I Want More Power Out Of My Rb20 What Mods Are Next?
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By Dose Pipe Sutututu · Posted
This is the other log file, if only we had exhaust manifold pressure - would understand what's going on a bit better Can you take a screenshot of your wastegate setup in the Kebabtech? Engine Functions --> Boost Control (looks like this): -
You just need a datalogger of some sort. A handheld oscilloscope could do it, because it will make the trace visible on screen, so you can look at the peak, or whatever you need to look at. And there are cheap USB voltage loggers available too. You could get a 2 channel one and press a button to feed voltage to the second channel at points that you want to check the sensor voltage, when you knew what the guage was saying, for example. -
By Dose Pipe Sutututu · Posted
it's not the issue with making power, it's the issue with controlling boost, and this isn't the first time I've seen a 6Boost having issue with controlling boost down low. The boost control here looks interesting. Looking at your logs, looks like it's set to open loop boost control strategy (which is fine). We can see VCT being kept on till about 6600RPM (no issue with that). Ignition timing (I'm assuming this is E85, seems within reason too, nothing too low, causing hot EGTS and boost spiking). There's about 15 degrees of advance when your boost shoots up, however can't be this as the timing isn't single digits. I'm assuming there's no EMAP data, as I wasn't able to find it in the logs. We can see your tuner sets the WG DC to 0% after 4300RPM, trying to control boost. My thoughts, what frequency is your wastegate set to? AND why aren't you using both ports for better control? -
While that sounds reasonable, this is definitely a boost control problem, but the real question is why are you having the boost control problem? Which is why I pondered the idea that there's a problem at ~4000rpm related to head flow. In that instance, you are not yet under boost control - it's still ramping up and the wastegate is yet to gain authority. So, I'm thinking that if the wastegate is not yet open enough to execute control, but the compressor has somehow managed ot make a lot of flow, and the intake side of the head doesn't flow as well as the exhaust side (more on that later), then presto, high MAP (read that as boost overshoot). I have a number of further thoughts. I use butterfly valves in industrial applications ALL THE TIME. They have a very non-linear flow curve. That is to say that there is a linear-ish region in the middle of their opening range, where a 1% change in opening will cause a reasonably similar change in flow rate, from one place to another. So, maybe between 30% open and 60% open, that 1% change in opening gives you a similar 2% change in flow. (That 2% is pulled out of my bum, and is 2% of the maximum flow capacity of the valve, not 2% of the flow that happens to be going through the valve at that moment). That means that at 30% open, a 1% change in opening will give you a larger relative flow increase (relative to the flow going through the valve right then) compared to the same increment in opening giving you the same increment in flow in outright flow units. But at 60% opening, that extra 2% of max flow is relatively less than 1/2 the increase at 30% opening. Does that make sense? It doesn't matter if it doesn't because it's not the main point anyway. Below and above the linear-ish range in the middle, the opening-flow curve becomes quite...curved. Here's a typical butterfy valve flow curve. Note that there is a very low slope at the bottom end, quite steep linear-ish slope in the middle, then it rolls off to a low slope at the top. This curve shows the "gain" that you get from a butterfly valve as a function of opening%. Note the massive spike in the curve at 30%. That's the point I was making above that could be hard to understand. So here's the point I'm trying to make. I don't know if a butterfly valve is actually a good candiate for a wastegate. A poppet valve of some sort has a very linear flow curve as a function of opening %. It can't be anyelse but linear. It moves linearly and the flow area increases linearly with opening %. I can't find a useful enough CV curve for a poppet valve that you could compare against the one I showed for the butterfly, but you can pretty much imagine that it will not have that lazy, slow increase in flow as it comes off the seat. It will start flowing straight away and increase flow very noticeably with every increase in opening%. So, in your application, you're coming up onto boost, the wastegate is closed. Boost ramps up quite quickly, because that's really what we want, and all of a sudden it is approaching target boost and the thing needs to open. So it starts opening, and ... bugger all flow. And it opens some more, and bugger all more flow. And all the while time is passing, boost is overshooting further, and then finally the WG opens to the point where the curve starts to slope upwards and it gains authority amd the overshoot is brought under control and goes away, but now the bloody thing is too open and it has to go back the other way and that's hy you get that bathtub curve in your boost plot. My position here is that the straight gate is perhaps not teh good idea it looks like. It might work fine in some cases, and it might struggle in others. Now, back to the head flow. I worry that the pissy little NA Neo inlet ports, coupled with the not-very-aggressive Neo turbo cam, mean that the inlet side is simply not matched to the slightly ported exhaust side coupled with somewhat longer duration cam. And that is not even beginning to address the possibility that the overlap/relative timing of those two mismatched cams might make that all the worse at around 4000rpm, and not be quite so bad at high rpm. I would be dropping in at least a 260 cam in the inlet, if not larger, see what happens. I'd also be thinking very hard about pulling the straight gate off, banging a normal gate on there and letting it vent to the wild, just as an experiment.
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Not a problem at all Lithium, I appreciate your help regardless. I've pulled a small part of a log where the target pressure was 28psi and it spiked to 36.4psi. I've only just begun using Data Log Viewer so if I'm sending this in the wrong format let me know.
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