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Old 04-28-2002, 10:09 PM   #1
STiWRXdotcom
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Default Is a Twin Turbo really worth it?

It seems to me that the second turbo would eatup to much of the first turbos power being that it is only a 4 cyl, is it worth paying twice as much for a twin turbo?
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Old 04-28-2002, 10:18 PM   #2
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I don't think that a kit has ben perfected for our car yet so I wouldn't really worry about it right now. I believe Kastle was running one for a while but its out for now. you might want to ask him.

Brad
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Old 04-28-2002, 10:29 PM   #3
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IIRC, the twin-turbo legacy (aka: liberty) 2.0L engines are not sequential turbos. They are two small turbos run in parallel, so that each turbo is fed essentially by two cylinders.

Brian
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Old 04-28-2002, 11:08 PM   #4
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Quote:
Originally posted by STiTuner
I don't think that a kit has ben perfected for our car yet so I wouldn't really worry about it right now. I believe Kastle was running one for a while but its out for now. you might want to ask him.

Brad
Is this true? He pulled it?
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Old 04-28-2002, 11:39 PM   #5
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Thumbs up Here's one...

It looks like Forced Air Technologies is developing one... http://www.forcedairtech.com/FORCED-...TAGE4-KIT.html

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Old 04-28-2002, 11:42 PM   #6
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That Pic is Kastle's Engine bay, but sounds like it didn't stay in for very long.
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Old 04-28-2002, 11:53 PM   #7
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from what ive read the two turbos were fighting eachother so they are gonna make some sort of dual throttle body design.
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Old 04-29-2002, 12:02 AM   #8
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Default Huh?

Huh? Why would they fight each other if they are both sized correctly? Dual intakes would only complicate the problem. There could be slight differences in boost levels on each side of the engine. I don't know how bad that would be but it can't be good for engine management. Imagine trying to adjust timing on each head and cam differently. It aint possible.

Sometimes people throw turbos in cars that they aren't suited for. Sounds like this might be the case.
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Old 04-29-2002, 12:10 AM   #9
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QUOTE]Originally posted by kastle
Well, I have an update.... This is directly from Robert...

It's virtually impossible to try to take 2 separate Turbos and make them charge into one single throttle body. The Turbos are trying to over pressure each other.

So what we are doing to try to resolve this problem now, to make the twin Turbo system work with the 2.5L engine and intake design, we are designing a dual throttle body set-up that will bolt on to your factory single throttle body intake. That will make it a true twin Turbo system and avoid this problem on future twin Turbo kits.

Customers are welcome to call so that I can personally answer their questions.
(928) 632-1251

Thanks, Robert
[/quote]
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Old 04-29-2002, 01:19 AM   #10
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Ahhh.
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Old 04-29-2002, 02:23 AM   #11
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yup, thats my engine (err, was my engine... ). And what boysetsfire posted is correct... right from Roberts mouth... But it was really fun while it was on there.
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Old 04-29-2002, 04:24 AM   #12
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Quote:
Originally posted by kastle
yup, thats my engine (err, was my engine... ). And what boysetsfire posted is correct... right from Roberts mouth... But it was really fun while it was on there.
i have NO doubt about that...those were twin GT15's right???

Jeremy

p.s.: 2 turbo's= 100% tuning NIGHTMARE!
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Old 04-29-2002, 04:25 AM   #13
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Ah! I am impressed to see the twin turbo fits nicely in the RS The kit looks awesome by itself...how much is it anyway?

-Benson (Another MY98 Owner)
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Old 04-29-2002, 04:27 AM   #14
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Quote:
Originally posted by bensonwrx
Ah! I am impressed to see the twin turbo fits nicely in the RS The kit looks awesome by itself...how much is it anyway?

-Benson (Another MY98 Owner)
IIRC the kit price was like 5g's, plus the tec-2 and other stuff, and now kastle needs a gearset.

jeremy
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Old 04-29-2002, 11:26 AM   #15
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More like $4500.... And tuning wasn't so bad, just had to have Shiv come out and personally tune the TEC-II. And you'll need all the extras that go with having a big-ass upgraded car: gears, exhaust, fuel system... etc...

I had upgraded to a Chalak 1/2 dog, but that just recently broke... searching for alternatives now...
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Old 04-29-2002, 04:18 PM   #16
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Sorry to hear the car is sick Kastle, happy gearbox selecting
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Old 04-29-2002, 05:34 PM   #17
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Wow, figured only a rich man can afford such setup; how's the performance goes? I hope it's all worth it.

-Benson (Another MY98 Owner)
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Old 04-29-2002, 05:53 PM   #18
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rich or massively leveraged.
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Old 04-29-2002, 06:25 PM   #19
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Quote:
rich or massively leveraged.
I'm not rich... I don't have massive amounts of leverage.... I'm just lucky...
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Old 04-29-2002, 07:01 PM   #20
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playing at those Indian casinos eh?
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Old 04-29-2002, 07:14 PM   #21
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nah.. don't gamble much... I just have a good job that pays very well, no credit debt and everything in order.... I pay cash for most everything I buy as it is...
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Old 04-29-2002, 08:44 PM   #22
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Lightbulb IMO

I like the setup. It's good to have people out there willing to sacrifice, literally in this case, their car's motor in search of more power. However after seeing all the downsides of aftermarket induction, they way I'm going to go is to drop in a WRX 2.0L turbo motor into my RS. There's something about having reliable power. The hard parts will be the wiring, etc.


Skylab™
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Old 04-30-2002, 03:52 PM   #23
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According to http://www.forcedairtech.com/FORCED-...TAGE4-KIT.html:
Quote:
... we've found that it's virtually impossible to try to take 2 seperate Turbos and make them charge into one single throttle body. The Turbos are trying to "over pressure" each other. So what we are doing to try to resolve this problem now, to make the twin Turbo system work with the 2.5L engine and intake design, is we are designing a dual throttle body setup that will bolt on to your factory single throttle body intake This will make it a true twin Turbo system and avoid this problem in the future.
The problem, of course, is the EJ2x's 1->3->2->4 firing order. During one engine revolution one turbo's turbine will receive two exhaust puffs to spin it while the other receives none. On the next revolution, the situation is reversed. I cannot see how a dual throttle body bolted onto the stock throttle body could possibly work if you wish to keep the shared intercooler.

Here's an ASCII drawing of an alternative solution which presumes a single pipe into the intercooler, fed by both turbos:
Code:
__________________________O______________________
                         /
                        /
From LH Turbo ->       /         <- From RH Turbo
                      /
_____________________/        ___________________
                    |    T    |
                    |    o    |
                    |         |
                    |    I    |
                    |    C    |
                    |         |
                    |    |    |
                    |    V    |
                    |         |
The diagonal line represents a hinged flap valve and shows the situation when the RH Turbo is receiving its two exhaust puffs and is producing boost. On the next engine revolution, the LH Turbo will get its two puffs and produce boost, which will push that flap valve over and keep the boost from trying to backspin the other turbo.

An alternative is to insure that each turbo is getting more-or-less evenly spaced exhaust puffs by re-routing the exhaust from one cylinder on each side over to the other side. Here's an example of such an exhaust manifold system:

Last edited by Jon [in CT]; 04-30-2002 at 03:57 PM.
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Old 04-30-2002, 05:30 PM   #24
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I am by no means an expert, but from everything that I have read a twin turbo setup is just not cost effective on the Impreza's 2.5L engine. They are complicated and will not provide a significant performance increase over a properly sized turbo with good engine management. Just my opinion but I think money is better spent elsewhere.
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Old 04-30-2002, 07:50 PM   #25
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Quote:
IIRC, the twin-turbo legacy (aka: liberty) 2.0L engines are not sequential turbos. They are two small turbos run in parallel, so that each turbo is fed essentially by two cylinders.
Not correct....they are sequential turbos, primary one is small & spools up real quick, secondary one is larger & takes over at around 4000rpm...

2 known problems with the factory TT setup:

1) dip or hole in torque curve when first turbo runs out of puff & second turbo staging. Couple of friends of mine say it's definitely noticeable...
2) Big bore exhaust systems can kill the primary turbo by allowing it to overspeed...

Despite that they sound wicked!, cross between the boxer "snarl/growl" and the Volkswagen V5 (not V6) "thrum".....
Still, I'd rather have one appropriately sized turbo -- much easier...
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