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I’m making this thread to get rid of some of the sicky's [img]smile.gif[/img]
Basic stuff on how your motor works
http://auto.howstuffworks.com/engine.htm
http://auto.howstuffworks.com/ignition-system.htm (timing)
First thing
Yes, you can boost your stock car! 6-7 Psi is usually "safe" and still get lots of power. Some people have been running 10 PSI daily on there motor.
Our motor is very strong and can take a lot. If set up and tuned. I will get into this later.
You might be asking "Where do I find parts?"
www.lmperformance.com
www.intense-racing.com
www.3800performance.com
www.zzperformance.com
www.tbyrnemotorsports.com/v6catalog.html
www.texas-speed.com/V6FBODY.asp
http://www.thunderracing.com/catalog...=vehicle&vid=5
www.ngk.com
Are the place's that carry a lot of stuff for our cars. The 3800 Series II you may have seen in some Front wheel drive cars, including the Super charged ones, Are for the most part the same short block. After that there are differences.
Don’t buy a gasket kit for a front wheel drive car. There intake ports are different then ours.
The heads use the same head gasket but the heads are not the same. Our fuel injectors are in our upper intake, FWD cars are in the heads.
Nothing swaps over from the cars, not even the supercharger, it will not fit!!
What Upgrades do I need to boost my car?"
Not as much as you might think. Linxs (pat) Member of the board has stock motor with a custom turbo kit on it and he has put down a best of 416 RWHP (rear wheel horse power) with an open Exhaust.Of course this took alot of tuning hours.
Since the 2 forms of forced induction for our motor are Supercharger and turbo chargers they take the place of needing a cold air intake...... or at least non of the intakes will work with them. So the only thing that's absolute necessary is spark plugs and PCV plug mod. You must get a plug that’s 1 or 2 heat range's colder (see http://www.ngk.com/charglossary.asp?kw=Heat+range for more info) this helps stop Pre-ignition.
Basic info about plugs
http://www.ngk.com/sparkplug411.asp
http://www.ngk.com/faqmain.asp?mfid=
http://www.ngk.com/glossaryImage.asp?imgID=54
Pre-ignition
Ignition of the air/fuel mixture prior to its timed ignition by a spark from the spark plug is referred to as "pre-ignition". This can be caused by a hot spot in the combustion chamber, improper timing, too hot a spark plug, low octane fuel, too lean an air/fuel mixture, or engine overeating.
http://www.ngk.com/glossary.asp?kw=Pre-ignition
Throttle body by-pass
http://home.comcast.net/~grayman99/TB-PCV.htm this explains why it is needed and 2 ways to do it...
Now everything else will let your stock motor breath more which means it’s making more power
If you car is a 1995-1999 your stock exhaust manifolds are crappy and don't flow well. Plus it's really hard to change the plugs. You can upgrade these with 2000+ years witch flow better and make plug changing a lot easier. Or buy headers
3 place's make headers
www.rksport.com
Pacesetters (found at many links above)
CIA
www.clearimageautomotive.com/Products/Exhaust/V6Headers.htm
Finally upgrade your exhaust.
Exhaust can be found at almost every link above. I could go on day's trying to explain each one, and find what one is better then other. But it really matters on how much money you have and what kind of sound your looking for..... But anything is better then stock.
Upgrade CAT converter.
Federal laws regulate this so be careful. You can get a high flow cat from almost any place. Most people seem to like the "Car sound" one. It’s cheap, and flows well.
You do not need to upgrade any internal motor parts. If you do it gets expensive really fast! Unless you’re trying to push the limits there is really no need.
Heads an cam can be replaced without removing the motor from the car
pistons and bottom end
many of the place's i listed above carry stronger parts you need to do this, also you must remove the motor and have all kinds of machine done to it. this is not cheap. know one yet ahs broken our crank shaft. do to raw power
Tuning:
Tuning is just getting going for these motors, there are 2 options.
www.hptuners.com (1997-up cars only)(1996 cars can put a 1997 PCM in there car plug and play)
And
Digital Horse Power
www.digitalhorsepower.com/home.htm
How much can my 3.4 or 3.8 handle?
The truth is to nobody actually knows, to my knowledge and many others on this board and other boards no one has broken a 3.4 or 3.8 because of raw power output.
Usually failure is do to pre-ignition, leaning out (to little fuel) or bad tuning.
Tuning now is getting easier and fuel upgrades are there.
Knock can be controlled with tuning, fuel, and just not getting stupid with the boost. Also P/P the heads can help prevent hot spots that also cause knock
Many people have been running 8-10 Psi for a while now and being smart about it is why there car is still in one piece.
Still 7 PSI seems to be the going rate for a everyday car and 10 psi at the track.
I don't want to go crazy but I would like a little more power from my FI car."
The cheapest things for this are
Changing out rocker arms for a little more lift.
P/p heads
P/p upper and lower intakes
Cam/valve-train
You can upgrade the cam with out removing the heads. Most people opp for this, the cam is like your lungs it controls how air flows in the motor.
http://auto.howstuffworks.com/camshaft.htm
This will add power but to get max power you will need to p/p the heads to compliment the cam. Allowing the air to flow "faster" less restricted also the "port" makes more area so more air can flow. More air in/out = more power.
IMO it’s smarter to replace the cam and heads at the same time or you'll be doing work over again. Costing you more in the end. Also if you pick the right valve-train you can rev the motor higher with tuning.
Forced induction: Written by HAZ-Matt
http://auto.howstuffworks.com/turbo.htm
http://www.powerdyne.com/tech.htm
This is my take on the matter. First I would like to say "Dammit Jim! I'm a doctor, not a mechanic!" (Well, not a doctor yet but you get the idea). However, I am a scientist and I feel that my description is accurate. I wrote this because I felt that the above guide got some of the major points correct, but misstated some of the other concepts (no offense meant to T-Punk). I also added descriptions of the different classes of compressors because I feel that is very important to understanding FI. If anyone has a grievance with my guide, let me know.
The HAZ-Matt Guide to
FORCED INDUCTION
SUPERCHARGING
The centrifugal supercharger is the only type of after market supercharger that has been fitted to a 4th Gen F-body at the time of this writing. As they are not mounted on top of the intake manifold (as any of the positive displacement type blowers are) they are easier to retrofit to vehicles that started their lives NA. It would not be economically feasible to adapt an M90 roots supercharger from a GTP to a 4th Gen F-body. If you are not satisfied by that statement, do a search or build the kit yourself.
By the way, a turbo (aka turbosupercharger, aka turbocharger) is a form of supercharger that is driven by exhaust gases. It is technically a subtype of superchargers because the defining feature of a supercharger is that it compresses air. The method of driving the compressor is irrelevant to the definition.
Roots Compressor
One of the earliest compressor designs. It essentially consists of a series of rotating lobes on a set of rotors within a housing. Early designs had fewer lobes that were cut straight making them noisy and relatively inefficient. Modern roots blowers have the lobes twisted axially and have tighter tolerances and better housing designs. Efficiency has been improved greatly. While the roots blower is simplistic, reliable, and can build boost off idle, it is still somewhat hampered by the inherent inefficiency of the compressor design and by the fact that the bulky nature of the unit precludes adaptation into cramped engine bays.
Lysholm (aka Screw) Compressor
The screw has all of the pros of a roots compressor with efficiency as good as or greater than that of a centrifugal design. Screw compressors are internally similar to a roots compressor except that each rotor has an extra lobes, and the lobes are not ground in the same way. The lobe design allows near interlocking of the lobes which increases thermal efficiency. They also have better high boost characteristics than a basic roots type compressor.
Centrifugal Compressors
These simplistically consist of a “fan” (vaned wheel) inside a scroll type housing. The compressor sucks air in and the vanes push the air to the outside edges of the scroll, causing pressurization. This design relies on “centrifugal force” to compress the air (the author is aware that technically centrifugal force is not a real force, but that’s how this compressor got its name). Because centrifugal compressors are not positive displacement, they do not have good compression characteristics at low speeds, and must reach high speeds for any significant compression to occur. At high RPMs, however, this compressor type is very efficient. Crank driven centrifugal superchargers generally are internally geared to operate the wheel in the 10K RPM range, whereas turbochargers may operate at over 100K RPMs.
TURBOCHARGING
Turbochargers are simply exhaust driven centrifugal superchargers. The compressor is directly linked to a turbine that is placed within the exhaust system. The compressor section of a turbo is generally smaller than the compressor of its cousin the crank driven centrifugal supercharger because it is going to spin at 10 times the RPM. The turbine looks like the compressor section of the turbo, except that the flow path is reversed and energy is taken out of the high kinetic energy exhaust gases in order that energy may be put into the intake charge (via compression). It is the turbine (in conjunction with the wastegate) that allows a turbo to function at many different RPMs at a single of engine speed. This allows greater tunability as compared to a crank driven supercharger.
Wastegates
As alluded to before, the wastegate is a system that can limit turbine RPM of a turbo. In a sense, a turbo is a positive feedback system. As the turbo creates more boost, it also creates more exhaust flow. If unchecked, the turbo would spin up to some ungodly RPM and something would eventually break. It is the wastegate’s job to limit flow through the turbine and thus control turbo RPM. In the simple case, the gate is controlled by manifold pressure. When the pressure is great enough (how great depends on the spring used in the wastegate) the gate opens and some of the exhaust gases bypass the turbine. Boost controllers generally manipulate the amount of manifold pressure the wastegate “sees” and fools it into thinking the manifold pressure is less than it actually is.
Blow off valves
The job of a blow off valve is to limit boost spikes and vent excess boost in the case that the wastegate is not doing its job. In a completely closed intake system, when the throttle plate closes during boost (as during a shift) a pressure wave would travel backwards to the compressor of the turbo (or supercharger theoretically) and cause a decelerative force on the compressor. Minimally, this would reduce compressor RPM and decrease performance after the shift, or in the worse case it could damage the turbo. A blow off valve, like a wastegate, samples manifold pressure. When the manifold pressure is less than the pressure in the intake piping, the valve opens and the pressure in the intake is reduced.
A bypass valve is like a blow off valve except that instead of venting the excess intake pressure to atmosphere, it pipes it back to before the compressor.
INTERCOOLERS
All this air compression will cause the temperature of intake charge to increase (i.e. can’t beat thermodynamics). Intercoolers are an attempt to bring the temperature of the air closer to ambient. Lower temperature air decreases the chance of detonation and also results in a higher flow rate through the engine. Flow rate is proportional to power output. Intercoolers received their name because some piston engine era warplanes utilized twin stage superchargers in order to maintain engine power at high altitudes. Even though many of those aircraft ran on 160 octane leaded fuel, heating of the intake air was a concern (see Rolls Royce Merlin engine design). A device, essentially a radiator, was placed between the first and second supercharger stages, and the “intercooler” was born. A similar device could also be placed after the second stage and was called the “aftercooler.” Although technically what we see on the automobiles today are more directly related to aftercoolers (some supercharger kits refer to them in this way) apparently intercooler sounds ‘cooler’ (pardon the pun) and that is what description we commonly use for these little radiators.
The two main types of intercoolers are the air-to-air and air-to-water types; the main difference is which medium accepts heat from the intake charge.
Air-to-air intercoolers exchange heat between the intake charge and the ambient air. Efficiency is commonly in the neighborhood of 80%. Air-to-air intercoolers must be placed in a location with sufficient airflow or they will not be able to effectively exchange heat. Two subclasses of air-to-air intercoolers are the cheaper tube and fin design, and the more robust and efficient bar and plate design. The main advantage of an air-to-air intercooler is simplicity of design.
Air-to-water intercoolers may operate at efficiencies greater than 100% if the water is at a temperature below ambient. These systems do not need to be placed in the path of airflow, so there is some freedom in choosing a location for it within the vehicle. The actual intercooler portion of the system is generally smaller than a comparable air-to-air intercooler. Unfortunately, air-to-water systems are more complex in that they need a coolant reservoir and some method to extract heat from the coolant.
TURBO VS SUPERCHARGER
In simplistic terms, the engine functions as an air pump. The more air and fuel that is pumped through, the more power you can make. In order to pump the air, pressure on the intake side must be higher relative to pressure going out the exhaust. In a naturally aspirated engine, valve timing events are used to create a pressure. Since you are reading this guide, you are probably not interested in naturally aspirated engines, so we can leave it at that. That said, we can all agree that it makes no sense to build a naturally aspirated performance engine. From a performance standpoint, it would generally make sense to use some means to pressurize the intake, while using some means to decrease the pressure in the exhaust path. The second part is easy; almost everyone and their brother has some type of exhaust work. The first job is a little trickier. Fortunately we have superchargers (and turbos) to save the day.
A crank driven supercharger will most definitely increase the pressure on the intake side of the engine. Since it is limited to the intake track, it will not adversely affect the pressure in the exhaust. The pressure on the intake side should always be greater than the pressure in the exhaust. However, power doesn’t come free, and you must use some of that newfound torque to spin the supercharger. How much that takes is calculable, but is purely academic because significant power is netted. In the case of positive displacement superchargers, boost can be had at very low RPMs, and in the case of the centrifugal and screw supercharger, good efficiency can be had. Other reasons to choose a supercharger are that the retrofit to an NA car should be smoother because there are no changes to be made to the exhaust path. The power curve is predictable because boost is largely dependent on RPM of the motor and not some less tangible factor such as engine load.
Now why would anyone want a turbo? Turbo systems are more complex because they require revision to the intake and exhaust sides of the motor. From the air pump standpoint, at first glance they seem to be inferior to a supercharger as you are placing a restriction in the exhaust flow path (i.e. the turbine). And given what we know of centrifugal compressor efficiency at low RPMs, there may be a significant portion of the rev range before the turbo will reach threshold and begin to create boost (this is what “lag” is). However the relative independence from engine RPM is the turbo’s greatest advantage over any other supercharger type. Boost can be reset with ease, and therefore tunability is also greatly increased as compared to a crank driven unit. While the adiabatic efficiency of the compressor may not be as great as that of a screw type supercharger, the drive mechanism is much more efficient, as a turbo relies on utilization of largely wasted kinetic energy in the exhaust gases. All of this combines to form a versatile, tunable unit that has the potential to make more power than a crank driven supercharger.
So a turbo must be superior to a crank driven supercharger, right? If that was the case the crank driven supercharger would have died out long ago. For all out power the turbo reigns supreme, but life unfortunately is full of compromises. Packaging is a huge concern during a retrofit of forced induction onto an NA motor, and in that instance the crank driven supercharger has the turbo beat handily. The user must decide on his or her priorities and decide from there.
[ September 25, 2005, 03:25 PM: Message edited by: viper04af ]
Basic stuff on how your motor works
http://auto.howstuffworks.com/engine.htm
http://auto.howstuffworks.com/ignition-system.htm (timing)
First thing
Yes, you can boost your stock car! 6-7 Psi is usually "safe" and still get lots of power. Some people have been running 10 PSI daily on there motor.
Our motor is very strong and can take a lot. If set up and tuned. I will get into this later.
You might be asking "Where do I find parts?"
www.lmperformance.com
www.intense-racing.com
www.3800performance.com
www.zzperformance.com
www.tbyrnemotorsports.com/v6catalog.html
www.texas-speed.com/V6FBODY.asp
http://www.thunderracing.com/catalog...=vehicle&vid=5
www.ngk.com
Are the place's that carry a lot of stuff for our cars. The 3800 Series II you may have seen in some Front wheel drive cars, including the Super charged ones, Are for the most part the same short block. After that there are differences.
Don’t buy a gasket kit for a front wheel drive car. There intake ports are different then ours.
The heads use the same head gasket but the heads are not the same. Our fuel injectors are in our upper intake, FWD cars are in the heads.
Nothing swaps over from the cars, not even the supercharger, it will not fit!!
What Upgrades do I need to boost my car?"
Not as much as you might think. Linxs (pat) Member of the board has stock motor with a custom turbo kit on it and he has put down a best of 416 RWHP (rear wheel horse power) with an open Exhaust.Of course this took alot of tuning hours.
Since the 2 forms of forced induction for our motor are Supercharger and turbo chargers they take the place of needing a cold air intake...... or at least non of the intakes will work with them. So the only thing that's absolute necessary is spark plugs and PCV plug mod. You must get a plug that’s 1 or 2 heat range's colder (see http://www.ngk.com/charglossary.asp?kw=Heat+range for more info) this helps stop Pre-ignition.
Basic info about plugs
http://www.ngk.com/sparkplug411.asp
http://www.ngk.com/faqmain.asp?mfid=
http://www.ngk.com/glossaryImage.asp?imgID=54
Pre-ignition
Ignition of the air/fuel mixture prior to its timed ignition by a spark from the spark plug is referred to as "pre-ignition". This can be caused by a hot spot in the combustion chamber, improper timing, too hot a spark plug, low octane fuel, too lean an air/fuel mixture, or engine overeating.
http://www.ngk.com/glossary.asp?kw=Pre-ignition
Throttle body by-pass
http://home.comcast.net/~grayman99/TB-PCV.htm this explains why it is needed and 2 ways to do it...
Now everything else will let your stock motor breath more which means it’s making more power
If you car is a 1995-1999 your stock exhaust manifolds are crappy and don't flow well. Plus it's really hard to change the plugs. You can upgrade these with 2000+ years witch flow better and make plug changing a lot easier. Or buy headers
3 place's make headers
www.rksport.com
Pacesetters (found at many links above)
CIA
www.clearimageautomotive.com/Products/Exhaust/V6Headers.htm
Finally upgrade your exhaust.
Exhaust can be found at almost every link above. I could go on day's trying to explain each one, and find what one is better then other. But it really matters on how much money you have and what kind of sound your looking for..... But anything is better then stock.
Upgrade CAT converter.
Federal laws regulate this so be careful. You can get a high flow cat from almost any place. Most people seem to like the "Car sound" one. It’s cheap, and flows well.
You do not need to upgrade any internal motor parts. If you do it gets expensive really fast! Unless you’re trying to push the limits there is really no need.
Heads an cam can be replaced without removing the motor from the car
pistons and bottom end
many of the place's i listed above carry stronger parts you need to do this, also you must remove the motor and have all kinds of machine done to it. this is not cheap. know one yet ahs broken our crank shaft. do to raw power
Tuning:
Tuning is just getting going for these motors, there are 2 options.
www.hptuners.com (1997-up cars only)(1996 cars can put a 1997 PCM in there car plug and play)
And
Digital Horse Power
www.digitalhorsepower.com/home.htm
How much can my 3.4 or 3.8 handle?
The truth is to nobody actually knows, to my knowledge and many others on this board and other boards no one has broken a 3.4 or 3.8 because of raw power output.
Usually failure is do to pre-ignition, leaning out (to little fuel) or bad tuning.
Tuning now is getting easier and fuel upgrades are there.
Knock can be controlled with tuning, fuel, and just not getting stupid with the boost. Also P/P the heads can help prevent hot spots that also cause knock
Many people have been running 8-10 Psi for a while now and being smart about it is why there car is still in one piece.
Still 7 PSI seems to be the going rate for a everyday car and 10 psi at the track.
I don't want to go crazy but I would like a little more power from my FI car."
The cheapest things for this are
Changing out rocker arms for a little more lift.
P/p heads
P/p upper and lower intakes
Cam/valve-train
You can upgrade the cam with out removing the heads. Most people opp for this, the cam is like your lungs it controls how air flows in the motor.
http://auto.howstuffworks.com/camshaft.htm
This will add power but to get max power you will need to p/p the heads to compliment the cam. Allowing the air to flow "faster" less restricted also the "port" makes more area so more air can flow. More air in/out = more power.
IMO it’s smarter to replace the cam and heads at the same time or you'll be doing work over again. Costing you more in the end. Also if you pick the right valve-train you can rev the motor higher with tuning.
Forced induction: Written by HAZ-Matt
http://auto.howstuffworks.com/turbo.htm
http://www.powerdyne.com/tech.htm
This is my take on the matter. First I would like to say "Dammit Jim! I'm a doctor, not a mechanic!" (Well, not a doctor yet but you get the idea). However, I am a scientist and I feel that my description is accurate. I wrote this because I felt that the above guide got some of the major points correct, but misstated some of the other concepts (no offense meant to T-Punk). I also added descriptions of the different classes of compressors because I feel that is very important to understanding FI. If anyone has a grievance with my guide, let me know.
The HAZ-Matt Guide to
FORCED INDUCTION
SUPERCHARGING
The centrifugal supercharger is the only type of after market supercharger that has been fitted to a 4th Gen F-body at the time of this writing. As they are not mounted on top of the intake manifold (as any of the positive displacement type blowers are) they are easier to retrofit to vehicles that started their lives NA. It would not be economically feasible to adapt an M90 roots supercharger from a GTP to a 4th Gen F-body. If you are not satisfied by that statement, do a search or build the kit yourself.
By the way, a turbo (aka turbosupercharger, aka turbocharger) is a form of supercharger that is driven by exhaust gases. It is technically a subtype of superchargers because the defining feature of a supercharger is that it compresses air. The method of driving the compressor is irrelevant to the definition.
Roots Compressor
One of the earliest compressor designs. It essentially consists of a series of rotating lobes on a set of rotors within a housing. Early designs had fewer lobes that were cut straight making them noisy and relatively inefficient. Modern roots blowers have the lobes twisted axially and have tighter tolerances and better housing designs. Efficiency has been improved greatly. While the roots blower is simplistic, reliable, and can build boost off idle, it is still somewhat hampered by the inherent inefficiency of the compressor design and by the fact that the bulky nature of the unit precludes adaptation into cramped engine bays.
Lysholm (aka Screw) Compressor
The screw has all of the pros of a roots compressor with efficiency as good as or greater than that of a centrifugal design. Screw compressors are internally similar to a roots compressor except that each rotor has an extra lobes, and the lobes are not ground in the same way. The lobe design allows near interlocking of the lobes which increases thermal efficiency. They also have better high boost characteristics than a basic roots type compressor.
Centrifugal Compressors
These simplistically consist of a “fan” (vaned wheel) inside a scroll type housing. The compressor sucks air in and the vanes push the air to the outside edges of the scroll, causing pressurization. This design relies on “centrifugal force” to compress the air (the author is aware that technically centrifugal force is not a real force, but that’s how this compressor got its name). Because centrifugal compressors are not positive displacement, they do not have good compression characteristics at low speeds, and must reach high speeds for any significant compression to occur. At high RPMs, however, this compressor type is very efficient. Crank driven centrifugal superchargers generally are internally geared to operate the wheel in the 10K RPM range, whereas turbochargers may operate at over 100K RPMs.
TURBOCHARGING
Turbochargers are simply exhaust driven centrifugal superchargers. The compressor is directly linked to a turbine that is placed within the exhaust system. The compressor section of a turbo is generally smaller than the compressor of its cousin the crank driven centrifugal supercharger because it is going to spin at 10 times the RPM. The turbine looks like the compressor section of the turbo, except that the flow path is reversed and energy is taken out of the high kinetic energy exhaust gases in order that energy may be put into the intake charge (via compression). It is the turbine (in conjunction with the wastegate) that allows a turbo to function at many different RPMs at a single of engine speed. This allows greater tunability as compared to a crank driven supercharger.
Wastegates
As alluded to before, the wastegate is a system that can limit turbine RPM of a turbo. In a sense, a turbo is a positive feedback system. As the turbo creates more boost, it also creates more exhaust flow. If unchecked, the turbo would spin up to some ungodly RPM and something would eventually break. It is the wastegate’s job to limit flow through the turbine and thus control turbo RPM. In the simple case, the gate is controlled by manifold pressure. When the pressure is great enough (how great depends on the spring used in the wastegate) the gate opens and some of the exhaust gases bypass the turbine. Boost controllers generally manipulate the amount of manifold pressure the wastegate “sees” and fools it into thinking the manifold pressure is less than it actually is.
Blow off valves
The job of a blow off valve is to limit boost spikes and vent excess boost in the case that the wastegate is not doing its job. In a completely closed intake system, when the throttle plate closes during boost (as during a shift) a pressure wave would travel backwards to the compressor of the turbo (or supercharger theoretically) and cause a decelerative force on the compressor. Minimally, this would reduce compressor RPM and decrease performance after the shift, or in the worse case it could damage the turbo. A blow off valve, like a wastegate, samples manifold pressure. When the manifold pressure is less than the pressure in the intake piping, the valve opens and the pressure in the intake is reduced.
A bypass valve is like a blow off valve except that instead of venting the excess intake pressure to atmosphere, it pipes it back to before the compressor.
INTERCOOLERS
All this air compression will cause the temperature of intake charge to increase (i.e. can’t beat thermodynamics). Intercoolers are an attempt to bring the temperature of the air closer to ambient. Lower temperature air decreases the chance of detonation and also results in a higher flow rate through the engine. Flow rate is proportional to power output. Intercoolers received their name because some piston engine era warplanes utilized twin stage superchargers in order to maintain engine power at high altitudes. Even though many of those aircraft ran on 160 octane leaded fuel, heating of the intake air was a concern (see Rolls Royce Merlin engine design). A device, essentially a radiator, was placed between the first and second supercharger stages, and the “intercooler” was born. A similar device could also be placed after the second stage and was called the “aftercooler.” Although technically what we see on the automobiles today are more directly related to aftercoolers (some supercharger kits refer to them in this way) apparently intercooler sounds ‘cooler’ (pardon the pun) and that is what description we commonly use for these little radiators.
The two main types of intercoolers are the air-to-air and air-to-water types; the main difference is which medium accepts heat from the intake charge.
Air-to-air intercoolers exchange heat between the intake charge and the ambient air. Efficiency is commonly in the neighborhood of 80%. Air-to-air intercoolers must be placed in a location with sufficient airflow or they will not be able to effectively exchange heat. Two subclasses of air-to-air intercoolers are the cheaper tube and fin design, and the more robust and efficient bar and plate design. The main advantage of an air-to-air intercooler is simplicity of design.
Air-to-water intercoolers may operate at efficiencies greater than 100% if the water is at a temperature below ambient. These systems do not need to be placed in the path of airflow, so there is some freedom in choosing a location for it within the vehicle. The actual intercooler portion of the system is generally smaller than a comparable air-to-air intercooler. Unfortunately, air-to-water systems are more complex in that they need a coolant reservoir and some method to extract heat from the coolant.
TURBO VS SUPERCHARGER
In simplistic terms, the engine functions as an air pump. The more air and fuel that is pumped through, the more power you can make. In order to pump the air, pressure on the intake side must be higher relative to pressure going out the exhaust. In a naturally aspirated engine, valve timing events are used to create a pressure. Since you are reading this guide, you are probably not interested in naturally aspirated engines, so we can leave it at that. That said, we can all agree that it makes no sense to build a naturally aspirated performance engine. From a performance standpoint, it would generally make sense to use some means to pressurize the intake, while using some means to decrease the pressure in the exhaust path. The second part is easy; almost everyone and their brother has some type of exhaust work. The first job is a little trickier. Fortunately we have superchargers (and turbos) to save the day.
A crank driven supercharger will most definitely increase the pressure on the intake side of the engine. Since it is limited to the intake track, it will not adversely affect the pressure in the exhaust. The pressure on the intake side should always be greater than the pressure in the exhaust. However, power doesn’t come free, and you must use some of that newfound torque to spin the supercharger. How much that takes is calculable, but is purely academic because significant power is netted. In the case of positive displacement superchargers, boost can be had at very low RPMs, and in the case of the centrifugal and screw supercharger, good efficiency can be had. Other reasons to choose a supercharger are that the retrofit to an NA car should be smoother because there are no changes to be made to the exhaust path. The power curve is predictable because boost is largely dependent on RPM of the motor and not some less tangible factor such as engine load.
Now why would anyone want a turbo? Turbo systems are more complex because they require revision to the intake and exhaust sides of the motor. From the air pump standpoint, at first glance they seem to be inferior to a supercharger as you are placing a restriction in the exhaust flow path (i.e. the turbine). And given what we know of centrifugal compressor efficiency at low RPMs, there may be a significant portion of the rev range before the turbo will reach threshold and begin to create boost (this is what “lag” is). However the relative independence from engine RPM is the turbo’s greatest advantage over any other supercharger type. Boost can be reset with ease, and therefore tunability is also greatly increased as compared to a crank driven unit. While the adiabatic efficiency of the compressor may not be as great as that of a screw type supercharger, the drive mechanism is much more efficient, as a turbo relies on utilization of largely wasted kinetic energy in the exhaust gases. All of this combines to form a versatile, tunable unit that has the potential to make more power than a crank driven supercharger.
So a turbo must be superior to a crank driven supercharger, right? If that was the case the crank driven supercharger would have died out long ago. For all out power the turbo reigns supreme, but life unfortunately is full of compromises. Packaging is a huge concern during a retrofit of forced induction onto an NA motor, and in that instance the crank driven supercharger has the turbo beat handily. The user must decide on his or her priorities and decide from there.
[ September 25, 2005, 03:25 PM: Message edited by: viper04af ]
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