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Old 03-11-2018, 03:42 PM   #1
MtnXfreeride
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Default Carbon Build Up On Valves

I dont have an FA engine WRX yet - but I am curious now that they have been around a few years - are people needing to get walnut blasting done on these engines yet? What kind of interval? Is it even done at the dealership yet and is needing it covered under anything other than the 36K/3yr warranty? Price?

Sounds like from reading, it is a problem on most but NOT ALL DI engines. Some have a better design to resist build up in the valves.
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Old 03-11-2018, 05:00 PM   #2
Stanley Yahtzee
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it builds up, rather quickly. there are a few good threads here with pictures if you search they will probably come up. as far as warranty/dealership offering that service i have no idea. i should prob find out tho as my wrx is approaching 5000 miles.
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Old 03-11-2018, 06:20 PM   #3
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52K miles on my '17 and no problems from it. I haven't looked in there but starts and runs well. Bone stock w/OCI of 6K miles Pennzoil Platinum 5W30. Maybe after I see the plugs I'll take a peek.
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Old 03-11-2018, 06:39 PM   #4
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Originally Posted by tramp View Post
52K miles on my '17 and no problems from it. I haven't looked in there but starts and runs well. Bone stock w/OCI of 6K miles Pennzoil Platinum 5W30. Maybe after I see the plugs I'll take a peek.
yes, subaru wouldnt be selling the car if this was a serious problem. carbon buildup is not likely to cause an engine failure, the mechanical opening and closing of the valves will keep them clean enough to operate. the issue is it restricts flow just enough to reduce power, it happens so slowly over time that you would likely never notice it either.
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Old 03-11-2018, 08:11 PM   #5
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The power difference is like ~10whp. Not really a big deal at all.

There is a couple of threads that are ungodly long by now. Tl;Dr is until you start getting idle problems and misfires don't worry.
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Old 03-12-2018, 10:02 AM   #6
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From what i've seen, it builds up rather quickly (usually under 15,000 miles and theres significant buildup from pictures posted here) although, it doesnt seem to get progressively worse. Pictures i've seen of cars with 50,000 looks almost the same as 15,000 miles. I'm approaching 60k. I'm sure I have buildup and i'm looking to get it walnut blasted this spring/summer. Looking to get it done at my tuner actually so I'll see if they could put the car on the dyno, see what it puts down, then walnut blast and re-dyno to see how much it picks up.

I've also been considering a WMI kit to help keep them clean after the walnut blasting, but at clost to $2500 for the kit, install and retune, you could walnut blast 4 times (in my case up to 240,000 miles) and i'm happy with my power level (right around 320/320) so thinking it may not be a financially sound decision to do WMI.
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Old 03-12-2018, 11:06 AM   #7
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Stickied at the top of this forum is the main thread:

https://forums.nasioc.com/forums/sho....php?t=2756556
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Old 03-12-2018, 03:21 PM   #8
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I think the build up is not that stable to pass certain thickness so it would start falling off getting sucked into the cylinders.
Not a huge deal really considering these engine makes soot like crazy anyway.
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Old 03-12-2018, 07:28 PM   #9
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Agree with others here, it seems to buildup quickly but then not get any worse. Power loss is very small and gradual, so almost impossible to notice.

The fact that it builds back up so quickly makes me think walnut blasting is a waste of time and money.

If I had my time again I dont think I would have bothered with the egr and tgv delete.
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Old 03-12-2018, 08:43 PM   #10
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Did you get much performance from the TGV delete?
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Old 03-12-2018, 11:21 PM   #11
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Subaru deals with carbon on the valves on DIT engines in this manner:
The injector sprays in a fan pattern into a v shaped recess across the combustion chamber crown. The intake valves open into this recess. During warmup (called Stratified Mode) there is an injector pulse during the intake stroke and compression stroke. The pulse during intake sprays on the back of the valves while they are open. Subaru tells us that warm-up is when most carbon deposits occur and this is suppose to reduce build-up.
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Old 03-13-2018, 12:00 AM   #12
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Quote:
Originally Posted by samjryder View Post
Did you get much performance from the TGV delete?
Most tuners say 10 HP give or take. It's not a huge gain, but for the price and ease of installation it's definitely worth it. More important, TGV deletes combined with EGR deletes should greatly reduce charge air temps which should reduce "tip in" or "cruise" knock greatly. I bought my used TGV deletes for about $45 and for that price it's kind of a no-brainer.

Last edited by YungBoba; 03-13-2018 at 12:07 AM.
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Old 03-13-2018, 06:55 AM   #13
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Quote:
Originally Posted by Elbert Bass View Post
Subaru deals with carbon on the valves on DIT engines in this manner:
The injector sprays in a fan pattern into a v shaped recess across the combustion chamber crown. The intake valves open into this recess. During warmup (called Stratified Mode) there is an injector pulse during the intake stroke and compression stroke. The pulse during intake sprays on the back of the valves while they are open. Subaru tells us that warm-up is when most carbon deposits occur and this is suppose to reduce build-up.
I also believe there's some wash into the intakes under light load during Atkinson phase-sub 2K RPM.
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Old 03-14-2018, 12:02 AM   #14
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Quote:
Originally Posted by Elbert Bass View Post
Subaru deals with carbon on the valves on DIT engines in this manner:
The injector sprays in a fan pattern into a v shaped recess across the combustion chamber crown. The intake valves open into this recess. During warmup (called Stratified Mode) there is an injector pulse during the intake stroke and compression stroke. The pulse during intake sprays on the back of the valves while they are open. Subaru tells us that warm-up is when most carbon deposits occur and this is suppose to reduce build-up.
It may help but it certainly doesnt keep them clean!
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Old 03-14-2018, 07:08 AM   #15
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Quote:
Originally Posted by Harey View Post
Agree with others here, it seems to buildup quickly but then not get any worse. Power loss is very small and gradual, so almost impossible to notice.

The fact that it builds back up so quickly makes me think walnut blasting is a waste of time and money.

If I had my time again I dont think I would have bothered with the egr and tgv delete.
dosent the egr delete prevent carbon buildup from happening again?
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Old 03-14-2018, 09:26 AM   #16
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Quote:
Originally Posted by Elbert Bass View Post
Subaru deals with carbon on the valves on DIT engines in this manner:
The injector sprays in a fan pattern into a v shaped recess across the combustion chamber crown. The intake valves open into this recess. During warmup (called Stratified Mode) there is an injector pulse during the intake stroke and compression stroke. The pulse during intake sprays on the back of the valves while they are open. Subaru tells us that warm-up is when most carbon deposits occur and this is suppose to reduce build-up.
Interesting. Always wondered about the odd extra loud under load cold start on mine. Wasn’t this introduced on the 2016 model? If so, wonder if this mode made a difference in build up from the 2015.
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Old 03-14-2018, 11:45 AM   #17
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Originally Posted by CBSWRX View Post
Interesting. Always wondered about the odd extra loud under load cold start on mine. Wasn’t this introduced on the 2016 model? If so, wonder if this mode made a difference in build up from the 2015.
I have stratified cold start on my 2015. Loud AF for the first 10 seconds or so.
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Old 03-14-2018, 12:46 PM   #18
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Once I start to mod I really want to focus on eliminating or reducing carbon buildup. The thought of the engine getting less efficient/lose power over time makes me sweat.

Always interested in threads like this, and read most of the carbon buildup sticky. Ive decided on tgv/egr deletes and meth injection, after a walnut blasting.

Just waiting to get deeper into this warranty before I start.
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Old 03-17-2018, 08:40 AM   #19
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Quote:
Originally Posted by CBSWRX View Post
Interesting. Always wondered about the odd extra loud under load cold start on mine. Wasn’t this introduced on the 2016 model? If so, wonder if this mode made a difference in build up from the 2015.
The noise results from the injector pulse during compression. It occurs late in the stroke and as a results the fuel/air charge is still burning when the exhaust valves open. That makes the catalyst warm up quicker so that the car goes into closed loop faster.
Much simpler and way fewer parts than the old way (secondary air) of dumping more gas in the intake and pumping extra air into the exhaust to burn it.

A variation of this was introduced originally with the Toyota D-4S system in 2013 BRZ, then the current system with 2014 Forester DIT, 2015 WRX DIT. The 2017 Impreza DINA (Direct Injection Normally Aspirated) and 2018 Crosstrek DINA use a similar strategy as well.

What I would recommend for fighting carbon build-up is a simple induction cleaning with Seafoam, MOC, or Subaru branded cleaner as a maintenance procedure. That will also keep the TGV cleaner. We include it in our major maintenance service every 30,000 miles at the shop I work. I recall we were doing it every 15,000 miles back in the eighties on fuel injected cars.

Last edited by Elbert Bass; 03-17-2018 at 08:52 AM. Reason: Add induction service
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Old 03-18-2018, 03:08 PM   #20
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These DIT carbon buildup issues have made me hesitant to upgrade to the FA20 WRX, I'll probably look elsewhere for a car with a port/DI injection setup when I'm ready to upgrade.
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Old 03-19-2018, 12:14 AM   #21
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You have a 2011 wrx with weak piston ringlands... this is a bit of carbon on the intake valves

This issue is blown way out of proportion. I challenge anyone without a dyno to feel the difference between some carbon buildup on the intake valves and clean ones. Once there is a bit of buildup it doesnt get any worse. Hence, why Subaru arent concerned with it.

Every engine has its pros and cons. FA20 is a much better engine than the EJ. Cant wait for an FA24 in the STI!
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Old 03-19-2018, 12:17 AM   #22
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Quote:
Originally Posted by Elbert Bass View Post
What I would recommend for fighting carbon build-up is a simple induction cleaning with Seafoam, MOC, or Subaru branded cleaner as a maintenance procedure. That will also keep the TGV cleaner. We include it in our major maintenance service every 30,000 miles at the shop I work. I recall we were doing it every 15,000 miles back in the eighties on fuel injected cars.
Have to dig up the link with photos but it was shown that those sprays do nothing for the carbon buildup on the intake valves.
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