Turbo lag and latency
11-05-2017, 12:48 PM
#1
Turbo lag and latency
Hello folks
Every time I google about turbo lag for any reason, I stumble into spats where people claim that there is lag and that there is no lag for the same engine. "It has all its torque at 1800 rpm! How can that be laggy?"
As far as I can understand, this boils down to a big misunderstanding: "Lag" means different things to different people.
* One is the time it takes from when you step on the gas and torque comes on.
This can be because at low rpms, the exhaust gas flow is low and the turbo doesn't spool up fast enough.
It could also be because the manufacturer dialed in a lethargic gear behaviour in an auto tranny to improve mileage.
* The other is how much torque the engine delivers at low revs.
A highly strung naturally aspired racing engine usually has a thin power band at peak rpms and is dead below. Some people call this "lag" even though it pertains more to valve timing.
I would hereby posit that everyone start using different terms for these different behaviours.
Call the first one "latency", because that is usualy the technical term for such behaviour in other technologies. The reaction time from sitmulus to response.
Call the other one "torquey" or lacking thereof, because that is exactly what it is. Let us get into the endless confusion about what torque is another day. We're not talking about the quantity here, but the distribution across the rev range.
Because the term "lag" is in a state of confusion that it has become useless. Especially because in the more high profile cases, lag comes from a combination of both the aforementioned.
A highly strung turbocharged racing engine will have both wild valve timing, making it weak down low - AND a huge turbo with a lot of inertia that needs both a lot of exhaust gas and time to get spinning. To the point that no matter how much throttle you give, below a certain rpm it will not give full boost.
Every time I google about turbo lag for any reason, I stumble into spats where people claim that there is lag and that there is no lag for the same engine. "It has all its torque at 1800 rpm! How can that be laggy?"
As far as I can understand, this boils down to a big misunderstanding: "Lag" means different things to different people.
* One is the time it takes from when you step on the gas and torque comes on.
This can be because at low rpms, the exhaust gas flow is low and the turbo doesn't spool up fast enough.
It could also be because the manufacturer dialed in a lethargic gear behaviour in an auto tranny to improve mileage.
* The other is how much torque the engine delivers at low revs.
A highly strung naturally aspired racing engine usually has a thin power band at peak rpms and is dead below. Some people call this "lag" even though it pertains more to valve timing.
I would hereby posit that everyone start using different terms for these different behaviours.
Call the first one "latency", because that is usualy the technical term for such behaviour in other technologies. The reaction time from sitmulus to response.
Call the other one "torquey" or lacking thereof, because that is exactly what it is. Let us get into the endless confusion about what torque is another day. We're not talking about the quantity here, but the distribution across the rev range.
Because the term "lag" is in a state of confusion that it has become useless. Especially because in the more high profile cases, lag comes from a combination of both the aforementioned.
A highly strung turbocharged racing engine will have both wild valve timing, making it weak down low - AND a huge turbo with a lot of inertia that needs both a lot of exhaust gas and time to get spinning. To the point that no matter how much throttle you give, below a certain rpm it will not give full boost.
