?? about my MBC

[Bohrn]

Ok, so I got a boost guage, and apparently, I was only running 10psi!! That would never do, so I did some research into commercially availiable manual boost controllers. While they seem cheap and great things, I couldn't wait a week or 2 for one to get here and after exchange, duty, tax, shipping&handling, I was going to have to pay $125+ for a 50us$ part.

So, I did some more research on how to make one, and went shopping. I got all the parts and put it togeather. It is a ball and spring/tee type. Tested it with a bike pump to open at approx 15psi. Mounted it on the car and took it for a conservative spin.

Well, it spiked up to 17 or so, so I backed off and cranked it down a few notches. Now it goes to 15psi, (lucky or what ), but it only holds 15psi for a second or so, then falls to 11. So I turn it up again, now it spikes to 17.5psi briefly, and then falls to 12 or so and slowly climbs to 15. This is the best that I can tune it.

What do you all think?? Different spring?? Fatter line to the wastegate?? The turbo side hose is a larger, thicker hose and the one running to the wastegate is kinda puny, and I was wondering if it was able to properly send the signal. Or do I need a 1/16th" bleeder hole in the wastegate side of the "T"

I see a small (1/16th") bleeder hole in the attached pic that I don't understand. Would this help my situation?? I do not want to drill the hole unless I am sure it will help.

thanx, John

 

[importracer150]

i'm under the understanding that the bleeder fitting helps to control boost creep by not allowing the pressure to build too fast. not having that small bleeder hole would cause the controller to creep.

 

[Bohrn]

So if what I am seeing is creep, then that will help it. But I thougth creep was when you start out with your set pressure, and then as you keep it WOT, the pressure starts to increase, until you lift. This is not what I am getting, I get a big spike at first then it falls off.

I am new to this sort of thing, but I am learning, I just don't understand what is not quite right here. Maybe the ball bearing is "floating"??

Also the bleeder hole is after the ball bearing. So until the bearing lifts due to high pressure, the hole does not come into play.

Or am I completely out to lunch and I should go back to Chevies I hope not, I love this thing


edit\\ Just had a thought...maybe without the bleeder hole, the boost builds up inside of the controller, and does not allow the ball bearing to close again??

 

[gstspyder1998]

Where did you get the intructions to make the MBC???

 

[kylemoto]

The little hole is for purging.

If the hole is not there, after the wastegate circuit gets pressurized the MBC can act as a one way check valve - which means your wastegate stays stuck in the open position.

I am thinking of this design too - bleeder type valves begin opening the wastegate all the time, which takes away part throttle power and response.

Kyle

 

[Bohrn]

::gstspyder1998; I don't remember where I got that diagram, but it was about 2 weeks ago on the internet that I found it. I was just following links from dsmtuners or some similar site.

::kylemoto; I was thinking along the same lines as what you said. I think I will drill, unless someone tells me otherwise?? I guesss I will have to re-calibrate, dangit, I painted nice + - marks and a 0 reference point. Oh well, I have some laquer thinner and more red paint

thanx for the help guys


edit// I just thought I should clarify; I am not using EXACTLY the same design as the one in the pic, but it is based on it. My main body is a brass "T" fitting, not a 90deg with a hole in the top. It is about half the size as well. About the same size as a StarTac flip phone.

 

[kylemoto]

Originally posted by Bohrn
::gstspyder1998;

::kylemoto; I was thinking along the same lines as what you said. I think I will drill, unless someone tells me otherwise?? I guesss I will have to re-calibrate, dangit, I painted nice + - marks and a 0 reference point. Oh well, I have some laquer thinner and more red paint

thanx for the help guys

Bohrn, please send pics when done! Should be nice to loook at.

Also, I was thinking some more. The relief hole shouldn't be very big - the larger this hols is the less pressure the wastgate will see! If it too big the wastegate never shuts!

Kyle

 

[Bohrn]

well, I don't have a digital camera, so it will be a while till I develope the film and scan it in.

as for the hole, I will experiment, starting at 1/16th" as it is the smallest bit I have hehe.

as for the size, too big would make the wastegate never open, right?? the boost from the turbo would all blow out the hole and none would go down the pipe to the wastegate actuator, thereby never telling it to open the wastegate.

again tho, I am very new at this, so please advise...

 

[kylemoto]

Originally posted by Bohrn
well, I don't have a digital camera, so it will be a while till I develope the film and scan it in.

as for the hole, I will experiment, starting at 1/16th" as it is the smallest bit I have hehe.

as for the size, too big would make the wastegate never open, right?? the boost from the turbo would all blow out the hole and none would go down the pipe to the wastegate actuator, thereby never telling it to open the wastegate.

again tho, I am very new at this, so please advise...

You are right! Too big a relief hole and the wastegate never opens. Too much boost! The 1/16 inch drill should be a good starting point

Kyle

 

[InferiorWang]

ive seen that pic before. I also have a link to another page that shows u how to make an MBC just a little different but with the same concept.
http://www.c-speedracing.com/howto/mbc/mbc.html
hope this helps

 

[Bohrn]

yea, I saw that setup too, but I decided that I liked the idea of having a seperate body section and an adjusting screw with a locking nut on it. Altho the c-speedracing one is simpler and cheaper. It doesn't have a bleeder hole tho, I wonder if he has the same problem my setup does?

 

[Atari007]

Wow... It is kind of a coinsidence <sp?> but I just built the same exact MBC the other day and it does...well... the same exact thing as it is doing to you.... it kinda scared me a little bit, and I dont like it being that flakey, so... I just ordered a JoeP last night and will install it this week Im tired of messing with the home-made one... hehe...

 

[Bohrn]

I've pretty much got it licked, I hope. I drilled that 1/16th" hole in the body of the MBC after the ball valve. I then had WAY too much boost. So I backed the spring way off, and started over. I am now able to get 75% throttle in 3rd gear now at 16psi. I need to cut another link outta the spring tho as I am running outta threads on the adjusting screw.

Also I am gonna replace the vacuum hose going to the wastegate actuator with a larger, sturdier hose, as I think I am loosing some signal steadyness, (for lack of a better term), due to the skinny, soft hose now in place. I have a much better one coming into the MBC.

Aside from soft-footing it tho, it is alot better. The car is faster now at 50-65% throttle than it was before my $20 harwarestore special at full throttle. Great stuff.

How do I know, besides watching the boost guage(Autometer Phantom) if I am hurting my car?? Do I need an air/fuel ratio guage?? I wonder about long pulls at part throttle with 15psi on. I also wonder about those 18-22psi spikes I had before I had it tuned a bit. Are there some do's and don'ts now that I should know about?? And what do I tell my wife or dad to do when they drive my car?? Or when I take it into a shop??

thanx guys

John