Lets argue about VGT/VNT Diesel Turbos on a gas motor. - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-30-2013, 06:26 PM   #21
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Originally Posted by Leafy View Post
If you just kept it in tiny AR mode it will spool fast but run out of steam up top, even running the EWG.
Yeah, I think that is exactly what Pinky was trying to do. No need for steam up top on autocross, so keep it in little AR mode. Then set it for the normal sweep for the drag race where you do want the extra power.

Or I've completely misinterpreted what Pinky was thinking (likely).
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Old 09-30-2013, 08:19 PM   #22
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Originally Posted by thenuge26 View Post
If you set up a WG actuator to control it, could you then use the Megasquirt's EBC to control it?
Well... yes. In theory, but it won't work normally. The problem is that an ebc is going to trim and hold a solenoid to achieve a target.

The beauty of these turbos is that you can hold a target kpa/map, but then still adjust flow. Getting an ebc to do that would require a constantly moving target based on rpm, boost, or both. Basically you'd want your target to be a sliding scale that looks like a Rotrex power curve.

Not sure how close MS Ebc could come to that, but I bet it'd be way easier to set it up pwm vs. Rpm and just ignore load or map. Control psi levels independently with manual controller.


That said, he's not using megasquirt I don't think.
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Old 09-30-2013, 08:22 PM   #23
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I would just control psi level with the VGT, if boost too high, open VGT more, if boost too low, close VGT more.
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Old 09-30-2013, 08:37 PM   #24
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Good luck with that. An F2 is capable of building 30psi+ on one of these ******* wide open.

Let alone unregulated and a small block chebby.
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Old 09-30-2013, 08:39 PM   #25
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Originally Posted by concealer404 View Post
Good luck with that. An F2 is capable of building 30psi+ on one of these ******* wide open.

Let alone unregulated and a small block chebby.
But it wont be unregulated, you're controlling the VGT, which is how you control boost on a VGT turbo.
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Old 09-30-2013, 09:04 PM   #26
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You aren't understanding.

Your idea might work on a diesel... But as i just plainly said, you aren't going to be able to decrease boost by opening this ****** unless we're talking about setting it so small it's an engine brake to wide open.

It's simply not going to work once this thing is on boil at any sort of RPM.

As i just said: Wide open, and i mean WIDE open, it took a wastegate to keep one of these ******* to "just" 32psi on an F2T. That's a 2.2 litre motor. It wouldn't decrease boost by opening it wider, because it was already open all the way. Not sure how to make that more clear.
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Old 09-30-2013, 09:12 PM   #27
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Quote:
Originally Posted by thenuge26 View Post
Yeah, I think that is exactly what Pinky was trying to do. No need for steam up top on autocross, so keep it in little AR mode. Then set it for the normal sweep for the drag race where you do want the extra power.

Or I've completely misinterpreted what Pinky was thinking (likely).
Yeah, that's the idea. I wish I had the money to really mess with the variable geometry aspect of it, mapped somehow to boost and load, but that would eat up a bunch of my budget. So instead we'll mess with it to find a position that spools hard and another that spools slower bit builds more boost, up to the EWG ceiling. Will it work? I dunno. We may end up with pistons changing holes the first time we fire it up, or it might work like a charm. Only one way to find out.

The majority of people adapting VGTs to gas motors fit an EWG actuator to the VG vane control rod, so at low boost it spools like crazy, and as you start building pressure it shifts to a more open vane setup, ultimately passing the most efficient point and beyond into bypass. It sounds to me like this would end up with a turbo that could possibly build boost at idle (no boost present on the WG signal hose, so turbo rests in Big Spooly mode. I'm hoping that the volume of exhaust at idle wont be enough to really spin it up, or it could get weird. (I'm imagining a sort of feedback loop where it's boosting at idle, which speeds it up, which adds exhaust gas volume, which boosts more, which speeds it up, and on and on....?)

Anyway, the fun is in the messing with it, and this seems the perfect platform to experiment a little. If it all goes wrong it'll make for good video and I'm only out a few himdred bucks.. But if it works, the sight of this beast of a turbo under the hood will be worth the trouble all by itself.
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Old 09-30-2013, 09:23 PM   #28
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Originally Posted by Pinky View Post
It sounds to me like this would end up with a turbo that could possibly build boost at idle (no boost present on the WG signal hose, so turbo rests in Big Spooly mode. I'm hoping that the volume of exhaust at idle wont be enough to really spin it up, or it could get weird. (I'm imagining a sort of feedback loop where it's boosting at idle, which speeds it up, which adds exhaust gas volume, which boosts more, which speeds it up, and on and on....?)
.
That would just end up making compressor surge at worst and killing the turbo, and at best its anti-lag.
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Old 09-30-2013, 10:01 PM   #29
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This is why I said you better make damn sure you have a really big wastegate. And maybe a popoff valve in the Intake tract.
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Old 09-30-2013, 11:07 PM   #30
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Originally Posted by concealer404 View Post
You aren't understanding.

Your idea might work on a diesel... But as i just plainly said, you aren't going to be able to decrease boost by opening this ****** unless we're talking about setting it so small it's an engine brake to wide open.

It's simply not going to work once this thing is on boil at any sort of RPM.

As i just said: Wide open, and i mean WIDE open, it took a wastegate to keep one of these ******* to "just" 32psi on an F2T. That's a 2.2 litre motor. It wouldn't decrease boost by opening it wider, because it was already open all the way. Not sure how to make that more clear.
Duly noted. Just curious, you guys definitely were going all the way to bypass on the actuator, right? As I understand it, at least with the VGT (vane, not nozzle) turbos, the range on the actuator starts with the vanes tight and spooly, then as they open it somehow (obvious wizardry of some sort) flows more across a different area of the turbine wheel thingy, eventually reaching a maximum speed (and maximum boost) setting that when passed begins to bypass first some and then essentially all of the gases making **** spin. There really ought to be some point at which it's bypassing enough to not be building 30+ psi. I mean, wouldn't that turbo on it's OEM 6+ liter application be making a bazillion pounds of boost at all times if it's uncontrollable behind a 2.2 liter? I just cant get my head around the difference, although maybe it has something to do with diesels not throttling air to control speed, but instead controlling the amount of fuel injected.. (?? Maybe?)

Weird thing is that there are people somehow controlling these beasts; I'm taking a lightly traveled path here admittedly, but not exactly breaking new trails. In searching for info on whether it's even feasible I've come across numerous forum postings saying they were running VGT's, mostly with the cobbled up EWG actuator strategy I've mentioned, so I figured we'd give it a go. If it absolutely does not work I toss it's $150 *** on the shelf and go junkyarding for a conventional Holset. I'd need to plumb the EWG either way, so it's not really that big a deal. The only things that count towards the budget are the things on the car when you roll it into the GRM tech inspection.

Anyway, we'll see. The beauty of playing with a sub $2k car is the total lack of ***** associated with the possibility of spectacular, nay even epic failure. Lets strap it on, set a big *** wastegate to 12 psi and see what happens. I'll film it for sure.
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Old 09-30-2013, 11:12 PM   #31
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The highest shaft speed setting should be the tiny AR setting. Because ultimately the amount of air you flow is determined by the shaft speed. If you held exhaust entropy, flow, velocity, etc constant, as the AR increased the turbine shaft speed would decrease and the compressor would flow less air, which would make for less boost.
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Old 09-30-2013, 11:12 PM   #32
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Originally Posted by sixshooter View Post
This is why I said you better make damn sure you have a really big wastegate. And maybe a popoff valve in the Intake tract.
Where would I buy this pop tart valve of which you speak? Don't roots blowers have something like that in case of backfire? I might be able to cobble up something back where the EGR used to live, using the springs they use to hold down a plate.. (?)
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Old 09-30-2013, 11:19 PM   #33
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Originally Posted by Leafy View Post
The highest shaft speed setting should be the tiny AR setting. Because ultimately the amount of air you flow is determined by the shaft speed. If you held exhaust entropy, flow, velocity, etc constant, as the AR increased the turbine shaft speed would decrease and the compressor would flow less air, which would make for less boost.
Ok, I've got that part, but in my head it works like a road bike, you have those big *** gears that spin the wheel fast but cant exert much push, and those gears where you gotta crank the **** out of it but you can climb anything; that's how I'm sort of processing this whole variable geometry notion. Plus there's the setting where if you go too far the chain comes off (bypass) and none of your work is resulting in anything really spinning much. Am I way off base here?

(BTW, thanks for entertaining my screeching ignorance on VGT's - I appreciate being able to hear from someone with direct experience.
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Old 09-30-2013, 11:23 PM   #34
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Originally Posted by Pinky View Post
Where would I buy this pop tart valve of which you speak? Don't roots blowers have something like that in case of backfire? I might be able to cobble up something back where the EGR used to live, using the springs they use to hold down a plate.. (?)
McMaster-Carr

Or you could rig up a ebay bov to open at a set pressure. I also know there were OEM ones of these.

And the bike annology isnt really correct. The tiny setting is going to give the exhaust gas the most push on the turbine, which also gives it the highest speed. Think of it more like gears in the car and engine braking. 1st gear give the most engine braking, but you cant downshift to first to engine brake when you're doing 80mph, because you'll overspeed the engine.
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Old 10-01-2013, 08:08 PM   #35
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The EGT concerns with running a VGT are more than just durability-related. There's also a distinct propensity for vane sticking as EGTs rise. Sluggishness, hysteresis, sticking, general crabbiness.

You can imagine what this could do to your day.

Run E85, run it fat.
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Old 10-01-2013, 10:05 PM   #36
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Weld waste gate shut. Build servo to control flow of garden hose sprayer into airbox. Consider this "water injection".


Best of all, with a few wal-mart spray nozzles, and some McMaster Carr adapters, you could have port specific water injection. Spray a light mist at low RPM (think, watering flowers), and blast that ****** at 6k (Cleaning gunk from drive-way seams).

I know nothing about electricity, but I can promise you MegaSquirt can probably handle that. Or weld a spigot to the throttle cable mount, for extra ghetto-ness. More throttle = more water.
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Old 10-01-2013, 10:10 PM   #37
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New plan.

Run stock ECU. Add sliding plate to intake pluming. Use plate to divert air out of intake, lowering total air available to engine. Stock ECU adds fuel as normal, but the "missing" air we sent out that divert-er, now makes the car have a 7:1 AFR.
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Old 10-01-2013, 10:35 PM   #38
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That's... actually been done. I've seen morons create boost leaks on purpose to richen their **** up.
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Old 10-01-2013, 11:10 PM   #39
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That's... actually been done. I've seen morons create boost leaks on purpose to richen their **** up.
Pinky, I do have an opening nights/weekends for consulting. Under the table of course, for the budget.
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Old 10-07-2013, 09:23 PM   #40
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So, one of the guys at the shop just called me and said the turbo arrived. "It's kinda big" he says, accompanied by shrieks of laughter from the other idiots in the background...

"How big?" I innocently inquire...

"Really big. 80 pounds big."

Now, SuperTrav is occasionally given to exaggeration, and he's only been around little ***** turbos like my MSM turbo, so I figure he's just making a big deal about nothing. Besides, an *80* pound turbo? Fuggetaboutit, the dudes gotta be mistaken. But there's something about the howling idiots in the background that makes me curious, so I tell him to text me a picture of it.

Whoa. Now THAT'S a turbo.

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