I'm going to post some info here to maybe help on the debate of which compressor is more efficient in terms of temps, otherwise known as adiabadic efficiency. Here is a link showing some compressor maps, sorry it takes so long to load, especially if you have 28.8K like myself.

http://www.rbracing-rsr.com/turbosupermaps.html

On my 2003 F-150 4.6 I have a T-61 Turbo. Its max efficiency is 76%. At 10 PSI and 5000 rpm i'm in the 73% efficiency zone. Thats a pressure ratio of 1.68, flowing 608 cfm or 44.3 pound per minute of air, whichever you prefer. According to my calculations the discharge temps at the compressor at this effeciency is roughly 201 degrees at 85 degrees ambient temp.

On the 112 Eaton Roots blower, at 10 psi and just over 600 cfm, it takes roughly 50 hp to turn the blower and discharge temps according to the compressor maps is about 190 degrees. It doesn't give ambient temps so you can't really calculate the compressor effeciency from this map, but its probably pretty close to my turbo. Unless the map means that the compressor adds 190 degrees to ambient temps, which would give you 275 degree temps. I'm not really sure on this one. But from what I understand the roots blower is not as efficent as my turbo is.

If you look at the Vortech S-Trim map, you will see that at 1.68 pressure ratio, 600 CFM flow rate, it has an efficiency of 70%. Which should give you, at 85 degrees ambient temps, 206 degree charge temps.

If you look here you can find a compressor map at the 2.3 whipple compressor.

http://www.opconab.com/www/files/lys...m_lys2300r.pdf

I know, it isn't easy to read. The air flow is in frigging cubic meters per minute, thats just insane for us americans to try and figure out. I'm not gonna bother calculating those numbers into CFM. The max effeciency on the blower is 66%. A little worse than the Vortech. At its max effeciency, at 85 F inlet temps, discharge temps are 213 F. Of course this effeciency depends on the amount of flow. The max effeciency is very, very small on the twin screw map. Maybe someone can convert 600 CFM or 44.3 pound per minute to cubic meters per minute, then we would have a better idea of the effeciency at this flow rate.

To sum it all up, It appears that for me and my engine at my power levels, the turbo is most effecient, the centrifical is next in line, and the roots and twin screw are the 2 at the bottom. This can all change with another engine and other flow rates that particular engine needs. I'm not taking sides here, just trying to post valid info for all to see. And of course all these numbers are per my calculations and my math, which is highly possible its worng. The compressor maps on the other hand are not wrong. Let me also say that the differences in effeciency at my flow rates that I need for my engine are so small they would hardly be noticable if at all.

Let me say one more thing and I'll shut up for a while.

Turbo > everything else..... But thats for another thread.


Marlon

 

Marlon......Take a bow. You've answered the question that initiated this thread more accurately and completely than any one to date, myself included. You've also made another very good point. We can all go around claiming that our supercharger of choice is the best for any given application. We can cite advantages of our favorite type of blower and elaborate the shortcommings of the blowers that we favor least. We can debate to the point of making derogatory comments about one anothers knowledge and/or experience, or the lack thereof. We can believe that our supercharger is the one that everyone should install. Until...........We get spanked by a turbo. If you have not, be patient. You will.

 

Marlon - excellent post - excellent indeed.

Twinscrew - "Spanked by a turbo" - there is reason for that actually.

Engines as you know have sad efficiency numbers, somewhere in the 10-15% range. I forget exactly what it is, but its really low.

This means for every potential horsepower that could be taken out of the fuel, 15% of that best case actually rotates the crank, and the rest of the potential horsepower is completely wasted, in the form of exhaust flow, heating of the block, pistons, rods, crank, oil, cooling system, fenders, firewall, the underside of the vehicle, and the ambient air around the vehicle.

You'd have to admit that's a lot of waste...

Superchargers remove horsepower from the crankshaft, in order to provide additional boost over atmospheric pressure, to increase power at the crank. And this works very well, extremely well, to a point where you have exceeded the blower's cfm rating then there just isn't any more power to be had, and power gains just roll off. There is no such thing as a perpetual motion machine, and superchargers are no exception.

On the other hand, turbochargers utilize some of that wasted energy I've mentioned above... by capturing the high temperature, high pressure, high flow exhaust gases though its impeller housing, the turbo can take what is normally "waste" energy and turn it around into something useful, i.e. creating a positive pressure on the intake side. This too is not a perpetual motion machine and therefore there is a point where you exceed the cfm rating of the turbo, and that's the end of the power gain.

But the point here is that you're utilizing energy that is otherwise completely wasted, so there is no "stealing" from the crank.

This is why as a general rule, turbocharged engine can make more power per cubic inch than a supercharged engine, however this can only be a general rule because compressor efficiency, head/intake flow capacity, ambient temperature, humidity, the fuel's composition, (insert endless list here) all play into this.

So instead we make generalizations without the math. Things like "Superchargers offer more off the line power", which is a fairly true generalization, as the supercharger, at idle, is already powered by the crank. Turbochargers require some exhaust flow, above idle, in order to be useful, hence the concept of turbo lag. You can undersize the turbo and significantly reduce the lag effect, however the top RPM range you can hit with that engine will be lower - the turbo can actually become a cork at that point.

This is why a lot of homebrew turbocharger guys (like myself) experiment with twin turbos - by using two smaller turbos, you can spool them quicker. Not because they are smaller per se, but because the rotating mass of the turbo impellers, the shaft etc are smaller, less bearing friction, etc. So using two half-sized turbos as compared to one large turbo, can offer somewhat quicker spool up times. The drawback of course is plumbing, fabrication, and that whole mess.

 

Marlons post, while very well done, doesn't prove much. It states the temp at 5000 rpm's for the turbo, but does not state a rpm range for the rest of the power adders mentioned. I feel that adiabatic efficiency at one specific rpm, does not prove as much as volumetric efficiency at the complete range an engine is most commonly operated at. Not just at low rpm's, or just at wide open throttle either. Maybe displayed in a graph form, showing the rpm's, and the VE at common intervals of rpm starting at zero, with each respective power adder. This would be a more accurate method of measuring the true efficiency of any power adder, provided the testing was done with as many of the controll factors being as equal as possible. The power adders would have to be tested on the same engine, at the same ambient temperature, using the same gasoline, at the same rpm intervals, and at the same boost level. The only variant there could be, would be the fuel pressure and engine tuning. This could be different with each type of compressor, to ensure that the engine is running in the optimum state of tune, best suited for the particular method of boost being tested at the time. I also feel that the AE does not prove much, because the boost temperature is being measured directly from the output of the compressor. This is not a real world test, since most such systems do not utilize the boost at the compressor output temperature. It is most common to use an inter cooler. The effect of the heat produced by any of the forced inductions mentioned, can be nullified (or nearly so) by an efficient inter cooler placed somewhere between the boost pressure and the engine. Some will argue whether an air to air or air to water is better. I tend to think that the air to water is less dependant on ambient temperature for it to do it's job more consistently. Some say it depends on the application and the type of boost. Either method chose, the inter cooler will change the way the engine "sees" the adiabatic efficiency of the supercharger or turbo. The actual air being ingested by the engine, is not even close to the temperature of the air as it leaves the compressor. Most people know that cooler air into an engine, can produce more power, because it's denser Since an inter cooler is only capable of lowering the boosted air temp by so much, with most things being equal in the test, then the final temperature of the air being ingested by the engine will be closely related to the temperature of the air as it comes out of the power adder. This is true. But you need to understand one thing. This role that the temp of the boost actually plays in helping the engine builds usable power, is much less pronounced at the now cooler temps (because of the inter cooler), then at the higher temps of the boost directly at the source. In other words, the AE of each individual compressor may at first seem like a method of determining the OVERALL efficiency, but it isn't. The amount that the un cooled air HARMS the peak power output of a test engine, is on a different scale then the amount that the inter cooled denser air HELPS the engine. The efficiency of the inter cooler has more to do with the overall power gained from the charger, then the actual AE of the charger. Is this understood, or just sound like hotter air.

 

You bring up some very good points Stevef100s.

I may not have stated it in my post, but 5000 rpm was the basis for all the calculations I did on every compressor. I used 5000 rpm, 600 cfm of air and 10 psi on all the compressors to show which compressor is most effecient at peak horsepower for my application in particular. In terms of effeciency compressor maps do not lie, they tell the truth. Of course this is only for MY particular engine. To carry the information in my post to other applications is a generalization at best.

I just tried to use compressor maps, and real world data on my application in particular to show which compressor is the most effecient because there was a dabate on which was more effecient. I also stated that this is true for my engine, but could possibly change on other engines with other flow rates and boost levels. Thats why these calculations have to be done for every single application to see which is best for that particular engine. You are also right in saying that a graph showing this data for all compressors on a given engine over its entire powerband would be better, but that would just take too long. One day I might get a wild hair and do that

Now on my application I have an intercooler that is around 97% effecient. But I didn't bring this up in my post because I was trying to show the effeciency of the compressor itself, not the effeciency of the whole system. I'm sorry if I misled anyone, it was not intentional.

So to sum it all up, at peak horsepower levels for my engine the vortech compressor puts less heat into the compressed intake charge than the twinscrew compressor does. This is all I was trying to show in the first place. As far as which one is better suited for a particular application, well that just depends on that application. Which is better and which is best can be debated endlessly, but the effeciency of a compressor can be proven scientificly.


Marlon

 

All true Marlon, but just because one charger is has more adiabatic efficiency at peak horsepower, it does not prove which is more efficient. How often is an engine run at peak horsepower? As I already stated, just because one charger shows it has more adiabatic efficiency then another, it does not mean it makes the engine have more VOLUMETRIC efficiency. The volumetric efficiency is the true measurment of how efficient an engine is, with ANY mod you can do to one.

 

Well I'm sorry I wasn't very clear. I was only trying to take each type of compressor and show which compressor was more adiabatic effecient (because I thought that is why this thread was started in the first place) in my particular application. I was trying to prove nothing else at all. All these other points can be debated endlessly and when you are done you are right back where you started. Sorry if I misunderstood the originaly intention of this thread. But looking back I see it had nothing to do with how much heat a compressor put into the intake charge, but how much HP a supercharger took to turn it when not under boost. The adiabetic effeciency debate must have come up later. I will post nothing else on this thread.


Marlon

 

Wow! I finally got back to this thread. Good discussions here, just what I like. For a while I thought the name of this site should bechanged to Ford Truck *Drivers* becuase the most anyone could talk about is where to pu the gas and oil.

So let's try this for a question. According to Boyle's law temperature increases as pressure increases. Which compressor adds the least additional heat to the intake charge?

 

That really depends on what two (or more) compressors you're comparing, being that there are so many out there.

 

As a general rule, stricly speaking on heat effeciency and nothing else, roots blowers are by far the worse, cents and twin screws being somewhat similar depending on the specific compressors you want to compare. Its hard to mathmaticly compare a cent and a twinscrew because of the availability of compressor maps. But if you want to compare 2 particular compressors and can find compressor maps for them, its not difficult to determine which will put the least amount of heat into the compressed air.


Marlon