Thread: Gtir T28 Not Holding Boost?

I rebuilt a GTiR T28, slapped a Disco Comp housing on it and put it on a VET tubular manifold. At the time I had to adjust the wastegate arm (GTiR is adjustable), this made it boost to 14 psi and level off at 10-11 psi by redline.

I then adjusted the arm down, which made it boost up to 8 psi and then level down at 7psi. Now the compressor housing didn't have an Oring, thus it had a boost leak there, this even showed up at lower psi's while doing a leak test.

This week I took out the turbo, added a rubber oring, put it back together and slightly tightened the WG arm (it was moving way too easily while off). Today I did a leak test, found and fixed a leak at the fuel pressure regulator, then did another test and it was holding boost semi well: 1 psi per 1.5 seconds until it got down to 5 psi, then it was 3+ seconds per psi loss.

I installed and MBC, turned it fully off, still had a 1-2 psi loss by redline. Then cranked it up a little, got to 15 psi, but would drop off at 10 psi by redline. If this is a boost leak, it has to be something HUGE, unless it's really something else. I'm beginning to think the GTiR wastegate might be at fault here. Did a search and haven't really found anyone else having a similar issue.

Any ideas? Gotta have a good running SR20 for this weekend's race wars

sounds like your wastegate gave up... maybe the spring inside is broken or just weak and can't hold much boost anymore

Pull the hose off the actuator and try free boosting using the throttle and see if it still drops off.

Its tricky and dangerous, but will tell you if its a control issue or something else.

My car (VET Gtir turbo, tubular manifold, Blitz boost controller, 38mm external) would drop boost quite badly. Lost the power supply to the boost controller when i took stereo out, and with the way the external is connnected this caused a freeboost. Boost rose way faster and would hold a lot more boost, of course this is at partial throttle, but by god it felt fast.

If boost were getting by the wastegate, wouldn't it come out the exhaust? Stick your head up the muffler during the next test and see if you find the missing air.

C

Should I take the downpipe off to get my head closer to the source?

I'll try pulling the line and will turn off high cams (Just a precaution to avoid over boosting). If it is the wastegate at a certain point it will open by itself and let exhaust out.



Oh I guess you haven't heard, I converted to a compressed air engine, The reason I still have a turbo is for the super cool noises

I'm brain dead here... but did the o-ring increase the spacing between the comp wheel and the housing? Could be a clearance issue.

When I first tried to install it it definitely did, but I didn't tighten it fully before. This time around I tightened all of the bolts that hold the brackets. It is sitting flush now. This is why I did another boost leak test, and there wasn't a drop of air leaking out of the comp housing. Before it would leak at 5 psi and it would be impossible to get up to 10psi while doing a boost leak test.

external gate

my VET has the same turbo, and had this issue. Would hit hard and fall right off. installed aftermarket valve springs and problem solved. holdin 18psi straight to 8000rpm with an internal gate.