slick Posted August 3, 2006 Report Share Posted August 3, 2006 Basically, comparing a turbo against a centrifugal supercharger. I can find turbo charts easy. But, I'm having a bit harder time finding compressor maps for a centrifugal supercharger. Are they comparitive when it comes to trim sizes, or do you generally have to choose larger for the SC compared to the turbo. BTW, this isn't for me. Well maybe, but definately not right now. Thanks. Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted August 3, 2006 Report Share Posted August 3, 2006 i'm curious about this as well. i've never really looked at CSCs. hell, i've never even really looked at compressor maps period. probably going to be alot different (simpler?) than picking a turbo compressor though, considering boost increases with RPM as opposed to engine load. hopefully someone that knows will chime in. i think Mars has a CSC on his 60*V6 Cavalier. i don't know if he's on this forum or not. Quote Link to comment Share on other sites More sharing options...
slick Posted August 3, 2006 Author Report Share Posted August 3, 2006 Yep, I know how the CSC's work very well actually. What my plan is to actually build a homebrew CSC. My main concern is whether the outlet of the compressor housing is going to be too big or not, and thats why I'm looking for more info. CSC's work well at about 40,000-60,000 RPM, which obviously means gear reduces. At 3000 RPM engine speed, shooting for 40,000 rpm compressor speed, thats about a 13:1 ratio. Gears and pulley's aren't expensive, and I can find a compressor housing with the blade and shaft for a decent price. I'm just more concerned on the size. Quote Link to comment Share on other sites More sharing options...
slick Posted August 4, 2006 Author Report Share Posted August 4, 2006 I'm going to bump this up with another question. How fast does the compressor fins move, in rpm, while under boost? Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted August 4, 2006 Report Share Posted August 4, 2006 I just saw this thread. Let me find my book from Internal Comubstion Engines class I took during senior year. I'm pretty sure it has examples of the maps. Quote Link to comment Share on other sites More sharing options...
slick Posted August 5, 2006 Author Report Share Posted August 5, 2006 I just saw this thread. Let me find my book from Internal Comubstion Engines class I took during senior year. I'm pretty sure it has examples of the maps. Awesome! Quote Link to comment Share on other sites More sharing options...
slick Posted August 6, 2006 Author Report Share Posted August 6, 2006 Well, from my understanding, the compressor in a turbo, under boost, spins at about 150,000 RPM. Is this correct? And, the compressor in a CSC spins at about an average of say ~55,000 RPM. So, would this mean that I would choose a compressor housing, to match the comprobable turbo output, 3x the size of a normal turbo? Quote Link to comment Share on other sites More sharing options...
Mach 5 Posted August 7, 2006 Report Share Posted August 7, 2006 The problem with superchargers is the boast is gradually increased with RPM. You can increase boast through the use of an underdrive pulley. I do believe about 100,000+ is right but there is much lag through the use of a turbo when compared to a supercharger. This is because they take time to spool up. Quote Link to comment Share on other sites More sharing options...
Mach 5 Posted August 7, 2006 Report Share Posted August 7, 2006 The thing about superchargers is power is always available. Id say if you boast the effeciency of a supercharger you can make the power more equal to a turbo. Turbos are easier to install though. The only thing with a turbo is that you will need a preoiler and coolant lines for it and maybe an intercooler as well. Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted August 7, 2006 Report Share Posted August 7, 2006 Well, from my understanding, the compressor in a turbo, under boost, spins at about 150,000 RPM. Is this correct? And, the compressor in a CSC spins at about an average of say ~55,000 RPM. So, would this mean that I would choose a compressor housing, to match the comprobable turbo output, 3x the size of a normal turbo? I found the book and I'll read it/take notes on it tomorrow nite and report then. However, I'm about 90% sure that the relationship you speak of is not linear. Quote Link to comment Share on other sites More sharing options...
slick Posted August 7, 2006 Author Report Share Posted August 7, 2006 Well, from my understanding, the compressor in a turbo, under boost, spins at about 150,000 RPM. Is this correct? And, the compressor in a CSC spins at about an average of say ~55,000 RPM. So, would this mean that I would choose a compressor housing, to match the comprobable turbo output, 3x the size of a normal turbo? I found the book and I'll read it/take notes on it tomorrow nite and report then. However, I'm about 90% sure that the relationship you speak of is not linear. Thats what I was thinking. I knew it couldn't be that simple. Quote Link to comment Share on other sites More sharing options...
slick Posted August 7, 2006 Author Report Share Posted August 7, 2006 The thing about superchargers is power is always available. Id say if you boast the effeciency of a supercharger you can make the power more equal to a turbo. Turbos are easier to install though. The only thing with a turbo is that you will need a preoiler and coolant lines for it and maybe an intercooler as well. How is a Centrifugal supercharger harder to install than a turbo? With a CSC, it is a custom mount, add a pulley to the crank, add a belt, route some tubing, and your done. Turbo, you have a fab a custom crossover pipe(For these cars), tubing, coolant lines, and oil lines. Quote Link to comment Share on other sites More sharing options...
slick Posted August 8, 2006 Author Report Share Posted August 8, 2006 Robby, did you happen to find that book you spoke of? Quote Link to comment Share on other sites More sharing options...
z284pwr Posted August 8, 2006 Report Share Posted August 8, 2006 The thing about superchargers is power is always available. Id say if you boast the effeciency of a supercharger you can make the power more equal to a turbo. Turbos are easier to install though. The only thing with a turbo is that you will need a preoiler and coolant lines for it and maybe an intercooler as well. Disagrees.... I don't think you can ever get a SC as efficient as a turbo. A. It requires power to make power, especially if you are going to get compressors that are big enough to compare to a turbo in efficiency. The drag caused on the crank by spinning the thing when not in "boost" demand, is less efficient and your overall "power" is reduced the amount of power it takes to spin the thing. B. SC are linear indeed, obviously, the faster your RPM the faster the SC spins, making more power. As where a turbo, yes, it may not spin as fast as a SC, BUT, when it does spool, it will spin faster than a SC, SO, it will make MORE power at a LESS RPM, so you now have a A LOT more under the curve power, so, you hit power, and you continue to make power until redline, as where a turbo, you are slowly building more boost until redline. So....from 0 RPM to we'll say 2500 RPM, you are going to have more power than a turbo, BUT, at 2500, this turbo has now matched your speed, thus making the same power, then, it starts spinning faster, making MORE power, so now, from 2500 to Redline, we'll say 6000, you are not only make more boost, but more power, pulling away while the SC, is slowly from 2500 to redline trying to gain. Its a losing situation for a SC. C. If its a non "Procharger" style SC, whatever its call, you will, just like a turbo, be compressing air, and what happens to compressed air, it gets HOT. So, a SC that doesn' have the ability to plumb the boost through an intercooler, yes they have those ones you can mount between the intake and the SC, but it will not be able to be as efficient as a front mount intercooler, or hell, even a water to air intercooler. So you are spinning slower, with just as much hot air....losing again.. SCs are good for one thing, bottom end torque/HP, once a turbo spools, its a losing battle. No I'm not really biased on this either, I grew up with SCs. Its just to many facts that show turbos are more efficient and are capable of MUCH better performing engines. Oh yeah, and remember, in most cases that involve racing, you only need bottom end to get going....Whats the point of a SC at top end, where you are only there for the first half of the track. Plus, with a properly sized turbo. You will get fast enough spool that the SC's advantage is slim to none. Especially if you take into the fact of an automatic you are brake boost the thing launching with boost, so a SC's advantage is nothing. Okay /MY opinion... Quote Link to comment Share on other sites More sharing options...
slick Posted August 8, 2006 Author Report Share Posted August 8, 2006 Hell, I totally agree. I'm just interested in seeing if I can build a CSC with a turbo compressor and a few other odds and ends, that would be the appropriate size for a FWD V6 thats common in the w's. Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted August 9, 2006 Report Share Posted August 9, 2006 Robby, did you happen to find that book you spoke of? Here ya go. Alright, found the book and found time to read about it. Im typing these notes as I read the section. First, a little history. P.H. Roots first invented the supercharger in 1859 for use in the emerging steel industry. Superchargers first appeared in pistion driven airplanes around 1910. 3 Types of psitive displacement superchargers: Roots - about 50% efficiency Vane Screw - can be near 90% efficient 2 Types of dynamic compressors Radial (Centrifugal) Axial Here are three graphs. I'll explain what each is saying and what the variable names mean. I couldn't do these as attachments, so I'll just put 'em on photobucket and show them here in smaller size. Sorry for the glare in a couple of them. Its hard to take a pic of text book page. Also, uploading pics on dial up sucks (just thought I'd add that). Graph 1: Comparison of different positive displacement compressors. Piston is the piston in engine, Roots and Lyhsholm are types of blowers. - P2/P1 is outlet to inlet pressure ratio. - m_dot/m_dot_cr is the ratio of mass flow rate to the critical mass flow rate. The critical mass flow rate is the flow rate at which the flow will become choked. A choked flow is one thats velocity is near the speed of sound at which a drastic pressure reduction occurs. This pressure drop is such that air will not flow into the engine because the pressure in the cylinder is higher than that before the valve. - s/c_o is the mach number based on rotor tip speed - eta_c is the efficiency Graph 2: Comparison of dynamic compressors Most variables are the same as in graph one, but more lines are on this graph - the solid black line is the line for a constant s/c_o - dashed line is for constant eta_c or efficiency - solid/dotted line is the surge line. The surge line represents a boundary between stable and unstable operation conditions. To the left of the surge is unstable, to the right, stable. Surge is a self-sustaining flow oscillation. This occurs when the mass flow rate is reduced at a constant pressure ratio. At a point somewhere on the internal boundary layers on the compressor blades and flow reversal occurs. Is the mass flow rate is lowered even more a complete flow reversal occurs which relieves the adverse pressure gradient. This relief then means flow reversal is no longer needed and the flow returns to initial conditions and the cycle repeats. Graph 3: A close up of a Schwitzer centrifugal compressor. Every variable is already defined. BTW, these notes were taken from Internal Combustion Engines Second Edition by Colin R. Ferguson and Allan T. Kirkpatrick Chris, I know this isn't exactly what you're looking for but, you could probably get useful info from it. What you're wanting to do is match the mass flow rates of a tubo and CSC right? If so, you can find a mass flow rate for the turbo from the graphs you found. So, just use that in one of these CSC tables to get m_dot/m_dot_cr then use a desired P2/P1 to get s/c_o and thus find rotor tip speed. s is the rotor tip speed and is defined by s = omega (rotational speed)*D/2. If you want anything else I'll see what I can do. Quote Link to comment Share on other sites More sharing options...
slick Posted August 9, 2006 Author Report Share Posted August 9, 2006 Those should work pretty fairly well for what I have in mind. My only question is, are these compressor maps for any certain sized SC, or are they just general maps to follow some guidelines upon? Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted August 9, 2006 Report Share Posted August 9, 2006 The third graph says "with D=99mm compressor wheel" so I guess that's the only one that has a size to it. The others are just guidelines. You might could back compressor size out of the tables. Quote Link to comment Share on other sites More sharing options...
slick Posted August 9, 2006 Author Report Share Posted August 9, 2006 Hmm.. alrighty. I'll see what this does for me. Thanks for the help Robby! Quote Link to comment Share on other sites More sharing options...
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