View Full Version : Possible way of setting a ball+spring MBC
Here is a technical question/suggestion for you, I would value input.
I was talking to Ian at billing about problems he was having in safely setting his ball and spring MBC before installation.
It occurred to me today that you may be able to get a working setting in the following way using the OEM boost gauge:
1. Disconnect the vacuum pipe from the boost sensor.
2. Find some way of plumbing in the MBC in the vacuum line and reconnect the boost sensor (might require some different diameter pipes to be connected together).
3. Drive the car and adjust the MBC so that the boost gauge is working and showing peak boost as normal.
4. Adjust the MBC up in small increments until the boost gauge no longer works (might take a few trys).
5. Adjust the MBC back down in small increments until the gauge reads peak boost again (it won't show anything until peak boost then it will move suddenly)
6. Remove the MBC from the vacuum line and reconnect the boost sensor as stock.
7. Install the MBC at the turbo like you are supposed to. It should now be at or just below stock boost and can be adjusted up in small increments to increase boost.
Would this work? My concern is if there is the volume of air required to open the valve in a vacuum line and how accurate this measurement would be in the actuator hose. Another option would be to T off of the actuator line but still use the boost sensor to show boost (this might be a better bet actually as the pipes could be the correct diameter).
Of course if you have access to an aftermarket gauge you could use this instead.
:) :)
I can tell. This MBC is driving you as nuts as it's driving me.
I have a suggestion, two actually.
1: How about you PM me your address and I'll post you the MBC, you can play with it 'til your hearts content? If you come up with a plan, let me know, post it back and I'll be happy as Larry. I'll buy you a beer next time I see you. If you don't come up with a plan, keep the MBC.
2: How about I bring the car, the MBC and my stock of SVH over one evening next week and we can play with it until we kill or cure it. As payment I'll but you dinner and a couple of beers?
Whajasay?
:) :)
I can tell. This MBC is driving you as nuts as it's driving me.
I have a suggestion, two actually.
1: How about you PM me your address and I'll post you the MBC, you can play with it 'til your hearts content? If you come up with a plan, let me know, post it back and I'll be happy as Larry. I'll buy you a beer next time I see you. If you don't come up with a plan, keep the MBC.
2: How about I bring the car, the MBC and my stock of SVH over one evening next week and we can play with it until we kill or cure it. As payment I'll but you dinner and a couple of beers?
Whajasay?
I'm just intrigued as to why it didn't work and it would be interesting for other owners to know. Perhaps the spring is too strong and it needs too much boost to overcome it.
How about a compromise. Mail the MBC over and I'll try and set it up on my car. If it works then we can meet up. The MBC I fitted to the Disco was no problem. We just set it low and turned it up until the boost changed. Bit of a drag keep driving-stopping-driving but you don't need to test it WOT to get a setting.
There's LOADS of good info about various types of MBC on www.autospeed.com, from the very simple to the ridiculously complex. You may need to sign up for a month to view all the articles but it's well worth it, loads of stuff on there from jap turbonutter cars to holdens with superchargers etc.
Dillinger
12-08-04, 08:31 PM
okay i got my MBC in the post this morning!
before i put it on i'd like to understand exactly what its doing so we can work out what its 'settings' are likely to be.
the way i understand it is that it sits inbetween the turbo and the wastegate. its job is to restrict the air that goes to the wastegate and delay its opening?
the ball and spring get pushed back by the pressure and when that happens the air can flow as normal. the spring can be compressed by the screw which makes it more resistant. therefore more pressure is needed to move the ball and open the flow.
so, my thoughts were that to safely install it, have the spring as uncompressed as possible so that air flows at gentle pressures. ive since found that even on its weakest setting its quite resistant. no amount of lung power in my case could shift it ;)
also, theres a pinhole in one side that leaks pressure. not much but i wasnt expecting to see one at all.
physics bit:
I got some aquariam hose and connected one end to the 'input' in the MBC, and the other to a foot pump (acting as my turbo!).
on its weakest setting, it took roughly 1-2 PSI to open the valve and let air through.
on its stongest setting, it took roughly 15PSI to open.
idiot bit:
how much pressure comes out of the turbo to the wastegate? is it what the guage reads on the dash? (in my case, around 6)
if so, would installing it in its weakest state have no effect since it would be opened at 1-2?
so assuming i'm after 8psi i'd have to adjust the screw until the footpump opened it at 8.
(theoretical boost 1-15psi)
or.. is the amount it takes to open the MBC ADDED to stock. ie installing it on its weakest means 6+1. strongest means 6+15 (7-21 psi)
just trying to bend my head around what its doing. i could just install it on its weakest anyway and see what it does, i'd just like to know what its doing. :bigeyes:
Bondango
12-08-04, 08:36 PM
its a peice of peace to understand and fit :bigeyes:
Ok you NEED a boost gause to set it, if you dont have one (not the stocker) then DO NOT ATTEMPT IT!
Fits as you said between wasted gate and Turbo Actuator Boost line.
With the MBC at its lowest setting, take the car for a drive and boost. You shouldnt see any change over the Stock boost level.
Now, Turn the MBC 1/2 a turn and take another Drive, Full boost should be a little more.
Keep doing this procedure until your reaching desired MAX boost. And remember Fuel cut is at 11psi unless your running a FCD or Lex AFM.
AND DONT BE SILLY WITH IT!!!! its one sure way to sink that headgasket!
I installed some cheap £40 MBC I bought from Halfords 6 months back, I would gradually turn the MBC and drive the car thru different gears (i.e 2nd gear WOT and 5th gear WOT). Although my turbo was shimmed to 10 PSI so the boost would never drop below that.
Also keeping the vacuum hoses of the MBC as short as possible reduces any boost spike, but not too short as the MBC will be touching the hot turbo!
how much pressure comes out of the turbo to the wastegate? is it what the guage reads on the dash? (in my case, around 6)
if so, would installing it in its weakest state have no effect since it would be opened at 1-2?
so assuming i'm after 8psi i'd have to adjust the screw until the footpump opened it at 8.
(theoretical boost 1-15psi)
or.. is the amount it takes to open the MBC ADDED to stock. ie installing it on its weakest means 6+1. strongest means 6+15 (7-21 psi)
For simplicity the pressure at the turbo nipple is the same as at the inlet manifold. (This is not strictly the case). Therefore the pressure you need to set on the MBC is the desired boost pressure - 8psi in your example.
I'm afraid I don't have a good enough understanding of the physics invloved to comment in detail but your procedure may fall down because your foot pump gauge may well be too inaccurate for this purpose. What you see as 8psi might be 5psi or 10psi. This is probably the biggest problem.
In addition I was wondering about relative densities. The air in your foot pump has not been heated to the same extent as the air from a turbo and is therefore more dense. I would consider that this has no bearing on pressure, but may have a bearing on the pressure differential between both sides of the valve. (Anyone care to comment on this?)
Obviously an MBC could be set-up in small steps from low to high until the desired boost has been reached. My original post was aimed at a specific example that Ian and I had spoken about where his MBC seemed to be set too high even at it's lowest setting, and I was looking from a reliable way to test and set it using equipment that we all had. If he had just installed the device at it's lowest settings and driven off down the road at WOT he would have hit FC.
Dillinger
13-08-04, 07:11 PM
fair enough, theres a lot more to it that i naively suspected ;)
im going to hold off installing it until i can get a new boost gauge, as i booted it on the way home from work and the needle stops just short of the 8 psi indicated. so if installing it even on its weakest setting increases it, its going to hit the top and i'll have no idea what its actually boosting. :eek:
i really need a metal headgasket. im sick of being paranoid and pussyfooting around. :)
Obviously an MBC could be set-up in small steps from low to high until the desired boost has been reached. My original post was aimed at a specific example that Ian and I had spoken about where his MBC seemed to be set too high even at it's lowest setting, and I was looking from a reliable way to test and set it using equipment that we all had. If he had just installed the device at it's lowest settings and driven off down the road at WOT he would have hit FC.
What you described there is boost creep, even at low settings. Build up of pressure takes far too long to react with the wastegate actuator. The best way to control boost with a MBC is to keep all vacuum hoses short as possible. It worked for my car and I had my wastegate shimmed.
Bondango
13-08-04, 07:24 PM
What you described there is boost creep, even at low settings. Build up of pressure takes far too long to react with the wastegate actuator. The best way to control boost with a MBC is to keep all vacuum hoses short as possible. It worked for my car and I had my wastegate shimmed.
Becuase an MBC works differently than a BleedValve there should be NO Boost creep at all, thats why they are higly favoured :yes:
Dillinger
13-08-04, 07:25 PM
What you described there is boost creep, even at low settings. Build up of pressure takes far too long to react with the wastegate actuator. The best way to control boost with a MBC is to keep all vacuum hoses short as possible. It worked for my car and I had my wastegate shimmed.
ahh right, so even if the MBC is being opened very early (2 psi), the delay caused by it having to pass through the MBC valve slowly (and potentially longer hoses) means that it takes longer to open the wastegate and in that time the turbo will still be increasing?
so using PSI as a base to open the valve is innacurate, as the delay means it'll go higher too?
sorry for being a :donkey: , im keen to learn. :yes:
Becuase an MBC works differently than a BleedValve there should be NO Boost creep at all, thats why they are higly favoured :yes:
My controller has a spring providing tension under the adjusting knob with a bleed nipple at the bottom of the controller. If that makes it a bleed valve, i had no boost creep with it.
I found out my old boost controller is a ball & spring type.
A basic bleed valve would open the wastegate at too low a PSI and at a gradual rate.
The story so far ...
Last night I had a chance to check out the MBC that Ian sent me.
1. First I decided to check it like Ian did using a tyre pump. The MBC appeared to work and I could adjust the pressure shown on the gauge by adjusting the MBC.
2. Then I hooked up another gauge on the outlet side of the MBC and tried again. No pressure reading at the second gauge. I concluded that the air was escaping via the small hole in the MBC. If I put my finger over the hole I could get pressure on the second gauge.
3. I installed the MBC on my car and went for a drive. Sure enough I couldn't control the boost.
4. I soldered up the hole in the MBC and went for another drive. Got controllable boost.
5. Then I considered what the hole is for. I decided it was there to relieve pressure once the boost has decreesed allowing the wastegate to close again. In theory if the boost isn't relieved the wastegate will remain open, but I hadn't noticed that the wastegate was held open so I decided to check it out further.
6. Went back to the tyre pump and second gauge. Sure enough the pressure was being relieved. Soapy water told me that air was leaking down the thread of the adjusting bolt.
7. I don't consider this a satisfacory solution because over time the threads may become clogged and stop leaking so today I am going to drill a new, smaller hole in the solder I applied last night and check it again both off and on the car.
Some other observations:
1. I found that the boost was fairly stable although it does tend to overboost slightly (9psi) before returning to the desired boost (8psi) at WOT. My EBC is much more accurate and will only spike between shifts and sudden throttle closures.
2. I saw no boost creep.
3. I didn't think that the boost came in as suddenly with the MBC as with the EBC but this is a very minor difference.
more news as it breaks ...
OK the final update:
In the previous post I said that I had soldered the hole up. Well the original hole was about 2mm diameter. I drilled a 1mm diameter hole in the solder to replace it. I had previously also shortened the spring in the MBC by about 1 full turn (approx 3-4mm) to allow some finer adjustment.
This morning I put it back in my car and went out for a drive.
I now have a fairly stable boost, maximum spike I recorded was 0.4psi at WOT. I think this is very acceptable with peak boost set at 8psi
I think the crux of the problem was the amount of air that was being bled away by the larger hole. I'm sure that this would not be a problem at higher boost settings but at a modest 8psi it was simply too large.
A couple of simple calculations shows that making the hole smaller has a significant effect on the amount of air that can pass:
Area of 2mm circle (pi r^2) = 3.14 square mm
Area of 1mm circle (pi r^2) = 0.795 square mm
The area of the larger hole is nearly 4 times larger than the small hole.
Bottom line is that if you want to put one of these on your car you need to make sure that the bleed hole is not too large if you are looking for modest boost levels. I think someone previously posted a valve with two adjusting knobs. Perhaps this is covered by one of these adjustments?
I also visited a local pneumatic supply company to enquire about the valve. They didn't stock anything the same, so I guess it's not a standard part in their line of business. They do stock T-joints and the pipe adapters though. None of the T joints they held had a hole drilled in it.
One final thought is regarding the solder I used to fill the hole. It was solder with a melting point of around 180degreesC so should be able to withstand the heat of an engine bay OK. A better solution might be to either drill the correct sized hole in the first place or maybe to use something like braze, which I believe is a harder material with a higher melting point, to fill the hole.
Bondango
22-08-04, 04:27 PM
i bought one of ebay the other day, and im going to use it instead of the AVCR but gonna record the boost curves and spikes using the AVCR to compare them...stay tuned
Dillinger
22-08-04, 06:44 PM
thanks for the updates lofty.
the MBC i bought does have a 1mm hole already so im hoping it might be okay. i'm still going to hold off installing it until i have a more reliable way of seeing what its doing first though. (new boost gauge would be a start)
am i right in thinking an EBC shows you what you are boosting on a display, so you dont really need to buy a new guage? just thinking if a new guage is £50-100 i might just give in and get an EBC. ;)
am i right in thinking an EBC shows you what you are boosting on a display, so you dont really need to buy a new guage? just thinking if a new guage is £50-100 i might just give in and get an EBC. ;)
Yes. My Blitz SBC-id has a built in boost gauge. It seems fine to me.
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