proxlamus© Posted June 12, 2006 Share Posted June 12, 2006 so i am having some overboost issues and I have a manual ball and spring boost controller... I have it as loose as I can, and I am still hitting 19psi + with my Holset HY35W.. If I recall reading bastaads older posts... should I drill a small vent hole on the MBC? if so.. where would be an ideal spot? This is the boost controller I have Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 12, 2006 Share Posted June 12, 2006 Drill the tiny hole in the line that goes to the actuator. I drilled it in the hex of the barbed fitting. Use a very small bit. Maybe 1/64" to start. On your photo. The barb fitting on the right gets drilled. To calibrate it, hook a bike pump or compressor and a gauge to the bottom fitting and set the knob to whatever cracking psi you want. Just listen for air opening the ball valve. Quote Link to comment Share on other sites More sharing options...
mtcookson Posted June 12, 2006 Share Posted June 12, 2006 What type of wastegate are you using? Quote Link to comment Share on other sites More sharing options...
Nigel Posted June 12, 2006 Share Posted June 12, 2006 The hole is to prevent pressure being trapped between the MBC and the wastegate actuator, holding it open and slowing boost response. If you're experiencing boost spikes, drilling that hole won't help. If anything, it will make it worse. Are you sure the MBC is the problem? What happens if you bypass it? Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 12, 2006 Share Posted June 12, 2006 Boost spikes can be caused by: -A tight actuator or wastegate. -A restrictive hose/fitting in the line to the actuator. -Too long of a hose leading to the actuator. -Too small of a wastegate. -Sticking BOV if it holds open a little and then snaps shut...like mine did. BTW, you DO need that vent hole no matter what or the wastegate will stay open. Quote Link to comment Share on other sites More sharing options...
Thumper Posted June 12, 2006 Share Posted June 12, 2006 Drilling a vent hole in the mbc will not fix a overboost/boost creep problem. It will fix a boost spike or boost drop but not boost creep. Your boost creep is the same problem 73turbo240z and I had. The wastegate isn't flowing enough air to lower the boost. Remember this turbo was used on a 5.9l I6 running at 18psi stock. I ported the wastegate just about to the max. I don't know if you can port it more. Your only two choices is try to port it more or go external. Its weird that it was ok on my car and its creeping on yours. The either means your engine is flowing less air than mine, your exhaust is more free flowing, or your engine is burning more exhaust from a more efficient burn than mine. What exhaust are you running right now? Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted June 12, 2006 Author Share Posted June 12, 2006 I am running a full 3" exhuast.. no pre muffler or resonator.. just an Apexi N1 muffler.. the way my boost is being handled right now is 10psi in 1st gear, 15-20psi in 2nd and shoots to 20psi + in 3rd, 4th, 5th.... the wastegate is the stock internal wastegate on the Holset turbo.. and the wastegate actuator is the stock 280zx turbo actuator... i'll try running it without the boost controller and see what happens... Fortunatly I have overboost protection on megasquirt right now.. so it cuts fuel and spark at 17.5psi ... but I hate doin that to my engine Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 13, 2006 Share Posted June 13, 2006 Your wastegate is not opening quick enough or it's not flowing enough. It's that simple. I wish there was more I could say but that's it. Tripple check that your actuator is in healthy shape. You might want a larger actuator. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted June 13, 2006 Author Share Posted June 13, 2006 I totally removed the MBC from the system and am running 5psi and it stays at 5psi.. no spikes.. then the mbc is on.. loose or tight ant 20psi again I have searched all over and no one has given me a good answer.. I know the MBC needs to be hookd up properly.. but even the Joe MBC has no instructions to check.. Does the bottom fitting one go to the wastegate or vacuum/boost source? LoL thanks guys Im willing to bet.. the MBC is on backwards Quote Link to comment Share on other sites More sharing options...
Nigel Posted June 13, 2006 Share Posted June 13, 2006 The fitting opposite the adjustment knob should connect to the boost source (intake manifold), and the side fitting goes to the wastegate actuator... Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted June 13, 2006 Author Share Posted June 13, 2006 thanks Nigel.. i sent Joe P MBC an email and they said it almost WORD for word as you did.. hmm.. I'll try shortening the lines and see what I can do Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted June 13, 2006 Author Share Posted June 13, 2006 damnit i keep typing stuff which makes no sense... is this diagram right or is it backwards? Quote Link to comment Share on other sites More sharing options...
Nigel Posted June 13, 2006 Share Posted June 13, 2006 That should be correct... Nigel Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 13, 2006 Share Posted June 13, 2006 I gave you very good advice...did you try it? Bicycle pump or compressor and a gauge to make sure the valve is opening at the set pressure. Hook up a peice of hose with a gauge to the source (bottom fitting) and pump to 15psi (or whatever) and it should start bleeding out the other side. Where are you connecting for boost source? Mine connects right on the exit of the compressor for the fastest response. Also push a little stick inside the bottom fitting and push up gently to open the ball. Blow into the other side fittng to make sure you are getting flow when the ball unseats. If you dont understand how it works...read here and look at the diagrams. http://www.well.com/~mosk/boost.htm Quote Link to comment Share on other sites More sharing options...
mobythevan Posted June 13, 2006 Share Posted June 13, 2006 haha, those joe mama MBC suck , I have one on my talon and then ball slipped by the spring and shut the output side permanently, had to take it apart and put the ball back in the correct place. I kept adjusting and adjusting and guess what, always too much boost, until I fixed the ball. Verify the ball is working correctly like the others say and use a compressor or something. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted June 13, 2006 Author Share Posted June 13, 2006 you guys have given me SUPERB advice... ughmm.. but one problem.. I had the boost controller on *cough* BACKWARDS *cough* .. I know stupid stupid move.. but its so easy to mix up.. Im going to pick up some more vacuum lines in a few minutes .. the battery stopped holding charge Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 13, 2006 Share Posted June 13, 2006 DoH! Don't worry, shyt happens. Now back to the drilling the hole thing...make sure you drill a little pinhole or you will be posting about boost falling off in between shifts. Drill it on the "To Wastegate" side. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted June 13, 2006 Author Share Posted June 13, 2006 Results are... holds 16psi dead even... NO spikes... even with a MBC !!! hot damn! im so dumb.. hhaha THANK you soo much guys Quote Link to comment Share on other sites More sharing options...
Thumper Posted June 13, 2006 Share Posted June 13, 2006 I'm glad it wasn't the boost creep I experienced. That would have been a PIA. Have you had a chance to tune it better to get better boost response? Quote Link to comment Share on other sites More sharing options...
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