Im trying to understand how a variable vane turbo works?

Thats my problem!!! I have a copy of the offical mitsubishi bulletin how to adjust /reduce the overboost. They say its done by adjusting limit screw A....yet everybody on the forums say to adjust the limit screw B !!!! what Im trying to undertand is how by altering the angle of the vanes changes the boost pressure. The implication from what I've read is by angling the vanes more radialy towards the centre of the turbine this SLOWED the turbine down and hence reduced the boost pressure. Having the vanes tangentially speeds the turbine up and would increase the max boost. Anyone out there help me undressand thiss more !!! Nik
 
Before making adjustments I would do the oven cleaner trick.

I would imagine from what you are saying that the canes are lazy and need freeing up given the over boost only occurs in certain circumstances.
 
I wouldn't bother as the L200 is designed to overboost and if you think this is incorrectly set then get the manufacturers operating data online and check it is boosting correctly, it is overboosting within its designed parameters, and that would be your starting point to diagnosing it is within or outside the parameters.
One friend is a diesel specialist and spends more time on turbo diesels correcting these parameters whin clueless idiots (generally boy racers) try and wind them up for more power and he has to reset them when they lose power or begin blowing out masses of black smoke.

Martyn G has hit on one of the problems and that is light loading or slow driving but this is not a major problem with automotive turbos as varnish build up generally called gumming, and incorrect oil changes using the correct oil are and these are easily remedied, using the correct oil such as grade and low or medium SAPS is crucial and allowing the turbo to spool down and stop before switching the engine off, are.

Varnish is created when you encounter a situation called "heat soak" and this is when the turbo overheats, all turbos rely on a specific quantity of oil to lubricate and cool them and usually they have a restrictor built in somewhere to control the oil flow and if you heavily run an engine and suddenly turn it off you have the turbo spinning at anything over 100,000 RPM and generating heat and you have shut off its lubrication and cooling when you switch the engine off, much better to let the engine idle for a minute or two to let the turbo spool down and stop with a full supply of engine oil cooling and lubricating it.
This scenario creates a thin film of varnish on shafts and joints within the turbo itself and this builds up and gets thicker and thicker to the point where it becomes too thick for the turbo to cope with and it begins to bind the turbocharger and prevents it functioning properly.
 
I think this is a known issue for a VW marine engine and there is a recommended spray to help free it, can't remember it's name though!
 
You must log in or register to reply here.

Share this page

Top