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Another modification I’ve been keen to trial for some time. I finally found time to remove venturi and whip out the plate.
The 1kz has a throttle plate installed in the intake system (actually referred to as a venturi). It shouldn’t be confused with the throttle on a petrol engine which is to control the engine.
Its function on the 1kz is twofold:
One – Its major roll is as part of the EGR system, especially at idle where it is used to create manifold vacuum and draw in exhaust gas via the EGR system.
Two – On engine shut down it fully closes which smooths out the traditional diesel shut down shudder.
On my Prado I have a couple of issues with it, firstly being stepper motor controlled it’s slow to respond. Coming off idle, low RPM or when backing off between gear changes it give a significant feeling of throttle/turbo lag.
It also stalls the Turbo as it closes giving significant turbo lag
Secondly at low speed/low RPM, light throttle driving any slight movement of the accelerator petal causes the plate to open/close which can result in significant drive line backlash.
So once again using my rig as guinea pig; I’ve removed the plate.
Potential Pros –
:arrow: Reduced Turbo lag, especially between gear changes. (Like fitting a blow off valve)
:arrow: Better off idle response.
:arrow: Increased low rpm performance and driveability
:arrow: Potential for a minor fuel economy increase at low RPM/light load cruising.
:arrow: Reduced light throttle EGT’s
:arrow: Reduced intercooler heat soak/temperature spike off idle.
Potential Cons – (there's always some :roll: )
:arrow: The EGR system will be compromised. (But if you’re doing this mod then the EGR system is probably be blocked/disabled already)
:arrow: The engine will shut down rough – Like an old school diesel (Yes your wife will notice, and no, she won’t like it :evil: )
:arrow: In the event of a catastrophic Turbo failure, there is potential for the engine to “run away” - rare but still a risk worth considering (although with a manual vehicle if you catch it early and realise what’s happening you can stall the engine) Remember there are plenty of diesel Turbo engines without plates, including some Toyota motors (1hd-t for example)
So, in the real world:
:arrow: Hard to say but I seem to have a smoother idle and slightly easier starting
:arrow: Much better off idle response and excellent response between gear changes. Turbo lag between gear changes is now all but nonexistent. This gives a very good increase in drivability in a manual vehicle.
:arrow: Only done just over 50km so Jury’s out on any economy gain (if there even will be any)
:arrow: Engine shut down is a little rough. Exactly like any diesel without a throttle plate (like anything early/mid 1990’s) it gives a good shudder - very truck like now. Most won’t like this.
:arrow: Further driving has also shown faster Turbo cool down times, a result of increased idle airflow.
All in all I’m quite happy with this mod so far. The increase in driveability far outweighs the disadvantages for me.
Mick
The 1kz has a throttle plate installed in the intake system (actually referred to as a venturi). It shouldn’t be confused with the throttle on a petrol engine which is to control the engine.
Its function on the 1kz is twofold:
One – Its major roll is as part of the EGR system, especially at idle where it is used to create manifold vacuum and draw in exhaust gas via the EGR system.
Two – On engine shut down it fully closes which smooths out the traditional diesel shut down shudder.
On my Prado I have a couple of issues with it, firstly being stepper motor controlled it’s slow to respond. Coming off idle, low RPM or when backing off between gear changes it give a significant feeling of throttle/turbo lag.
It also stalls the Turbo as it closes giving significant turbo lag
Secondly at low speed/low RPM, light throttle driving any slight movement of the accelerator petal causes the plate to open/close which can result in significant drive line backlash.
So once again using my rig as guinea pig; I’ve removed the plate.
Potential Pros –
:arrow: Reduced Turbo lag, especially between gear changes. (Like fitting a blow off valve)
:arrow: Better off idle response.
:arrow: Increased low rpm performance and driveability
:arrow: Potential for a minor fuel economy increase at low RPM/light load cruising.
:arrow: Reduced light throttle EGT’s
:arrow: Reduced intercooler heat soak/temperature spike off idle.
Potential Cons – (there's always some :roll: )
:arrow: The EGR system will be compromised. (But if you’re doing this mod then the EGR system is probably be blocked/disabled already)
:arrow: The engine will shut down rough – Like an old school diesel (Yes your wife will notice, and no, she won’t like it :evil: )
:arrow: In the event of a catastrophic Turbo failure, there is potential for the engine to “run away” - rare but still a risk worth considering (although with a manual vehicle if you catch it early and realise what’s happening you can stall the engine) Remember there are plenty of diesel Turbo engines without plates, including some Toyota motors (1hd-t for example)
So, in the real world:
:arrow: Hard to say but I seem to have a smoother idle and slightly easier starting
:arrow: Much better off idle response and excellent response between gear changes. Turbo lag between gear changes is now all but nonexistent. This gives a very good increase in drivability in a manual vehicle.
:arrow: Only done just over 50km so Jury’s out on any economy gain (if there even will be any)
:arrow: Engine shut down is a little rough. Exactly like any diesel without a throttle plate (like anything early/mid 1990’s) it gives a good shudder - very truck like now. Most won’t like this.
:arrow: Further driving has also shown faster Turbo cool down times, a result of increased idle airflow.
All in all I’m quite happy with this mod so far. The increase in driveability far outweighs the disadvantages for me.
Mick
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