Install is the 7.5 Yellow spring and it seems pretty consistent at least in my case that the guage reads 1.5-2psi over the isntalled spring rate. It's done this on me with the 5lb,7lb and the 10lb springs. But my previous problem had several causes and one of them was a small hole in the passenger side wastegate. While troubleshooting all my runs were done on wastegate only. with only the lower wastegates plumbed and the upper open to atmosphere. It only overboosted until I re did all the vacuum lines. After replacing them all the 5lb spring hit 7.7psi consistently. After I got that under control I plumbed the EBC with new vacuum lines. Whatever you do stay out of it until you get past this bump. Piston Glitter looks like artwork but it hurts your heart.

And it equally hurts when she gives the rings back to you.....

So with the BP kit boost spike is somewhat common? Would it be better to just upgrade the whole wastegate assembly right off the start to avoid potentially catastrophic failure. Really curious because I'm ready to buy a BP kit or possibly something else for my 350z HR.

I'm recently more inclined to think it's possible that the actual spring rate is off than the design of the wastegates. But what it would take to prove that is several sets of Tial springs of the same rate. It may not be completely off but maybe small variances between batches. The 1.5 psi consistent differences I've seen aren't "spikes" at all but rather the guage reading consistently above the spring rate. The actual spikes I did have were directly caused by a hole in my passenger side vacuum line to the wastegate lower.

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So I guess this is the solution I've been looking for. I just need to know which spring to use.

This video will help a bit.

https://youtu.be/cPu1J5Xrx8w

I never had any issues with boost spikes with mine ...started with yellow spring and was around 7-8 lbs ....was steady with no issues ....added a mechanical boost controller ...tuned to 14lbs .....I did drop spring to the green one (5lbs) if I remember right ....doing this made the boost controller less sensitive and more stable when increasing ....running like this and holding steady at 14 with no issues

Boost creep is an uncontrolled increase in boost as the RPM's go up. So if you are starting at say 8psi at 4k RPM, and hitting 12psi by 7k RPM, then it is considered boost creep.

I have not had any customers experience boost creep, this includes the local guys, where I installed the same kit you guys are running.

I believe there is something else at play with those that are having issues controlling boost. Two wastegates are more than enough for this system. With the original 350Z kit, I used one of these wastegates, and it was more than enough to bleed off the exhaust gases to keep boost steady at 5psi on spring pressure, with a much smaller turbine to boot.

Sasha in the video I linked , at some point he referenced something I believe you have also said. Basically in the case of boost creep it generally shows up when people use too light of a wastegate spring. A fluctuation in boost in my opinion is not a "spike". Using the graph feature on the Greddy Profec, if I have a boost setting of 12.5 and it bumps momentarily into 12.8-13psi I can live with. A spike is what happened when I went from 9psi to 23psi.With the graph feature it's more observable as literally a bump or a spike.

Yeah, I didn't watch the video, but have been around the block a couple of times :).

I think a variance of up to 1psi is acceptable, and that is why a base map for any and all kits should not be used under WOT. Each kit (TT/ST/SC...etc.) requires custom tuning, not only for maximum performance, but more importantly engine longevity.

If anyone wants to see what boost creep looks like, I can take them for a ride in my car =)