I probably have too much time on my hands so I'm trying to learn about choosing the correct supercharger and have found this site as sent to me by Jim L. to very interesting as it goes thru the steps: http://www.motorgeek.com/viewtopic.php?t=2747
But there are some calculations that either do not show up correctly, or I'm not reading them correctly. They are as follows:
"Tout (in F) = (((Tin (in F) + 460) * (Pressure Ratio0.283)) - 460)
For 15psi of boost at sea level at an ambient temp of 85F (85F in this case so that our computed CFM ends up matching that of the compressor map).
Tout = (85 + 460) * 2.020^.283 - 460 = 205F "
I can't follow the math shown here (2.02 is the pressure ratio; I have no idea where the .283 came from). Can anybody explain this?
Tom
It looks like the equation is using temperature units of degrees Rankine.
Regards, Neil Tucson, AZ
This is my favorite resource for this sort of calculation & plotting.
http://not2fast.com/turbo/glossary/turbo_calc.shtml
It looks like that might be a constant that the pressure ratio is taken to the power of, but I'm not real strong on math.
I like Borg Warner's Matchbot program.....
http://www.3k-warner.de/en/aftermarket/matchbot.aspx (http://www.3k-warner.de/en/aftermarket/matchbot.aspx)
... you can use it for other compressors than theirs to some degree by using the program to generate the pressure ratios and air requirements for different boost levels for the engine in mind and then print out the map you are working with and plot the points on that map. I have some explaination of that in this years build for Hooley's Stude where I picked out the turbos to be used. Here is a link to those pages, both with a BW turbo and using their data on a non-BW turbo compressor.....
http://purplesagetradingpost.com/sumner/Hooley%202013/13%20-%20hooley-construction-2013-1-a.html (http://purplesagetradingpost.com/sumner/Hooley%202013/13%20-%20hooley-construction-2013-1-a.html)
Also for me right now the Matchbot program is not plotting the points on the compressor map like it use to. I called them and I'm waiting on a reply back. All of the info generated seems good though so there again print the map out and plot to it,
Sum
Thanks for the other links. The formula I posted directly from the motorgeek site appears to have an error, because the ^ is missing, replaced instead by a 0, which then made the following example (which may be correct) different. I found a math site (again supplied by Jim L.) that had a function "x to the power of y". With this formula, and raising 2.02 (the pressure ratio) to the power of .283, I got the answer as shown. What this part of the formula does is calculate the temperature of the air exiting the supercharger, the change in temperature is then subsequently divided by the SC efficiency to get the actual change in temperature. Yes the temperature is in degrees Fahranheit (sp?) so degrees Rankine must be used in the formulas, hence the 460 fudge factor. I'll play with the numbers as a math assignment for the future. One wonders how the old timers ever got it right without computers and the internet. I'm thinking an educated or WAG and give it a try.
Tom
Quote from: Koncretekid on December 17, 2013, 10:56:50 AM... What this part of the formula does is calculate the temperature of the air exiting the supercharger, the change in temperature is then subsequently divided by the SC efficiency to get the actual change in temperature.....
The Borg Warner calculator gives you that also.
They have a large number of required inputs....
(http://purplesagetradingpost.com/sumner/bvillecar/Matchbot%20Inputs-1.jpg)
....good if you know for sure what they are but the results could be skewed by wild guesses :-)
You also get a lot of ouput info....
(http://purplesagetradingpost.com/sumner/bvillecar/Matchbot%20outputs-1.jpg)
In addition if you use one of their turbo maps it plots the info on the map if that is working at the moment.
Here are larger screen views of the above part of their calculator and there is more to it than what I've posted here.....
http://purplesagetradingpost.com/sumner/bvillecar/Matchbot%20Inputs-1.jpg (http://purplesagetradingpost.com/sumner/bvillecar/Matchbot%20Inputs-1.jpg)
http://purplesagetradingpost.com/sumner/bvillecar/Matchbot%20outputs-1.jpg (http://purplesagetradingpost.com/sumner/bvillecar/Matchbot%20outputs-1.jpg)
A number of people pick a turbo compressor just based on how much HP potential it has, but that can be way off depending on the displacement of the engine and other factors. The only way to feel you are headed in the right direction is taking the time to do the calculations and plot them on the compressor map you are considering. This was a lot harder a couple years ago when you had to do all of the calcs manually using the formulas in books like Corky Bell's. Now these online calculators make it much simpler,
Sum
Yes, on the Rankine temperature scale, absolute zero is 0 degrees R and zero degrees Farenheit is 460 degrees Rankine. :-P
Regards, Neil Tucson, AZ
As with most things here, it's never simple, is it?
I put my first turbo on an Opel Kadett in 1969. No internet to do research. Spent a huge amount of time looking for books. Remember those? First try I undersized the exhaust and after a trip around the block everything was glowing red. Worked fine after that.
QuoteI'm thinking an educated or WAG and give it a try.
You are slightly incorrect. There are only WAGs and SWAGs. After you do a Wild As
s Guess and do some research, it becomes a Scientific Wild As
s Guess.
Dean, I think you missed one in the process. You take a WAG, then study and make an EWAG (educated wag) and then do some experiments that result in you being able to make a SWAG based on what you've seen happen.
My experience has been that it's a "STUPID" WAG. :-D
Ron
TURBOCHARGERS by Huge Macinnes [HPBooks] explains everything from sizing turbos, figuring temps, water injection
and a lot more.
JL222
I found the definitive answer to my question here: http://www.not2fast.com/turbo/glossary/turbo_glossary.shtml#compressor_efficiency
"Compressor Efficiency (Turbocharger Efficiency)
Compressor efficiency is a measure of how well the compressor wheel uses its kinetic energy to compress air (the remainder of the energy is turned into heat in the compressed charge). In an ideal system, compression of the input fluid would raises its temperature adiabatically. This is never the case in the real world, so all calculations must take the compressor efficiency into account.
In order to calculate compressor outlet temperature, you must know compressor efficiency, pressure ratio and ambient temperature.
(PR^0.283 - 1) * Tambient
Trise = ---------------------------
Ec
Trise = increase in temperature
PR = pressure ratio
Tambient = ambient temperature (in an absolute scale, Kelvin or Rankine)
Ec = Efficiency of the compressor
The exponent of the pressure ratio arises from the molecular structure of the gas. Diatomic gasses (like N2 and O2) have seven degrees of freedom, five of which are excitable at STP. Thus gamma = 7/5 in the equation P(V^gamma) = constant, and we can derive an exponent of 1 - (1/gamma) = 0.285. For real air, containing non-diatomic molecules like CO2, a better value is 0.283. For more on this, see the gas thermodynamics section of Nuclear Weapons FAQ (!) (scan down to section 3.1.6).
So, for example, my Garrett T04E compressor running at PR of 2.5, Ec of 0.75 in the good old summer time with a temperature of 27 degrees Celsius (300 Kelvin) produces:
(2.5^0.283 - 1) 300
Trise = ---------------------
0.75
= 118°"
So now you now where ^.283 came from. There are probably a couple of you on here that understand all of that. By the way, you can find the root .250 of any number on a common calculator because this is actually the square root of the square root of the number. I found that by doing this using the number 2 as the pressure ratio, that taking the sq. rt. of the sq. rt. gave me an answer within 4% of using the computer to find the .283 root. In case you want to do the math and don't happen to have access to the net, like on the Salt Flats. Assuming, of course, that you have all the other information and formulas at hand.
Yep, not only is the calculator itself handy, but the documentation is detailed.
One thing I've noticed is that the compressor sizing is a little conservative for modern motorcycle engines. My little stock-head 1000cc Kawasaki did just fine with 62mm S-housing compressor, even thought most calculators would predict surge.
Dean
I was wondering about using a smallish charger. Rotrex make a C8-8 in a CCW version that will give me a 1.8 PR at about 10psi boost (probably as much as the BSA can stand, maybe more) which is about a 50% boost in hp, but it is close to the surge line. Still, I could start with less of an overdrive to begin with. The CCW is attractive in that I can drive it direct from the crankshaft. And it is a small package with its own built in oil pump. But, the intake is only 34mm and output 28mm?? Sounds small for producing up to 75hp.
I'd see if you can find someone who is using it, and get some real-world feedback. Or talk with a Rotrex tech or distributor and see what they think.
Quote from: Koncretekid on December 19, 2013, 12:36:34 PM
I was wondering about using a smallish charger. Rotrex make a C8-8 in a CCW version that will give me a 1.8 PR at about 10psi boost (probably as much as the BSA can stand, maybe more) which is about a 50% boost in hp, but it is close to the surge line. Still, I could start with less of an overdrive to begin with. The CCW is attractive in that I can drive it direct from the crankshaft. And it is a small package with its own built in oil pump. But, the intake is only 34mm and output 28mm?? Sounds small for producing up to 75hp.
75 HP would be ....
(http://www.vespalabs.org/@api/deki/files/1353/=rotrex_c8-8_compressor_map.png)
http://www.vespalabs.org/@api/deki/files/1353/=rotrex_c8-8_compressor_map.png (http://www.vespalabs.org/@api/deki/files/1353/=rotrex_c8-8_compressor_map.png)
.... in the neighborhood of .0625 kg/sec of air and that is way over on the right side of the map and getting into the 50%-60% efficiency area so probably producing very hot air. You really need to use one of the calculators to see for your motor were the plotted point would be and see if it even falls over there or off the top or right side. 2 different motors (different displacement, rpm, etc. ) won't necessarily plot the same point at say 75 HP output in your case. 75 HP with that compressor is probably going to be hard. Looks like you need to think larger where the 75 HP isn't right at the compressor's upper limit,
Sum
I'm working on 2.0 pressure ratio at 300 Cu/Meter per hour on this map (650cc engine, 10,000 rpm 4-valve twin). Looks like about 13,000 rpm on the blower with ice water intercooling. That 2.0 pressure ratio is not so much boost at 6000 ft density altitude, I was told. I suspect I will need full bypass up to at least 3500 engine RPM....or more?
my oh my...so much to learn.
JimL
The AISIN AMR500 is worth a look. Often used by the VeeDub people and I've seen them fitted to Harley's as well. Compact and they often pop up on eBay at reasonable prices.
Cheers
Robin
A week ago I couldn't even read a supercharger map. Now with the aid of online formulas I can run thru the numbers and actually see what comes out, more or less. Unfortunately, the more I learn, the less I seem to know about this subject. It's going to be a slow learning curve, especially for those of us who have been basically out of the loop for 40 years or so, not to mention age related learning issues, constant access to the beer cabinet, and naptime.
Quote from: JimL on December 19, 2013, 10:45:47 PM
I'm working on 2.0 pressure ratio at 300 Cu/Meter per hour on this map (650cc engine, 10,000 rpm 4-valve twin). Looks like about 13,000 rpm on the blower with ice water intercooling. That 2.0 pressure ratio is not so much boost at 6000 ft density altitude, I was told. I suspect I will need full bypass up to at least 3500 engine RPM....or more?
my oh my...so much to learn.
JimL
MatchBot shows the engine needing about 390 cu/meter per hour for the engine at a 2.0 pressure ratio,
Sum
Sum, is that at 12 psi base atmospheric pressure?
Thanks for whatever you can figure.
My 2.0 target is only 11.5 psi after the intercooler, at Salt Flats air density. I know the blower can do it, but the engine cant take it.
JimL
Quote from: JimL on December 20, 2013, 01:53:23 PM
Sum, is that at 12 psi base atmospheric pressure?
Thanks for whatever you can figure.
My 2.0 target is only 11.5 psi after the intercooler, at Salt Flats air density. I know the blower can do it, but the engine cant take it.
JimL
Here are my inputs and the outputs. Ignore the turbine inputs/outputs.
I was mainly figuring the air requirements for the engine at that rpm, altitude, etc.. Guesses on intake restrictions, ve, etc..
Load...
http://www.3k-warner.de/en/aftermarket/matchbot.aspx (http://www.3k-warner.de/en/aftermarket/matchbot.aspx)
... the calculator and play with it with what you feel are realistic numbers and take the air flow and pressure ratios and plot them on your map of choice after printing it out for different rpms and boost numbers.
You have to change the m3/sec to m3/hour for the air needed (multiply by 3600). Also click on the link under the picture to enlarge it so you can see it. I didn't spend much time on this so errors are probable 8-). It does look like the compressor you showed could handle the air requirements.
(http://purplesagetradingpost.com/sumner/bvillecar/jiml-1.jpg)
http://purplesagetradingpost.com/sumner/bvillecar/jiml-1.jpg (http://purplesagetradingpost.com/sumner/bvillecar/jiml-1.jpg)
Good luck and does the 125 HP sound close to what you would be expecting,
Sum
Thanks, we are pretty close with numbers. This blower was made for 500cc-1200cc engines (typically small cars). I have a bit more flow capability than typical production small car engines, and I am able to run at extremely low (less than 150F) cylinder head temperatures for several miles.
Because I can absolutely prevent over-boost, I can run higher compression pistons than might be used with a turbo. I want to preserve as much as possible the gains made, to date, while picking up what we can get without stealing it all back from the end of the crankshaft.
125hp would be more than 50% increase in power from the engine that is currently running this bike 160-165 mph. I think that could be another 10 mph?
Or it might break badly....
JimL
Quote from: JimL on December 20, 2013, 04:03:00 PM
Thanks, we are pretty close with numbers. This blower was made for 500cc-1200cc engines (typically small cars). I have a bit more flow capability than typical production small car engines, and I am able to run at extremely low (less than 150F) cylinder head temperatures for several miles.
Because I can absolutely prevent over-boost, I can run higher compression pistons than might be used with a turbo. I want to preserve as much as possible the gains made, to date, while picking up what we can get without stealing it all back from the end of the crankshaft.
125hp would be more than 50% increase in power from the engine that is currently running this bike 160-165 mph. I think that could be another 10 mph?
Or it might break badly....
JimL
If 83 HP is getting you 165 mph then 125 HP gets you 189 mph, on paper :-). That is getting pretty close to 200 :-D. 200 mph needs 148 HP.
Since the MatchBot calcs are based on a turbo the gains might not be the same HP wise as what is charted there if you are using up HP with the crank driven compressor??? If it was the turbo they are showing turbo shaft HP as 13.8, but are taking that into consideration when figuring the net HP of 125 if I understand it right. Not sure how to figure your HP figures to drive the compressor,
Sum
Quote from: JimL on December 20, 2013, 04:03:00 PM
... 125hp would be more than 50% increase in power from the engine that is currently running this bike 160-165 mph. I think that could be another 10 mph?
Or it might break badly....
JimL
My guess is you will be riding 5 miles instead of 3 if you want to, and it might stay together....
It is all part of the fun :-D
Sumner beat me to it
First note here...I screwed up a supercharger reply to Tom and put it on the other thread in this section. Sorry fellows, now you have to fish it out of the wrong thread....but when you read the big goof up I made on that supercharger system, it'll make perfect sense how I could put the little story in the wrong place. :oops:
Thanks for the calcs on speed, however, based on how much work/modifications it took to go from 150 to 165 I think it wont get anywhere close to 190 and probably not even 180. I've been able to easily feel the power gains, in recent years, by how this thing can spin up the rear wheel in 2nd and even 3rd gear. It used to be mostly a 1st gear issue, even with lower gearing and less weight.
It is hard to believe how the last 20 years have slipped by. Back when Dan and I started on that Modified Roadster we thought we'd have it figured out in a few years. Didnt happen and we never got past about 180-185 despite more boost, bigger injectors, and finally a Pectel fuel injection.
The point is, expectations get lower even when you work harder than ever at going a tiny bit faster. That 200 is someone elses world, and certainly not available to a 650 pushrod twin, but it would be fun to run long course again! We will see what happens.
Thanks again, JimL
Quote from: JimL on December 20, 2013, 07:34:18 PM....The point is, expectations get lower even when you work harder than ever at going a tiny bit faster.
Yep easy paper HP makes easy paper speed.
I just modified my HP needed spreadsheet that I attached above and attached the modified one. It now lets you also enter the new anticipated HP and calculates the new anticipated speed base on know speed and HP.
To use it download it and save it then you can enter numbers,
Sum
Here is an interesting experience driving superchargers with multi-rib belts.
Years ago, I built a 3.4 V6 Corolla with my son, Matt. In order to make room for "stuff", I chopped off the original fan coupler pulley mount (on front of engine). I then built several belt drive systems that didn't work while running his blower at 9.5 lbs (sea level). Note that I converted from 4-row belt to 6-row (by using a crank pulley off a Camry aluminum V-6).
It kept spitting belts when trying to run the blower above 15,000 rpm. I tried multiple positions of a tension idler, on the "slack side" of the belt. One day, I lucked out and caught the belt partially walked off as I shut down the engine. It was walking off on the straight run "pull" to the crankshaft.
After more experimenting, I learned the belt liked a back side tension roller, just after it left the blower pulley (see pic below). I suspect this reversing of bend, under highest load, was restraightening the web inside the belt. The tension idler position ended our belt problems with this car. It was a cute car, and BAR certified legal...anyway, this belt system worked for years and almost 80,000 miles after the conversion.
Perhaps it will work for my new project, as well.