Why manual boost valves / mig tips spike

I found this forum whilst browsing:

http://www.nissanforums.com/z32-chassis-300zx/47003-90-300zxtt-boost-questions.html

Here is a quote about why boost jets are bad news. They've always been a pet hate of mine as my first Zeds engine blew due to having jets that were setting the boost too high, combined with a dodgy boost gauge, resulting in several blown pistons.

I've always known what they can spike, but never realised why.

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Quote:

Originally Posted by dragknt

The last thing was for anyone that has a Profec B Spec-II...like what settings they use, and stuff. I'm trying to find a balance between performance and babying the car, so I want to do everything as safely for the engine as possible.

Thanks for your help...It'd be a -while- until I could afford the bigger IC's. :/ A friend of mine has a Neon SRT-4 that he has under a manual boost controller, and his stock gauge shows boosts of 14 or 15psi, spiking at 17. His ECU turns on the 'check engine light' every now and then for overboost. I think he's being an idiot for running it like that... I haven't ran against him, yet, but my goal is to bury him on the first run. =)

-dragknt

Manual boost controller are a waste of money and for the ill informed. What you described is a good example of what a manual BC does (very ineffecent) If it's a hot day he'll miss his target boost and on a cold day he'll over shoot causing detonation and boom the engine is dead.

The electronic BC takes care of all that plus easy to dial in your boost from inside the car and you won't be getting spikes like the manual one as well.