'96 940 CD HPT estate - MBC questions - Page 3

mikkey850 · Feb 16th, 2014, 15:50

:/ plans might be ruined. A loud tapping has appeared from the second cylinder back from the bulkhead

TonyS9 · Feb 16th, 2014, 18:08

Are you sure its not just an exhaust gasket?

mikkey850 · Feb 16th, 2014, 19:09

I think you could be right after listening to it again. I will have a look through the week

mikkey850 · Feb 18th, 2014, 10:37

Just a quick question.

When people say they are "running" 12psi. Does anyone get a spike before it settles? My friend seems to think that some cheaper boost controllers often spike up before settling when you hit the throttle.

Regards.

Michael.

Steve940estate · Feb 18th, 2014, 11:32

Getting them to work properly is a bit of a balance between getting the boost you want and controlling the spike. It also depends on what type of boost control you use.
The spike occours when the boost rises quicker than the MBC can operate and then open the wastegate.

To some extent you want a bit of spike as this gives more boost at lower engine revs. You can do this by fitting a restrictor in the line from the turbo to the wastegate actuator, that could be some sort of pneumatic valve or a piece of metal with a hole in it (mig welding tip)
I have found that using a bleed valve rather then the ball and spring type valve allows more adjustment. To make them work you need a restrictor so you can control the spike and it reduces the volume of air you need to bleed off. The bleed then lowers the amount of pressure going to the wastegate actuator and stops the wategate opening so quickly.

People have built all sorts of complex mechanical systems to control boost and it really makes you think trying to work out how they work. The easiest way is to compare them to how water comes out of a hose. If you put your finger over the end you can only hold it for so long before the pressure builds up and you can't any more. Thats how a ball and spring valve works. A bleed valve is really just the effect of turning the tap off a bit. To complicate things the air can compress which is what causes the spikes.

mikkey850 · Feb 18th, 2014, 12:08

Thanks for that Steve940estate. I am kinda of new to this concept. The only Turbo car I have tinkered with was an old 306 Dturbo which seemed to work a little differently (adjusting the length of the actuator arm)

I believe the present I have waiting is a Ball and spring type, which I thought was the better one to have, but looking at your description to an extent makes me think it will be more so a sudden surge of power rather than a smooth delivery. This doesn't bother me but I am worried about the potential of a spike. Say if I want to run 14psi but there is a 18psi spike for a split second, will this bugger my turbo or engine?

Regards,

Michael.

Steve940estate · Feb 18th, 2014, 13:39

Most people seem to use the ball and spring type and seem to think they are better.
I made one, it worked OK but just didn't seem to work as well for what I was doing. The added benifit of the bleed valve is that you can adjust them from inside the car and having long pipes doesn't seem to affect how they work.

When setting up you need to put the engine under a reasonable amount of load at speed so change down to third at about 50mph and stick your foot down. Probably best to get a passenger to keep an eye on the gauge to see what it does. Start from having no tension on the spring and carefully go from there. Just make sure you don't go too high if you get a spike. I haven't see the boost spike all that much it's normally just an overshoot if you are really trying hard.

No two ball and spring valves will work exactly the same and you might find the spring is slightly too stiff to give a low enough boost, all you can do it try it carefully.

munday · Feb 18th, 2014, 15:17

Just to complicate things further I am running a ball and spring type as a bleed valve!

There is a good thread on here that both myself and Steve contributed to that has some real good setup info

Steve940estate · Feb 18th, 2014, 18:06

Quote:

Originally Posted by munday

Just to complicate things further I am running a ball and spring type as a bleed valve!

I'm trying to work out what that does, whats your plan for doing that as it isn't something I have seen or even considered.

I have links to all sorts of stuff I have read about and they might be in the thread Munday mentioned. I will have a look later.

munday · Feb 19th, 2014, 08:44

Quote:

Originally Posted by Steve940estate

I'm trying to work out what that does, whats your plan for doing that as it isn't something I have seen or even considered.

I have links to all sorts of stuff I have read about and they might be in the thread Munday mentioned. I will have a look later.

This is the thread: http://www.volvoforums.org.uk/showthread.php?t=177594

Using the ball and spring as a bleed valve just means that I dont permanently have a vac leak, its only open when it needs to be and vents to atmosphere

Feb 16th, 2014, 15:50	#21
mikkey850 Member Last Online: Aug 21st, 2015 13:04 Join Date: Dec 2013 Location: York	:/ plans might be ruined. A loud tapping has appeared from the second cylinder back from the bulkhead

Feb 16th, 2014, 18:08	#22
TonyS9 Premier Member Last Online: May 19th, 2024 20:22 Join Date: Jul 2009 Location: Holywood	Are you sure its not just an exhaust gasket?

Feb 16th, 2014, 19:09	#23
mikkey850 Member Last Online: Aug 21st, 2015 13:04 Join Date: Dec 2013 Location: York	I think you could be right after listening to it again. I will have a look through the week

Feb 18th, 2014, 10:37	#24
mikkey850 Member Last Online: Aug 21st, 2015 13:04 Join Date: Dec 2013 Location: York	Just a quick question. When people say they are "running" 12psi. Does anyone get a spike before it settles? My friend seems to think that some cheaper boost controllers often spike up before settling when you hit the throttle. Regards. Michael.

Feb 18th, 2014, 11:32	#25
Steve940estate Steam Driven PC Owner. Last Online: Mar 4th, 2024 23:50 Join Date: Dec 2004 Location: Not sure.	Getting them to work properly is a bit of a balance between getting the boost you want and controlling the spike. It also depends on what type of boost control you use. The spike occours when the boost rises quicker than the MBC can operate and then open the wastegate. To some extent you want a bit of spike as this gives more boost at lower engine revs. You can do this by fitting a restrictor in the line from the turbo to the wastegate actuator, that could be some sort of pneumatic valve or a piece of metal with a hole in it (mig welding tip) I have found that using a bleed valve rather then the ball and spring type valve allows more adjustment. To make them work you need a restrictor so you can control the spike and it reduces the volume of air you need to bleed off. The bleed then lowers the amount of pressure going to the wastegate actuator and stops the wategate opening so quickly. People have built all sorts of complex mechanical systems to control boost and it really makes you think trying to work out how they work. The easiest way is to compare them to how water comes out of a hose. If you put your finger over the end you can only hold it for so long before the pressure builds up and you can't any more. Thats how a ball and spring valve works. A bleed valve is really just the effect of turning the tap off a bit. To complicate things the air can compress which is what causes the spikes.

Feb 18th, 2014, 12:08	#26
mikkey850 Member Last Online: Aug 21st, 2015 13:04 Join Date: Dec 2013 Location: York	Thanks for that Steve940estate. I am kinda of new to this concept. The only Turbo car I have tinkered with was an old 306 Dturbo which seemed to work a little differently (adjusting the length of the actuator arm) I believe the present I have waiting is a Ball and spring type, which I thought was the better one to have, but looking at your description to an extent makes me think it will be more so a sudden surge of power rather than a smooth delivery. This doesn't bother me but I am worried about the potential of a spike. Say if I want to run 14psi but there is a 18psi spike for a split second, will this bugger my turbo or engine? Regards, Michael.

Feb 18th, 2014, 13:39	#27
Steve940estate Steam Driven PC Owner. Last Online: Mar 4th, 2024 23:50 Join Date: Dec 2004 Location: Not sure.	Most people seem to use the ball and spring type and seem to think they are better. I made one, it worked OK but just didn't seem to work as well for what I was doing. The added benifit of the bleed valve is that you can adjust them from inside the car and having long pipes doesn't seem to affect how they work. When setting up you need to put the engine under a reasonable amount of load at speed so change down to third at about 50mph and stick your foot down. Probably best to get a passenger to keep an eye on the gauge to see what it does. Start from having no tension on the spring and carefully go from there. Just make sure you don't go too high if you get a spike. I haven't see the boost spike all that much it's normally just an overshoot if you are really trying hard. No two ball and spring valves will work exactly the same and you might find the spring is slightly too stiff to give a low enough boost, all you can do it try it carefully.

Feb 18th, 2014, 15:17	#28
munday Member Last Online: Nov 9th, 2016 11:50 Join Date: Jun 2012 Location: Basildon	Just to complicate things further I am running a ball and spring type as a bleed valve! There is a good thread on here that both myself and Steve contributed to that has some real good setup info

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