[mattr34]

any advice greatly recieved, r34 gtr ran 1.0 bar on stock turbos, oil seal failed so replaced with -7 that came with new actuators, all fitted correctly but took it for mapping and will only make 0.8 bar now. obvious things have been checked, vac pipes, boost leaks.
car doesnt have a boost controller was just running de-restricted boost on stock setup.
was thinking weak actuators but mitivac test shows opening at 10psi same as stock actuators when tested

 

[kingsley]

This is just a complete random guess as I know nothing of the size of your new -7 compared to the old stock turbos, but if the new one has a much bigger wastegate, might it be that it's bleeding off enough exhaust to regulate boost at the slightest movement, whereas the stock ones had to open a bit further?

And/or, is the spring rate different on the new actuator? If they both started to open at 10psi, is the new one more open at 11psi than the old ones?

10psi is about 0.7 bar so I'm not overly surprised you're only getting 0.8 bar.

Cheers,
Kingsley.

 

[mattr34]

Thank you for your reply, from what i can see stock were .53 a/r with .48 exhaust housing and the -7s are .42 a/r with .64 exhaust housing

 

[mattr34]

For any future reference turned out there was a home brew brass restrictor stuffed about 2 inches down the pipe at the pcm valve with a 1. 5Mm hole in it, drilled out to 2mm now gives 1.05 bar.

 

[gtrluv]

could someone tell me what -7 as it relates to turbo in reference to the previous message

 

[Vihis]

2860-7.

http://www.turbobygarrett.com/turbo...s/turbogroup/catalog_pdf/GT2860R_707160_7.pdf

 

[gtrluv]

thanks for the link

 

[kingsley]

Aha

So it sounds like the PCM valve couldn't draw off enough actuator pressure due to the 1.5mm restriction. This presumably didn't matter on the stock turbos because the small wastegates couldn't regulate boost unless they opened wider anyway, but keeping pressure from building up in the actuators on your new turbos is more important if the wastegates can flow more. Either that, or the preload on the actuator rod is lower on the new turbos? Or both perhaps.

Cheers,
Kingsley.