twin turbo subaru in testing [Archive]

Flo4Legacy

08-30-2005, 06:48 PM

AFAIK, the only manufacturer fooling around with twin-charging (on any car < $50K) is VW. Popular Mechanics reports that they're working on a 1.4L that makes 170-180bhp for the Golf / Polo lineup.

VW recently announced that 1.4l twin charged FSI (direct injection) gas engine.
Twin charged means in this case, that VW uses a supercharger and a turbo. The engine offers (in german spec) 170 HP and 240 NM.

Reason for the supercharger is to avoid the "power hole" at low rpm that conventional turbo charged with small displacement tend to show. Up to ~ 2400 rpm the supercharger is doing the job, over that the turbo kicks in. VW claims that the consumption is at 7,9 liter for 100 km - but that only counts in certain conditions, real life mileage may vary.

That sounds very interesting, but I would also would prefer a Subaru with a hybrid engine. ;)

King Ding187

08-30-2005, 11:08 PM

Hey everyone,

What's the point of a twin-turbo? Unless it's sequential, which would be a mess with a boxer engine (imagine the exhaust piping), the parallel setup is just twice as inefficient without offering any advantage outside of marketing. Yes, Porsche is using marketing as a justification for a twin... Just like Subaru did with the tt Legacy.

I have to disagree. Twin turbos on a flat six make perfect sense. Porsche seperates the cylinder banks so each turbo is only pressurising it's own cyinder bank. The negative aspects of twin turbos when they are trying to pressurise the same manifold are gone. On top of that you get rid of the a lot of the length required for the exhaust manifold made for a single turbo on a boxer engine minimising the energy lost by the exhaust gases before the turbos. It's not a marketing ploy, it's smart engineering. Given the choice between a single turbo flat six or a twin, I'd take the twin anyday.

Jon [in CT]

08-30-2005, 11:14 PM

I have to disagree. Twin turbos on a flat six make perfect sense. Porsche seperates the cylinder banks so each turbo is only pressurising it's own cyinder bank. The negative aspects of twin turbos when they are trying to pressurise the same manifold are gone. On top of that you get rid of the a lot of the length required for the exhaust manifold made for a single turbo on a boxer engine minimising the energy lost by the exhaust gases before the turbos. It's not a marketing ploy, it's smart engineering. Given the choice between a single turbo flat six or a twin, I'd take the twin anyday.Ditto!

THAWA

08-30-2005, 11:14 PM

King Ding187

08-30-2005, 11:34 PM

Can you really state a good reason for FHI to go back to the twin turbo setup? They left that setup in favor of the twinscroll quite a few years ago, so why would they go back to it? The twinscroll setup is better in just about every way.

This is all in reference to a hypothetical new twin turbo flat six, not a new twinturbo four. The twinscroll is a better setup by far than the sequential twin turbo fours Subaru made, but imho so were the single turbo variants offered at the same time. A good reason for the twin turbo setup would be a Subaru with 911 Turbo like engine prowess, I think that's a good enough one. I'm sure a limited run of twin turbo legacies on the line of say the run of s203's and such would sell with no problems whatsoever.

HB_Dad

08-31-2005, 01:26 AM

the person that told me this works at a dealership and is really in the loop when it come to Subaru.

hey it might happen and it might not, i doubt it. just wondering if any one else had heard this.... seems there is something to this.

:lol: :lol: http://forums.nasioc.com/forums/showthread.php?t=755849 :lol: :lol:

AVOjapan

08-31-2005, 05:09 AM

Actually, the reference to Porsche twin-turbo's brings to mind a story I read a while ago in one of the car magazines on Porsches old turbocharged race cars. It seems that they started out with twin-turbo setups originally, but over time went to a single turbo setup. When it got down to it, the single turbo setup was simply more efficient at making power.

The thing is, the less amount of parts and piping in the system, the more efficient it is going to be. Many of the big horsepower aftermarket tunes of GT-R's and Supra's here dump the twin turbo setups and go for a single setup for just that reason.

What it is is this - twin turbo setups sound sexy. They look sexy. They are sexy to brag about.

Cheers,

Paul Hansen
www.avoturboworld.com | www.sevenphotos.com | www.scoobymag.com

UCD-WRX

08-31-2005, 05:46 AM

Hey Paul,

That's what I was saying... the sequential 3rd gen RX7s were the same way. Convert to one turbo for more power...

There is one advantage to twin turbos, aside from marketing. Packaging. In some cars, especially big V8s, it's just too hard to bring the piping to one common place. Where would you cross over? Under the motor (and hit the ground)? Over the motor (and need a bigger hood / make the area around the intake piping / manifold super-hot)?

Aside from tight packaging constraints, though, singles are always better than doubles. One 80% efficient turbo is better than two 75% efficient turbos with twice as much plumbing, twice the intercooler losses, etc.

UCD-WRX
Shameless plug for my coilover poll: http://forums.nasioc.com/forums/showthread.php?t=819418

Phil Jr.

08-31-2005, 05:58 AM

Twin turbo setups, either sequential or non-sequential are used to reduce lag and make a fat torque curve along the RPMs. Sure it makes more sense to use one massive turbo on a supra or GT-R if your only desire is huge HP #s and 1/4 times.

The B5 audi S4 uses a non-sequential turbo setup VERY effectively. 500+ awhp is realized without drastic engine mods and very decent driveability.

SUBE555

08-31-2005, 08:12 AM

I agree on the reason for using a single turbo especially in a straight six, but unfortuntaly, yes, piping gets to be a drastic mess and a single turbo off each cylinder bank with a short manifold is ideal. The Audi is indeed a perfect representation of this working (aside the KKK turbo reliability. :p)

Beaverboy

08-31-2005, 01:25 PM

Twin turbo setups, either sequential or non-sequential are used to reduce lag and make a fat torque curve along the RPMs. Sure it makes more sense to use one massive turbo on a supra or GT-R if your only desire is huge HP #s and 1/4 times.
Every report I've read comparing the current Legacy twinscroll turbo setup to the older twin sequential setup says the twinscroll is much more responsive at all RPMs.

I don't understand what all these arguments are about when the twinscroll is proving so effective. The proof is in the pudding. I'll take a single twinscroll turboed H6 over a twin-turboed H6 anyday.

Open the bonnet of the Turbo version and you will face a bigger surprise. No twin-turbo any more. Now just one turbocharger and intercooler. You know Legacy was renowned for its sequential twin-turbo, an arrangement that activates one turbo at low rev and both turbo at high rev. You know this enabled a linear and refined power delivery, but if you remember my old report, in reality it was not all that great, neither especially responsive nor as punchy as Impreza’s single turbo engine.

http://www.autozine.org/html/Subaru/Legacy.html

stephenmeade

08-31-2005, 01:29 PM

Every report I've read comparing the current Legacy twinscroll turbo setup to the older twin sequential setup says the twinscroll is much more responsive at all RPMs.

I don't understand what all these arguments are about when the twinscroll is proving so effective. The proof is in the pudding. I'll take a single twinscroll turboed H6 over a twin-turboed H6 anyday.

Current twinscrolls have the benefit of AVCS, in some cases on both the intake and exhaust, whereas the older twin sequential setup had static cam phasing. Also, from what I have heard, the main complaint of the older twin sequential setup was not responsiveness but the rather rough transition zone with the sequential turbos.

Stephen

MomentumTurbos

08-31-2005, 01:41 PM

Current twinscrolls have the benefit of AVCS, in some cases on both the intake and exhaust, whereas the older twin sequential setup had static cam phasing. Also, from what I have heard, the main complaint of the older twin sequential setup was not responsiveness but the rather rough transition zone with the sequential turbos.

Stephen
actually, man, I got a twinscroll vf38 (yes, a 38, not a 37) off Kastle like a year ago, sold it to a buddy who put it on a Swift GT motor, which is like a 1.3 litre engine, and it spun up on there at under 1000 RPMs. Definitely no AVCS there........ the 38 was a BB turbo, and twinscroll, and it had NO lag on one of the smallest four cylinders in the world. I think he has it on his website www.turbinetech.ca

CapeRex

08-31-2005, 02:40 PM

When I filled out my new Subie owner survey,they asked which car company Subaru should be viewed like the most or something like that,and I said Porsche.

They also asked the one they should be LEAST like,and I said Saturn.:)

C17LOAD

08-31-2005, 05:30 PM

I thought we were talking about a parallel twin turbo setup, with one turbo running off of 3 cylinders, and having no cross over piping or anything. Seems like you could have a fairly simple system and have it be quite effective as well. Maybe Im just a dreamer but a 3.3L or 3.5L flat 6 with an appropriately sized turbo for each bank would have plenty of power and torque for either a high performance tuned Legacy or a high torque tuned Tribeca.

UCD-WRX

08-31-2005, 05:54 PM

Hey Everyone,

There is nothing wrong with a two-turbo setup, one turbo driving each bank. It's still more efficient than a supercharger :D A two parallel turbos system, even with separate intake manifolds, etc., is still two system inefficiencies instead of one.

So, while there's nothing wrong with it, for a given horsepower peak, a two-turbo setup will require more boost, have more lag, create more heat, and take more peripherals (oil lines, etc (reliability issue)), in addition to costing the OEM about twice as much to build (two small turbos cost about 1.9 times the cost of only one big turbo) etc.

Note, I said 'given horsepower peak.' What I mean is if Subaru marketing decides a new car should have 300 crank horsepower, they have two ways to go about it (with no regard to the aftermarketability of the car). Find one turbo that flows enough air within the sweet part of the map to make 300 hp or find two turbos that, in the sweet part of their compressor maps, flow the right air to make 150 hp each.

If you look at a compressor map, a smaller turbo has a smaller (tighter looking) curve. The peak operating range of the turbo is narrower. Throw two turbos like that on a car and the engine rpms over which the little turbos makes their peak efficient flow will be fairly narrow.

Now replace the two with one bigger turbo. It will flow more air on the compressor side over a broader range of turbine rpms which means it will be flowing more air across a broader range of engine rpms. You get, essentially, a broader powerband, for the same peak power.

This is basically the same argument over 1.6L versus 2.5L engines! A 1.6 liter motor may make the same peak power as a 2.5 liter motor, but it will do so over a narrower range of RPMs.

An appropriately sized single turbo is always better than two smaller (yet still appropriately sized for half the engine) turbos, UNLESS the packaging is simply too difficult.

When people say one turbo is laggy compared to two, they're often comparing differently idealized turbo setups. If the single turbo is capable of making 450+ hp in the application, of course it will be more laggy than a twin setup that is only capable of making 300 hp. You exchange laggy for greater power potential. But the OEM doesn't usually care how much power the aftermarket can get out of the car without changing turbos! So they won't chose a 450 hp turbo... they'll usually chose a 300 hp turbo for a 300 hp application.

How much power can a 2.0L USDM WRX make, with a stock turbo? Barely the same as a bone stock STI? See, the OEM sized the WRX turbo to be just right for 227 hp...

BTW, 227 was decided on by the marketing division, for sure. Just like 300 for the STi was a marketing decision. It's all marketing. I'm sure that if SOA decides that they're ready to battle for 911 (997 or whatever) market share, they'll offer a twin turbo. For right now, marketing only cares about beating other sub-$40k cars (from Mustang GT to EVO), so they are more concerned with 300 hp, reliability, cool electronic gizmo's, etc.

UCD-WRX
Shameless plug for my coilover poll: http://forums.nasioc.com/forums/showthread.php?t=819418

Bundyboyz

08-31-2005, 06:14 PM

I know the truth behind SOA twin turbo setup plans...

the user decides to run either the small turbo... or the large and small at the same time.

small turbo for when gas is 5.00 a gallon
small and large for when gas is back under 2.00 a gallon

:D

UCD-WRX

08-31-2005, 06:24 PM

small turbo for when gas is 5.00 a gallon
small and large for when gas is back under 2.00 a gallon
Hey Bundyboyz,

Subaru could save a lot of money, then, by just forgetting about the large turbo. Gas here is over $3/gallon and only expected to go to $4 in the next few weeks.

Yay.

Well, time to start riding a motorcycle :)

UCD-WRX
Shameless plug for my coilover poll: http://forums.nasioc.com/forums/showthread.php?t=819418

SUBE555

08-31-2005, 08:22 PM

Time for Subaru to bring an R2, I think they'd sell like hotcakes for commuters if they can match the 56mpg they can apparently do in Japan. I'd sure buy one. I want the 2WD model only though.

UCD-WRX

08-31-2005, 08:25 PM

Time for Subaru to bring an R2, I think they'd sell like hotcakes for commuters if they can match the 56mpg they can apparently do in Japan. I'd sure buy one. I want the 2WD model only though.
Hey Sube555,

I'm almost certain Subaru of America would not bring a 2WD car here. One of their key advertising features has been their status as the only AWD-only car company... But hey, I bet they could sell a bunch of those, especially if gas goes through the $4 mark.

UCD-WRX
Shameless plug for my coilover poll: http://forums.nasioc.com/forums/showthread.php?t=819418

Phil Jr.

09-01-2005, 05:56 AM

I don't understand what all these arguments are about when the twinscroll is proving so effective. The proof is in the pudding. I'll take a single twinscroll turboed H6 over a twin-turboed H6 anyday.

:lol: What "proof" are you talking about? The original TT Legacy (S401) was a EJ20 TT....not an H6 or anything. And it didnt suffer from lag either, the project was abandoned becuse they couldnt get the transition of the sequential turbos correct. Comparing the responsiveness of the S401 to further advanced and developed engines is sort of trivial IMO.

actually, man, I got a twinscroll vf38 (yes, a 38, not a 37) off Kastle like a year ago, sold it to a buddy who put it on a Swift GT motor, which is like a 1.3 litre engine, and it spun up on there at under 1000 RPMs. Definitely no AVCS there........ the 38 was a BB turbo, and twinscroll, and it had NO lag on one of the smallest four cylinders in the world. I think he has it on his website www.turbinetech.ca

The vf38 as used in the spec-c is indeed a small and efficient turbo, but what do you mean by "it spun up on there at under 1000rpms?" If you are saying it was making 12psi+ on a 1.3L before 1000rpm then I am throwing a BS flag. Ill believe it when I see a dyno and get a full list of mods. Twin scroll turbos are great, but they arent the end all. And they definately cant offer the top end of other solutions.

a two-turbo setup will require more boost, have more lag

???? Have more lag? Care to explain how that is?

If you look at a compressor map, a smaller turbo has a smaller (tighter looking) curve. The peak operating range of the turbo is narrower. Throw two turbos like that on a car and the engine rpms over which the little turbos makes their peak efficient flow will be fairly narrow.

Now replace the two with one bigger turbo. It will flow more air on the compressor side over a broader range of turbine rpms which means it will be flowing more air across a broader range of engine rpms. You get, essentially, a broader powerband, for the same peak power.

This is basically the same argument over 1.6L versus 2.5L engines! A 1.6 liter motor may make the same peak power as a 2.5 liter motor, but it will do so over a narrower range of RPMs.

An appropriately sized single turbo is always better than two smaller (yet still appropriately sized for half the engine) turbos, UNLESS the packaging is simply too difficult.

A large sized turbo MAY be flowing more air than a small turbo at different given RPMs, but it wont reach its peak efficiency or power until later in the RPM range. Do you really think small displacement/large displacement engines is a good analogy to TT vs single turbo engines?? I sure hope not.

SUBE555

09-01-2005, 07:33 PM

Hey Sube555,

I'm almost certain Subaru of America would not bring a 2WD car here. One of their key advertising features has been their status as the only AWD-only car company... But hey, I bet they could sell a bunch of those, especially if gas goes through the $4 mark.

UCD-WRX
Shameless plug for my coilover poll: http://forums.nasioc.com/forums/showthread.php?t=819418

I've been round the Subaru block and I know AWD is there big ticket here and most parts of the world, though unfortunately, most people just don't care, especially when they just want something efficient, like I'm looking for, for commuting mostly, some 15k miles a year that is. I'd really be interested in seeing a diesel though, I think they could make a small one at 60-70mpg for the little R2 and it would be more responsive than the gas engine. Especially if gasoline goes to the $4 mark. As I was coming home today I saw the prices going up again (they can only change prices once per day in WI by law and well.)

Anyways, back to the performance side of things...

Phil Jr. just to get your stats right, the VF38 is used in the foreign Legacy 2.0GT and is a smaller unit, the VF37 is larger and is in the regular STi 2.0L while the VF36 is used in the STi RA Spec C. That was in the V8 models, I'm not sure what's used in the new V9, though could likely be the same.

On another note, I was going to write Subaru in hopes of a Legacy STi, but at the current point and time with fuel prices as they are and outlook being pretty muddy, I'm taking a raincheck on that. Maybe it should be more on the side of asking for the R2.

Phil Jr.

09-02-2005, 06:20 AM

sorry, confused the vf38 and vf36, but I didnt think the vf38 was a twinscroll

I still want to see a dyno of that swift.

jedi_master

09-02-2005, 10:09 AM

I bet Subaru product development reads this stuff like the daily comics....
+1

And Subaru wouldn't bring a twin turbo to market here anyway- Americans are scared now because of gas prices.

Jon [in CT]

09-02-2005, 11:18 AM

And Subaru wouldn't bring a twin turbo to market here anyway- Americans are scared now because of gas prices.The price of gasoline has little affect on the sales of high performance cars, and any Subaru with a 3.0L 6-cylinder twin turbo 375 HP engine would be considered high performance.

Jonathan_Yi

09-02-2005, 02:29 PM

Correct me if I'm wrong, and this is purely for semantics, but isn't a setup that uses 1 turbo for each bank called Biturbo not twin turbo.

RedBean

09-02-2005, 05:13 PM

Correct me if I'm wrong, and this is purely for semantics, but isn't a setup that uses 1 turbo for each bank called Biturbo not twin turbo.
I believe the terms biturbo and twin turbo is just a name and does not denote the particular setup. If anything, shouldn't it be the other way around? Don't cars that have turbos in parallel (one for each bank) use two turbos of the same size, i.e. twins, versus cars that run them sequentially usually have one small and one large, i.e. two or bi?

Phil Jr.

09-04-2005, 08:56 AM

I thought it was Audi that originally called their twin turbo cars "biturbo"....just to be unique and original, just like how they call their wagon's "avants". I didnt think biturbo or twin turbo meant anything different. Arent porches said to be twin turbo vehicles?

THAWA

09-06-2005, 11:22 AM

:lol: What "proof" are you talking about? The original TT Legacy (S401) was a EJ20 TT....not an H6 or anything. And it didnt suffer from lag either, the project was abandoned becuse they couldnt get the transition of the sequential turbos correct. Comparing the responsiveness of the S401 to further advanced and developed engines is sort of trivial IMO.

That's not the original TT Legacy. The original TT Legacy came in either RS or GT format with the EJ20H engine. It had a horrible transition zone from primary to primary/secondary. It got better over the years, and by the time subaru made the s401 (EJ208) the transition zone was quite small, but it doesn't matter. They went to twin scroll turbos and haven't had near the complaints they had with sequential twin turbos. You should compare the s401 with other engines, as that is the pinnacle of twin turbo EJ's. If it can't keep up with a twinscroll, then why go backwards and use that setup?

jay25RS

09-06-2005, 11:30 AM

Correct me if I'm wrong, and this is purely for semantics, but isn't a setup that uses 1 turbo for each bank called Biturbo not twin turbo.

Audi's 2.7 Litre S4 is Bi-Turbo or Sequential Turbo.

Hennessey Motorsports' Vipers are Twin Turbo.

Sequential or Bi-Turbo'd engines have a small turbo and a larger one.

Twin turbo'd engines have two turbos of equal size.

-Jason

edit: for clarity.

Phil Jr.

09-06-2005, 05:31 PM

but Audi's "bi-turbo" S4 is a non-sequential setup.... :huh:

That's not the original TT Legacy. The original TT Legacy came in either RS or GT format with the EJ20H engine. It had a horrible transition zone from primary to primary/secondary. It got better over the years, and by the time subaru made the s401 (EJ208) the transition zone was quite small, but it doesn't matter. They went to twin scroll turbos and haven't had near the complaints they had with sequential twin turbos. You should compare the s401 with other engines, as that is the pinnacle of twin turbo EJ's. If it can't keep up with a twinscroll, then why go backwards and use that setup?

I agree it is pointless to use a TT design on a 2.0L 4cylinder engine that only needs to make about 300hp. But on an H6 engine aiming for 350-400hp, a TT setup could work very well, whereas a single twin-scroll turbo may not be ideal.

THAWA

09-06-2005, 05:48 PM

jay25RS

09-06-2005, 10:54 PM

but Audi's "bi-turbo" S4 is a non-sequential setup.... :huh:

I agree it is pointless to use a TT design on a 2.0L 4cylinder engine that only needs to make about 300hp. But on an H6 engine aiming for 350-400hp, a TT setup could work very well, whereas a single twin-scroll turbo may not be ideal.

Oops... Lol my bad... I meant to say it differently... Edited my original post for clarity.

-Jason

Phil Jr.

09-07-2005, 02:33 AM

Audi's 2.7 Litre S4 is Bi-Turbo or Sequential Turbo.

Sequential or Bi-Turbo'd engines have a small turbo and a larger one.

-Jason

edit: for clarity.

...The B5 S4 has NON-sequential turbos. As in it uses two identical K03 turbos. And Audi says the S4 has a "bi-turbo engine".....

SUBE555

09-07-2005, 08:13 AM

I'm going to have to disagree with you, a single turbo, even single scroll would probably be better than twin turbo. EJ257's are quite driveable and don't feel very laggy, at least, not laggy enough to complain about. Add another 500cc's into the mix and I don't think you'd really need to worry about responsiveness or driveability, especially if the valve/cam upgrades continue.

It's not a 2.5L flat four that the topic at hand is talking about. It's an H6 where there is sufficient lack of space for adequate 'hot' piping in the engine bay and would be very inefficient to do so anyhow making two matched parallel turbos a more efficient prospect IMO. An H6 with two heads and exhaust ports about as far apart as can be is very much different than an inline 6 or 4 where the ports are ALL very close together, where much of the big singles people mention work better. Sure singles are done on V-6's too, but more rare.

You need to think more about engine configuration, space claims, routings, etc as the space clamps down in a more stuffed engine bay featuring an H6 and how feasible it really may be to run 'hot' plumbing all over the place. As it is now that huge manifold is a energy sponge to an extent for us, super short manifolds to pressurize and reduce heat soak too would be a superior situation.

It has to be though of from a purely technical aspect in a design sense.

My opinion comes from me being a mechanical designer. :)

jay25RS

09-07-2005, 10:21 AM

...The B5 S4 has NON-sequential turbos. As in it uses two identical K03 turbos. And Audi says the S4 has a "bi-turbo engine".....

Ok, gotcha... I was misinformed then by friend who is an Audi enthusiast. I never took the time to investigate Audi's because I don't particularly give a damn about them lol. Thanks for correcting me. :alien:

-Jason

mlrtime

09-07-2005, 05:44 PM

a twin turbo diesel make decent HP and 35+ mph would be nice. AWD assumed.

THAWA

09-07-2005, 11:23 PM

It's not a 2.5L flat four that the topic at hand is talking about. It's an H6 where there is sufficient lack of space for adequate 'hot' piping in the engine bay and would be very inefficient to do so anyhow making two matched parallel turbos a more efficient prospect IMO. An H6 with two heads and exhaust ports about as far apart as can be is very much different than an inline 6 or 4 where the ports are ALL very close together, where much of the big singles people mention work better. Sure singles are done on V-6's too, but more rare.

You need to think more about engine configuration, space claims, routings, etc as the space clamps down in a more stuffed engine bay featuring an H6 and how feasible it really may be to run 'hot' plumbing all over the place. As it is now that huge manifold is a energy sponge to an extent for us, super short manifolds to pressurize and reduce heat soak too would be a superior situation.

It has to be though of from a purely technical aspect in a design sense.

My opinion comes from me being a mechanical designer. :)

First of all, I know what the topic is about. I was stating that if driveability isn't much of a concern with a 4 cyl 2.5l engine, then adding two more cylinders and 500 more cc's would make driveability even less of a concern. How much larger do you think the EZ30 is than any DOHC EJ engine? Take a minute to look at an EZ30 in an enginebay, then try and say the same things. A flat 6 does seem much larger than a flat 4 in theory, but look at the actual applications before you make these claims about it being too large to have a single turbo setup. Also a parallel turbo setup would need more exhaust piping than a single, not to mention intake piping, and all the sensors that would be related to that. You're adding more complication than there needs to be. Besides, there's no way subaru would make a parallel turbo engine. The only engines that get more than one turbo are Legacy based cars, the legacy is made for driveability, street driveability. Two parallel turbos aren't the greatest thing for driveability.