JCT

I've spent quite a bit of time researching turbo upgrade options and wanted to get your educated opinions for my daily driven 05 FXT 4EAT.

I feel it is very important to differentiate this thread from the others comparing these turbos, because it is 4EAT specific. A few hundred RPM difference can easily be adjusted for using a clutch pedal on a MT, but with an Automatic trans, it is much more important to match the turbo to the trans.

Like most people, I'm looking for bolt-on mods. I do not want to mod my transmission. Maybe Cobb will release 4EAT TCU tuning support like they have talked about, that would be great but until then - I think my trans is going to remain stock. (I believe with a 3200rpm stall speed)

I would like to have safe, streetable, semi-MPG friendly power so i can decide if I want horrible mileage or good mileage on a road trip with my right foot. So I'd prefer to stick to stock injectors.

Supporting mods:
STI TMIC
STI Hood scoop
Walbro Fuel Pump
STI Catless Uppipe
Cobb Catted Downpipe
STI CatBack Exhaust
INJECTORS STOCK STI/FXT

3 Options
(data from Subaru Turbo List - Newbies & FAQs - NASIOC)

IHI VF39 - 400-450?cfm at 18psi 250-325whp
Full boost between 3000-3500rpms.

IHI VF34 - 460cfm at 18psi, 250-325whp
Full boost between 3000-3500rpms. May spool faster than 39 due to roller bearing.

Evo3 16G - 575cfm, 275-375whp
Full boost between 3200-3700rpms.

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Is there a strong argument for or against these turbos for a 4EAT equipped FXT?

I don't see too much performance difference with the 34 to justify the additional cost over a 39. It seems that you'd either go with a 39 or step up to an Evo3 16G rather than paying the premium for a 34, unless you got a really good deal on it.

The faster spool of the VF39 and VF34 are great, but the Evo3 16G is pretty close with more upside. I've read claims of Evo316G's hitting full boost below 3k rpm, but I don't know if that is true.

Other than spool and output potential, are there other pros/cons I am missing when paired with a 4EAT driving in the real world? I'm speculating boost creep will be a non-issue with my catted downpipe.

Note - I may post this on Nasioc as well, since there are a lot of 4EAT owners there.

In a Nutshell....
What is the best turbo to use on a 4EAT Suby with STI/FXT injectors (upgraded pump) that provides loads of power with the best daily driver experience?

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05 XT 4EAT

Andy_PHA

I just installed a blouch 18G on mine. First and most importantly we do not see anywhere near the same whp numbers as an equally equipped 5MT, so plan on seeing number more similar to the ones on the left above. So with that out of the way I'd say save some money and just go with the VF39 or 43/48 (depending on if you are worried about the cracking issues of the 39). If you just want more than you're getting with stage2 this will be fine. But again don't expect to see much more than 250whp because of the power robbing 4eat.
With an 8cm 18g I saw peak torque by about 2700 rpm so I'm not feeling much lag at all. All I notice is a bit more delay from a stop than with stage 2. And again that's with an 8cm hot side and a true large tdo6 housing.

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06 FXT Limited 4EAT 18G powered.

XT06'

The vf34 is more expensive but the spool up time compared the the vf39 is noticeable. And for a daily driver the fast spool of the 34 will be nice. The 16 is the probably going to be the nicest and have the most power potential of the three. If you have the money go with the 16g.

You post doesnt say, but do you have an accessport? If you havent tired a stg 2 setup i would suggest it before upgrading.

g00fy

I'd say go for the EvoIII with an 8cm housing to avoid boost creep, and get max power. Otherwise I'd swing for a VF43 or I'd bite the bullet get injectors and an 18 or 20G with 8cm housing. From what i've read boost creep/spike is an issue with the Td04's, VF34's, and 39's, the VF43 has an over sized wastegate to help combat the issue, but the 8cm housing on the big turbo's is probably your best bet to avoid it without going external wastegate.

But before you get any of these upgrades I'd recommend a tranny cooler!!! They're not very expensive and the benefits far out weigh the costs.

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20G powered 05XT CGM w/fully built IPT 4EAT

JCT

Yes, I have a Cobb AP V2 that should be here in the next couple of days. I haven't even gone to stage 2 yet, but I read about so many people going there and then wanting more that I just assume I will want more. Part of why I bought a FXT was the ease of doing an STI conversion so I'm pretty committed to a turbo upgrade.

I could be mistaken, but since I'm environmentally conscious and run a catted DP, I don't think boost creep will be an issue for me. (?)

With that in mind, I believe a 7cm housing would provide me quicker spool than 8cm without boost creep issues on the Evo3 18G. And it would save $100+.

I decided against the VF43 because there is no OTS support for it. If I'm going with that size of turbo, I may as well go VF39 since there is so much support, maps and replacement turbos for it out there and no real performance hit vs. the 43. The 39 is the only option that will allow me to run OTS maps. However, If I got a screaming deal on a VF43, i'd definitely consider it.

I prefer stock injectors because you have to draw the line somewhere and i don't want to end up getting really bad gas mileage. It's not a cost thing, injector upgrades aren't too expensive, I just want to draw a line and try not to cross it, because I know from experience with past vehicles if you dont' draw a line, it will never be enough and I'd keep redoing what I've already done. :) Maybe injectors arent' the best thing to draw a line with, IDK.

Do any of you see a DISADVANTAGE to spooling too fast with the 4EAT, like with the VF34? I'm not really sure what the ideal full boost rpm is with a 3200 stall torque converter. I have always thought that the faster your turbo spools, the better. But I read a thread somewhere that someone specualted it might be bad to boost too soon with a 4EAT, but I'm struggling with why. It may not have been a good source.

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05 XT 4EAT

g00fy

From what i understand you want max boost to hit right around where your torque converter locks up. If you hit max boost after that your gonna feel lag, if you hit max boost before that the turbo's gonna be running out of breath before you start putting the power down. If andy PHA can hit max torque at 2700rpms with a Td06 18G 8cm then I'm willing to bet the EvoIII 8cm will probably not have spool issues.

Also cruise around Nasioc and search boost creep, except for the guys with 8cm housings and external wastegates, most people do end up with some sort of creep or spike especially after they get a good hi-flow exhaust. With the 4eat lag isn't as seriouse of an issue as it is with manuals. Most guys say a 20g or Green is the best combo with a 4eat because the torque converter still puts load on the motor before it's completely locked up, so when it does finally lock up your either approaching max boost or your way past it. In my situation i have a high stall converter around 4k, and with my TD04 by the time my converter locks up the car's outta breath, and creeping to around 17 - 18psi instead of 16.9.

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20G powered 05XT CGM w/fully built IPT 4EAT

Christian.

Someone has given me this link and asked for my input. I will explain the best I can below.

IHI VF39 - These turbos are developed for 2.5L that run on poor gas. These are a good combination for this vehicle IMO. Just watch out for boost creep due to improper WG design or running with a catless exhaust.

IHI VF34 - These turbos are developed for 2.0L that run on great Japanese pump gas. They are designed to run higher boost on 2.0L engines then to taper boost quickly by redline. These turbos usually run out of air on a 2.5L engine. These have never performed well at our elevation and these are a bad combination for a 2.5L IMO. This turbo may work well at sea level.

Evo3 16G - This turbo usually works best on a 2.0L and I love to use these on 2.0L engines. A 2.5L engine usually uses a 18G or a 20G for a better match.

A good tuner should be able to use AVCS to almost eliminate turbo lag on the 4EAT.

Take care,
Christian.

blackbus

having owned a vf34 and 8cm 20g, I'd suggest the vf34 for an automatic and what you are looking for. I think the 20g would be too laggy with an auto. vf34 = instaboost on tip in.

Andy_PHA

oh and just for the record I'm running the forester specific catted TXS TBE and an 8cm housing and I was still having boost spike issues. I'm not 100% sure it wasn't because of the new vac hose I had to use with the turbo, or what. It wasn't totally uncontrollable, but it was there none the less. I personally think the 18G will be a good match once I get all my issues straightened out.

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06 FXT Limited 4EAT 18G powered.

Integrity Performance

The spool and max power output on those 3 turbos is wrong when looking at our 2.5L motors. Heck the power output numbers are off for ANY subaru motor. On the 2.5 they spool a LOT faster than that, and make more power. 300whp on 34/39 on a 2.0L is almost impossible without meth or race gas. 300whp on a 2.5L takes a typical stage 2 setup or less. (speaking of an average reading dyno)

And the EVO3 16G spools the same or faster than the 34/39s.. Mitsu based turbos are more efficient, so even an 18G lays down as much low RPM power as a 34/39.



Also, keep in mind, that being at Xpsi by Xrpm doesnt dictate how much power you are making at that rpm. The evo3 16G will be flowing more air at 10PSI than a VF34/39 does at 14PSI.

The 34/39 are 35lb/min turbos. The evo3 16G is a 39lb turbo, with better housings and wheels. Potential for roughly 40-50whp more than the 34/39 and the same spool or better.

If you have the option of a mitsu based turbo VS an IHI, its never a good idea to go with the IHI unless money is a factor.

The ONLY IHI you should consider for a 2.5L would be the VF22 or possibly the VF23. Even those are kinda small.

blackbus

f it! just get the 20g! hahaha

I wish I went with the 20g from the get go. When I had my vf34 tuned, the aussie tuner said "aye mate, that's a tiny turbo. What is it, a vf22? You need to get atleast a 20g mate." Almost 4 years later I did.

JCT

My logic in not getting a big turbo was I wanted better gas mileage, but I've been reading I could actually get BETTER mileage from a 18g or 20g than a smaller turbo?!?!

I realize that a larger turbo could be more efficient in some cases, but if I need to get larger injectors to support it, it seems that I would be using more fuel.

How big of a turbo can you get and still have a very well mannered daily driver?

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05 XT 4EAT

AChan10

dang... plus the cost of a 20g... man...

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2004 Sierra Gold FXT

g00fy

I'm actually in the exact same situation with my 05' FXT and since i have to get injectors, I figure i might as well go for the gold and get an FPgreen to take full advantage of everything, or at the very least a TD06-20G 8cm.

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20G powered 05XT CGM w/fully built IPT 4EAT

JCT

Any ideas on gas mileage, daily drivability and tunability of the 18G vs 20g vs FP Green?

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05 XT 4EAT