[jwebb335xi]

Hey guys,

I have a simple question, but the answer is probably somewhat complicated. Simply put, i'd like to know what the delta between boost and boost request should look like on a healthy car with a reasonable tune.

I've posted a log from this afternoon below. It was about 85*f and this was probably run #4, but they're all similar. I took this because I got 3-4 on a private road to about 95MPH.

As you can see, the car wants about 19PSI in the low \3K rpms and it's getting about 18PSI. At 5K, it's getting about 16 but it wants more like 17.5 (i.e., in the upper RPMs, it's not getting as much as it's asking for...)

http://www.datazap.me/u/jwebb335xi/t...=0&data=3-4-24

I don't think these numbers are necessarily bad and I don't have any errors whatsoever. Over the past two weeks, I've replaced my valve cover and gasket, ALL vacuum lines, O2 sensors and installed a catch can for good measure. BMW was kind enough to replace my HPFP, and at 99.4K miles, i'm pretty happy with that.

I'm wondering if I ditch my ER charge pipe and Forge diverters for something with fewer connections, like a single TurboSmart, or swap from yellow to red springs in the DV's i might hold boost longer.

Note, the car dyno'd 2 weeks ago at 477TQ / 375 AWHP, but on my second run, it dropped becasue boost only hit 10 PSI over 5K RPMs (hence, the vacuum lines, tightening and re-tightening ALL connections from turbo to TB....).

Thanks for the comments!

Stay Tuned.

[RSL]

Originally Posted by jwebb335xi

Hey guys,

I have a simple question, but the answer is probably somewhat complicated. Simply put, i'd like to know what the delta between boost and boost request should look like on a healthy car with a reasonable tune.

I've posted a log from this afternoon below. It was about 85*f and this was probably run #4, but they're all similar. I took this because I got 3-4 on a private road to about 95MPH.

As you can see, the car wants about 19PSI in the low \3K rpms and it's getting about 18PSI. At 5K, it's getting about 16 but it wants more like 17.5 (i.e., in the upper RPMs, it's not getting as much as it's asking for...)

http://www.datazap.me/u/jwebb335xi/t...=0&data=3-4-24

I don't think these numbers are necessarily bad and I don't have any errors whatsoever. Over the past two weeks, I've replaced my valve cover and gasket, ALL vacuum lines, O2 sensors and installed a catch can for good measure. BMW was kind enough to replace my HPFP, and at 99.4K miles, i'm pretty happy with that.

I'm wondering if I ditch my ER charge pipe and Forge diverters for something with fewer connections, like a single TurboSmart, or swap from yellow to red springs in the DV's i might hold boost longer.

Note, the car dyno'd 2 weeks ago at 477TQ / 375 AWHP, but on my second run, it dropped becasue boost only hit 10 PSI over 5K RPMs (hence, the vacuum lines, tightening and re-tightening ALL connections from turbo to TB....).

Thanks for the comments!

Stay Tuned.

The car doesn't want boost, the DME targets LOAD. See any correlation here? http://www.datazap.me/u/jwebb335xi/t...-24&solo=17-18



Target can be anywhere relative to boost or boost can be anywhere relative to target as shown above, so who's to say what delta should look like on a healthy car? It all depends on mods, conditions and mostly the tune. Boost mean is what you want to pay attention to, not boost. Just under target is probably "best" and some margin under isn't necessarily a bad thing. Your boost curve is following the target very well. If you wanted boost closer to target, some adjustments would be needed from your tuner to get mean closer.

Stock turbos are going to fall on their face >5500rpm. They just don't move enough air to out-flow the motor at high RPM and over-supply air to maintain that pressure in the intake. The motor consumes all of the air they supply and pressure (boost) falls. Changing the charge pipe or valves isn't going to change a thing unless you have a leak and it doesn't look like it. It wouldn't matter if you commanded a 25psi target up there, not going to get that out of them and when under target, they'll only go as high the WGDC/PID will let them push. You'd really have to lean on the WGDCs to keep 17-18psi @ 5500rpm on stock turbos.

[jwebb335xi]

Originally Posted by RSL

The car doesn't want boost, the DME targets LOAD. See any correlation here? http://www.datazap.me/u/jwebb335xi/t...-24&solo=17-18



Target can be anywhere relative to boost or boost can be anywhere relative to target as shown above, so who's to say what delta should look like on a healthy car? It all depends on mods, conditions and mostly the tune. Boost mean is what you want to pay attention to, not boost. Just under target is probably "best" and some margin under isn't necessarily a bad thing. Your boost curve is following the target very well. If you wanted boost closer to target, some adjustments would be needed from your tuner to get mean closer.

Stock turbos are going to fall on their face >5500rpm. They just don't move enough air to out-flow the motor at high RPM and over-supply air to maintain that pressure in the intake. The motor consumes all of the air they supply and pressure (boost) falls. Changing the charge pipe or valves isn't going to change a thing unless you have a leak and it doesn't look like it. It wouldn't matter if you commanded a 25psi target up there, not going to get that out of them and when under target, they'll only go as high the WGDC/PID will let them push. You'd really have to lean on the WGDCs to keep 17-18psi @ 5500rpm on stock turbos.

Thanks for the well reasoned response. I like the way the car feels, and timing corrections are next to nothing. I think I'll ask my tuner to see if he can push a little more out of turbos in the upper end with WGDC, then call it a day!!

Of course, we'll be building an e30 map soon.

[Sgop335]

You may have a boost leak or the base wgdc / adder is not up to the task. With proper tune and no boost leak etc., boost can be 0.5 psi or closer to target. Had an enthusiast approach me for an e60 tune, that has boost and target look like yours among other issues. Fixed it, stock turbos
http://www.datazap.me/u/sgop335/e60v...3-4-21&mark=52

[RSL]

Originally Posted by Sgop335

You may have a boost leak or the base wgdc / adder is not up to the task. With proper tune and no boost leak etc., boost can be 0.5 psi or closer to target. Had an enthusiast approach me for an e60 tune, that has boost and target look like yours among other issues. Fixed it, stock turbos
http://www.datazap.me/u/sgop335/e60v...3-4-21&mark=52

There doesn't appear to be a boost leak, high WGDC would indicate that and boost follows target perfectly.

This is exactly why I said some margin under target is not necessarily a bad thing. These are extremely minor, but that is definitely not always the case. Throttle closures and PID is pulling DC pretty much everywhere. In other words, you're forcing boost mean higher and closer to (and over) target by adding base (adder) and the DME is trying to take it right back out. Adder and base are easy, but a more systemic approach needs to be used.

http://www.datazap.me/u/sgop335/e60v...-31&solo=15-16

If tunes don't already have target at boost ceiling, it would be easiest to just increase target to raise everything evenly across the board for more "boost", but still leave a margin.