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That was something I forgot to ask you about earlier. Unless I'm missing something in all this discourse, if you're running it in the normal position then you shouldn't have any problems with the stock spring. If, on the other hand, you're running it backwards, then you very well may be unseating the piston using the stock spring (when the boost pressure hits the face of the piston).
Like Simon, I prefer a design using as light a spring as possible. This valve is not simply an on/off switch for your boost, it's also insurance against damaging your impeller. Dean's preferences & setup favor maximum on-boost time, which is great for quick-shift/race-type driving, but may provide it at the expense of the turbo. If you're set up this way, I'd highly advise a VERY frequent tear-down & regreasing/resealing (via new O-rings) schedule for the valve. I'm looking for something which is going to provide an improvement in 99% of my driving, while at the same time provide a huge increase in engine protection. Being able to get into any of these valves is a great benefit for all us DIYers.
As you read in the earlier marathon session, I disagree with using a long air chamber here. To summarize the reasons I stated previously, it simply adds more variability to the piston's travel.
Dean:
I don't know what the internal design of the Turbo XS (or the Hyper) looks like, but it appears to me that the Bosch design does exactly what you keep saying should be done to the internal chamber volume. Rather than simply sticking a hose barb on the topcap, the cap is actually recessed down into the valve's chamber, reducing the amount of air needing to be vacuumed or equalized. They've left only enough room for the compressed height of the valve's spring. To do what you propose to a design which incorporates a flat or convex cap would most likely require a new cap design, & not simply an add-on part. As you stated before, you don't want to add shims to the piston-end of the spring simply because it adds mass at the wrong end. But because it also changes the spring's force & available travel, you don't want to add them to the cap-end either (unless you WANT to change the force, or are replacing the spring to compensate for the shorter travel).
Of course, the other obvious option is to add a "siphon tower" in the center of the cap which would nest inside the spring, but then how would you fasten it securely enough that you'd be comfortable with it? Depending on how the hose barb's attached, you might be able to use it to fasten the tower to the cap, too. But the Bosch unit already has this design (AND it's diaphragm presents lower mass to move than a piston).
Perhaps the real question is, "Why doesn't Bosch make their valves rebuildable?" Sure, they're cheap enough to replace whole, but you either have to guess that they're bad or rip 'em apart to find out.
posted by 32.102.170...
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