Boost spiking or drop off with MBC's

[sonofturd]

I've just fitted an mbc to my b230fk, virtually all the way open at the moment.
First thing I've noticed is that the boost rises then drops back when reaching higher rpms. A quick Google and this seems to be common with a lot of mbc's. Possibly made worse as my actuator is designed to open at a very low pressure anyway?
Was boosting at about 0.24bar (3.5psi) without mbc.
Now peaks at 0.3bar and drops to about 0.25bar.

My aim is to set the boost to 0.8bar (I have a fuel chip fitted).
If this spiking or whatever it is is likely to be caused by the mbc then should I just buy a 0.8bar actuator?
Are these any good?
https://m.ebay.co.uk/itm/Turbo-Actua...-/262839887267

[Laird Scooby]

I know most of the people that run modified turbos seem to avoid stuff from China/HongKong, there might be a better option, see what the turbo guys say.

If nowt else my useless post has given your thread a bump!

[TonyS9]

I believe the FK actuator is not good with bleed valves, you are better starting with a FT actuator or get an adjustable (or multi spring) actuator.

I run 14psi (1bar) with my FT on a bleed valve with extra fuel pressure.

[sonofturd]

I've wound the boost up a bit. When I initially go WOT it spikes to 0.8bar but then drops straight back to 0.6bar. Only drops a small amount at higher rpm. Assuming the spike is because of mbc and the slight drop at high rpm is because the engine is off cam?
I could get an adjustable actuator but is that just a more expensive way of achieving 0.8bar. I have no intention of increasing boost any further.

[barkster1971]

You have a decent boost gauge fitted?

[sonofturd]

Originally Posted by barkster1971

You have a decent boost gauge fitted?

It's one made by Tim so not particularly expensive but should be accurate.

[Jimsiss]

Which boost controller are you using?

[jonnyf90]

I ran 12psi (0.85bar) in my 940 LPT with no spikes or drops. The B230FK doesn’t really like revving over 5k - you just get a lot of noise and not a lot of extra movement.
All the power comes between 2.5k and 4.5k. You might want to check vacuum lines for leaks if it’s dropping off that much.

Cheers

[sonofturd]

Originally Posted by Jimsiss

Which boost controller are you using?

Looks very similar to this one.

http://www.google.co.uk/search?q=man...jekLlewxN6kdM:

I've moved it as close as possible to the turbo/actuator (there's virtually no hose between the boost controller and turbo/actuator now). Still spikes though. After speaking to a fee people and scouring the net , there's a lot of info that seems to say mbc's can give you that spike, also alot of info about boost tapering off at higher rpms. (Especially with actuators that have weak springs).

I think a different mbc that lifts off it's seat more progressively would make the world of difference with the spiking.

[Pete940]

It seems to vary... In my previous 940 the standard actuator coped fine with 12 psi. In my new 940 I'm getting a small spike and then back to about 7 psi. I'm blaming it on the actuator.