearings also eliminate the noisy whine of a geardriven blower. A side benefit of the Rotrex's high adiabatic efficiency is that intercooler sizes can be relatively smaller for a given boost level than a less-efficient type of supercharger.
Read more: http://www.hotrod.com/techfaq/hrdp_0...#ixzz2840nCmJF
These high impeller speeds produce adiabatic efficiency levels similar to an exhaust-driven turbocharger. Adiabatic efficiency describes an air compressor's ability to compress air without increasing air-charge temperature. The higher the efficiency, the lower the intake-charge temperature and the higher the density of the compressed air-cooler, denser air makes more power. In a perfect world, a compressor would be 100 percent adiabatic efficient, but in the real world, adiabatic efficiencies range from a low of about 40-50 percent for a Roots-type supercharger to slightly above 80 percent for the most efficient turbochargers. A typical centrifugal supercharger is about 60-65 percent efficient, but according to Rotrex, the higher impeller speeds its units generate elevate them into turbocharger efficiency ranges of up to 80 percent or higher.
"The machining tolerances required to produce a conventional gearset capable of operating at rpm levels that high are prohibitively expensive," says Rotrex Technical Sales Manager Bruce Harris, noting its primary advantage over geardriven competitors. The roller bearings also eliminate the noisy whine of a geardriven blower. A side benefit of the Rotrex's high adiabatic efficiency is that intercooler sizes can be relatively smaller for a given boost level than a less-efficient type of supercharger.
Read more: http://www.hotrod.com/techfaq/hrdp_0...#ixzz2840nCmJF
10-01-2012, 01:31 PM
#162
Ouch! Yes that is a lot. Was this done to get rid of the knock count? On an S4 I would say it should have been about half that amount for 7 psi. Either your intake temp is way high or your fuel is bad or combination of both. Where is your air filter located currently?
10-01-2012, 01:34 PM
#163
Rennlist Member
Ouch! Yes that is a lot. Was this done to get rid of the knock count? On an S4 I would say it should have been about half that amount for 7 psi. Either your intake temp is way high or your fuel is bad or combination of both. Where is your air filter located currently?
Cal gas aint the best..and it was bout 90d outside at the time.
And yes, that timing brought down knock to <10-15 counts in those cells per pull.
10-01-2012, 02:40 PM
#164
Rennlist Member
here is what I have read.
"The Rotrex supercharger’s unique traction drive also has the highest drive efficiency of any other blower with 98.4% efficiency which means less parasitic losses than traditional gear driven blowers allowing for better fuel economy when your foot isn’t buried in the throttle."
"A typical centrifugal supercharger is about 60-65 percent efficient, but according to Rotrex, the higher impeller speeds its units generate elevate them into turbocharger efficiency ranges of up to 80 percent or higher.
I will contact Rotrex and find out the exact numbers
"The Rotrex supercharger’s unique traction drive also has the highest drive efficiency of any other blower with 98.4% efficiency which means less parasitic losses than traditional gear driven blowers allowing for better fuel economy when your foot isn’t buried in the throttle."
"A typical centrifugal supercharger is about 60-65 percent efficient, but according to Rotrex, the higher impeller speeds its units generate elevate them into turbocharger efficiency ranges of up to 80 percent or higher.
I will contact Rotrex and find out the exact numbers
The drive efficency is something different to the compressor efficiency. The Rotrex compressor you supply hits peak compression efficency of 73% at 10 psig. The problem with centrif compressors is that they hit higher efficiency than a twin screw but over a much narrower operating range so you try to match compressor size with duty and I would think you have done that quite well.
You will be very hard pushed to find a centrif compressor that can hit 80%- indeed I suspect you will not find one.
Regards
Fred
10-01-2012, 02:53 PM
#165
Rennlist Member
The amount of power absorbed has everything to do with efficency, the more inefficient the compressor is the more power it takes to drive it. The heating of the air is the by-product of the inefficency [the energy put in has to go somewhere]. Thus the more efficient the machine the less you need to intercool it to get the temperature down because the temp is not so high to start with.
Industrial compressors typically operate at a compression ratio of 3:1, pushing 4:1 in the extreme. The higher the compression ratio the more heat you generate until you reach a point where the machine becomes a heater rather than a compressor for the kW you push it with and then you have to cool the gas before you compress to a higher pressure. In car the intercooler serves to help the engine be less inclined to pinking. No intercooling and you have to retard the ignition more/increase the AFR.
Regards
Fred
Regards
Fred