rb20 w/ rb25 turbo... cant boost past 10psi?!?! :(

[tpetrucci33]

Why wont my turbo spool past 10psi?! I have a manual boost controller!!

Well as you can see my current setup is an rb20 with the following mods:

rb20
rb25 turbo
mckinneys fmic
Agency Power manual boost controller
Full turbo back piping
screamer pipe on the dump

My manual boost controller is set up to flow from the fmic piping, to the mbc, then to the wastegate if that helps.

Any help would be greatly appreciated as I want to get my car to dial in at 14psi before my tune.
Thanks!!

[HYPNOTIK]

Don't run 14psi on that turbo unless you want to replace it. 12psi max.

Are you 100% sure that you have the boost controller hooked up correctly?(not backwards)

I'm assuming you have already tighten it down all the way and the boost still doesn't increase? If that's the case then you probly have a boost leak. Stock BOV?

[tpetrucci33]

yes stock bov.. but i dont think its because of a boost leak. i disconnected the wastegate and boost jumped for the half second i had my foot on the throttle haha. i got the air flowing into the wastegate i.e. the arrow pointing towards the wastegate on the mbc

[HYPNOTIK]

Your bov might be leaking. You've tried closing the BC all the way?(max boost) I have a greddy mbc on my car and I have to go up like 30 clicks before it starts doing anything.

[tpetrucci33]

im pretty sure its not leaking. i hold 10psi without the mbc. any other ideas?

[GSXRJJordan]

im pretty sure its not leaking. i hold 10psi without the mbc. any other ideas?

So you're saying at just wastegate pressure (no MBC installed, vacuum from throttle body to wastegate actuator) you see 10psi?

... and no matter what you do with the MBC in there, you never see more than 10psi?

... I wonder if the MBC is bad... :aw:

[clark]

^^ that's what i was gonna say. is it a cheapo MBC? the MBC i have is a turbonetics, BUT it's VERY sensitive, if i turn it a hair, it completely changes.

what i did to find the right adjustments was take the MBC off, blow in to one end and felt the air come out the other end while i turned the knob.

blow like you're doing a brethalyzer!

what chassis is this in??

i do agree with the open BOV because I've suffered that and it's the same symptoms.

it could also be that the wastegate flapper is stuck open

[Chernobyl]

Try another boost controller. Everything else sounds like it's working as it should. Or just crank the controller down as far as it will go.

I have the same setup btw. RB20 with RB25 turbo with RB20 wastegate. Ran 10psi stock, added a manual boost controller and had to crank it down a LOT to get the boost to go up some and it runs 11 now. Not really looking to push it past 11-12 on this turbo, so I haven't experimented further. Stock recirc valve, btw, and it holds the extra lb of pressure fine.

[steve shadows]

If you have an internal WG it is a total WASTE to use a MBC

the best way to control internally wg turbos is to use a Dual Solenoid Boost Controller design.

I suggest the Blitz Dual this one worked great for me and I recommend it for cars I am tunning. Just set it up +30 gain and you're done with it.

I would make sure to verify your turbo is going to be still in efficiency range over 8-9 psi. Most cases the stock Nissan Garrett Turbos are not going to make any more additional HP over 9 PSI max. This is very true for the T25 on the SR (dies at 12 PSI) and most T3s used on the VG30 and RB motors for Nissan.


I would upgrade soon, p.s. PM me for a quote. I am able to offer very cheap NEW garrett turbos through a friend of mine now. NEW CHRA with re-used new condition Air Research Housings. 650 bucks for a Brand New Bolt on T3/T4. very cool stuff

[tpetrucci33]

hmmm thats verry tempting. I dont know why the boost controller is working for this wastegate because it worked for the other turbo!!

[96Turbo]

try stretching out the spring in the MBC a little bit

[tpetrucci33]

thank you ill try that right now

[tpetrucci33]

looks to be a bleed type valve on the boost controller which is no bueno for adjusting and holding boost. maybe ill try a spring type controller

[96Turbo]

adjust it to bleed more air. unless it's already maxed out then i guess ur SOL. I've been thinking about crushing my wastegate actuator a bit to squeeze out a couple extra PSI on the cheap without resorting to an egay controller. don't go anything past 12psi on that turbo or it won't last long though.

[steve shadows]

MBC usually have a sweet spot and it's REALLY HARD to find the sweet spot because once you find it it's only like 5-10 dgrees for 5-20 PSI adjustments!

[tpetrucci33]

yea i opened it up all the way and got 10psi