Comments from other members have suggested that it is only direct injection (no port injection)

Subaru has officially advised that they have engineered their direct injection system to minimise carbon sludge build up.

Seagrass

 

Subaru has officially advised that they have engineered their direct injection system to minimise carbon sludge build up.

The other DI engines, especially turbos, are highly likely to have carbon intake issues, despite what Subaru is saying, since they haven’t defined what they have done to “minimize” carbon or what that means.

What else would Subaru "officially" say when they probably lack the longer term data, pro or con, to back up such statements? As in, "We have no idea if this will be an issue, and we're expecting that if it is an issue, it will be outside of the factory warranty and therefore at the risk of the owner to resolve it.". Not going to hear this.

 

My original Outback evaluation only found the engines only had direct injection. I was thinking that it will be losing some of the benefits of Top Tier gasoline because of the direct injection only. The following suggest there is remaining benefits for Top Tier. As you suspected, the intake valves will lose when using Top Tier.

The results showed that on average, Top Tier gasoline had 19 times fewer carbon deposits on injectors, intake valves, and in the combustion chamber when compared to regular gasoline. *
*Study Shows Top Tier Gasoline Worth the Extra Price

 

My original Outback evaluation only found the engines only had direct injection. I was thinking that it will be losing some of the benefits of Top Tier gasoline because of the direct injection only. The following suggest there is remaining benefits for Top Tier. As you suspected, the intake valves will lose when using Top Tier.

The results showed that on average, Top Tier gasoline had 19 times fewer carbon deposits on injectors, intake valves, and in the combustion chamber when compared to regular gasoline. *
*Study Shows Top Tier Gasoline Worth the Extra Price

That study applied if the gasoline with extra additives (top tier) could reach the engine intake areas, as it can with port injection. DI precludes that, so top tier fuel is not going to clean intake areas on direct injection engines.

I haven’t seen any evidence that Subaru, or for that matter the rest of the car makers in general, have developed any “magical solution” to carbon buildup in DI engines, particularly turbos. The only exception in the Subaru line is the BRZ, which is a joint Toyota enterprise, and features Toyota’s DI/PI combination approach. That seems to work.

The other DI engines, especially turbos, are highly likely to have carbon intake issues, despite what Subaru is saying, since they haven’t defined what they have done to “minimize” carbon or what that means.

Without specifics, it’s probably marketing.

EJ




Sent from my iPad using Tapatalk

 

There are kits to do it. Subaru sells one too. The dealer will do it for you. I think they charged me around $100 for my 2.0 DIT, and the carbon release fouled and killed both O2 sensors.

Never ran right afterwards, even with replacement. I am no fan of DITs.

 

There are kits to do it. Subaru sells one too. The dealer will do it for you. I think they charged me around $100 for my 2.0 DIT, and the carbon release fouled and killed both O2 sensors.

Never ran right afterwards, even with replacement. I am no fan of DITs.

What's contained in the kit?

 

Are the Forester DIT guys using catch cans, and if so, are they showing significantly less intake valve carbon?

 

Oil choice is probably as important, or more important, than fuel since oil vapors impact carbon buildup.

Best specs to look for are dexos1 Gen 2 and API SN+. According to SoA, the Subaru oil meets these specs.

@lfdal posted a Subaru Corp patent some time ago that talked about Subaru’s DI set up. This was from around the time that the 2015 WRX came out. I’ll see if I can find it but will need to look for it later.

 

@lfdal posted a Subaru Corp patent some time ago that talked about Subaru’s DI set up. This was from around the time that the 2015 WRX came out. I’ll see if I can find it but will need to look for it later.

This one? US20120080015A1 - Breather apparatus for engine - Google Patents

This breather apparatus has a rotation separator that is fastened to a camshaft, and that rotation separator has a base plate section and a plurality of protruding plates that extend from the base plate section. Moreover, a separator housing is provided in the cylinder head, and comprises an air intake on one end, and an exhaust outlet on the other end. Furthermore, a reed valve that opens and closes by the change in pressure inside a cam chamber is provided in the air intake. Blowby gas that is guided to the cam chamber hits against the protruding plates when passing in the radial direction of the rotation separator, and oil mist is captured by those protruding plates. Continuing, the blowby gas is guided from the cam chamber into the separator housing via the reed valve. When passing through the reed valve, the flow rate of the blowby gas changes, so oil mist is effectively captured by the inner wall surface of the separator housing.

 

I saw that when it was originally posted, but other than speculation there was never any explanation about what it accomplished.

And certainly, other than vague assurances, never have seen any hard evidence there is any real “cure” yet for DI carbon other than dual injector systems. Interestingly, I read some opinion by Subaru tech folks (or enthusiasts)that having to deal with intake carbon by walnut blasting was cheaper than maintaining twin injection systems. At least that was an admission of the issue, which is normally just outright denied.

If I still had a DI turbo I would be using the severe maintenance schedule, at least, and synthetic. And hope.





Sent from my iPad using Tapatalk

 

I read some opinion by Subaru tech folks (or enthusiasts)that having to deal with intake carbon by walnut blasting was cheaper than maintaining twin injection systems. At least that was an admission of the issue, which is normally just outright denied.

This young guy makes walnut blasting look easy. At first it may seem like he's just a stupid kid making a youtube video but the results are really good.