Turbo Lag
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From: Turkey Town (Gobble-Gobble)
the Evo VIII turbo has no where near what most experience as "turbo lag" But if u still would like to eliminate it, add a turbo back exhaust, and intake, as well as a boost controller so you can adjust the gain manually... If you still think its too much lag, then a supercharged car is maybe more for you... 
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From: UK
Main ways to reduce lag are as follows.
Reduce the back pressure after the turbo. You only need to reduce it not eliminate it. If the gasses are moving to slowly then it will have a negative effect on performance. This is a common problem with lightly modded cars, many fit 3inch pipes when 2.6 is probably better.
Intake. This you want to be as free flowing as possible. Make sure that the air that is being used is not drawn from a hot area and keep the feed low as the air will be denser. Don’t forget that the maximum negative pressure (ie the pressure that the intake is under) is 1bar. This means that your intake should always be of a larger diameter than the boost piping (ie piping after turbo).
Cams. A good set of cams with high lift will help kill lag. At the minute Piper are the best in the world (I’m not just saying that coz they are made over here, they really are), closely followed by JUN and Tomei. The best cams will have high lift (around 11mm on road application on both inlet and exhaust) and an aggressive profile. This is what makes the Piper cams so much better than HKS cams. The duration of the Piper 264 units at 1mm lift (50 thou) is more than that of the HKS 272 cams!!!! Some say that high lift and aggressive profiles are harder to set up (read idle). This is true to an extent but a GOOD tuner should be able to set them up fine. On the set up, you will want as little overlap as possible. The main thing with cams is to get them set up right, experience is critical.
Timing. You can significantly reduce the effects of lag if you advance the timing of the engine. This is because when the engine is not under boost, you are relying on the N/A side of the engine. Advancing the timing makes this side of the engine much more efficient, thus reducing the “lag”. This can be difficult to do on road cars as normal fuel won’t let you advance the timing as much as you would like to. You could use race fuel, but this is expensive. You could also fit a water injection system. This will enable you to run an engine with much more advanced timing with out the fear of detonation (a killer of engines). It will also let you run the turbo a little harder and still be safe.
Compression ratio. This only really applies to heavily modified cars or racers. By increasing the compression ratio you are doing a similar thing to advancing the timing. You are effectively making the engine more efficient. Is can be quite simple to do, you can just fit a THINNER head gasket. To have a grater effect you may want to fit higher comp. pistons, and if you really want to go to extremes then you could take some material off the top of the block. This is one of the most effective ways to reduce lag and what many turboed racers are doing!
Displacement. As the saying goes there is no replacement for displacement. On a turbo engine this can be used to kill lag. Because a larger engine will consume more air and fuel (at any given rpm), it will produce more exhaust gasses. This grater amount of gases will spin the turbo up earlier and thus reduce the effect of lag.
N2O. Although this is normally used to give a power gain, it can also be used to kill lag. N2O acts in a similar way to increasing the displacement of your engine. Thus when the N2O is on more exhaust gasses are produced and the turbo will spool earlier. The other effect that the N2O will have is a much cooler intake. The cooler the inlet charge, the denser the charge and thus more O2 per cc. mix this with more fuel and you have more power!
These are some of the ways to reduce the effects of lag. If I have missed anything then just say and any questions just ask.
Thanks Chris.
Reduce the back pressure after the turbo. You only need to reduce it not eliminate it. If the gasses are moving to slowly then it will have a negative effect on performance. This is a common problem with lightly modded cars, many fit 3inch pipes when 2.6 is probably better.
Intake. This you want to be as free flowing as possible. Make sure that the air that is being used is not drawn from a hot area and keep the feed low as the air will be denser. Don’t forget that the maximum negative pressure (ie the pressure that the intake is under) is 1bar. This means that your intake should always be of a larger diameter than the boost piping (ie piping after turbo).
Cams. A good set of cams with high lift will help kill lag. At the minute Piper are the best in the world (I’m not just saying that coz they are made over here, they really are), closely followed by JUN and Tomei. The best cams will have high lift (around 11mm on road application on both inlet and exhaust) and an aggressive profile. This is what makes the Piper cams so much better than HKS cams. The duration of the Piper 264 units at 1mm lift (50 thou) is more than that of the HKS 272 cams!!!! Some say that high lift and aggressive profiles are harder to set up (read idle). This is true to an extent but a GOOD tuner should be able to set them up fine. On the set up, you will want as little overlap as possible. The main thing with cams is to get them set up right, experience is critical.
Timing. You can significantly reduce the effects of lag if you advance the timing of the engine. This is because when the engine is not under boost, you are relying on the N/A side of the engine. Advancing the timing makes this side of the engine much more efficient, thus reducing the “lag”. This can be difficult to do on road cars as normal fuel won’t let you advance the timing as much as you would like to. You could use race fuel, but this is expensive. You could also fit a water injection system. This will enable you to run an engine with much more advanced timing with out the fear of detonation (a killer of engines). It will also let you run the turbo a little harder and still be safe.
Compression ratio. This only really applies to heavily modified cars or racers. By increasing the compression ratio you are doing a similar thing to advancing the timing. You are effectively making the engine more efficient. Is can be quite simple to do, you can just fit a THINNER head gasket. To have a grater effect you may want to fit higher comp. pistons, and if you really want to go to extremes then you could take some material off the top of the block. This is one of the most effective ways to reduce lag and what many turboed racers are doing!
Displacement. As the saying goes there is no replacement for displacement. On a turbo engine this can be used to kill lag. Because a larger engine will consume more air and fuel (at any given rpm), it will produce more exhaust gasses. This grater amount of gases will spin the turbo up earlier and thus reduce the effect of lag.
N2O. Although this is normally used to give a power gain, it can also be used to kill lag. N2O acts in a similar way to increasing the displacement of your engine. Thus when the N2O is on more exhaust gasses are produced and the turbo will spool earlier. The other effect that the N2O will have is a much cooler intake. The cooler the inlet charge, the denser the charge and thus more O2 per cc. mix this with more fuel and you have more power!
These are some of the ways to reduce the effects of lag. If I have missed anything then just say and any questions just ask.
Thanks Chris.
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nianlala
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Apr 22, 2007 09:32 AM
