Holset replaces K-14

[Gizmoman]

You said your MBC doesn't went? I hope there is a small hole somewhere between MBC and boost can so pressure can leak off? Otherwise you would open the wastegate once and it will stay open since pressure is trapped!  

You do make a good point but there's no vent on my DIYMBC - worked fine on the K-14. The boost pressure increased/decreased dead-on with my right foot when I was above 2K, and stopped climbing around 15-16 psi which is where I had it set. Keep in mind, it's a simple ball and spring seating against the surface of a drill-seat

Possibly the air leaked out between the jam nut at the adjustment screw or it didn't seal perfectly.

(EDIT) Also, not shown in the photo is a "T" in the pressure line that goes up to the IP. Possibly it vents that way.

[745 turbogreasel]

Some of the integrated ones bleed air by the valve for cooling.
I  dented my ball seat a tiny bit, and it was enough.

[theman53]

It would vent to the IP if it is what is controlling your LDA. The LDA has a vent to atmosphere, as long as it isn't plugged or something

[Gizmoman]

It would vent to the IP if it is what is controlling your LDA. The LDA has a vent to atmosphere, as long as it isn't plugged or something

Thanks theman - that splains it

[745 turbogreasel]

Pretty sure that LDA vent is on the other side of the diaphragm,  just so the LDA is free to move....Some of them even have a  sealed can  on the atmospheric vent side as part of some altitude compensation scheme.

[TimpanogosSlim]

Ball and spring type controllers work great! (NXS boost controllers on ebay etc.) but if there isn't a pinhole to bleed pressure between ball/ballseat and boost can somewhere (normally a smole hole drilled in the MBC) the pressure will be trapped between the seated ball and the boost can and wastegate will stay open. Just something to note for those who make their own MBC.

Right, thus the use of a reverse biased check valve that only opens when pressure is greater on the side of the wastegate actuator.

[CrazyAndy]

How about a light ball and spring valve going the other way in parallel?  It would not let air by while building or under boost (since pressures would be either against the ball or even on both sides so the ball wouldn't move anyway), but would let all the air back when letting off due to its light spring.  That way we would not have to bleed boost control air to atmosphere; a true closed system!

[Gizmoman]

I believe my MBC works because the ball does not seal perfectly.

The air fills the can and if the ball were perfectly sealed against the seat it would never retract. I just proved it by hooking up quality blow-nozzle to the boost can and when I pressurize it, it stays extended even when I let off on the lever and disconnect it from the air hose. As soon as I touch the lever on the blow nozzle, the rod retracts.
I just tested my MBC and no matter how tight I make the spring by turning in the adjustment screw, it leaks a teeny tiny amount.

[TimpanogosSlim]

How about a light ball and spring valve going the other way in parallel?  It would not let air by while building or under boost (since pressures would be either against the ball or even on both sides so the ball wouldn't move anyway), but would let all the air back when letting off due to its light spring.  That way we would not have to bleed boost control air to atmosphere; a true closed system!

You've basically described a check valve?

The plumbing becomes complex but what i am referring to is a 1 or 2 psi cracking pressure check valve oriented opposite the MBC and connected to the same lines. Whenever the pressure on the compressor side is lower than the pressure on the WGA side, it would vent back to the compressor side.

[Gizmoman]

The morning starts with resolving a possible exhaust flow issue.
Here is a shot of the adapter plate which matches to output port on the exhaust manifold.



Now the turbo will get every bit of exhaust flow possible.



Time to go mount it on the engine and start figuring out the WAIC mount, water and air plumbing.

[burn_your_money]

Pretty sure that LDA vent is on the other side of the diaphragm,  just so the LDA is free to move....Some of them even have a  sealed can  on the atmospheric vent side as part of some altitude compensation scheme.

Correct. It can not bleed through the LDA, but it could force the boost pin down, possibly enough to close the wastegate. This would make for smoke and high EGTs when off boost though since the pump thinks it is seeing boost.

[Gizmoman]

Pretty sure that LDA vent is on the other side of the diaphragm,  just so the LDA is free to move....Some of them even have a  sealed can  on the atmospheric vent side as part of some altitude compensation scheme.

Correct. It can not bleed through the LDA, but it could force the boost pin down, possibly enough to close the wastegate. This would make for smoke and high EGTs when off boost though since the pump thinks it is seeing boost.

So, should I drill a tiny pin-hole in my MBC? It bugged me that it wasn't seating so I took it apart and found a small piece of something on the seat which I blew out with air. Now it seats (and seals). I'm having to re-do it anyway as the hose barbs need to be larger to accommodate the barbs on the Holset.

On another note, I had noticed this oil stain under the engine several weeks ago and cleaned it up - figuring it was from my disconnected oil feed line. It was back again and was coming from the aluminum fitting the PO had welded to the pan - a tiny crack had developed.



Here is the fitting - a tiny crack at the weld



I took it off and found that the hole in the pan was way too small for a drain line - even for the K-14. No wonder I was getting oil in my charge air!



I drilled and tapped it for 1/8" NPT and inserted a brass plug smeared with red Loctite (that's how small it was).


The three new holes to the right are for the new feed line fitting





I will use red-loctite on the two attachment bolts as well. I wish I could have removed the pan for this mod but I can't get to the screws at the transmission without pulling the engine (not gonna happen). I did remove the oil filler tube on the end of the pan and used a small vacuum tube attached to my shop vac to get out the aluminum shavings. Actually there wasn't much to vacuum out - one of the benefits of working upside down - most of the shavings fell into my eyes .
The new drain hose is 5/8" ID - Gates automatic transmission hose, single braid.  FWIW, the previous #8 fittings had an ID of .38" - too small for a turbo drain line.

Anyhoo, let me know your thoughts on the air bleed for the MBC and thanks for clarifying that the LDA won't vent this pressure.

[Gizmoman]

Ball and spring type controllers work great! (NXS boost controllers on ebay etc.) but if there isn't a pinhole to bleed pressure between ball/ballseat and boost can somewhere (normally a smole hole drilled in the MBC) the pressure will be trapped between the seated ball and the boost can and wastegate will stay open. Just something to note for those who make their own MBC.

Right, thus the use of a reverse biased check valve that only opens when pressure is greater on the side of the wastegate actuator.

Just so I could get my head around the concept, I made this diagram. No doubt it would work perfectly.


It would be a bit of work though and I do think a tiny bleed hole would perform the same function (and take a lot less time). However, I don't know how many CFM the boost hose can transfer at boost pressure but the hole would need to be small enough to not bleed much of it, or it wouldn't move the pot diaphragm.

A quick calc using an online flow calculator says that at 20 psi a 1/16" diameter hole will bleed .66 CFM of 72 degree air. A 3/16" orifice (my hose diameter) will flow 5.96 CFM.
The orifice is dumping 11% of the pressure so if I adjust the  MBC to 21.7 psi, it will send 20 psi to the pot (while bleeding off 11% through the orifice).

Therefore, as my MBC can be adjusted to easily hold even 60 psi, I think a small bleed hole will work just fine unless I'm missing something.

[RabbitJockey]

i would just drill a hole, u can go much smaller than 1/16", it will only be leaking at full boost.

[vanbcguy]

My MBC has a very tiny bleed hole on the wastegate can side and works fantastic. I fear you may be over thinking this. :-)

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