im not jumping into a new boost controller just yet. i know all boost controllers taper. and my unos held fine on my viii tapering from 21 to 19 lbs. it may be broken or need to be cleaned and lubed as it was just sitting around for 7 months. i agree its not typical of the unos. maybe a bug crawled inside and died who knows. tapering that much means something isnt right just looking for options.

 

boost leak test done, presurized to 21psi not a sound.... looks like ill try changing the forge out there goes another 50 bucks.

 

do you think the taper could be because the forge is bleeding off too much pressure? anything else i can check before buying a new mbc?

 

I think that the boost should be tapering a bit.

 

im not arguing it shouldnt be tapering. as you said it should be tapering a bit. but i dont think it should be tapering 6-7psi to 15

 

so like i stated before i did a boost leak test and found nothing. i logged right after the boost leak test and the forge was actually went down to 15 psi on my last log at 7500 after hitting 21.5 at 4000. so i changed the forge out for a dejon tool mbc today. i took 2 logs to check for knock then i took 2 logs to log boost. 1st run showed 22.5 at 4000 and tapering to 17.5 at 7500. second log shwoed 23 at 4100 tapering to 17.8 by 7400. those taper points are more what i would expect. and with the forge it would dip down to the 17's at just over 6000 rpm. so either the forge had a problem or my car just didnt like it.

thank you for sharing in my experience

Eddie

 

One thing that doesn't look to have been mentioned at all yet, is which spring you have installed in the boost controller.

We include two different springs with the unit, each with it's own unique range of boost adjustment.

If you're not able to reach a given boost level with one (likely the softer one), then switch to the stiffer one and see where that gets you to.

 

i had one of the first batches with the soft spring that wouldnt hold above 19psi. when i bought the unit from Al said he installed the stiff spring for me before sending it out. given the fact that i was at 22 psi at around 12 clicks i assume its the stiff spring. im not sure where the other spring is. im not saying anything bad about the forge unit like i said before i know its not typical. but i also did not have any other springs to check.

Edit: i found the other spring and it was definately the stiff spring installed i took it apart and checked. stiff spring installed. everything seated nicely. still tapered to 15

 

I am having a similar experience. I recently installed a forge mbc on my evo 8 and it boosts to 20.5 and then immediately tapers to about 19 and then gradually tapers to 16 at around 7000 rpm. I used fresh tubing and tapped into the vac line between the bov and the intake manifold. I couldn't find any leaks. This is my first experience with a mbc but I haven't had a problem with ebcs in the past.

 

+1 on the MIVEC, -1 on the cylinder pressure theory.

It is normal and you cannot prevent it unless you had a larger turbo.

 

ALL YOU EVO IX USERS WILL HAVE SUBSTANTIAL TAPER NO MATTER WHAT.

 

how much more substantial will the taper be on the IX's as compared to the VIII's?

 

3-4 psi

It not rare to see 22 psi drop to 16-17 at 7000-7500rpms.

 

Hi all,

Did not want to open a new thread in regards of Evo IX and Forge MBC? So, just for me to be clear.... my car will spike ~1.6 bar in 3rd gear and taper to ~1.3 around 7800 rpm..... on 4th/5th the car will spike between 1.5-1.6 bar and it will taper to 1.3.

I think based on this thread that it is normal but want to confirm with the more experienced members.

 

Has very little to do with the boost controller.