stupid inconsistent boost...

ok here is the deal... When I built the k car i had inconsistent boost... Id sometimes get 10psi... sometimes Id get 15psi... I chocked it up to the TU 3" SV puck being loose and catching on the hole... I then fixed that (stainless wire behind the puck retainer) and it was all tightened up but still had a little play to seat flat against the ex housing. still have inconsistent boost control. 1st gear i never get full boost but i contribute that to the lack of loading and the slightly rich fuel curve... no big deal. ive tried different graingers and cleaned them and none are consistent. sometimes I get a nice, clean 15psi with little spiking when I roll on the throttle, sometimes when I have 15psi in 2nd and then I shift to 3rd I get 10psi once shifting etc. annoying.

fast forward to today. I just built a sweet new boost controller (i'll post about it later) and I install it. again... inconsistent boost control. sometimes 10, sometimes 17 (where I set it) and sometimes 15. sometimes if I roll onto it and it boost comes up really fast it will be more consistent.

here is the setup. TU 3" SV (doubt thats the issue), T1 large wastegate can on a stock T3 with the .63 a/r housing. I blew and sucked on the wastegate can feed hose and I cant detect any leak in the diaphram. I have short hoses from the boost source and the MBC and to the wastegate can... 12-15" tops overall. I dont think the boost controller leaks. I put in the ball and tightened down the allen screw and I blew on the input side and its air tight from what I can see.

only potential problems... I have the radio shack alligator clips holding the wastegate arm to the SV peg. possible binding? dont think so. I polished the arm at the end to make sure its smooth.

my boost source is a T in the vac line to the brake booster. I dont think thats an issue either. I just dont know what it could be. everything is cleaned out with electronics cleaner (mild solvent) and dried and reassembled and it still does this crap. all of the graingers and mbc's that ive put on the car have been inconsistent so I think it has to be some external source.

oh yeah.. I have a small restrictor used as a bleed between the MBC and the wastegate can to make sure its not held open.

any possible solutions? i think I might go to my buddies house and use his compressor and do some serious tests on the whole system.

thanks

Brian

I am no expert but I see 2 things-one is the restrictor and 2 is having it hooked up to manifold vacuum. I would get rid of the restrictor and use the compressor for the signal source.

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Originally Posted by turbovanman

...I would get rid of the restrictor...

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Won't work.
Without some sort of a small bleed to atmosphere (restrictor), boost pressure will be held between the mbc and wastgate can causing the wastgate to stay open all the time. It's the same reason for the small hole you have to drill into the fitting if you're building a boost control out of a grainger.

Brian,
You might try experimenting with the size of your bleed. I'd be tempted to try something a little bigger to start and see how that affects it.
Also, I agree with Simon's suggestion about using the compressor as the source for your boost control.
HTH,

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Originally Posted by tonyz2897

Won't work.
Without some sort of a small bleed to atmosphere (restrictor), boost pressure will be held between the mbc and wastgate can causing the wastgate to stay open all the time. It's the same reason for the small hole you have to drill into the fitting if you're building a boost control out of a grainger.

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Ok but what if the MBC has the hole like mine does?

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Originally Posted by turbovanman

Ok but what if the MBC has the hole like mine does?

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That's a different story. Providing it has the right size hole then it should be fine as-is.

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Originally Posted by Aries_Turbo

fast forward to today. I just built a sweet new boost controller

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That leads me to believe that he added the restrictor as a bleed because the boost controller he built didn't have the drilled hole.
I've done it myself. Use a "T" in the line between the mbc and the wastegate can with a restrictor open to atmosphere. It's a good solution if you don't have the proper size bit to drill a bleed hole. The only problem is that they can be a little picky about restrictor size. It takes a little experimenting to get it just right.

correct guys... I have the restrictor T'd in to relieve the pressure as the boost controller doesnt have one.

I also dont have the boost source from the turbo.. I cant remember if I capped that off or if I plugged the actual port on the turbo.. I'll try those things.

Im also going to go to the store and get a bunch of E clips for the rod/peg deal.... Im gonna hook up an air compressor to the system too and see if the wastegate is moving smoothly without binding.

also what hole is the proper size for the bleed? I had an adjustable bleed valve on my last setup so I could tune to the size but I cant find it anymore.

Thanks guys.

Brian

According to Gus' site it should be about .020.
HTH,

yeah I remember that.. I have whatever one of the stock restrictors from another vac harness is... the blue plastic one with the brass piece plugged in. I might try a mig welding tip.. that is .023" if im not mistaken.

Thanks

Brian

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Originally Posted by Aries_Turbo

yeah I remember that.. I have whatever one of the stock restrictors from another vac harness is... the blue plastic one with the brass piece plugged in. I might try a mig welding tip.. that is .023" if im not mistaken.

Thanks

Brian

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You can get different mig tip sizes so you should be able to get one pretty close.

yeah the local shop has the .023... thats why I mentioned it...

I really think its partially the wastegate arm binding though. im gonna play with it tomorrow.

Brian

The mig welding tips work very well. Although they are supposedly a couple thou larger than what the package says since the .XXX dia. wire must feed through it.

I have never had a problem with running manifold vac to the WG.

Even if you do get the boost to a more consistant operation, I still reccomend the compressed air trick for locating leaks. I have been thinking about it for a while but finally tried it today. I found three pretty sizeable leaks:eek: and one small one at the throttle body shaft. I would imagine the car is going to run just a bit better with all the holes plugged:o I tested mine at 45 PSI but that may be a bit much for your set up depending on your clamps/tubing...

Quote:

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Originally Posted by Aries_Turbo

yeah the local shop has the .023... thats why I mentioned it...

I really think its partially the wastegate arm binding though. im gonna play with it tomorrow.

Brian

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Something else you can try is to crimp the ends of the contact tubes slightly with a pair of vise grips. I had a bunch of large contact tubes that accumulated from a previous job mig welding aluminum. They wouldn't fit my machine, so I ended up using them for misc. stuff. One of the uses was for restrictors. They were too big for much of anything as the were but by slightly crimping the ends they could be made to work. Another option would be to crimp one completely shut and then drill the proper size hole if you have a set of jet drills. .023 should be pretty close, but if you end up needing to experiment, you can without having to buy a bunch of different size restrictors.

yeah I picked up some .025" ones from lowes... I'll tell you what.. they are a bit larger than what I was using before so we'll see. I got some changes to make.

yeah I outta pressure test the system some time. I have beads welded on every pipe and t-bar hose clamps. I doubt I'll pop them.

Brian