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Old 07-20-2012, 12:48 PM   #1
subime4life
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Default Does anyone have any experience with variable-geometry turbo chargers?

Old guy at work brought them up and I can't find much about them. I was wondering pros vs cons
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Old 07-20-2012, 01:39 PM   #2
freddy121389
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never heard of anyone using one on a subaru, they mainly use them on diesels.
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Old 07-20-2012, 05:19 PM   #3
subime4life
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I did see they used them on the 89 Shelby Daytona, a 91 fiat, and a 07 Porsche, so i was just curious to see if it's been done on a subaru
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Old 07-20-2012, 07:21 PM   #4
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ask a holset guy if its been done, my guess is no as It's hard to control the vanes. A dsm guy did it, just search around
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Old 07-20-2012, 08:02 PM   #5
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There was an Aerocharger guy who posted here a few times. Their turbochargers are interesting, but their compressor maps tell the story.

These turbos appear to work best in moderate boost applications... the surge line of the compressor maps don't look great above about 12-13 psi.

Looks like it would hit 13psi by about 2500 RPM on the 2.5L, but much higher boost and the 2.5L would hit the compressor surge line. You'd need to run some kind of funky boost curve in order to run higher boost than this. Something that would increase boost again at 3500-4000 RPM when 20psi won't surge. This would be difficult, given their turbos don't have a wastegate.

Overall it looks like their turbos are best suited to an application where 10-13 psi is a good thing. They don't seem to like 20psi at low RPM, but what compressor does like that?

It might be interesting to build something like a 13:1 de-stroke 2.34L running full time E85 or race gas to match the compressor map. It looks like it'd hold that 13 psi from <3000 RPM out to 8500 or so, and the high compression would make the most of that low boost pressure. Torque would still be low, something in the 250-300 ft-lbs. range, but it should hold it out pretty far. You'd want an engine that doesn't have the torque mountain like the Subaru 2.5L does. Compressor map seems much better suited to the EJ207 / 2.34 destroke style engine. You end up with a much different torque curve than Subaru guys are used to. It'd be more of a turbo'ed honda style graph where torque is low, but it keeps on going. Still, the largest of their turbos is a 540 CFM turbo, this is about in line with a big 16G or something along those lines. So even with high compression and E85, you'd probably only hit ~400 HP.

Last edited by Concillian; 07-20-2012 at 08:09 PM.
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Old 01-06-2013, 05:30 AM   #6
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Concillian
Thank you for explain.
Can you detailed explain how will work Aerocharger with EJ207?
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Old 01-06-2013, 06:25 AM   #7
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Quote:
Originally Posted by maxouni View Post
Concillian
Thank you for explain.
Can you detailed explain how will work Aerocharger with EJ207?

how about.....not worth a ****???
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Old 01-06-2013, 07:37 AM   #8
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This is all purely for the sake of conversation because otherwise its not worth it at all. Tell that guy at work to quit wasting his time on useless things.
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Old 01-06-2013, 10:35 AM   #9
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Check the diesel forums, it's not too hard to complete once u find a vgt controller.
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Old 01-06-2013, 02:45 PM   #10
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The only production car I know that used VTG in gasoline applications is the 911 turbo.
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Old 01-07-2013, 04:00 PM   #11
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The 3 major issues for variable geometry turbos on gas engines are excessive EGT's, sticking vanes, and controller options. I have recently done an excessive amount of research on the vgt turbos and found that the negatives outweigh the positives. Heres a little list that touches on a couple topics

Diesel exhaust is cold and slow, egts range from 1k to 1400 degrees max at the turbo inlet, gas exhaust is hot and fast and at cruise speeds tend to sit around 1300 to 1600 degrees (and can spike higher) which is 200 degrees above the maximum designed operating range of the turbo.this can of course lead to turbine meltdown and catastrophic engine failure.


After a while the vanes in the turbo will collect deposits from the exhaust (carbon) which will cause the vanes to bind (not open completley or close completley, thus creating an unpredictable boost condition).

Controlling the vane position will require an output control based on a 3 or 4 axis input table with rpm/tps/boost actual/ boost desired. The output will have to be pwm or stepper motor to control vane position.

Couple other things, vgt turbos dont use wastegates, are expensive to purchase, and the housings are fairly large to fit in the engine bay.

The only possible option is really the the holset as the garrett uses a turbo pedestal and o-rings for oil supply and return.

For the money and reliability I would simply buy a trubo designed for your application. Just my 2 cents.
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Old 01-08-2013, 03:21 AM   #12
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^^^^^^
Are the porsche guys having trouble with them? They've been running them stock for a few years at least.
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Old 01-08-2013, 04:55 AM   #13
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Quote:
Originally Posted by kellygnsd View Post
The only production car I know that used VTG in gasoline applications is the 911 turbo.
i remember the 89 dodge shadow csx had them, too.
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Old 01-08-2013, 11:42 AM   #14
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Havent heard alot about the reliability on the porsche vgt turbos but those are also water cooled to aid in egts.

Food for thought, there is probably a reason porsche only ran the vgt turbos for 2ish years before going back to a standard turbo design. Also, havent seen a lot or porsche 911's with 100k miles on them. Also havent seen a mess of 89 shelby csx's running around either.....

Not trying to hinder the idea of running a vgt turbo as I think it would be awesome to have a turbo with a changable exhaust a/r on the fly. The garrett gt3782va has in lamens terms a .4 to approx 1.1 exhaust a/r depending on vane position. Not 100% on the holset he351ve but I think its approx a .58 to 1.14 exhaust a/r depending on vane position. Hence 20 psi at 2300 rpm clear to redline with no boost taper. Sign me up! Its just the cost vs reliability and functionality thats scary.

One more thing, assuming one was to purchase a pair of porsche vgt turbos, what happens if it ever fails? Dont think there is alot of places willing to repair it with a warranty, and the cost has to be astronomical.
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Old 01-08-2013, 11:56 AM   #15
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Quote:
Originally Posted by Concillian View Post
There was an Aerocharger guy who posted here a few times. Their turbochargers are interesting, but their compressor maps tell the story.

These turbos appear to work best in moderate boost applications... the surge line of the compressor maps don't look great above about 12-13 psi.

Looks like it would hit 13psi by about 2500 RPM on the 2.5L, but much higher boost and the 2.5L would hit the compressor surge line. You'd need to run some kind of funky boost curve in order to run higher boost than this. Something that would increase boost again at 3500-4000 RPM when 20psi won't surge. This would be difficult, given their turbos don't have a wastegate.

Overall it looks like their turbos are best suited to an application where 10-13 psi is a good thing. They don't seem to like 20psi at low RPM, but what compressor does like that?

It might be interesting to build something like a 13:1 de-stroke 2.34L running full time E85 or race gas to match the compressor map. It looks like it'd hold that 13 psi from <3000 RPM out to 8500 or so, and the high compression would make the most of that low boost pressure. Torque would still be low, something in the 250-300 ft-lbs. range, but it should hold it out pretty far. You'd want an engine that doesn't have the torque mountain like the Subaru 2.5L does. Compressor map seems much better suited to the EJ207 / 2.34 destroke style engine. You end up with a much different torque curve than Subaru guys are used to. It'd be more of a turbo'ed honda style graph where torque is low, but it keeps on going. Still, the largest of their turbos is a 540 CFM turbo, this is about in line with a big 16G or something along those lines. So even with high compression and E85, you'd probably only hit ~400 HP.
Look at the compressor map as a complete picture too, they're not very impressive. Honestly I think that company would do a lot better if they just make turbines and housings that worked with other companies turbos. SO you could buy a BW256 for the sweet compressor map and robust bearing and throw that turbine on it, then get it rebalanced.

The rest of the VGT turbos either dont work well with gas engines due to EGTs or are a dealer only porche part that may or maynot be sized correctly for your engine. They were a nice theory, but now that the EFR turbos exist I really dont see their point in gasoline/ethanol powered aftermarket.
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Old 01-08-2013, 03:48 PM   #16
STIGR-Wagon-Dad
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I have not driven a chrysler 2.2 turbo in over 20 years but todays turbos can get the torque of the aerocharger and provide more power. the VF48 on my sti had similar response to the aerocharger. the aerocharger is pretty much a long forgotten turbo. the last time it was even mentioned in any magazine article was probably in the early 90's in turbo magazine. that's the last time i read about them.
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