mrlilguy157
Member
- :
- 07 mazdaspeed 3
yes sir. (yupnope)
i thought they were near 22psi though? I dont know. I'll have to digg up that thread. good question in all seriousnessanswering with quote from a site i found right quick:
Lag
A lag is sometimes felt by the driver of a turbocharged vehicle as a delay between pushing on the accelerator pedal and feeling the turbo kick-in. This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. The directly-driven compressor in a supercharger does not suffer this problem. Conversely on light loads or at low RPM a turbocharger supplies less boost and the engine is more efficient than a supercharged engine.
Lag can be reduced by reducing the rotational inertia of the turbine, for example by using lighter parts to allow the spin-up to happen more quickly. Ceramic turbines are a big help in this direction. Another way to reduce lag is to change the aspect ratio of the turbine by reducing the diameter and increasing the gas-flow path-length. Increasing the upper-deck air pressure and improving the wastegate response help but there are cost increases and reliability disadvantages that car manufacturers are not happy about. Lag is also reduced by using a precision bearing rather than a fluid bearing, this reduces friction rather than rotational inertia but contributes to faster acceleration of the turbo's rotating assembly.
Some car makers combat lag by using two small turbos (like Toyota, Maserati and Audi). A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher RPM. Being such small units they do not suffer from excessive lag and having the second turbo operating at a higher RPM range allows it to get to full rotational speed before it is required.
Lag is not to be confused with the turbo spooling up, however many publications still make this basic mistake. The spool-up time of a turbo system describes the minimum turbo RPM at which the turbo is physically able to supply the requested boost level. Newer turbocharger and engine developments have caused spool-times to steadily decline to where day-to-day use feels perfectly natural. Putting your foot down at 1200 engine rpm and having no boost until 2000 rpm is spool-up and not lag.
I'll let Ken disclose that information when he's ready to. Cool?
