Paolo Castellano
Enthusiast
* Turbos have recently become the power adder of choice for the informed consumer…. But, knowing what turbo system to choose and why, is why I would like to discuss some basic turbocharging principles:
I would like to lay out some ideals that turbo system designers strive to accomplish:
Before I do this, I would like to qualify this by saying a lot depends on the space constraints of a given car.
Turbo system designers and fabricators must make compromises unless they make the perfect turbo system and build a car around that system.
Ideally, an intercooled front mount twin turbo Viper with full T-04 turbos, pulling clean cool air from behind the fog lights will be the most efficient TT Viper for the street.
If done properly, a front mount Twin Turbo can pull clean air through holes in the core support via short, unrestrictive piping from the air filters located behind the fog lights.
The footwell mounted turbo systems would have to run much longer, (more restrictive) piping all the way up through the core support to place the filters behind the fog lights. While this could be done, most just pull hot air from the engine compartment or transmission tunnel.
So from an efficiency standpoint, starting with 200+ degree air or 70 degree ambient air, the system that pulls the cooler air will certainly be the most efficient(all other things being equal)
* Turbo Sizing - this is a very general term that encompasses many things:
- On the most basic level it means sizing the exhaust housing and exhaust wheel diameter to match the volume of exhaust gases coming out of the motor while matching the compressor(intake) housing and compressor wheel diameter to the amount of air you want to flow to make a target power level.
- For maximum turbo efficiency, we must get the exhaust gases out of the turbo at least as fast as they come in minimizing the work/energy the turbo has to do to deliver a fixed amount of air to the throttle bodies. Less restriction = higher efficiency.
- Properly sizing a twin turbo setup on an 8 liter motor would be equivalent to a single turbo on a 4 liter motor: The Garrett Catalog recommends using a Garrett GT-40 Turbo for a 3.5-5.0 liter motor. Note: the GT-40 turbo uses a T-04 exhaust housing.
-Due to space constraints associated with mounting the turbos in the footwells, most footwell mounted Viper tuner twin turbo systems use the smaller T-03 exhaust housings (which are sized for the exhaust gas volume of a 2.0-3.0 liter motor)
-They combine the T-03 exhaust housing with a relatively larger compressor wheel (to flow the air for the 4 liter motor).
- So, with this T-03/T-04 hybrid, the outlet flow can never match the inlet flow, effectively minimizing the efficiency of the turbo system.
-This restriction is called Backpressure . Backpressure is not your friend and should be minimized at all costs!
* Question: is 6 PSI with a smaller turbo the same as 6 PSI with a larger turbo on any given 488 CI Viper motor as far as how much power gets to the wheels?
-The simple answer is NO !
-The combination of the relatively larger compressor wheel and small(T-03) exhaust housing on the average Viper twin turbo system makes for more restriction PERIOD!
-The higher backpressure from the small T-03 exhaust housing makes the compressor wheel have to spin much faster to overcome the pressure differential than it would if it had the properly sized T-04 exhaust housing.
-Higher compressor wheel speeds generate HEAT . Heat is not a friend of power on the intake side of the equation!
-Less heat means less chance of detonation and better overall system durability.
-To conclude this point, we have learned that less restriction leads to lower compressor wheel speeds and therefore less heat at the same boost pressure!
*Spooling characteristics defined:
-The area ratio, A/R, of the turbine housing is the most influential in determining the spooling characteristics of a given turbine and compressor wheel combination.
-In layman’s terms, it is the internal volume of the turbine housing.
-A turbo is said to spool as the exhaust gases begin to spin the turbine wheel.
-A smaller A/R will fill up more quickly with a given amount of exhaust gas volume. Therefore a smaller A/R will spool more quickly but is volumetrically challenged to flow/discharge the higher volume of air as the RPM’s increase.
-In a nutshell, the small A/R hits hard at lower RPM’s but runs out of capacity to be efficient at higher RPM’s. Note: A Supra is the exact opposite of this.
-With Vipers there should never be turbo lag making anything less than 2500-3000 HP!
This next section is a comparison between the bolt-on system we have designed for the Viper and other boosted applications available. This is to show the overall value of our system and what the average Viper consumer should be expecting to get from US for your money:
* Driveability of T-03 vs T-04:
-Due to the information discussed above regarding the T-03/T-04 hybrid systems, it is now not surprising to see why these cars have been known to easily spin hot drag slicks most of the ¼ mile because of how brutally the power comes on. (Think of it as revving to 6000 and dumping the clutch every time the boost comes on, it might be fun the first few times but it really is not manageable.)
-With the higher flow afforded by the T-04 turbo, the system will actually make the same bottom end power (if not more) while having the flow capacity necessary to hold far more power all the way to the top of the RPM band.
-The gentler slope of the T-04's torque curve is representative of the boost coming on in a more linear fashion maximizing the driveability coefficient!
-Higher flow also means that the power will come on far more lineally and predictably. (you don’t go anywhere spinning your wheels unless you want to)
-Making the same or more power at lower boost levels generates less heat to be dissipated by the intercooler making for better detonation management and less need to run race gas to make big power.
-Less heat generated is less overall heat for your cooling system to dissipate.
-To summarize this point, a cooler running car with a more linear power curve is more fun and easy to drive!
* Turbos vs Superchargers:
-Here is a link to a general comparison between superchargers and turbochargers: http://turbochargedpower.com/Turbo%20vs%20Blowers.htm
-In general terms, turbos make more power per lb boost and do it more efficiently than a blower.
-Turbos have the ability to adjust the power output in an instant with a boost controller on the fly from the comfort of inside the car instead of having to change a pulley.
-Turbos also only compress the air when the engine is under load putting less wear and tear on the engine and cooling system in cruise mode (off boost).
-Turbos do not stress the crankshaft like the superchargers do from being driven off the crankshaft.
-Turbos do not have have the parasitic loss associated from having to be driven off the crankshaft!
-Turbos do not require the regular belt tightening(and replacement)of a high powered supercharger system, which is a major benefit at events.
* The last system you will ever need:
-Over the years, there has been a massive amount of change in the Viper aftermarket:
-Each new power adder runs its course until there comes something new to take its place……600-650 RWHP 35K N/A upgrades gave way to 600-650 RWHP 35K Superchargers, giving way to 600 RWHP 8K superchargers.
-Looking at past trends, customers would buy the ultimate Viper power upgrade package which became obsolete as fast as the cutting edge computer does when purchased from the major computer companies.
-Upgrading from one brand system to another is always a losing proposition!
In conclusion, Viper owners out there ideally would want to get one upgradeable turbo system that is the most efficient from the moment it starts pulling air into the system to the exhaust housing and exhaust wheel expelling the exhaust gases.
I would like to lay out some ideals that turbo system designers strive to accomplish:
Before I do this, I would like to qualify this by saying a lot depends on the space constraints of a given car.
Turbo system designers and fabricators must make compromises unless they make the perfect turbo system and build a car around that system.
Ideally, an intercooled front mount twin turbo Viper with full T-04 turbos, pulling clean cool air from behind the fog lights will be the most efficient TT Viper for the street.
If done properly, a front mount Twin Turbo can pull clean air through holes in the core support via short, unrestrictive piping from the air filters located behind the fog lights.
The footwell mounted turbo systems would have to run much longer, (more restrictive) piping all the way up through the core support to place the filters behind the fog lights. While this could be done, most just pull hot air from the engine compartment or transmission tunnel.
So from an efficiency standpoint, starting with 200+ degree air or 70 degree ambient air, the system that pulls the cooler air will certainly be the most efficient(all other things being equal)
* Turbo Sizing - this is a very general term that encompasses many things:
- On the most basic level it means sizing the exhaust housing and exhaust wheel diameter to match the volume of exhaust gases coming out of the motor while matching the compressor(intake) housing and compressor wheel diameter to the amount of air you want to flow to make a target power level.
- For maximum turbo efficiency, we must get the exhaust gases out of the turbo at least as fast as they come in minimizing the work/energy the turbo has to do to deliver a fixed amount of air to the throttle bodies. Less restriction = higher efficiency.
- Properly sizing a twin turbo setup on an 8 liter motor would be equivalent to a single turbo on a 4 liter motor: The Garrett Catalog recommends using a Garrett GT-40 Turbo for a 3.5-5.0 liter motor. Note: the GT-40 turbo uses a T-04 exhaust housing.
-Due to space constraints associated with mounting the turbos in the footwells, most footwell mounted Viper tuner twin turbo systems use the smaller T-03 exhaust housings (which are sized for the exhaust gas volume of a 2.0-3.0 liter motor)
-They combine the T-03 exhaust housing with a relatively larger compressor wheel (to flow the air for the 4 liter motor).
- So, with this T-03/T-04 hybrid, the outlet flow can never match the inlet flow, effectively minimizing the efficiency of the turbo system.
-This restriction is called Backpressure . Backpressure is not your friend and should be minimized at all costs!
* Question: is 6 PSI with a smaller turbo the same as 6 PSI with a larger turbo on any given 488 CI Viper motor as far as how much power gets to the wheels?
-The simple answer is NO !
-The combination of the relatively larger compressor wheel and small(T-03) exhaust housing on the average Viper twin turbo system makes for more restriction PERIOD!
-The higher backpressure from the small T-03 exhaust housing makes the compressor wheel have to spin much faster to overcome the pressure differential than it would if it had the properly sized T-04 exhaust housing.
-Higher compressor wheel speeds generate HEAT . Heat is not a friend of power on the intake side of the equation!
-Less heat means less chance of detonation and better overall system durability.
-To conclude this point, we have learned that less restriction leads to lower compressor wheel speeds and therefore less heat at the same boost pressure!
*Spooling characteristics defined:
-The area ratio, A/R, of the turbine housing is the most influential in determining the spooling characteristics of a given turbine and compressor wheel combination.
-In layman’s terms, it is the internal volume of the turbine housing.
-A turbo is said to spool as the exhaust gases begin to spin the turbine wheel.
-A smaller A/R will fill up more quickly with a given amount of exhaust gas volume. Therefore a smaller A/R will spool more quickly but is volumetrically challenged to flow/discharge the higher volume of air as the RPM’s increase.
-In a nutshell, the small A/R hits hard at lower RPM’s but runs out of capacity to be efficient at higher RPM’s. Note: A Supra is the exact opposite of this.
-With Vipers there should never be turbo lag making anything less than 2500-3000 HP!
This next section is a comparison between the bolt-on system we have designed for the Viper and other boosted applications available. This is to show the overall value of our system and what the average Viper consumer should be expecting to get from US for your money:
* Driveability of T-03 vs T-04:
-Due to the information discussed above regarding the T-03/T-04 hybrid systems, it is now not surprising to see why these cars have been known to easily spin hot drag slicks most of the ¼ mile because of how brutally the power comes on. (Think of it as revving to 6000 and dumping the clutch every time the boost comes on, it might be fun the first few times but it really is not manageable.)
-With the higher flow afforded by the T-04 turbo, the system will actually make the same bottom end power (if not more) while having the flow capacity necessary to hold far more power all the way to the top of the RPM band.
-The gentler slope of the T-04's torque curve is representative of the boost coming on in a more linear fashion maximizing the driveability coefficient!
-Higher flow also means that the power will come on far more lineally and predictably. (you don’t go anywhere spinning your wheels unless you want to)
-Making the same or more power at lower boost levels generates less heat to be dissipated by the intercooler making for better detonation management and less need to run race gas to make big power.
-Less heat generated is less overall heat for your cooling system to dissipate.
-To summarize this point, a cooler running car with a more linear power curve is more fun and easy to drive!
* Turbos vs Superchargers:
-Here is a link to a general comparison between superchargers and turbochargers: http://turbochargedpower.com/Turbo%20vs%20Blowers.htm
-In general terms, turbos make more power per lb boost and do it more efficiently than a blower.
-Turbos have the ability to adjust the power output in an instant with a boost controller on the fly from the comfort of inside the car instead of having to change a pulley.
-Turbos also only compress the air when the engine is under load putting less wear and tear on the engine and cooling system in cruise mode (off boost).
-Turbos do not stress the crankshaft like the superchargers do from being driven off the crankshaft.
-Turbos do not have have the parasitic loss associated from having to be driven off the crankshaft!
-Turbos do not require the regular belt tightening(and replacement)of a high powered supercharger system, which is a major benefit at events.
* The last system you will ever need:
-Over the years, there has been a massive amount of change in the Viper aftermarket:
-Each new power adder runs its course until there comes something new to take its place……600-650 RWHP 35K N/A upgrades gave way to 600-650 RWHP 35K Superchargers, giving way to 600 RWHP 8K superchargers.
-Looking at past trends, customers would buy the ultimate Viper power upgrade package which became obsolete as fast as the cutting edge computer does when purchased from the major computer companies.
-Upgrading from one brand system to another is always a losing proposition!
In conclusion, Viper owners out there ideally would want to get one upgradeable turbo system that is the most efficient from the moment it starts pulling air into the system to the exhaust housing and exhaust wheel expelling the exhaust gases.
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