mbc no good for low psi?
 

both times, year or 2 ago on old setup, and just yesterday i was trying to set a ball and spring type mbc for 9-10 psi and it just doesnt happen, are they no good for low psi ? kept seeing 11-12 psi and going up before i let off, screw was backed almost all the way out when i was done

Re: mbc no good for low psi?
 

Depends on the MBC design, and depends on your wastegate setting. Details!

Re: mbc no good for low psi?
 

i had this same problem, bought a turbo smart manual boost controller and the damn this would stay at 11-12psi. even turned down all the way, i asked the shop i got it from, and on one side there is a little ball a spring, tha manual boost controllers are set from 12psi to whatever you want,

so if you need to take out the small ball and spring and you will be able to go to wastegate pressure.

Re: mbc no good for low psi?
 

If it is a ball and spring setup it will have a bleed hole to let the pressure off to allow the gate to close. So even when it is loosened up all they way it will be hard to get boost all the way down to the pressure of the gate spring since you are still sort-of running a bleed valve with the loosened ball and spring setup.

Or at least I think that is how it is.

Re: mbc no good for low psi?
 

you need to cut the spring a little, i do that, now i can go from 6 to any psi

note: i use an internal wastegate set at 6psi

Re: mbc no good for low psi?
 

im using an external gate with a 6psi spring, the mbc is just a cheap ebay style one

wouldnt cutting the spring make it so it wouldnt have a "flat" top anymore for the screw to push on and probly start getting caught in the threads?

Re: mbc no good for low psi?
 

Be a man and just run 12 psi.

Re: mbc no good for low psi?
 

lol, I dont understand why you would want to lower you're boost pressure, unless you're running a gt42 and cant stop spinning tires.

Re: mbc no good for low psi?
 

GT42 isn't going to make significantly more power than a T04E at 12 psi. In fact, the last GT42 powered 2.0 I tuned made about 15-20 less than the last T04E powered 2.0 I tuned - that's also a K vs B series comparo, for what it's worth, with the 84mm B-series making more power off of the smaller less efficient turbo and "shittier" unported B-series head. Both K-series and GT-series are hype, don't buy into it. :1

If you are spinning tires at 12 psi you probably have an alignment problem or need to upgrade from cheap beater tires. All the turbo cars I've tuned that are fast launch in the 6500-8000 rpm area at whatever psi puts them at or around 400 whp, on 24.5" to 26" slicks, so there is a LARGE window of traction for drag radials given more conservative launching and lower power levels in an ungutted streetcar.

Re: mbc no good for low psi?
 

Yup, I went for a ride in ELspool's car the other night on 225 BFGs, it hooks well with 2 people in the car at 15-16 psi of boost.