Boost peaks, then drops.

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Dan_Gyoba

Turbo Swapper
Aug 9, 2007
1,836
0
0
Alberta
www.gyoba.com
Looking for suggestions here.

I've got one of the older Turbonetics bolt-ons with a 60-1 compressor on the front of it. Unsure what the A/R is on the hot-side turbine, but I think that it's 0.50. It's got an internal wastegate, connected to a BOSS turbo elbow, and RT downpipe. Good exhaust after that, so should be good. IC piping is all 2.5" including Spearco replica IC.

Inexpensive MBC, which is possibly to blame... but I'm not sure.

MBC is dialed in for 15 lbs, and when accelerating, the gauge will get to 15 lbs at about 3500 RPM, then drop back to 10 lbs or so by 6000. This is somewhat annoying, as I'd like it to hold boost. (It will hit and hold maybe 8 lbs without the boost controller in there at all.)

I figure that this means that the wastegate isn't closing fast enough, but not sure what I can to to help with this. The MBC is the type with the ball and spring. There's a small relief hole drilled, which I gather is supposed to relieve pressure on the wastegate actuator, but in this case, doesn't seem to be doing so fast enough.

I've considered a small increase in the vent hole size, as this should relieve pressure faster, thereby allowing the wastegate to close more quickly, but since when the wastegate needs to be open, that hole is basically a boost leak (Albeit a tiny one) which I don't really want to make worse if It's not going to help.

I suppose that the controller is cheap enough that I could afford to experiment. It'd suck if it's something else with the wastegate and buying a more expensive electronic controller won't help any.

Suggestions? Comments? All appreciated and given the consideration they deserve.
 
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Dan_Gyoba

Turbo Swapper
Aug 9, 2007
1,836
0
0
Alberta
www.gyoba.com
Did some experimentation, and I've determined that I now have an exhaust leak. :( This is not the source of the problem, but it's made spooling somewhat slower than the last time I had the car out, so it's harder to test stuff.

Pretty sure the exhaust leak came from one of the fine roads around here, where the bottom of the downpipe hit when the ruts in the road got too deep. :( I think it put too much stress on the manifold, and I'll probably have to helicoil the manifold studs. I'll see if I can apply any torque to them when things cool down.

Anyway, it does seem to be the boost controller not releasing pressure fast enough.

Anyway, what I'd like to know is this:

The wastegate controller has 2 ports on it. One opens the wastegate if there's pressure, and the other seems to close it. What I'd like to know is if there's a better way to connect a boost controller, even if it's a different type of boost controller.

It seems that the wastegate then opens or closes based on the difference in pressure between the 2 ports. Since the one is open right now, the pressure is being compared between the IC piping and atmosphere. It seems to me that if I were able to apply a regulated pressure to the atmosphere side, then the wastegate would open once the IC plumbing pressure exceeded that (Plus about 5 PSI or so) Is there a way to do that? How about a way to change that pressure from the driver's seat, so that boost control can be altered while driving? After all, the max amount of boost that I'd like to have the option to run isn't necessarily what I want to drive to the grocery store with.

I'd also accept recommendations for electronic boost controllers (Preferably inexpensive ones.)
 
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