I have a ihi rhb5. it was running 5psi. installed norgren mbc. car pulled hard to 10psi all night. next morning i shortend the vacuum lines to the mbc. Now the car pulls hard to about 4500 then no boost. or power. that was with full throttle. Made another pass and it cut out at 5psi. let off the throttle and then back on, it will boost again. but sometimes it will pull hard all thru first, shift to 2nd, nothing. no boost or power. Its different every pass.
setup- d15b vtec, 450's, crome. no codes. bad mbc? or wastegate not holding or whatever?

 

sounds like the wastegate is getting flung wide open, see what happens when you turn the mbc down some.

internal wastegate?

 

yeah internal wastgate. The mbc I have says + and - . So I put it all the way to - and tried gradually advancing it. but it stills seems to be doing it. Its wierd because the night before i had the mbc 3/4 turn off - and it ran **** at 11psi.

 

take the mbc off and if it is still acting wierd replace the wastegate or try to put a little oil in it.

 

which rhb5 is it? is it the vj-11 off a probe? or a vj-14 off a 323? your 1.5L shouldn't over boost it at 4500rpms. but those are small *** turbo's. either one should be good to a solid 6000-6500 on a motor that small. i know guys that run them on the mazda 1.8L and it drops at about 5000-5500. but that is a bit more flow and displacement also.

NEUMAN

 

Could the shorter vac lines to the mbc cause more push on the wastegate causing it to open more like **** said? Any possibility of running the old(longer) vac lines and see if it's back to "normal"
?

 

line length is not going to play a factor here.

NEUMAN

 

I may have confused wastegate response with wastegate accuracy. :1

 

I took the mbc off and just ran it at the stock 5psi. Runs fine like that, but still want to know why it was acting that way w/ the mbc on.

 

the turbo is a vj-11. its not overboosting at 4500, but it just stops boosting. As if I took my foot off the gas, but it is still floored. I let off the throttleand then get back on it, then it will go again. Its gotta be the wastegate malfuctioning or something