Subaru Forester XT: VF52 and Supporting Mods with Dyno Details (SH 2008-2012)

The project vehicle is a Subaru Forester XT SH 2008-2012 Model (it has the same engine as the Impreza WRX 2008), and the modifications are focused around an upgrade to the IHI VF52 turbocharger from the stock TD04. This is a detailed record of my power/engine modifications, and the real results that accompanied each upgrade individually. Professional eTuning was performed at each stage to ensure that everything worked safely as intended.

An eTune (email ECU tune) from TorquedPerformance was performed for every stage, and each change road dyno'd for my own personal records using Virtual Dyno (great software that is available free from virtualdyno.net). Please note that fuel type used, engine mileage, as well as environmental factors can effect the presented data. All road dyno runs were performed on the OEM wheels of 17"x7" with the standard 225/55R17 tyre size. The Power numbers quoted throughout is the estimated power at the wheels.

My Main Goal

The Forester SH is a modern looking car with high practical capabilities, mainly being large cargo space when all seats are folded down, for a car of it's small SUV size. The fact that the engine comes with a turbo from the factory means its been braced to handle a bit more power easily. And being a cheap second hand deal, it makes for a very attractive purchase.

I was specifically after a relatively safe tune throughout the entire process, I'd rather lose a few horses for engine safety, than gain a few by increasing the risk to the engine's life. I've also tuned for 95 Octane Fuel, but outside of tuning periods I always run 98 Octane Fuel for an extra level of 'safety'. Those that get eTuned on 98 Octane fuel or higher should get better numbers if everything is installed and functioning correctly.

The modifications I have made to the vehicle have been prioritised based on the highest power-gain-vs-cost. The exhaust is arguably an exception, it doesn't gain much power, but it eliminates any airflow bottlenecks, and I also just wanted my baby to sound nice!

Contents

1. Baseline Dyno: No Modifications
2. Stock ECU Remap: eTune
3. Full Turbo Back Exhaust (TBE): Ultrex
4. Turbocharger Upgrade: IHI VF52
5. Top Mount Intercooler (TMIC), Bypass Valve (BPV), Electronic Boost Control Solenoid (EBCS)
6. Air Intake: COBB SF Short Ram Intake (SRI)
7. Conclusion: Combined Dyno Graph

Baseline

Stock, No Modifications

Here's my baseline graph. Since I'm using a road dyno this will likely vary from others performing a run in the same vehicle. The main variables would be the road used as well as weather conditions during that time. The important thing is that you get a baseline, no matter how different to others it may seem, as you need this to see if you had any real gains throughout the ugprade process.

Baseline Road Dyno Results

Power: 126 kW (169 HP) @ 5184 rpm
Torque: 251 Nm (185 Lb-Ft) @ 3216 rpm
Max Boost: 13 psi (0.896 bar) @ ~2700 rpm

Stock ECU Remap Only [Stage 1]

eTune

Eric from TorquedPerformance is a very good eTuner with a nice, and well-priced, collection of preconfigured WRX ECU maps on his website. The Forester specific tuning will have to be a 'custom' map with a minimal additional cost - but it's well worth the money as he's really prompt with his replies (within 24 hours) - and this is very important since you'll be doing 2-4 runs with him per map to lock down the final verison. All tuning on my vehicle has been performed via eTune by Eric.

This was the first modification I wanted to perform, but it is mainly done to satisfy my curiosity, and to get a complete comparison between the upgrade steps. For those that don't intend to do much with the vehicle, definitely try this first - but for those that plan to get to an upgraded turbo quickly, or have had plenty of time driving a remapped ECU in another vehicle, definitely skip this one.

Performance wise, there was a boost in torque, but the main benefit I felt was the remapped throttle position. Instead of the OEM mapping where the throttle curve is touchy with minimal input, the throttle is much more progressive and natural, it makes first gear much more smoother. I believe the OEM configuration is to give new drivers the 'perky' engine feel without having to put your foot down, when all it's really doing is tricking them with this type of configuration via the drive by wire (DBW).

Here's a quick sketch up of how the the acceleration has been smoothed out for the pedal input - the aftermarket eTune provides a much more natural pedal feel.

Power Gains

+3.17% Power, +13.9% Torque

Power gains are minimal as expected, but there is a considerable gain in torque. There is a very noticeable difference in throttle feel, and for those that just want to enhance their vehicle without bolting on anything else, this is a great mod. Also notice the significantly smoother boost curve, allowing for smoother delivery of power.

Power: 130 kW (174 HP) @ 4906 rpm
Torque: 286 Nm (211 Lb-Ft) @ 3430 rpm
Max Boost: 16 psi (1.10 bar) @ ~2950 rpm

Turbo Back Exhaust (TBE) [Stage 2]

Ultrex Full Stainless Steel WRX MY11-MY14 Quad Tip Exhaust (Modified)

Ultrex are Western Australia based and are great to deal with. They do their own designed exhausts, as well as wheels. Rob from Ultrex helped me out with this one, although you can't find a premade Forester SH exhaust on their website, Rob made the appropriate modifications to the WRX down pipe to fit the Forester SH, and gave the appropriate tips to get the WRX exhaust fitted on to the Forester.

Stock downpipe (left) with restrictive plate, and
the Ultrex downpipe (right) with a fully open bell mouth.

I first ran just the Cat-back exhaust while I was still on the Stock ECU Remap. I just wanted a bit of a growl, and it really did the job well, with no drone - but obviously there was no power gains as the restriction is at the front of the downpipe coming out of the turbo. After installing the downpipe and retuning, there was some drone at certain RPM ranges, unfortunately around the cruise RPMS of around 2500-2800, but this is to be expected.

You can't have a no drone solution and have optimal performance, unless of course you have custom crafted Helmholtz Resonators in place/added to your personal specifications, which is much too expensive for this project - or you have a variable exhaust/butterfly valve that will change the air flow internally, costing from a cheap DIY with welding skills, to expensive aftermarket options. An example of variable exhausts is the Varex Muffler (XForce Website). The only issue I see with variable muffler types though, is that if you go lead foot when flow is restricted, the engine might run a bit richer than normal due to reduced air flow, but whether or not this is significantly harmful to the engine, I've not investigated, but I'm sure if you are careful with the throttle depending on the adjusted flow it'll be okay (this is too much consideration for myself).

Power Gains

+6.92% Power, +9.44% Torque

With the stock IHI TD04 turbo, when combined with any full flow TBE, the spin up and initial acceleration is insanely good. Unfortunately due to the small turbo the fun doesn't last long. But for those that don't like pushing the car into higher RPM ranges, this could a perfect setup. For myself though, I like to wide open throttle (WOT) to redline...

Power: 139 kW (186 HP) @ 4568 rpm
Torque: 313 Nm (231 Lb-Ft) @ 3461 rpm
Max Boost: ~16.3 psi (1.12 bar) @ ~2900 rpm

Turbocharger: Bigger & Better [Stage 2.52]

IHI VF52

I purchased this baby from Import Image Racing. These guys had a great price for the IHI VF52 (I haven't checked their website pricing recently). With the currency conversion at the time, the VF52 was a few hundred dollars cheaper than purchasing locally. The customer service from Josh was very prompt and friendly, and he was incredibly helpful. He gave me the best shipping option for International delivery at no extra cost, it got to me within the week.

Stock TD04 (left) vs WRX VF52 (right)

The IHI VF52 is the standard turbo on the WRX 2009 onwards. Unfortunately the 'bad' WRX was the one with the TD04, I'm sure Subaru just dumped the unwanted leftover TD04s from the WRX line into the Forester models for the next following years. Since the engines between the two are practically identical, going to a VF52 in a Forester SH (with a conservative tune) should be reliable and safe (I've not had any issues after a few years of driving).

Power Gains

+18.0% Power, +6.71% Torque

Probably the highest impact modification, and best bang for your buck power gain as well. Gains would be even better with a bigger turbo, but it would be a compromise with longer spool time. I don't notice the spool time difference going to the bigger VF52, since I usually just go straight past those early RPM ranges if I'm taking off speedily. The difference you do notice though, is the fact that it keeps pulling well past mid-range RPMs, and does a decent job up to redline - vastly different to the smaller TD04.

The power and torque curves shift about 200 RPM later than with the TD04 in the low RPM range, but after the intersecting point around 3200 RPM, the VF52 pulls a lot stronger, and tapers off at a lot lower rate than the TD04 heading to redline. The area under the graph is significantly larger after moving to the VF52. Basically, more power, and for longer.

Power: 164 kW (220 HP) @ 5514 rpm
Torque: 334 Nm (246 Lb-Ft) @ 3680 rpm
Max Boost: 18 psi (1.24 bar) @ ~3200 rpm

Top Mount Intercooler (TMIC), Bypass Valve (BPV), and Electronic Boost Control Solenoid (EBCS) [Stage 3.52]

Mishimoto TMIC Forester SH & Turbosmart Kompact BPV

The main purpose of upgrading the TMIC was mainly a peace of mind one - I didn't want the plastic end tanks on the OEM TMIC to pop off when I was in the middle of a fun boosting session. The Mishimoto is one solid well welded piece. I didn't want to go for an FMIC as there'd be a lot more work involved, and although possible gains in cooler temperatures, at a slight cost to air travel path length, I really wanted to keep the traditional Subaru functional hood scoop - especially since the next generation Foresters no longer had the hood scoop, it was the last Forester with a scoop (even if the scoop was not as aesthetically impressive as those found on earlier generation WRXs).

Mishimoto TMIC Installed - OEM fitment, but with more depth, for more cooling. The plastic engine cover fits over the top with no issues (not shown).

The Mishimoto was a second choice to be honest. What I really wanted, just didn't exist at the time, and still doesn't appear to have been created yet. My first option was the non-existent Forester SH Verticooler from Process West, if this was available, I would've thrown my money at it, even if it cost 50% more. Amongst all the aftermarket Forester SH compatible TMICs, the newly released Mishimoto TMIC turned out to be a very effective and economical option. The package from Prospeed Racing contained a Turbosmart Kompact Bypass Valve (BPV) at minimal cost. Also the fit of the Mishimoto is practically OEM, except this TMIC has a larger flow area.

Grimmspeed EBCS

The Grimmspeed Electronic Boost Contol Solenoid (EBCS) adds an extra port for control, changing it from the stock bleed style 2 port to an interrupt style 3 port . It allows for holding higher boost levels and higher accuracy in tuning - I think it is meant to reduce turbo spool time, but it's best to ask your tuner about this as I don't think I noticed much difference there. I know there was a choice between the Grimmspeed and a generic EBCS on the market, which was about half the price (~$60), but given the small price difference it felt safest to just buy the real thing with guaranteed quality control.

Power Gains

+6.71% Power, +1.80% Torque

The welded end tanks and EBCS allowed the eTune to increase my boost levels safely, increasing performance across the board.

Power: 175 kW (235 HP) @ 5536 rpm
Torque: 340 Nm (251 Lb-Ft) @ 4244 rpm
Max Boost: 19 psi (1.31 bar) @ ~3900 rpm (other runs were actually around 3300 rpm)

Short Ram Intake (SRI)

COBB SF Intake

At this point, after all the more expensive and effective engine bolt-on upgrades, I figured, what the heck - just do it. I was quite against an air intake initially, and especially an oiled filter, as that can cause issues with the O2 Sensor in the intake. Since I'm the kind of person that's happy to maintain my vehicle, cleaning the O2 sensor with a MAF Spray Cleaner, as well as Cleaning the Oiled Filter was no extra work for me. I wanted to see what power I could gain with this addition. One thing I definitely did gain though, is a BOV-type sound, when letting off the accelerator. I'm still running the Turbosmart Kompact BPV (as BOVs are bad for our engines), but the whoosh you get from this baby is pretty bloody addictive, begging you to flat foot until a gear change when an opportunity presents itself.

Power Gains

+5.14% Power, -0.03% Torque

I wasn't expecting much from this one to be honest. Torque can be considered unchanged, while there is a gain in power. The boost curve seems a bit odd on this one though, and also the amount of boost is reduced. It looks to provide a minor power gain after all the other mods have been installed. The torque curve looks a bit odd on this one, but the power curve is looking positive. If anything, the torque curve appears to have been smoothed out and the peak torque moved toward the higher RPM range.

Power: 184 kW (247 HP) @ 5826 rpm
Torque: 339 Nm (250 Lb-Ft) @ 4564 rpm
Max Boost: 18 psi (1.24 bar) @ ~3400 rpm

Conclusion

I'm content with its current performance (for now...). A Forester of this generation will never be as nimble as a WRX or STI, but power-to-weight off the line, with the current mods, it can beat a standard WRX/STI, but not necessarily handle as well with all the equivalent suspension mods. But in my opinion, the utility/carry capacity in combination with a safely upgraded engine in the AWD Forester XT is incredibly hard to beat price-wise when compared to any other vehicle available today.

The next steps I can consider for some more power are either Water Injection, or changing to E85 as a fuel source.

Here's a final overview of the progress that has been made thus far: