alright i remember a while back i said they did and id tell you, well i finally found the thread. The person saying this is a very very very knowledgable man about turbos, forced induction, and cars in general. ase master mech, numerous swaps and turbo set ups performed. He is a plethora of information.
"OK OK... I'm here. Now... let's start with the basics because quite a few of you believe myths to be true, and truths to be myths. Listen closely... I'm not going to speak from opinion, but provable facts and first hand personal experience. This post will be THE definitive post in this thread.
CSC = Centrifugal SuperCharger.
SC = SuperCharger
Turbo = Turbo.
OK, good. Let's start with efficiency...
Both turbos and superchargers compress the air and force it into the engine. In doing so, they heat the air, and this is the measure of efficiency- the less heat, the more efficient. There are several design factors that affect the thermal rise of the charge air- internal aerodynamics of the compressor (I'm referring to turbo, SC, and CSC), internal surface area, and the number of direction changes the air has to make. Hands down, a centrifugal compressor (turbo and CSC) wins this contest. It has less internal surface area, the air has to make less turns (it really only makes one turn), and due to the design, it is FAR more aerodynamic. Roots type compressors like the JR units will never see more than 55% efficiency. Centrifugal compressors can have efficiencies as high as 80%. The less heat you make, the higher the detonation threshold is. The higher the detonation threshold is, the more boost you can run. The more boost you run, the more power you make. With the Roots compressor and its lower efficiency, it feels slower because it's making less power. What do people do? They turn up the boost with different pulleys. What does this do? It makes more heat. What is a not so obvious consequence of heat in a Roots compressor? Decreased clearances between the rotors and the housing, as well as thermal expansion of the rotors themselves. The rotors can expand to the point of cracking and shedding their ceramic coating, as well as grinding away some aluminum from the housing. Guess where all this stuff goes next? Even if this didn't happen, you're limited to about 12 PSI in an unmodified Roots compressor due to thermal rise. Above 12 PSI, you have to add so much fuel and retard the ignition so much to overcome the heat- induced detonation, that you start to lose power. The cost of modifying a Roots compressor to achieve power above 12 PSI outweighs the actual gain in HP.
Now let's talk about lag...
Yes, turbos have lag. This is not bad, however. First off, though, let's look at why they have lag and why the lag is good. Turbos have lag because they are not an RPM based device. That is, they are not confined to a set speed dictated by crank RPM like an SC and CSC is. Why this is good is that it'll only give you the boost when you need it. The SCs are boosting all the time, constantly drawing power from the engine. The reason you don't see boost at partial throttle is because they have diverter valves to bleed off the boost when the engine VE doesn't need it. Basically, you're making power and throwing it away without using it. Kinda like buying gas and then dumping it out on the ground. At partial throttle, the turbo is spinning along, but not fast enough to make boost because it's a CFM dependent unit. The more air the engine can move through itself, the faster the turbo will spin. Off boost, you retain stock drivability and gas mileage with a turbo. With an SC, you gain a touchy throttle and wasted energy. Another great thing about the turbo and it's lag, is that you're less likely to have traction problems right off the line, and in a light FWD car, this is paramount to performance. With the advent of modern aerodynamics and ball bearings, turbo lag has pretty much been eliminated above 2000 RPM with the proper setup. Sure, the JR unit boosts 2 PSI at idle, but who drives around at idle? I don't. Do you? With a proper, thought out turbo setup, you can have little lag and haul ass top end, and virtually zero lag from the midrange on, and when you're racing, this is where the performance counts.
Now, if you'll noticed, I haven't mentioned the CSC at all in this part. Why? Because it combines the worst of both worlds- the parasitic drag of a supercharger, and the turbo lag of a grossly mismatched turbo. Now, since it's a supercharger, the compressor RPM is a fixed value of the crank RPM, meaning, if the crank is turning X RPM, the compressor wheel is turning Y RPM. It is a linear relationship and never changes. Since the CSC uses a centrifugal compressor like a turbo, the boost pressure and CFM rate increases proportionate to compressor RPM. That having been said, the faster the compressor spins, the more boost it makes. Since you don't want to over boost the engine (let's say for the sake of argument, the max. boost pressure is 10 PSI), the maximum boost pressure RPM is reserved for absolut engine redline. If it were set for 4000 RPM, the engine would overboost above 4000 RPM and blow up. Now, since the boost pressure is only achievable at absolut redline, the boost pressure rise is a function of the square of the crank RPM, that is, at half RPM, you'll be making one fourth of your maximum boost pressure in the case of a B16 set to run 10 PSI, that comes out to 2.5 PSI at 4000 RPM. Compare this to a modern turbo that will make 10 PSI by 3000 RPM, and I'm sure you'll see why Vortech superchargers havn't taken the import world by storm. I'd rather wait a second for full boost, than to wait 'till redline.
Cost vs. HP...
For this comparason, I'm going to use a D16Z6 in a 5th gen hatch because this is where my personal experience comes in.
I spent around a grand on a budget turbo setup for my '93 Si hatch and ran 10 PSI. I saw positive pressure as low as 2000 RPM, full boost by 2700 RPM, and above 3300 RPM, I had instant full boost when I floored the pedal. A friend of mine had an '89 base model Civic hatch with a Z6 and a JR SC in it, for which he spent about $2600 on just the blower. We were both running FMUs, and he was running 10 PSI as well. He had a weight advantage of about 300 lbs. Off the line, he had me. For about 10 feet. By the time I was at 4000 RPM in 1st gear, I was next to him, and by redline, he was at my rear bumper. By 100 MPH (roughly a 1/4 mile for me), he was a good 30 yards behind me. I have no idea what this equates to in HP difference, but a 90' lead at the end of the 1/4 mile is considered a solid trouncing.
Conclusion...
SCs have their place- low RPM, high torque applications such as two stroke diesels found in cranes and graders. Turbos do too- under the hood of a car owned by anyone that's serious about going fast. CSCs have a place too- the Dumpster."
Dont go on to say that top fuel dragsters use sc's so they must be good, its becuase of the rules of their class, like nascar uses carbs, solid axles, restrictor plates...class rules.
"OK OK... I'm here. Now... let's start with the basics because quite a few of you believe myths to be true, and truths to be myths. Listen closely... I'm not going to speak from opinion, but provable facts and first hand personal experience. This post will be THE definitive post in this thread.
CSC = Centrifugal SuperCharger.
SC = SuperCharger
Turbo = Turbo.
OK, good. Let's start with efficiency...
Both turbos and superchargers compress the air and force it into the engine. In doing so, they heat the air, and this is the measure of efficiency- the less heat, the more efficient. There are several design factors that affect the thermal rise of the charge air- internal aerodynamics of the compressor (I'm referring to turbo, SC, and CSC), internal surface area, and the number of direction changes the air has to make. Hands down, a centrifugal compressor (turbo and CSC) wins this contest. It has less internal surface area, the air has to make less turns (it really only makes one turn), and due to the design, it is FAR more aerodynamic. Roots type compressors like the JR units will never see more than 55% efficiency. Centrifugal compressors can have efficiencies as high as 80%. The less heat you make, the higher the detonation threshold is. The higher the detonation threshold is, the more boost you can run. The more boost you run, the more power you make. With the Roots compressor and its lower efficiency, it feels slower because it's making less power. What do people do? They turn up the boost with different pulleys. What does this do? It makes more heat. What is a not so obvious consequence of heat in a Roots compressor? Decreased clearances between the rotors and the housing, as well as thermal expansion of the rotors themselves. The rotors can expand to the point of cracking and shedding their ceramic coating, as well as grinding away some aluminum from the housing. Guess where all this stuff goes next? Even if this didn't happen, you're limited to about 12 PSI in an unmodified Roots compressor due to thermal rise. Above 12 PSI, you have to add so much fuel and retard the ignition so much to overcome the heat- induced detonation, that you start to lose power. The cost of modifying a Roots compressor to achieve power above 12 PSI outweighs the actual gain in HP.
Now let's talk about lag...
Yes, turbos have lag. This is not bad, however. First off, though, let's look at why they have lag and why the lag is good. Turbos have lag because they are not an RPM based device. That is, they are not confined to a set speed dictated by crank RPM like an SC and CSC is. Why this is good is that it'll only give you the boost when you need it. The SCs are boosting all the time, constantly drawing power from the engine. The reason you don't see boost at partial throttle is because they have diverter valves to bleed off the boost when the engine VE doesn't need it. Basically, you're making power and throwing it away without using it. Kinda like buying gas and then dumping it out on the ground. At partial throttle, the turbo is spinning along, but not fast enough to make boost because it's a CFM dependent unit. The more air the engine can move through itself, the faster the turbo will spin. Off boost, you retain stock drivability and gas mileage with a turbo. With an SC, you gain a touchy throttle and wasted energy. Another great thing about the turbo and it's lag, is that you're less likely to have traction problems right off the line, and in a light FWD car, this is paramount to performance. With the advent of modern aerodynamics and ball bearings, turbo lag has pretty much been eliminated above 2000 RPM with the proper setup. Sure, the JR unit boosts 2 PSI at idle, but who drives around at idle? I don't. Do you? With a proper, thought out turbo setup, you can have little lag and haul ass top end, and virtually zero lag from the midrange on, and when you're racing, this is where the performance counts.
Now, if you'll noticed, I haven't mentioned the CSC at all in this part. Why? Because it combines the worst of both worlds- the parasitic drag of a supercharger, and the turbo lag of a grossly mismatched turbo. Now, since it's a supercharger, the compressor RPM is a fixed value of the crank RPM, meaning, if the crank is turning X RPM, the compressor wheel is turning Y RPM. It is a linear relationship and never changes. Since the CSC uses a centrifugal compressor like a turbo, the boost pressure and CFM rate increases proportionate to compressor RPM. That having been said, the faster the compressor spins, the more boost it makes. Since you don't want to over boost the engine (let's say for the sake of argument, the max. boost pressure is 10 PSI), the maximum boost pressure RPM is reserved for absolut engine redline. If it were set for 4000 RPM, the engine would overboost above 4000 RPM and blow up. Now, since the boost pressure is only achievable at absolut redline, the boost pressure rise is a function of the square of the crank RPM, that is, at half RPM, you'll be making one fourth of your maximum boost pressure in the case of a B16 set to run 10 PSI, that comes out to 2.5 PSI at 4000 RPM. Compare this to a modern turbo that will make 10 PSI by 3000 RPM, and I'm sure you'll see why Vortech superchargers havn't taken the import world by storm. I'd rather wait a second for full boost, than to wait 'till redline.
Cost vs. HP...
For this comparason, I'm going to use a D16Z6 in a 5th gen hatch because this is where my personal experience comes in.
I spent around a grand on a budget turbo setup for my '93 Si hatch and ran 10 PSI. I saw positive pressure as low as 2000 RPM, full boost by 2700 RPM, and above 3300 RPM, I had instant full boost when I floored the pedal. A friend of mine had an '89 base model Civic hatch with a Z6 and a JR SC in it, for which he spent about $2600 on just the blower. We were both running FMUs, and he was running 10 PSI as well. He had a weight advantage of about 300 lbs. Off the line, he had me. For about 10 feet. By the time I was at 4000 RPM in 1st gear, I was next to him, and by redline, he was at my rear bumper. By 100 MPH (roughly a 1/4 mile for me), he was a good 30 yards behind me. I have no idea what this equates to in HP difference, but a 90' lead at the end of the 1/4 mile is considered a solid trouncing.
Conclusion...
SCs have their place- low RPM, high torque applications such as two stroke diesels found in cranes and graders. Turbos do too- under the hood of a car owned by anyone that's serious about going fast. CSCs have a place too- the Dumpster."
Dont go on to say that top fuel dragsters use sc's so they must be good, its becuase of the rules of their class, like nascar uses carbs, solid axles, restrictor plates...class rules.
