4th F-Body - View Single Post

fbodyrs96 · November 4th, 2009, 02:38 AM

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.

How BOV's works
www.turbov6camaro.com/bov.doc

How Wastgate's works
http://www.turbov6camaro.com/gate.htm

Misc. Links:

Grayman's Supercharger resource
Lots of info about the Powerdyne and some general FI tips.
http://home.comcast.net/~grayman99/guide.htm

TurboV6Camaro's Website
Andrew has some great stuff on his website too, including FI tuning instructions.
www.turbov6camaro.com

Squirrel Performance Turbo Calculator
This is a straightforward tool to plot points on a compressor map for you
http://www.squirrelpf.com/turbocalc/

GTurboP Turbo Grand Prix
Has some good info about turbos on the GP
http://www.gturbop.com/

Stealth316 Guide
This one is from a guy with a Dodge Stealth, but has some good info about compressor maps and turbos.
http://www.stealth316.com/1-tech.htm

Nicoclub Turbo DYI rebuild

http://forums.nicoclub.com/zerothread/178185

Garrett's Turbo Info page
http://www.turbobygarrett.com/turbob...o_tech101.html

Garrett Catalogue
http://www.limitengineering.com/catalog.pdf

November 4th, 2009, 02:38 AM	#2
fbodyrs96 4th F-Body Poser Join Date: Nov 2009 Location: m Posts: 156	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. How BOV's works www.turbov6camaro.com/bov.doc How Wastgate's works http://www.turbov6camaro.com/gate.htm Misc. Links: Grayman's Supercharger resource Lots of info about the Powerdyne and some general FI tips. http://home.comcast.net/~grayman99/guide.htm TurboV6Camaro's Website Andrew has some great stuff on his website too, including FI tuning instructions. www.turbov6camaro.com Squirrel Performance Turbo Calculator This is a straightforward tool to plot points on a compressor map for you http://www.squirrelpf.com/turbocalc/ GTurboP Turbo Grand Prix Has some good info about turbos on the GP http://www.gturbop.com/ Stealth316 Guide This one is from a guy with a Dodge Stealth, but has some good info about compressor maps and turbos. http://www.stealth316.com/1-tech.htm Nicoclub Turbo DYI rebuild http://forums.nicoclub.com/zerothread/178185 Garrett's Turbo Info page http://www.turbobygarrett.com/turbob...o_tech101.html Garrett Catalogue http://www.limitengineering.com/catalog.pdf