Rotrex Supercharger thread
10-01-2012, 03:13 PM
#166
Man of many SIGs
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Clearly you have never studied thermodynamics!
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
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
Victor
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
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
Last edited by Fabio421; 10-01-2012 at 03:32 PM.
10-01-2012, 03:41 PM
#167
The quote Victor gave us from Rotrex showing 98.4% efficiency must mean the parasitic loss encountered from the internal drive system of the supercharger NOT the compressor efficiency (claim of 98.4% would be absurd). Not sure how that compares to blowers with gear or belt driven step-up drives. In that Hot Rod article it says Konigsegg uses them on one of their supercars and that is some serious credibility!
10-01-2012, 03:53 PM
#168
That is a warm ambiant. What was your AFR running at?
10-01-2012, 04:25 PM
#169
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I believe what he is saying Fabio, is that you seam to like to spew a bunch of random bologna into a forum that is trying to accomplish something. I realize you are a turbo guy and believe your stuff is better. Hell we are all Prejudice to what we have and who we are...... Meaning if your bald you believe bald people are the best!! Or in this case if you have a twin screw, you believe the twin screw is best power solution, or in your case a turbo. Simply put they all have good and bad. Turbos create lots of heat,exhaust back pressure, and take a lot to install. Twin screws have great low end torque, but require a different intake, and take away crank power. The Rotrex is easy to install with great top end power, but also takes crank power. So why don't you quit spewing your random stuff trying to convince people turbos are best in the Rotrex forum. Most people aren't stupid, can do some research, and can make up there own minds. When you bring rain to a parade, remember it rains on both sides of the streat.
Here is the actual information and formulas needed... at max RPMs the pressure ratio 1.63766. Which equivilates to just under 25 killowats of power. So 650cfm or .375k/sec comes out to be about 30HP at max RPMs. The nice thing about a centrifugal system is that it is only using that much power at max rpms. Meaning virtually no loss at at low rpms.
To answer everyone's question! With a Stage 1 kit, at 6200 you will get a little over 6lbs of boost. This in turn CAN add 180HP to the engine and apx 30 of it will be used by the supercharger in rotation and heat. The other 150HP goes tward the wheels
Here is the actual information and formulas needed... at max RPMs the pressure ratio 1.63766. Which equivilates to just under 25 killowats of power. So 650cfm or .375k/sec comes out to be about 30HP at max RPMs. The nice thing about a centrifugal system is that it is only using that much power at max rpms. Meaning virtually no loss at at low rpms.
To answer everyone's question! With a Stage 1 kit, at 6200 you will get a little over 6lbs of boost. This in turn CAN add 180HP to the engine and apx 30 of it will be used by the supercharger in rotation and heat. The other 150HP goes tward the wheels
10-01-2012, 04:40 PM
#171
Rennlist Member
I believe what he is saying Fabio, is that you seam to like to spew a bunch of random bologna into a forum that is trying to accomplish something. I realize you are a turbo guy and believe your stuff is better. Hell we are all Prejudice to what we have and who we are...... Meaning if your bald you believe bald people are the best!! Or in this case if you have a twin screw, you believe the twin screw is best power solution, or in your case a turbo. Simply put they all have good and bad. Turbos create lots of heat,exhaust back pressure, and take a lot to install. Twin screws have great low end torque, but require a different intake, and take away crank power. The Rotrex is easy to install with great top end power, but also takes crank power. So why don't you quit spewing your random stuff trying to convince people turbos are best in the Rotrex forum. Most people aren't stupid, can do some research, and can make up there own minds. When you bring rain to a parade, remember it rains on both sides of the streat.
Here is the actual information and formulas needed... at max RPMs the pressure ratio 1.63766. Which equivilates to just under 25 killowats of power. So 650cfm or .375k/sec comes out to be about 30HP at max RPMs. The nice thing about a centrifugal system is that it is only using that much power at max rpms. Meaning virtually no loss at at low rpms.
To answer everyone's question! With a Stage 1 kit, at 6200 you will get a little over 6lbs of boost. This in turn CAN add 180HP to the engine and apx 30 of it will be used by the supercharger in rotation and heat. The other 150HP goes tward the wheels
Here is the actual information and formulas needed... at max RPMs the pressure ratio 1.63766. Which equivilates to just under 25 killowats of power. So 650cfm or .375k/sec comes out to be about 30HP at max RPMs. The nice thing about a centrifugal system is that it is only using that much power at max rpms. Meaning virtually no loss at at low rpms.
To answer everyone's question! With a Stage 1 kit, at 6200 you will get a little over 6lbs of boost. This in turn CAN add 180HP to the engine and apx 30 of it will be used by the supercharger in rotation and heat. The other 150HP goes tward the wheels
With good gas, and competent tuning...one I dont have...the other we're working on slowly.
10-01-2012, 04:56 PM
#174
Man of many SIGs
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I believe what he is saying Fabio, is that you seam to like to spew a bunch of random bologna into a forum that is trying to accomplish something. I realize you are a turbo guy and believe your stuff is better. I have no "stuff". I am not a peddler of forced induction products. I have no dog in this fight other than wanting the facts to be well represented. Hell we are all Prejudice to what we have and who we are...... Meaning if your bald you believe bald people are the best!! Or in this case if you have a twin screw, you believe the twin screw is best power solution, or in your case a turbo. Simply put they all have good and bad. Turbos create lots of heat,exhaust back pressure, and take a lot to install. Twin screws have great low end torque, but require a different intake, and take away crank power. The Rotrex is easy to install with great top end power, but also takes crank power. So why don't you quit spewing your random stuff trying to convince people turbos are best in the Rotrex forum. Most people aren't stupid, can do some research, and can make up there own minds. When you bring rain to a parade, remember it rains on both sides of the streat. Show me where I have said that. I haven't even mentioned turbo's. I could give two damns what type of forced induction someone chooses. Someone mentioned that the centrifugals take up 1/2 the HP they add. I thought this was false and way too high so I looked it up and posted what I found and a link to where I found it. You come back with a response regarding efficiency so I corrected what I saw as a mistatement regarding what that means. If you don't like me participating in a public forum just because the thread happens to be discussing a product that you are selling, thats tough. Get over yourself Victor. If I see something worth commenting about, I will. If I see something that looks less than factual, I will call it out if I think I have the facts to post. If I see someone avoiding proper questions I'll call that out too. If I see someone doing something right, I'll applaud that. An example of this is when I complimented the installation of your kit. It looks to be very clean from what I've seen.
Here is the actual information and formulas needed... at max RPMs the pressure ratio 1.63766. Which equivilates to just under 25 killowats of power. So 650cfm or .375k/sec comes out to be about 30HP at max RPMs. The nice thing about a centrifugal system is that it is only using that much power at max rpms. Meaning virtually no loss at at low rpms.
To answer everyone's question! With a Stage 1 kit, at 6200 you will get a little over 6lbs of boost. This in turn CAN add 180HP to the engine and apx 30 of it will be used by the supercharger in rotation and heat. The other 150HP goes tward the wheels
Here is the actual information and formulas needed... at max RPMs the pressure ratio 1.63766. Which equivilates to just under 25 killowats of power. So 650cfm or .375k/sec comes out to be about 30HP at max RPMs. The nice thing about a centrifugal system is that it is only using that much power at max rpms. Meaning virtually no loss at at low rpms.
To answer everyone's question! With a Stage 1 kit, at 6200 you will get a little over 6lbs of boost. This in turn CAN add 180HP to the engine and apx 30 of it will be used by the supercharger in rotation and heat. The other 150HP goes tward the wheels
Victor, like I've said to you before. I want to see you succeed. Stop making inflated claims. All it's going to do is make you look bad in the long run. It's very easy for you to discount what I have to say and just pretend like I'm bashing you. Why not try to post some facts and stay away from the fantasy. We have enough of that here already and alot of your potential customers don't know any better. They will believe what you say and end up dissapointed down the road. Keep peoples expactations at a reasonable level and they will remain happy customers and encourage others to buy your product? Speaking of buying your product, how have you evaded the RL mods so far? This type of blatent peddling from a non vendor when there are site sponsors who sell the same type of product would never have been allowed to go this long in the past.
10-01-2012, 05:07 PM
#176
Rennlist Member
Thread Starter
Victors not peddling anything. A few of us have installed a kit that he has and he is jumping in off and on to either clarify questions or refute blatant lies about his product. I don't see him selling anything here. Now, if he chooses to have Roger or someone sell his wares, it will be announced and then the pissing can stop about that.
This all started with someone asking about a kit that was on E-bay, not I'm sure it isn't rocket science to figure out a lot of us were talking about this kit well before that thread came up. I want Victor to be here, talking about what he knows on this set up and if he sells a few off of R-list, good for him.
This all started with someone asking about a kit that was on E-bay, not I'm sure it isn't rocket science to figure out a lot of us were talking about this kit well before that thread came up. I want Victor to be here, talking about what he knows on this set up and if he sells a few off of R-list, good for him.
10-01-2012, 05:18 PM
#177
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That info came from Rotrex. And yes we are making up to 450chp with the stage 1 kit and 6 plus psi boost (this means over 6). Most max about 6.5 to 7. What dont you understand !??
10-01-2012, 05:26 PM
#178
So someone running 6 psi x 19.3 would show an increase of 115 hp at the wheels under ideal conditions.
Not bashing bud, I think this setup is great!
10-01-2012, 05:31 PM
#179
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Being a Danish company, seems they are much better known and regarded in UK/Europe than they are in the US, but I guess that's to be expected.
*I don't have a Rotrex on my 928 (yet?!
), but I do on my (non-Porsche) track car, as do a few other people I know. FWIW I will add one story about these units, even if it's not on a 928.. My buddy's (currently championship leading) racer with a C38 which was regularly being over-spun (by some 15+%) due to a rev limit that had evolved beyond the initial sc pulley calcs. We're talking abuse to the point where finally during one race the charger actually siezed solid, spat him off the track and the blue unicorn juice turned horrible treacle black.
However, cooled it down, changed the fluid, lo and behold it unseized, and the car went out and ran the second race without problems (albeit shifting a little earlier to keep within the rpm limits). In fact it happily went on to do a few more races without issue; pretty impressive really!Long story short: these are great bits of kit and pretty bulletproof when installed correctly.
Last edited by c_span; 10-01-2012 at 05:34 PM. Reason: Figured this would provide distraction from the arguing and bickering..
10-01-2012, 05:32 PM
#180
Rennlist Member
Victor,
Please help me out here, I am simply trying to understand this stuff. I tried to go through the math and got lost.
You wrote:
Where does the 1.63766 come from? With a 6psi boost (0.41 bar), wouldn't the pressure ratio be 1.41? Or is pressure ratio something other than compressor inlet vs. outlet pressure?
The 650cfm makes sense (I get 700), as does 0.37 kg/sec air flow, or thereabouts. And if you go to the pressure map for the C38-91 (here), air flow of 0.37 kh/s and PR of 1.63 puts you about where the "75" is, 75% adiabatic efficiency. Is that correct (except for not understanding where the 1.63 comes from)?
But that indicates a compressor RPM of 60k. But with a 80mm pulley won't the compressor be turning more like 80k at 6500 crank RPM? (Pulley ratio of 130mm/80mm and a drive ratio of 7.5). That's where it stops making sense to me.
Thanks!
(And just to clarify, I am simply trying to understand this stuff because engineering stuff interests me. My only business interest is representing Sharktuner sales and support for JDSporsche, it makes no difference to me how the horsepower gets generated).
Please help me out here, I am simply trying to understand this stuff. I tried to go through the math and got lost.
You wrote:
The 650cfm makes sense (I get 700), as does 0.37 kg/sec air flow, or thereabouts. And if you go to the pressure map for the C38-91 (here), air flow of 0.37 kh/s and PR of 1.63 puts you about where the "75" is, 75% adiabatic efficiency. Is that correct (except for not understanding where the 1.63 comes from)?
But that indicates a compressor RPM of 60k. But with a 80mm pulley won't the compressor be turning more like 80k at 6500 crank RPM? (Pulley ratio of 130mm/80mm and a drive ratio of 7.5). That's where it stops making sense to me.
Thanks!
(And just to clarify, I am simply trying to understand this stuff because engineering stuff interests me. My only business interest is representing Sharktuner sales and support for JDSporsche, it makes no difference to me how the horsepower gets generated).