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Thread: boost control

  1. #1
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    boost control

    I have been messing with trying to get boost under control and come on to boost real fast but haven't had much luck. I have raised the max airflow limit to 6000 and also lowered everything it to 2000 and that didn't seem to change anything. The only thing that I have noticed that changes the boost is changing the min. wastegate duty. If I have a lower number in there it seems real laggy, and if I put it at a higher number like 80 it comes into boost fast but seems like the wastegate is just held shut and isn't controlling boost. I don't have a boost gauge so I can't see anything over what the map sensor can read. I would like it to just come onto boost quick and hold at like 35 pounds. Anyone know what I could do to achieve that, or what tables I should be changing. thanks

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    You also have your charge air flow tables, which control the wastegate solenoid, then fueling has to be high enough to push the turbo harder. Timing will affect boost as well.

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    Work with the fuel tuning, get it to come in a bit sooner which will help to lite the charger faster, timing will help too for sure, but to much will get you spark knock with gasers, you can raise the cylinder pressures to much with a diesel and cause all kinds of bad stuff. So be mindful with your tuning far as timing goes.

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    Are you talking about one of the tables under the wastegate compensation? Like would lowering the turbo speed values make the wastegate open sooner?

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    When I put the min. duty up to 80 it has real good responds, but it just maxes out my map sensor at 51.4 psi absolute. So I can't see how much boost it is really going up to. I would like it be running like 35 pounds of boost. I don't want to be pushing the charger too hard and over spin the turbo.

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    What?s your model year?

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    Quote Originally Posted by ryan_axberg View Post
    Are you talking about one of the tables under the wastegate compensation? Like would lowering the turbo speed values make the wastegate open sooner?
    Don?t need to mess with the turbo speed settings.

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    its an 05
    What tables do you usually use?

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    If you go to the airflow tab, all the tables under estimated airflow, those are a part of what determines your final wastegate solenoid position to control boost/airflow.

    If you subtract your map absolute pressure from your baro pressure you?ll have your boost pressure.

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    cool thanks Jim, I'll give that a shot

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    I just lowered all of the estimated airflows down alot and that didn't work. then I lowered the turbo speed table down 30 percent also and that didn't lower my boost. I just checked and my vaccum line is in good shape and connected on both sides. I have a log and a tune file. Can you see anything that seems off to you. It feels powerful, I just want boost to be under control.

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    I would invest in a boost gauge and pyro. That turbo speed parameter shouldn?t be available, it?s meant for vgt turbo control. You?ll need to use timing and fueling control to control max boost. You are probably pushing things beyond what the wastegate solenoid can effectively control.

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    I have a pyrometer and egts are even lower than they were with a stock tune, so I'm not concerned about that. And for boost I would just like to have it sit around 35 psi. The map sensor can read 51.4 absolute pressure, so thats like 37 psi. I was considering a while back to put a external wastegate on the manifold and welding shut the internal wastegate and just put like a 35 pound spring on it if I can't get boost sorted. When you say using timing and fuel, that would mean more timing so its not getting as much heat and pressure in the manifold to spool up the turbo and less fuel? I want to make as much power as I can on the setup that I have. I made my own 4 inch intake and it has 4 inch straight pipe, I wondering if those things plus the stock wastegate just isn't able to let enough exhaust bypass the turbo to keep it at the boost I want. What is your experience with a max effort tune on a stock turbo setup?

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    Max effort on stock turbo and injectors is about 3200us duration, 175-180MPa fuel pressure and 32* main timing, can go higher on timing but I would use a dyno to watch what happens with your torque as you bump up timing. Something to keep in mind if just using the map sensor and a baro sensor to determine boost pressure is once you push the turbo hard enough it sucks baro down, it?s a giant vacuum on the ambient air density at the baro sensor so it?s not going to be highly accurate as to what you are really getting for boost when pushing it.

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    thats intersting. I will have to get one and see how much boost im really getting. How much boost do you think is safe on the stock turbo? Maybe like 40 psi max do you think? And I'm at sea level so the turbo wouldn't have to be working as hard for 40 pounds of boost compared to elevation

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    40 psi max on stock turbo, you?ll be right on the edge of what it can push. Turbos move air more easily at higher altitudes than they do at sea level.

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    the shaft speed would be a bit higher for truck that is at 1000 feet elevation compared to where I am at which would put it in a different and I'm sure more inefficient spot on the compressor map

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    Quote Originally Posted by ryan_axberg View Post
    thats intersting. I will have to get one and see how much boost im really getting. How much boost do you think is safe on the stock turbo? Maybe like 40 psi max do you think? And I'm at sea level so the turbo wouldn't have to be working as hard for 40 pounds of boost compared to elevation
    40 PSI is at seal level and 40 psi at elevation are two different things. If our starting absolute is 11.9PSI at elevation 51.9psi absolute would be 40 psi above it. But at sea level if our starting was 14.7 obviously we'd have 54.7psi absolute. This is why trucks and cars make more or less boost on the same static waste-gate settings when changing elevation. A 10lbs waste-gate spring will open when it reaches that threshold, but as we change elevation atmospheric pressure on the backside of the waste-gate changes as well. So you will make the atmospheric difference in boost pressure with the same waste-gate spring on the same setting. This only truly matters if you're goal is X amount of absolute boost or X amount of Actual HP. You will have to spin the turbo faster at elevation to produce equivalent power. It may start pushing your turbo outside it's efficiency range or compressor island, producing more heat than the added boost is worth.

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    Quote Originally Posted by JaegerWrenching View Post
    40 PSI is at seal level and 40 psi at elevation are two different things. If our starting absolute is 11.9PSI at elevation 51.9psi absolute would be 40 psi above it. But at sea level if our starting was 14.7 obviously we'd have 54.7psi absolute. This is why trucks and cars make more or less boost on the same static waste-gate settings when changing elevation. A 10lbs waste-gate spring will open when it reaches that threshold, but as we change elevation atmospheric pressure on the backside of the waste-gate changes as well. So you will make the atmospheric difference in boost pressure with the same waste-gate spring on the same setting. This only truly matters if you're goal is X amount of absolute boost or X amount of Actual HP. You will have to spin the turbo faster at elevation to produce equivalent power. It may start pushing your turbo outside it's efficiency range or compressor island, producing more heat than the added boost is worth.
    Well said.

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    that makes sense. Thanks for the explination. Jut to continue on the boost on my truck, I left everything the same except I changed the minimum wastegate duty to 0 percent instead of 80 and it seemed in complete control over the boost. Only went up to 25 psi. But it was way more sluggish to get there.