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First time turbo tuning noob question, wastegate opening?

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Road tuning Link G4X and just starting to get into positive territory in the map. I have my rpm limit at 5000. At about 70% throttle I took the load to about 140 kpa and the power began to cut out. I initially thought I hit the rev limit. I was watching lambda and it stayed below 1 for the whole pull. I did a second pull but watched rpm and it started cutting at around 4500. Each time I pulled off the throttle when I felt it cut out. I checked my logs and saw that MAP leveled off or dropped before rpm peaked. So, my conclusion is my wastegate is opening. I am just on the spring right now without a boost controller. Spring is supposed to be 10 psi. Boost pressure is leveling off at 6.5 psi or less. Is my conclusion correct?

Well could be...

Well, for some reason the forum won't allow me to attach anything, so...

If the forum doesnt allow the extension then put your files inside a zip folder.

Log. Earlier it wouldn't let me attach anything.

Attached Files

You have hit the RPM limit in one of your pulls in the log at about time mark 2:02. With the RPM limit set at 5000, and the default control range of 200RPM, it will start to apply a limit at 4800. Otherwise I dont see anything else in there that would effect boost - although in all of your pulls except the last one you have lifted off well before boost has leveled off so it is hard to see if there is actually a problem of not.

Thank you. I know you don't have the benefit of experiencing the event, but the log kind of parallels what I felt. Yes, the last one was a let's make sure it is dropping off pull. And in the last pull, it sure looks like MAP levels off while still holding throttle and rpm still climbing.

Been a storm here for the past two days with some snow. I'll up my rpm limit and try a few more after the weather improves.

Yes I tend to lift off. Surprised by the rpm limit for one and when the boost hits, it made me pee a little.

You really need some data at WOT to prove what's happening here. Since you haven't gone beyond about 70% TPS, depending where your wastegate pressure source is taken from, this can affect when the wastegate opens. For example with the throttle at 70% the boost pre-throttle will likely be a little higher than reported by the MAP sensor, hence if the wastegate pressure source is pre throttle then the wastegate would tend to open a little earlier. I'd also be inclined to check your BOV isn't blowing open or you have a boost leak.

The watsgate spring is only a guide to the actual boost you'll achieve since it's also affected by EMAP as this tends to push the wastegate valve open. So for the same spring, a large turbo with low EMAP will tend to see higher boost than a small turbo with higher EMAP.

Thank you, Andre. I will keep those points in mind. I tested the spring with diaphragm pressure before install and it started to open at 12 psi and was fully open at 14 psi. I did consider that EMAP was going to help open the WG, and now realize the back pressure could be helping a lot more than expected. I thought about the BOV as well, but that is getting positive pressure to the top of the diaphragm during boost, and shouldn't open. I can hear it open when I let off. Wouldn't a boost leak have to be significant (such as the BOV opening) to cause the MAP to level off?

Cut or drop off power?

Could there be a restriction limiting intake air flow or exhaust? Do you have a filter or cold air feed, as it wouldn't be the first time someone was caught by a hose collapsing if it's a little restrictive already.

The lambda being steady would seem to eliminate a fuel or ignition problem, as it'd show it leaning out.

As Adam pointed out, the traces don't seem to match what you're thinking - you're backing off early, before there's any sign of the boost dropping, and it them seems to drop as a result of less throttle being used?

Might be completely missing the point, though - it's darn late/early and well past bedtime...

Appreciate the help, Gord. I do have a filter. It is a dual element and has a lot of surface area and I'm pretty sure the inlet coupler is too short to collapse. Any other boots or couplers are under pressure.

The early throttle release happened in the first pull when the rpm limit kicked in. But, on the second pull, the MAP clearly levels off before I let off. Cut or drop off? I guess the terms will have to be defined. During the pull there is steady acceleration until whatever happens, happens. It feels like a sharp drop in acceleration, like the torque goes away. Both instances, the rpm limit and the other, prompted my release of the throttle.

Much of the snow has melted so I may be able to try again tomorrow. Thanks guys.

Well, I must have been hitting the rev limit. I turned it up, although I still didn't go over 5k, and no perceivable cut in power. But, the MAP still levels off pretty low in my opinion. This time with 100% throttle, it went up to 128 kpa then leveled off. At my elevation, atmospheric is 79 kpa, so 49 kpa of boost. 7 psi on an advertised 10 psi spring.

It is about time to put this thing away for winter. I'll check for boost leaks and hook up the boost control while she's in the barn.