VF turbo upgrade! Oem upgrade for your Td04s!
Many will speak of the Td04 turbo as the the biggest limitation of the Forester's arsenal. It is a bottleneck for those searching higher horsepower figures but it has it's perks. With an offroad build on a Fxt you will find it spools quickly and really feels like a small 6 cylinder rather than a turbo four. Helping you make low end power for slower off road terrains and gets you off the line without any drama while giving up the higher end rpm power. It makes lower rpm cruising much easier, i.e. 5th gear at 45 mphs is possible while the vf39 struggles to keep up enough power and will bog when trying to slightly accelerate.
On the other hand there is a bit of lag to the VF turbos. Just part of single scroll life but that is the fun of turbos or at least to me it is. My VF39 will start making a power around 3100 which is a bit late versus the little Td04. As much as I enjoy the harder boost later in the powerband of the VF39 I do sometimes miss the pluckiness of the Td04 for around town driving. Stage 2 will see the VF singing at 19 psi of boost on a pump gas tune.
I truly enjoy this upgrade for it's simplicity. With a the addition of a downpipe, STi intercooler, VF39 and tune you are enjoing a new setup. You don't need to upgrade fuel pumps, injectors, uppipes, oil lines, etc.. You can start with the minimal list above and build onwards after the fact. Making it an amazing horsepower per dollar upgrade.
If you are really power hungry you will need to look a larger turbo than the VF with 330 hp being a maximized power figure. But with Oem fitment and quality it is a great stepping stone or stopping point for many. Cobb even has their own off the shelf tunes that will get you going for the time being until you want to get a protune.
A few items to upgrade but not necessary,. After installing this on my Forester I would highly recommend an Iag braided oil feed line. The stock hardline is very tough to get into the proper location and can be quite the struggle. The lower coolant hose off the turbo to the engine see extreme heat on the lower side of the turbo and right above the uppipe. Another hose that sees it’s fair share of heat degradation is the oil return hose. If you have the turbo off this is the best time to replace it as it is wedged deep behind the uppipe, turbo, and transmission.
The 90 degree hose from the Sti intercooler makes contact with the turbo but it isn’t the best fit. After reading of a few popping off I upgraded to the Grimmspeed silicone intercooler hose. The 90 degree hose is a bit on the large size so it can be trimmed to fit your specific setup! Adding the Grimmspeed hood scoop splitter can help lower those intake temps with a specifically made for the Forester to 04-07 STi intercooler. The larger 02-03 STi will work in conjunction with the GS splitter to help direct that air flow to the intercooler.
Questions, comments, thoughts? Leave them below!
Amazon links: Vf39 new turbo
Subaru turbo lower coolant hose
Subaru turbo oil return hose