VGT Turbo M20 Sleeper ('87 325 Sedan)

[mikey.antonakakis]

I've been taking non factory turbo cars to drag strips for years and nobody ever hit me with that one. My motorcycle helmet was all I needed to break into the 11s in a car that had an obviously aftermarket turbo setup. I guess nobody cares in FL.

Yeah, I left a CV joint all over Bradenton's track circa 2011, when I first put this car together lol.

[varg]

Well, that was a bust. Apparently I needed a fireproof jacket due to the non-factory turbo setup. Oh well.

I've been taking non factory turbo cars to drag strips for years and nobody ever hit me with that one. My motorcycle helmet was all I needed to break into the 11s in a car that had an obviously aftermarket turbo setup. I guess nobody cares in FL.

[mikey.antonakakis]

No major updates yet - I moved this summer, so between prepping the old house for sale, moving, and an onslaught of house projects at the new house, have had the car in storage until a week or two ago. Finally got it back home in time for winter, lol. Still runs great! Might try to get the 2.9L stroker stetup (with the Mahle Motorsport pistons and aftermarket rods) built this winter if I can find a good machine shop around here.

[Northern]

Maybe a bit out of place, but looking good!

[mikey.antonakakis]

I always find it funny when they throw those rules in there for a street car.
Don't forget your fireproof jacket when getting groceries.

I’ve at least got a jacket on its way now, along with a new helmet. It would be fun to get some autocross time soon too (maybe in the neighbor’s Lotus?), and I’ll definitely need it for that.

We felt a little out of place at the drag strip lol

[Panici]

Well, that was a bust. Apparently I needed a fireproof jacket due to the non-factory turbo setup. Oh well.

I always find it funny when they throw those rules in there for a street car.
Don't forget your fireproof jacket when getting groceries.

[mikey.antonakakis]

Well, that was a bust. Apparently I needed a fireproof jacket due to the non-factory turbo setup. Oh well.

[mikey.antonakakis]

Car is back on the ground, brakes and clutch work. Planning to drag race tomorrow. Second test drive earlier this evening (after a very quick trip around the block to bed the new front pads) made it clear that I forgot to tighten an intake clamp. Other than that everything seems good to go for tomorrow.

[mikey.antonakakis]

In non-turbo news, I cooked the brakes recently while collecting data to characterize boost response vs engine speed, MAP, and vane position. Was using the brakes to hold RPM while the turbo spooled, back-to-back runs for over an hour. So I figured it was a good time to swap in the new brake lines from Garagistic, new rotors and pads, and ABS delete.

Originally planned to use Hawk HP+ pads I bought a long time ago. Started with just rear pads and rotors so I could do more VGT characterization, and holy cow were those Hawk pads annoyingly loud after a few miles. Threw in some cheap Duralast pads for now, nice and quiet again.

Brake line swap and ABS delete has been kicking my butt a bit. Fronts were easy, but those rear flex lines above the subframe are a huge pain, and despite using flare wrench(es, I tried several), a few of the nuts absolutely refused to budge after 35 years. Ended up having to remake both rear hard lines that run along the trailing arms. Got the brake line swap finished, at least.

ABS delete is also mostly done, but apparently I ordered the wrong tee fitting for the front brake lines (ordered inverted flare for some reason, instead of bubble flare), the correct one should get here today, so hopefully I can get the car functional again tonight by finishing up the ABS delete and doing the front pads and rotors. Might also add a secondary diff mount while the car is in the air, should be a relatively quick job.

If I do get the car going again tonight, I'm planning to head to the drag strip tomorrow morning for some 1/4 miles runs. I don't plan to launch very hard, want to try to save the rear axles for next year, so don't expect any amazing ETs. Mostly curious what the trap speed will look like on 11psi (180kPa MAP is what I've been running for the time being). The drag strip is more like 4500ft elevation so turbo response will be noticeably better compared to the 6000-6500ft I've been tuning at. Will also be a good chance to check on how well my MAP-targeted closed-loop dome pressure boost control is working. Should keep MAP at 180kPa despite the ~5kPa increase in ambient pressure, if I have it tuned properly.

Untitled by Mikey Antonakakis, on Flickr

[mikey.antonakakis]

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:

[Panici]

...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!

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?

[mikey.antonakakis]

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.



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).

[mikey.antonakakis]

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:

[mikey.antonakakis]

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?).

[Panici]

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?