Garrett 4094 VVT/Boost tuning?

[Donovan]

I just blew up the factory turbo on my LBZ and I am replacing it with a GT4094 VVT and diamond eye downpipe this weekend. I have heard that the 4094 requires the vanes to be closed a bit more to spool due to the increased size of the exhaust housing. I have some ideas on how to go after this by closing the vanes a bit, but I have never done any VVT tuning before.

Does anyone have any advice or tunes that they would be willing to share?

Thanks

[Donovan]

Whoops....I just found this thread: http://forum.efilive.com/showthread.php?13226 sorry for the retread!

[robof16]

Yes. Vane limit tables must be modified. Beyond just increasing the amount they close to 88%, I highly recommend running limits on how far they close as boost starts to rise rapidly so you don’t have drive pressure spikes. At higher loads and RPM I am limiting the vane position to somewhere in the 40’s IIRC. At low load/RPM I did an experiment to see if 88% was too much and just creating extra drive pressure with no associated boost increase, and as it turns out, there was a noticeable increase in boost by going from 85% vane limit to 88%. It took a lot of work to build the vane limit table but worth it – the objective was to increase safety margin a little by limiting drive pressure to 60 PSI.
I didn’t have a drive pressure gauge with the stock turbo but I’m sure it would have scared me to see what happens on a max effort tune.
The 4094 is awesome BTW.