What is TURBO LAG? (info)
02-13-2005, 01:20 AM
#1
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What is TURBO LAG? (info)
What Is Turbo Lag?
Turbo Lag is a term used to describe the time that it takes from when you push the accelerator to full throttle to when the turbocharger comes onto boost. Since turbochargers are designed and sized to operate at specific rpm ranges and air flow conditions, some turbo lag is inherent in the system. Turbos can be sized for specific applications to perform best at low, mid, or high rpm ranges. However, just like any performance add-ons such as cams, manifolds, heads, etc., you can't have peak performance at all rpm ranges.
To fully understand turbo lag, you must first understand the operation principles behind what causes a turbo to make boost. Like most forced induction systems, boost is not made by rpm alone. There is a big difference in the airflow through an engine at 6000 rpm in neutral, 6000 rpm in first gear at part throttle, and 6000 rpm in high gear at full throttle. Turbochargers are even more effected by these airflow differences and especially load differences than most other devices. This is why you may be able to see a small amount of boost with a positive displacement supercharger at WOT in neutral but you will most likely not even see zero inches of vacuum at WOT in neutral with a turbocharger.
Being that turbochargers are so sensitive to air flow and especially loads, you will get very different turbo lag characteristics on the same vehicle during different conditions. For example, the loads placed on the system in lower gears are not as high as the loads placed on the system in the higher gears. This applies to 1st, 2nd, 3rd gear etc., as well as to rearend gears and tire sizes. Short tires with low gears such as 4.88's will not produce engine loading like a taller tire with 3.08 gears. This situation also applies to the weight of the vehicle, including any trailers that the vehicle may be pulling.
A given turbocharged vehicle may produce full boost in first gear by 3500 rpm. This same vehicle may produce full boost in 4th gear by 2300 rpm. The same vehicle, when pulling a heavy trailer, may produce full boost by 1800 rpm even in 1st gear. These conditions are more specific to manual transmission vehicles as the boost has to build in each gear after the throttle is closed during the shift. Automatic transmission vehicles operate differently as they can be "loaded" by stalling up the converter and placing enough load to build boost before the vehicle even moves. Also, with an automatic transmission, the throttle is not shut during shifts which causes the boost to "pop up" because the turbo is supplying enough air flow to feed the boosted engine at high rpms and suddenly the rpms are drastically cut down by the shift as well as increased load has been placed on the system at the same time. This can cause an engine that is accelerating in 1st gear with low boost to instantly go to full boost upon shifting into 2nd gear.
Turbo Lag is a term used to describe the time that it takes from when you push the accelerator to full throttle to when the turbocharger comes onto boost. Since turbochargers are designed and sized to operate at specific rpm ranges and air flow conditions, some turbo lag is inherent in the system. Turbos can be sized for specific applications to perform best at low, mid, or high rpm ranges. However, just like any performance add-ons such as cams, manifolds, heads, etc., you can't have peak performance at all rpm ranges.
To fully understand turbo lag, you must first understand the operation principles behind what causes a turbo to make boost. Like most forced induction systems, boost is not made by rpm alone. There is a big difference in the airflow through an engine at 6000 rpm in neutral, 6000 rpm in first gear at part throttle, and 6000 rpm in high gear at full throttle. Turbochargers are even more effected by these airflow differences and especially load differences than most other devices. This is why you may be able to see a small amount of boost with a positive displacement supercharger at WOT in neutral but you will most likely not even see zero inches of vacuum at WOT in neutral with a turbocharger.
Being that turbochargers are so sensitive to air flow and especially loads, you will get very different turbo lag characteristics on the same vehicle during different conditions. For example, the loads placed on the system in lower gears are not as high as the loads placed on the system in the higher gears. This applies to 1st, 2nd, 3rd gear etc., as well as to rearend gears and tire sizes. Short tires with low gears such as 4.88's will not produce engine loading like a taller tire with 3.08 gears. This situation also applies to the weight of the vehicle, including any trailers that the vehicle may be pulling.
A given turbocharged vehicle may produce full boost in first gear by 3500 rpm. This same vehicle may produce full boost in 4th gear by 2300 rpm. The same vehicle, when pulling a heavy trailer, may produce full boost by 1800 rpm even in 1st gear. These conditions are more specific to manual transmission vehicles as the boost has to build in each gear after the throttle is closed during the shift. Automatic transmission vehicles operate differently as they can be "loaded" by stalling up the converter and placing enough load to build boost before the vehicle even moves. Also, with an automatic transmission, the throttle is not shut during shifts which causes the boost to "pop up" because the turbo is supplying enough air flow to feed the boosted engine at high rpms and suddenly the rpms are drastically cut down by the shift as well as increased load has been placed on the system at the same time. This can cause an engine that is accelerating in 1st gear with low boost to instantly go to full boost upon shifting into 2nd gear.
hope this helps.... :thumbsup
02-18-2005, 10:40 AM
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Originally Posted by vwjetta
if turbo lag is a bad thing can some please explin what a tubo timer is?
you dont even need a turbo timer, just baby your car the last 10 mins of your drive home.
02-18-2005, 12:32 PM
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Originally Posted by vwjetta
if turbo lag is a bad thing can some please explin what a tubo timer is?
http://iv.modnmod.com/articles/turbo1.htm
http://iv.modnmod.com/articles/turbo2.htm
for general boost info.
02-18-2005, 01:04 PM
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Originally Posted by v8_kllr
turbo timers are for people to lazy to wait in their cars for 3 min while the turbo cools down during idle.
you dont even need a turbo timer, just baby your car the last 10 mins of your drive home.
you dont even need a turbo timer, just baby your car the last 10 mins of your drive home.
02-18-2005, 01:33 PM
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Originally Posted by munch
even if you baby it you should still let it idle for a min or two
Letting u'r car idle let's u'r manifold and turbo get hot, and "stores" more heat, so even tho u are flowing oil for a while longer... once u'r turn off the car and the oil stops moving, there's still more heat build up from idling, when as u would if u took it easy for a few mins and turned off the car right away.
Anyone care to chime in?
02-18-2005, 03:11 PM
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When my mom had an older turbo volvo, she never let it cool down and she blew 2 turbos.
I've always heard to let the turbo cool down for a bit. I think with ones that allow coolant to cycle through them are less prone to failure..
I've always heard to let the turbo cool down for a bit. I think with ones that allow coolant to cycle through them are less prone to failure..
02-18-2005, 05:42 PM
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I usually allow my rad fan to kick in after a hard run and wait till its done since my turbo is watercooled, I also have a turbo timer now. . .Just watch the egts while its cooling off!
02-18-2005, 05:59 PM
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Originally Posted by NOTORIOUS VR
Actually, I've heard the opposite..
Letting u'r car idle let's u'r manifold and turbo get hot, and "stores" more heat, so even tho u are flowing oil for a while longer... once u'r turn off the car and the oil stops moving, there's still more heat build up from idling, when as u would if u took it easy for a few mins and turned off the car right away.
Anyone care to chime in?
Letting u'r car idle let's u'r manifold and turbo get hot, and "stores" more heat, so even tho u are flowing oil for a while longer... once u'r turn off the car and the oil stops moving, there's still more heat build up from idling, when as u would if u took it easy for a few mins and turned off the car right away.
Anyone care to chime in?
Turbos operate is such high heat, not only because of the hot gasses but also because of the friction of the unit itself, a turbocharger is usually way hotter than the the manifold because gasses hit the fins and transfer energy longer then in the manifold where they basically pass by, the faster your engine revs are the more times the hot gas hits the fins, and the hotter the turbocharger gets.
So when you just stop driving at 3k rpm for example(regular city driving), gasses were hitting the fins three times as much as if you would stop at idle, this means that if you just turn off the car the turbo is still VERY hot compared to idle speed.
But turbos are built to handle such heat, whats the cooldown for ?
well its actually because of the oil, if you turn off the engine as soon as you stop driving, the oil stops pumping through the turbo, since the unit is still really hot the oil may burn and cause "coking", which is buildup in the turbo oil lines, this decreases the lifespan of your turbo since while driving you need the oil to cool down your turbocharger and now you have a partially clogged artery.
What about heat buildup ?
The heat addition to the turbo at idle is much slower than its cooldown time from driving conditions, metals cool down much faster at higher temperaturescheck out metal factories, look how fast metals lose their red colors.
Vasically its like a xsquare graph, cools really fast from high temperatures and then slows down on cooling.
So why turbo Timers?
Good turbo timers turns off your engine right when the fast cooling effect stops and the heat buildup begins, thats why its really not effective when you let it cool down yourself by a rought estimate, major calculations go into turbo timers to get you the exact point.
please if you have any corrections post them.
03-10-2005, 10:52 PM
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You clip the exhaust wheel.
It is measured in degrees. 10 degrees seems to be pretty common. This gives an inefficient turbo more top end flow, creating more hp/tq. Side effects are it stresses the wheel/shaft and shortens its life.
It is measured in degrees. 10 degrees seems to be pretty common. This gives an inefficient turbo more top end flow, creating more hp/tq. Side effects are it stresses the wheel/shaft and shortens its life.