Boost spike, fade or leak!

[hottboost]

I have did boost leak test! ( fixed leak at bov flange ) When I go wot in 3rd boost will spike to 25psi then drop right back to 19psi. I have changed boost controlers ( now using hallman pro ), tried adjusting wastegate actuator, and tried adjusting bov. Guys I am stuck. I used to spike about 3 psi. What could be causing this?? I have checked turbo for shaft play and there is no in and out and very little side to side. I am ready to take it to a shop but I just hate to let other people work on my car. Any other ideas would be great!

Carl

 

[CanadianTSi]

Classic case of spike.

Are you tee'd into your BOV line for the MBC or does it have its own source (compressor housing) ? Also try to keep your MBC lines as short as possible.

 

[hottboost]

It is running off of the compressor housing. The lines for the mbc are about 8 in each. What so you recomend for me to do. Also once apon a time I ran t'd to bov and It controled it alot better only 3 psi spike. What can I do?? Thanks for the help.

 

[Mr Peepers]

I have two ideas on how to reduce boost spike, only ideas, so someone please give me feedback if they are plausible.

Adjust the wastgate(you stated it was adjustable) to a stiffer setting.
Why? Because the MBC will have to work harder against the pressure relief(bleeder hole) on the wastegate side to overcome the spring. Hopefully causing it to start opening the wastegate sooner, and more progressively to combat the pressure spike.
Note: The MBC will have to be turned down to balance out the extra pressure required to move the wastegate.

Another idea. I believe the chance of a MBC being prone to boost spike mainly depends on the weight of the spring and ball, and the size of the pressure relief hole. If you have the tools and are confident enough in your abilities, you could drill out the pressure relief hole one size larger. You will find this hole somewhere near the wastegate side of the boost controller, and it's usually about 1/16" in diameter. If you find the hole to be 1/16"(find out by seeing which bit fits) carefully drill it out to 5/64" with the MBC apart and clean out any debris when finished. Hook everything back up and see if it reduces the spike. Repeat maybe one more time to the next size bit if it helped but didn't completely cure, although I wouldn't go much farther.
Why? Because the MBC will need to open sooner, hopefully opening the wastegate sooner and more progressively until peak boost pressure is reached.
Note: The MBC will also have to be turned down to balance out the pressure bled from the increased size of the relief.

If you have done everything else and my ideas are confirmed, maybe you could give it a shot, I would test it on my car but the engine is missing

 

[hottboost]

I am not a wiseman, but I was following your previous thread on the same issue. Have you tried shortening the lines to and from your mbc as much as possible? You said you've done a boost leak test but that is often irrelevant to spiking(still one of the best things you can do anyway). What about tapping the line for your mbc as close the the compressor housing as possible? Please give more information.

I have two ideas on how to reduce boost spike, only ideas, so someone please give me feedback if they are plausible.

Adjust the wastgate(you stated it was adjustable) to a stiffer setting.
Why? Because the mbc will have to work harder against the pressure relief on the wastegate side to overcome the spring. Hopefully causing it to start opening the wastegate sooner, and more progressively.
Note: The mbc will have to be turned down to balance out the extra pressure required to move the wastegate.

Another idea. I believe the chance of a mbc being prone to boost spike mainly depends on the weight of the spring and ball, and the size of the pressure relief hole. If you have to tools and are confident enough in your abilities, you could drill out the pressure relief hole one size larger. You will find this hole somewhere near the wastegate side of the boost controller, and it's usually about 1/16" in diameter. If you find the hole to be 1/16"(find out by seeing which bit fits) carefully drill it out to 5/64". Take the mbc apart and clean out any debris. Hook everything back up and see if it reduces the creep. Repeat maybe one more time to the next size bit if it helped but didn't completely cure, although I wouldn't go much farther.
Why? Because the mbc will need to open sooner, hopefully opening the wastegate sooner and more progressively until peak boost pressure is reached.
Note: the mbc will also have to be turned down to balance out the pressure bled from the increased size of the relief.

If you have done everything else and my ideas are confirmed, maybe you could give it a shot, I would try it on my car but the engine is missing

I shortened the actuator arm as far as possible befor and it would just affect how I adjusted the mbc. Spike was still the same. The mbc is new so I know it doest have debris in it. I may try to do that and see if it works. Is it worth it to go back to being t'd to the bov?

 

[Mr Peepers]

I would do testing on my car for the drilling part, but I can't condone you trying it without me knowing if it worked for sure, or even having any other side effects. Also, I don't want to risk you drilling too large without having an easy way to make the hole smaller again. I would wait until there is some input from a wiseman. Like I said, they are only ideas.

When you said adjustable I assumed external. The reason I said to clean out any debris was because after drilling it there may be metal shavings. I would have the mbc apart when I drilled it anyway.

-Matt

 

[hottboost]

I have two ideas on how to reduce boost spike, only ideas, so someone please give me feedback if they are plausible.



Another idea. I believe the chance of a MBC being prone to boost spike mainly depends on the weight of the spring and ball, and the size of the pressure relief hole. If you have the tools and are confident enough in your abilities, you could drill out the pressure relief hole one size larger. You will find this hole somewhere near the wastegate side of the boost controller, and it's usually about 1/16" in diameter. If you find the hole to be 1/16"(find out by seeing which bit fits) carefully drill it out to 5/64" with the MBC apart and clean out any debris when finished. Hook everything back up and see if it reduces the creep. Repeat maybe one more time to the next size bit if it helped but didn't completely cure, although I wouldn't go much farther.
Why? Because the MBC will need to open sooner, hopefully opening the wastegate sooner and more progressively until peak boost pressure is reached.
Note: The MBC will also have to be turned down to balance out the pressure bled from the increased size of the relief.

If you have done everything else and my ideas are confirmed, maybe you could give it a shot, I would test it on my car but the engine is missing

Good job. I drilled out the hole on the mbc ( 5/64 ) and it help lower the spike to about 4-5 psi. Thanks. Do you think I should go to the next size and drill it out a little bigger???

Carl

 

[Mr Peepers]

Only if you have a way to make the hole smaller again if it doesn't work out. If I would do it on my car, I would go as far as making it adjustable with a screw etc for testing purposes. If you did make it any larger(or even now) I would recommend routing it back into your intake behind the MAF(there is a nipple that should be blocked off) and before the turbo inlet. When the you are under boost it acts as a boost leak, even with new ball and spring MBC's. Enlarging this hole makes it act a little more like a bleeder MBC so the is some sacrifice. Glad to hear it worked out!

3/32" would be the next size up, if you want to try it please post your findings.

 

[hottboost]

I did it with my homemade mbc and it really didnt help any more so Ill leave the hallman alone for now. Thanks for your help this is a good thread. I would like to see a few more people try it or give a little insight as this could be a good tech article.