Turbo Lag

Submitted: Friday, Apr 16, 2004 at 21:02
ThreadID: 12121 Views:2765 Replies:4 FollowUps:6
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Hello all , Been having an argument with the guys at work regarding a definition for turbo lag. Here are the options . Dont be scared to say if we are way off line . Thanks 1. The dead band at the low end of the rev range before the engine is on boost. 2. Loss of power between gear changes due to backing off the throttle , stalling the turbo impeller due to loss of exaust flow 3. Being too scared to fit an after market turbo ( ha ha )
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Reply By: Member - TonyG (NSW) - Friday, Apr 16, 2004 at 21:17

Friday, Apr 16, 2004 at 21:17
Hi Glen,

I am no expert but I thought it was the dead band at the low end of the rev range before the engine is on boost.

On my navara, the turbo kicks in about 1800rpm

Thanks

TonyG
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Follow Up By: Glenn D - Friday, Apr 16, 2004 at 22:02

Friday, Apr 16, 2004 at 22:02
Thanks Tony!
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Reply By: GO_OFFROAD - Friday, Apr 16, 2004 at 21:53

Friday, Apr 16, 2004 at 21:53
Turbo lag is the turbo dropping below the maximum boost, which means the engine cant make max power, anti lag items include things like a fuel injector which uses fuel injected into the turbine to stop lag on wrc cars when the throttle is backed off, which is why you hear them pop pop pop out the exhaust on over run.

Another anti lag device is using gas, co2, air pressure injected into the turbo to keep it on boost during gear chnages, or for low down rpm, or where the exhaust gases arent sufficient to get the turbo on max boost for max power.

So lag can be during gear changes, or before the turbo has built up maximum boost from low rpm.
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Follow Up By: Glenn D - Friday, Apr 16, 2004 at 22:10

Friday, Apr 16, 2004 at 22:10
Thanks for the reply . I dont go for the low rev range theroy normally remedied by sequential turbo charging. I think turbo lag is between gear shifts remedied with a blow off valve ( unloads compresor side of turbine and stops it stalling with no driving force - exaust )
P.S - I am only interested in replies that support my theroy!!!!!!!!!!
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Follow Up By: GO_OFFROAD - Friday, Apr 16, 2004 at 22:16

Friday, Apr 16, 2004 at 22:16
A blow off valve will only work if the turbo is overboosting, which would mean flat changing, and low end lag wont be fixed by sequential turbo, unless you can identify the source of the low end lag, like my 90 series prado td, it has low end lag in standard form, becuase the fuel is very lean down low to pass emmissions, so that would be fuel lag, not enough fuel burning to boost the turbo, so when you overcome this, the turbo boosts faster, which makes the engine burn more fuel more rapidly, which boost the turbo, which makes more power, and so on, so the faster things can be made to happen down low, the faster it multiplies as you accelerate.

Lag is lag, regardless.....
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Follow Up By: Glenn D - Friday, Apr 16, 2004 at 22:32

Friday, Apr 16, 2004 at 22:32
Sorry , Im used to road cars . Flat chaging !!!!! Subaru Liberty B4 and any twin turbo RX7 s use twin turbos to effect to reduce the dead spot low down in revs ! Blow off valves only vent pressure between gear changes .Keep the impeller spinning !! Sorry if I am being a smart arse but I am in an argument about DEFINITION
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Follow Up By: GO_OFFROAD - Saturday, Apr 17, 2004 at 07:26

Saturday, Apr 17, 2004 at 07:26
But you need excess pressure to be able to vent it with a blow off valve, which wont help low rpm lag......

Your discussion may be fun, but dont forget you have 2 ears and one mouth, so you should listen twice as much as you speak ;-)
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Reply By: prado_95 - Saturday, Apr 17, 2004 at 21:36

Saturday, Apr 17, 2004 at 21:36
A couple of things that may impact of the meaning;

1. diesel engine
2. petrol engine

light turbo diesel engines tend to operate on boost (ie usually have boost under constant steady driving conditions). Petrols are usually on vacuum under constant steady driving conditions.

Both will be slow to come onto more boost at 'low' revs (Cat D9 being an example exception - idle=900rpm redline=1200rpm). The operative word here is low - its relative to when the wastegate opens, or full boost achievable at desired revs is reached as the case may be.

The dead band may not always be at low revs (ie 3000rpm WOT acceleration on petrol will likely see some delay in coming to full boost avail at those revs @ max load).

The percieved delay will be greater on petrol engines, since they must transition from vacuum to positive pressure, while a (light) diesel will likely already have positive intake pressure.

These points will vary with engine, and its state of tune. Some engines dont even have a wastegate (medium / heavy haulage - until very recently).

That muddied the waters for you any??
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Follow Up By: Glenn D - Thursday, Apr 22, 2004 at 17:29

Thursday, Apr 22, 2004 at 17:29
Thanks !!
Now I can win some arguments!!
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Reply By: Glenno - Monday, Apr 26, 2004 at 02:55

Monday, Apr 26, 2004 at 02:55
4wd Monthly had an article a few months ago about some mob who sold replacement turbines which were of a slightly different shape. The result being there was much less turbo lag as they spun up just above idle.

Cheers,

Glenno.
AnswerID: 55945

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