When should peak boost come on in my 3.0 Turbo?

[Tom F2]

I have SC cams, a Euro exhaust and a K27-7200. Also, a pesky and hard to pin down vacuum leak. So, I would guess that I am not going to see the boost come on as quickly as it would if everything were correct. However, I would like to get an idea of what to expect, as I go about trouble shooting the vacuum leak. Currently, I see peak boost (0.8 bar) at 3600 to 4000 rpm. I get, at best, 0.5 bar at 3000 rpm. No boost to speak of below 2400, maybe 2200. What are owners of similar cars seeing? Thank you in advance. Tom

[RarlyL8]

Mine is a 3.3L with SC cams, Euro exhaust, and K27-7200.
Boost starts in the low to mid 2000s and is all in (0.75bar) by 3000rpm.

[plaidseats]

1977 930 with stock 3.0L. Boost builds from 2500 to 3000, jumps to peak above 3200 or so.

[Tom F2]

This makes it clear that I am losing a lot to the leak. Thanks for the input.

[plaidseats]

Well what do you know, my turbo seems to have gone south. I'm having the same problems that you described last-couple weeks ago. My boost is gone til over 4000 rpm, regular highway driving, zero. What was your problem eventually? Was it easy to diagnose? My turbo seems to have gone out fairly quickly. It's a weekend car, driven an hour a week or so.

[930turbo]

My stock build is all in at 3000 RPMs. I have a 1.0 BAR spring and the gauge is @ 1.0 at 3k. It breaks the tire loose in first gear too. It's pretty cool!

[plaidseats]

Yea, that's how mine was last week. All in at 3K. Hit 3200 and POW, you're on boost. Not this weekend.

Did a search and learned a couple things but I'll take any additional input I can get.

[Tom F2]

Originally posted by plaidseats
Well what do you know, my turbo seems to have gone south. I'm having the same problems that you described last-couple weeks ago. My boost is gone til over 4000 rpm, regular highway driving, zero. What was your problem eventually? Was it easy to diagnose? My turbo seems to have gone out fairly quickly. It's a weekend car, driven an hour a week or so.

My problem was bad injector blocks and a leaky hose. Fixed, and now I see full boost by 3,200. Maybe a quarter bar at 2,400.

[Tom F2]

Originally posted by Tom F2
My problem was bad injector blocks and a leaky hose. Fixed, and now I see full boost by 3,200. Maybe a quarter bar at 2,400. Nothing below 2,000.

[bkreigsr]

I'm running the same set-up on my 77 except the turbo is a 7200 'S' unit. I never really watch the gauge that close, but partial (.5-.6) feels like anywhere between 1,500-2,500, full boost (sometimes overboost if she spools up very quickly) is seen well below 3.500.
gauge indicates 1.0 at full boost, but I only have a .8 spring so that's another reason I don't look at the gauge that much.

you must have been seeing massive clouds of oil smoke at star-up when the turbo went, no?

Bill K