Re: mbc no good for low psi?
 

Both internals and externals will see pressure in them before full boost (where they open almost full tilt), but internals are cheap mass-produced garbage with almost no spring preload. Put a Tial on with the firering, and you'll get an idea of what preload is.

A MBC has a spring in it thats preloaded to not move ONE BIT until target psi is met. Technically it will, but when target psi is met, that tiny 'pre-leak' has just pre-presurized the tubing/wg so you don't spike.

The cheap MBC I was given has set at ~14psi 2/3 of the way out, and would not go below 10psi w/o cutting the spring...in half.

Re: mbc no good for low psi?
 

Well wouldn't that be the problem? You have an 11psi spring in there and want to run 7psi. Dont manual boost controllers allow you to only turn up the boost? The lowest boost you should be able to get is limited by spring that is in the wastegate. What you could do is get a 3psi or whatever size spring and then use the manual boost controller to limit the amount of boost that the wastegate sees.

Re: mbc no good for low psi?
 

you suck at reading.

i put the 11psi spring in there and am going to switch vac source from the manifold to the comp housing, we'll see. while i was at it i took my 38mm knock off all the way apart, i mean all the way, after i noticed the diaphram assembly was wobbly , the 4 set screws had came loose

Re: mbc no good for low psi?
 

welp. i guess the big red spring was 6psi too. took the small red out and put the big red in, connected the wg line to the comp housing figureing my enging would get about 9-10psi. still get 5-6. stupid ssauto springs

Re: mbc no good for low psi?
 

Put in both.

Re: mbc no good for low psi?
 

ok.


also what if i seal the bleed hole on the mbc and cut the spring? will that let me do lower boost?