how do you calibrate the vanes, there seem to be no adjustment?
I dont know - I'm an engineer - not a mechanic - and dont pretend to be, I'm just quoting from the old courses and the manufacturers data.
I found this in my notes, from an Allied Signal/ Honeywell/ Garret Bulletin:
Garrett® VNT™ turbos are highly complex units, engineered and calibrated to meet the exacting performance parameters of automotive manufacturers.
The first requirement is to set the turbo's critical minimum flow vane position. This intricate process takes account of the large number of parts and extremely tight tolerances within the Garrett® VNT™ and involves using a highly accurate turbine flow bench to measure and compensate for any variation in gas flow through the vanes of the turbo.
Highly skilled technicians then set and lock the minimum flow position to suit the requirements of each individual application. It is only when the ‘minimum vane open' position is set that it is possible to calibrate the unit (to three decimal places), using four checkpoints to ensure correct operation.
Each of these steps is vital in ensuring the optimum performance of Garrett® VNT™ turbochargers. Indeed, these engineering complexities cannot be compromised – which is why Honeywell's official Aftermarket distributors are committed to supplying only new Garrett® VNT™ turbos that are quality assured and matched to the original OEM specification.
Any attempt at remanufacture, using substitute parts, is fraught with difficulty because of the turbo's technical complexities and can lead to potentially serious problems, such as:
Conflict with the engine management system
Low flow/pressure, causing poor response, poor overall performance and increased emissions
Over-rich diesel fuel/air mix, causing excessively high temperatures, damaging both the turbo and the engine
High flow/pressure, leading to the over-speeding of the turbo, wheel bursting and damage to turbo and engine
Excessive boost pressure, causing physical engine damage
"Garrett® VNT™ turbos are highly complex and meticulously calibrated components renowned for their performance," says Ed Goodwin, Director, Independent Aftermarket Europe. "Our distributors are committed to safeguarding the interests of their customers by protecting the integrity of the technology – and will therefore supply only new replacement Garrett® VNT™ turbochargers."