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VGT Turbo M20 Sleeper ('87 325 Sedan)

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    #91
    I'm in the same boat, though - I think my timing map is pretty conservative at the moment, except for maybe at peak torque at a little over 5000rpm where I can hear the slightest knock if I add any more timing. I'm looking at getting some dyno time in the near future, turns out these guys are not too far from me and have more old BMW experience than any other shops around here, and seem laid back about letting me do the tuning myself. Also seem quite confident that they've developed good timing maps for turbo M20s specifically. Mine might be a little more limited than most due to eta pistons with 885 head.

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      #92
      Z3 rack swap started, about 30min and close to pulling the rack out. Just need to loosen motor/trans mounts, lift the engine an inch or two, and then should be able to pull it. Garagistic swap kit should finally arrive tomorrow. They were backlogged on delrin steering couplers, with they delay they offered to swap me for aluminum and they discounted me without me asking or without them even mentioning it. Such a great supplier!!

      Hey Future Self: this last part of pulling the old rack probably didn’t end up being as easy as you thought!

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        #93
        Biggest pain on removal: splines didn’t want to let go on the rack end of things, but not too terrible. The rack is totally free now, and almost has enough room to escape its confines behind the oil pan, but not quite. Don’t want to bend the tabs, so next I just need to jack the engine an inch or so, but wife and baby are asleep above the garage some I’m not going to make a huge racket rolling the floor jack around tonight.

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          #94
          Rack came out without a fight this morning, lifted the engine about 1-1.5" and there was plenty of room (not too hard, undo downpipe-to-midpipe v-band, pop air filter off turbo, loosen intercooler supports, and lift). Had to do a little persuading to get the knuckle assembly off the steering column. Ready for modification/rebuild, Garagistic kit out for delivery. We'll see how well the splines go back on...

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            #95
            Z3 rack (“031”) install finished, also swapped the solid aluminum transmission mounts for 95a Garagistic poly and replaced the steering flex disc with aluminum. Quick and rough home garage alignment and a 5min drive, whoa, what a difference! Partially from the quicker rate, yes, but also the lack of slop now. Huge improvement!

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              #96
              Originally posted by mikey.antonakakis View Post
              Z3 rack (“031”) install finished, also swapped the solid aluminum transmission mounts for 95a Garagistic poly and replaced the steering flex disc with aluminum. Quick and rough home garage alignment and a 5min drive, whoa, what a difference! Partially from the quicker rate, yes, but also the lack of slop now. Huge improvement!
              I have the Z3 rack on my E30 as well. Makes a huge difference coupled with a slightly smaller steering wheel. (370mm vs 385mm)
              Difference between feeling like driving a bus, and a sporty car.

              Definitely go for an alignment. I basically toasted a set of front tires driving around with my garage alignment for a few months.
              '87 BMW E30 325is Turbo
              '86 BMW E28 535i
              '98 BMW E36 328i
              '90 Mazda NA Miata Turbo
              '04 Jeep TJ
              '05 Yamaha R6

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                #97
                Okay, time for some fun stuff, more data! The big updates are that the car now has EGT and exhaust manifold pressure measured at the turbine inlet. It's also running the turbo control system (wastegate dome pressure control and VGT control) on the new PCBs I designed.
                So now with EMAP I can calculate drive pressure ratio and see the effect of the VGT. I can even do something like alter my VGT algorithm to seek a target drive pressure ratio (say, 2:1) during spool-up, rather than having an open-loop setup.

                Quick sample datalog below, 1st through 3rd gear up to ~30-105mph in about 10s, not flatshifting. Note that the bottom plot is recording wastegate dome pressure, turbo speed, VGT vane position (calculated as nozzle size), EMAP (exhaust manifold pressure), EGT, and drive pressure ratio.

                I think I can get more aggressive with the VGT actuation, drive pressure ratio starts to drop immediately as boost builds, peaks around 1.4:1 near redline with vanes (almost) fully open. Dome pressure control is working great, within 0-5kPa of boost target, and it's in a sort-of open-loop mode (not trying to directly control MAP). Note also that wastegate dome pressure is kept high during spool-up to ensure the wastegate stays closed.

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                Last edited by mikey.antonakakis; 09-28-2022, 01:55 PM.

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                  #98
                  Quick update for now. I've done a lot of datalogging and data analysis to get the VGT working more optimally during spool-up. I've made a huge improvement, as shown below in datalogs starting around 4000rpm in 2nd gear.

                  The lighter colored lines are the previous calibration/algorithm, and the bolder lines are today's setup. MUCH faster spool-up, even with the starting conditions being very different. Today I just stomped the throttle after coasting in 2nd gear, vs. the older data being a 1-2 WOT upshift. In other words, turbine shaft speed with the new data started at 13k, vs. 45k with the old data.

                  Despite that, with the new setup it spooled much more aggressively and hit target boost sooner, and the difference was much more pronounced at the 2-3 shift with a more even playing field (although the new tuning still had a little disadvantage due to a bit of a short-shift). For the 2-3 shift, 0.7s vs. 1.7s to hit target boost. I didn't flatshift, but it would have spooled faster if I did.

                  Click image for larger version

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                    #99
                    Did a lot more VGT characterization testing last night. Basically holding a steady RPM and setting a fixed vane position during spoolup, and letting it spool to its limit, and repeating, varying RPM and vane position. Logged 42 distinct combos to work on characterizing the relationship between RPM, vane position, MAP, drive pressure ratio, and rate of building boost.

                    During testing I definitely found the surge limit of the turbo a few times, as seen by the jagged MAP signal. This was a pretty aggressive vane position, a little over 90% closed at 3000rpm. In this sample, the surge is mostly caused by the small VGT opening restricting flow through the engine - which is cool, because that means I'm not actually at my boost limit at this engine speed of 3000rpm - I can open the vanes a little more and get the surge to go away.

                    You might also notice the wastegate dome pressure signal going a little wonky during the surge event, but it's unrelated. It's doing this because I'm getting close to the boost target so it starts to modulate its pressure to avoid overshoot (not really important at 3000rpm, but makes a big difference at higher RPMs). During spool-up, I keep dome pressure quite high due to the high exhaust manifold pressure resulting from the VGT clamping down. For instance, in the data below, the steady state condition during the surge has EMAP of 278kPa. MAP 158kPa, and dome pressure 250kPa (all in absolute pressure). So there's a 92kPa net pressure on the wastegate piston, in addition to the wastegate spring which by itself gives about 51kPa boost over barometric pressure; opposing that net force is the nearly 200kPa pressure differential across the wastegate valve in the manifold (EMAP minus downpipe pressure, which should be equal to baro), which is trying to push the wastegate open.

                    In fact, you can see the wastegate start to open at the cursor (vertical blue line) when the dome pressure drops down to about 200kPa - notice how EMAP (salmon colored line) drops at that point, while the vanes remain constant. This drop in EMAP (and drive pressure ratio) is due the wastegate valve unseating itself and relieving some exhaust manifold pressure. Looks like it actually starts to happen at about 230kPa dome pressure.

                    Time to process a pretty big set of data (multiple samples of each of the 42 test points).


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                    Last edited by mikey.antonakakis; 10-21-2022, 08:06 AM.

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                      Originally posted by mikey.antonakakis View Post
                      During testing I definitely found the surge limit of the turbo a few times, as seen by the jagged MAP signal. This was a pretty aggressive vane position, a little over 90% closed:
                      Pretty neat to see the surge limit.
                      Do you have a compressor map for your setup to reference?
                      '87 BMW E30 325is Turbo
                      '86 BMW E28 535i
                      '98 BMW E36 328i
                      '90 Mazda NA Miata Turbo
                      '04 Jeep TJ
                      '05 Yamaha R6

                      Comment


                        Originally posted by Panici View Post

                        Pretty neat to see the surge limit.
                        Do you have a compressor map for your setup to reference?
                        Supposedly it’s a standard 7-blade HX40 compressor. Maps are out there, overall it’s a pretty decent compressor for good top end power (flows enough at reasonable pressure ratios, like 2-3, for maybe 700 crank HP?).
                        Last edited by mikey.antonakakis; 10-21-2022, 10:22 AM.

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                          And to prove that point of "not *actually* the surge limit at 3000rpm" here is 3000rpm again with vanes closed about 85% (was 91% in the previous datalog). Made more boost, limited only because the wastegate dome started dropping pressure, as evidenced by the slight drop in EMAP/drive pressure ratio, and the "knee" in the rate of boost increase. So, I can essentially turn up the boost target, or use less of a buffer at 3000rpm. Right now that "dome pressure control active" threshold is a fixed value, I should probably turn it into an RPM-based value:

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                            So I've changed the VGT operation a bit (again...). Now using a RPM- and MAP-based lookup table to determine optimal vane position during spool-up, table was written based on a hundreds of datalogs (the collection process of that data absolutely roasted my brakes... would be nice to have a dyno for this!).

                            The data in this screenshot was prior to some refinement of the new lookup table, so the fluctuations around full boost are tamed. Part of why they happened here are what the datalog shows - stomping it in 2nd gear at 2000rpm got me to full boost in 4 seconds (not great, but that's what 2000rpm gets you at altitude), and it absolutely roasted the tires at 4200rpm, shot straight to the 7000rpm redline. Kept my foot in it until just before the wheelslip stopped, but still short shifted a bit. 2.93 gearing means it lit up the tires at 44mph, redline is about 74mph. After the not-flat shift to 3rd, with MAP falling to 17kPa, full boost came back in 0.6s or so.

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                            Another slightly newer 2nd-3rd gear sample, this time with flatshift. Still spinning the tires, they were warmer this test so they didn't spin as bad. WOT at 3800rpm got me full boost in 1.1s. Flatshift took 0.5s and MAP only dropped to 158kPa (vs 180kPa target). This shift sounded like a gunshot, hence the MAP and drive pressure spikes. EMAP (not shown directly) actually rose slightly during the shift, before the big bang (where it spiked).

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                            Last edited by mikey.antonakakis; 10-25-2022, 10:48 PM.

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                              Originally posted by mikey.antonakakis View Post
                              ...it absolutely roasted the tires at 4200rpm, shot straight to the 7000rpm redline. Kept my foot in it until just before the wheelslip stopped, but still short shifted a bit. 2.93 gearing means it lit up the tires at 44mph, redline is about 74mph. After the not-flat shift to 3rd, with MAP falling to 17kPa, full boost came back in 0.6s or so.
                              That sounds like a lot of fun!

                              Originally posted by mikey.antonakakis View Post
                              This shift sounded like a gunshot, hence the MAP and drive pressure spikes. EMAP (not shown directly) actually rose slightly during the shift, before the big bang (where it spiked).
                              Assuming you are cutting spark and not fuel on flatshift? How long do you cut ignition?
                              '87 BMW E30 325is Turbo
                              '86 BMW E28 535i
                              '98 BMW E36 328i
                              '90 Mazda NA Miata Turbo
                              '04 Jeep TJ
                              '05 Yamaha R6

                              Comment


                                Originally posted by Panici View Post
                                That sounds like a lot of fun!


                                Assuming you are cutting spark and not fuel on flatshift? How long do you cut ignition?
                                Retard to -20 and cut spark as needed, no fuel cut :)

                                EDIT: Settings, not much tuning done on these yet:
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                                Last edited by mikey.antonakakis; 10-28-2022, 08:03 AM.

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