[sussexa]

What are you reading 28psi on i calibrated my mechanical boost gauge at work and found it low a psi or 2 under 5psi and a 2-3 psi high in 25-30 psi.i watch boost gauge but dont base much on it go by map sensor.
Not sure what software you guys have but for boost issues id be logging actual boost, desired boost, vnt% and maf airflow.
With some data from a few logs you should be able to confirm operation of vnt mechanism and also boost leaks if maf rises but boost does not but id start by cleaning map sensor first and checking ign on if it reads same as atmospheric mb.
At 28psi id say either vnt not opening up fully and not lowering shaft speed enough, or mapped or boxed too high.
Is it decatted?
Over fuelling/late injection may also cause high egt boost creep etc.
If i kept my foot in i used to see +300mb over requested due to decat and green box causing creep and also high egt temps 750-850*c im sure if i kept my foot in longer it would have gone higher.upto point of going over desired boost i dont think it used to go much over 600*c
Ps isnt 28psi=more like 2900mbar and 27psi=2860mbar from map sensor at sea level?

 

[sussexa]

Yep i am mapped for 2850mb on a 55 trim 52mm wheel,about most i wanna go upto 4500.
To nutron
Have you still got any turbos in bits, if so can you measure up the turbine exducer and vnt vane heights and maybe a pic of the vnt ring layout?
My jtdm had a gta1749v with about 6mm vane height but ive heard a few refs to later gtb layout but never seen inside the mv.the earlier model had 5mm odd vane height, from the turbine spec is the mv nearer 7mm?
Thanks if you can, no probs if not possible.

 

[sussexa]

those sizes seem identicle to my gta1749v, it would be nice to see a hybrid with the 43inducer 39.5mm exducer i put in my 52mm hybrid.but and big but i understand it would take a lot more work to machine your housing im guessing youd need a pretty good cnc miller or custom tool.
At least in mine i just shaped my own tool for lathe, opened up bore to 40.5mm and cut new profile to give same as original clearances on the new turbine(it was 8+mm tip height, so had to sit deeper also.also big but was turbine was over £100 on its own.
Id still like to see some vnt% on 220+hp with original turbine size.