regulator-based MBC for 5kcstq, 15psi [long]

[Ken]

Hi Javad,

I put some comments and questions below.

Quoting JShadzi at aol.com:
>
> >I was originally collecting parts to convert a WG cap over to adjustable
> style, so I could get some of the boost I had when I blew the lower WG hose.
>  But then I read that it wouldn't increase max boost, just the WG cracking
> pressure.  That makes sense.  I may still do the mod, just to be able to
> tweak things.
>
> That is only true if you are using the stock WGFV, in manually controlled
> configuration, cranking down pressure on the spring will absolutely raise
> boost.  Using my wastegate I can increase boost pressure by about 4 psi from
> all the way up to all the way down.  Think about it, push down on a spring,
> it takes a lot less force to copress that first inch than the second inch.

That does make sense.  I guess with the stock system, the WGFV will just apply more vacuum to the upper chamber to lower the boost to the mapped target?

A concern I have about adding preload to the spring is that it may decrease the total travel available for the WG.  It's almost like the orifice is being made smaller (at WOT/target boost) by reducing the travel.

> >Btw, if you take out the WG allen bolt from the underside, you can just push
> out the plug, you don't need to drill a hole and pull on a screw or
> >anything.
>
> I drilled it out and used a course gauge (12 I think) 9/16" bolt.  The stock
> bolt is very fine thread metric, it takes too many turns to acutally increase
> pressure (unreasonably high resoloution), by using a coarse thread bolt, a
> more practical adjustment resoloution can be acieved.

Did you rethread the WG cap for the different thread pitch?

The bolt I got was a direct fit, per the specs online/archived.  I still need to cut the nut in half tho'.

> >Where can I get the valve spring shim washers that are recommended as WG
> spring seats, so that the spring doesn't bind when adjusting the preload?
>
> I've just used plain old washer's for that.

The washers I saw at the store didn't have a large enough hole in the center of them to perfectly fit onto the upper WG spring perch.  Do you drill out the plain old washers to fit the perch?

Thanks,

Ken

p.s.  Since I'm posting again, I was thinking about how now that I'm running the SchrapnelKnobben mod on my car, I can switch back to the stock WG spring.

My idea is that it would provide the following changes/benefits:

One feature that I like about this mod is that, I believe, the WG doesn't even begin cracking until the boost (lower chamber) exceeds the regulated pressure (upper chamber).  So, unlike a simple stiffer spring, the WG isn't partially open before target boost is achieved.  With a spring type mod, you are "chasing" boost as exhaust leaks past the WG before max boost is achieved.

With a stock spring and Schrapnelknobben mod, the WG closing force is more pressure-based than mechanical/spring force-based.  That may allow me to run closer to the edge of detonation, since the WG may be quicker(?) when biased towards pneumatic control.  Seems like it would, since I would be putting out higher pressure on the upper chamber than currently, so the WG would stay totally closed until that higher limit.

In other words, I've got boost pressure trying to push the WG open at 3psi, and the WG is holding the additional 12psi.  So, it's leaking "some exhaust" between 3psi and 15psi.  After swapping in the stock spring, I should have no boost trying to push the WG open until about 9psi, then the spring will take care of the additional 6psi.  So, boost may build up quicker between 3 and 9 psi after going back to the stock spring.

I realize this all happens at the same time, and I can't attribute specific pressures to one or the other (spring vs. regulator).  But is the concept valid?  Quicker boost buildup, due to reduced WG leakage (higher WG cracking point)?