I was doing some logging today to rule out some reasons why I'm getting large amount of knock sums.

As another test I decided to turn my MBC all the way down (Forge spiking @ 15psi).

I would have thought that - when looking at my boost gauge - I would hold 15 psi all the way to redline.

I still had some taper - went down about 2 psi.

I'm thinking that since I installed the 272's - and changed the VE - the turbo just can't keep up with the flow.

Is my reasoning correct?

Or - do I have some deeper issue i.e. faulty WGA etc.

FWIW - I have ordered a Forge WGA and it's on its way.

 

The MBC is a perfect pressure regulating device meaning as soon as air overrides spring, air pressure goes by and will continue to pass untill differential psi, including a constant bleed output, equalizes to MBC spring tension. When properly setup it just so happens to controll boost via WGA rather nicely.

The boost taper you see here at 15 psi, since supply is not an issue, has nothing to do with the MBC - it's doing it's job by letting the air pass at set psi, it's directly related to actuator moving from full deflated (WG close, manifold @ 15 psi) to full inflated (WG open, manifold @ 13 psi). So basically your seeing a 15 psi boost spike while your MBC is actually set to regulate at 13 psi.

I bet if you hook a pressure source to the mbc with it's 15 psi setting it will open at 12 - 13 psi or less.

You can overcome most of this taper with a tighter network of hoses and tees (like dont hook your MBC to your DV source with five feet of soft silicone tubing)

Keep in mind the mechanism of action regarding boost taper is quite different at 25 psi in first gear with a stock 16G. Totally different drama here .

If your spiking is rather bothersome even when setup good then the bleed port might be clogged

 

Thanks for the detailed explanation.

Good stuff!