Carbon Buld-Up

[0SuperDuper0]

Anyone having performance issues later down the road due to carbon build-up? I used only Top-Tier gas, air filter is clean and have a 22' XT 13K miles on it. I also used injector cleaner every oil change and really notice accelerating and performance isn't like when driven out of the dealer.

[silverton]

I'll assume by top-tier you mean chevron, shell, etc and not arco.   you should probably also be using premium, even if it calls for regular.

injector cleaner every oil change seems extremely excessive, maybe do it every 30k or 60k if you feel you absolutely need to. but fuel is not dirty (it's not the 70s any more), especially if you're getting top tier, and the fact that gasoline is a pretty aggressive solvent just on its own.

[fourD2]

Two questions, why premium if the owner manual calls for 87 octane.  Not disagreeing with you, just wondering why the manufacturer would recommend an inferior grade of gasoline if indeed there were deleterious effects down the road.

The other question I have is why filling stations that are purportedly top tier do not have the top tier logo on the gas pump any more.  In my area of the mid-west Quick Trip, BP, Mobile and Cenex all used to tout their top tier status with a sticker certifying such.  None of the stations carry the top tier logo any more.  

I did inquire about this by sending an email to Top Tier and received a generic response with a list of stations certified as top tier.  No explanation was given for dropping the logo.  

One of the managers at Quick Trip told me they no longer pay the fees associated with top tier certification, which purportedly are substantial.  He did not know whether the additives that qualify the gas as top tier were still being added to the gasoline product.  

[blusubado]

well you'll lose performance by using anything other than the E87 fuel that the engine was tuned for. higher octane doesn't mean more power. it just means higher resistance to knock 

[dgoodhue]

On 12/20/2023 at 12:52 PM, blusubado said:

well you'll lose performance by using anything other than the E87 fuel that the engine was tuned for. higher octane doesn't mean more power. it just means higher resistance to knock 

You won't lose performance by using anything other more than 87 octane.

Cobb did some testing with the ascent motor and found that at WOT the stock tune was not pulling timing so there would be no HP gains at WOT.  Cobb did find that that tune did occasionally pull timing from detonation at part throttle and higher octane clean that up. I assume the Legacy 2.4T motor would be the same. 

[dgoodhue]

On 12/19/2023 at 10:53 AM, 0SuperDuper0 said:

Anyone having performance issues later down the road due to carbon build-up? I used only Top-Tier gas, air filter is clean and have a 22' XT 13K miles on it. I also used injector cleaner every oil change and really notice accelerating and performance isn't like when driven out of the dealer.

A couple years ago, I saw some who dynoed a WRX with about 50-60K miles with before and after to see what carbon build up losses were. It looked like it had some carbon build up but it only end up being a couple hp. I would assume that Subaru does think it will be an issue until the engine is high mileage and well past the warranty. I haven't looked lately though.  The early WRX and FXT with DI should have a good amount high mileage models by now.

[silverton]

On 12/20/2023 at 9:52 AM, blusubado said:

well you'll lose performance by using anything other than the E87 fuel that the engine was tuned for. higher octane doesn't mean more power. it just means higher resistance to knock 

higher resistance to knock = more power, or at the very least more efficient power

Edited December 22, 2023 by silverton

[blusubado]

by no means will it give you more power in any way what so ever. you will lose a couple horsepower if anything. it burns at a different rate than your engine is tuned for. if you have a knock from using e87 then you might want to take it to the dealer for a tune up

Edited December 22, 2023 by blusubado

[silverton]

1 hour ago, blusubado said:

by no means will it give you more power in any way what so ever. you will lose a couple horsepower if anything. it burns at a different rate than your engine is tuned for. if you have a knock from using e87 then you might want to take it to the dealer for a tune up

17 hours ago, dgoodhue said:

Cobb did some testing with the ascent motor and found that at WOT the stock tune was not pulling timing so there would be no HP gains at WOT.  Cobb did find that that tune did occasionally pull timing from detonation at part throttle and higher octane clean that up. I assume the Legacy 2.4T motor would be the same. 

if higher octane cleared up that pre-det, there must be improved something.  pistons, rods, and bearings dont like detonation.

I doubt Cobb is doing these things on a 'busted' motor, so I doubt a 'tune-up' would correct it.

[dgoodhue]

On 12/22/2023 at 11:26 AM, blusubado said:

by no means will it give you more power in any way what so ever. you will lose a couple horsepower if anything. it burns at a different rate than your engine is tuned for. if you have a knock from using e87 then you might want to take it to the dealer for a tune up

I have seen good running turbo engines on 93 octane add 110 and 116 octane gas. The results were not measurable at the track.  I don't know if that would be measurable on and dyno. I have my doubt that going from 87 to 93 would  show up within the tolerances of a dyno if it ran without detonation at 87. At the very least, it isn't going to measurably slower.

On my '12 GT, onerun I missed 4th at the track,  my DAM from 1 to 0.875 on that run. My track time drop 0.2s and 1.5mph until I reset  (DAM is how Subaru's ECM reacts knock retard).  If the Ascent part throttle knock that Cobb reported is triggering DAM to be dropped below 1.0, it absolutely is lower the power.

LOL Bring to the dealer, what are going to tell, the DAM isn't 1.0?  Do that if you want to waste your time and money on tune up for how Subaru intended the vehicle to.  Even if they were to really look it, they are just going to tell you it is within spec.  From my experience the EJ 2.5i and FB 2.5i, all don't have 1.0 DAM on 87. (I am not sure on the DI models, as I haven't seen a datalog go those.) I would guess at least 50% (I am probably being generous at 50%) of the new cars on the road don't run perfect on 87 octane without the ECM's knock prevention strategy.  I actually think from what Cobb posted the FA24DIT is actually run pretty good on 87 compare to the masses.

[dgoodhue]

Blusabado My advice is don't google a topic and pretend to be an expert. I started ecm tuning 25 years ago and experience tuner on a few of my car. I have more expertise in reading datalogs. I can see from a mile away that you are inexperience in those topics. Stick to what you know. If you google a topic, state the facts but don't extrapolate.

[blusubado]

I didnt Google crap, this is what's being taught at schools like UTI where i went to. you use the fuel that the manufacturer has tuned the engine for. so let's not be presumption as if you know me. lets stick to the facts of the subject and keep our opinions to ourselves 

[dgoodhue]

1 hour ago, blusubado said:

this is what's being taught at schools like UTI where i went to. you use the fuel that the manufacturer has tuned the engine for.

Did you complete and pass a UTI certification program?

I have REAL hard time believing that UTI did not discuss the topic of spark timing using knock sensors as feedback.

[blusubado]

yes I did 2 years there taking auto/diesel/industrial/BMW back in 2010-12. and I said more octane will not give more horsepower. so using e93 instead of e87 will not give you more power 

[fuzzysoul]

On 12/24/2023 at 11:43 AM, dgoodhue said:

My advice is don't google a topic and pretend to be an expert.

Heysoos Christos. This thread was about carbon, and erryboddy starts arguing like these cars run on cable-actuated throttle bodies. Anybody mention a single thing about crankcase ventilation? PCV valves? Catch cans? Or ... I dunno, PULLING THE INTAKE MANIFOLD AND SHOVING A BORESCOPE INTO THE BLOODY HO-

Sorry. Sorry. I'll calm down. I promise.

Has anyone with a 2020+ Turbo Legacy or Outback pulled the manifold and checked their actual, physical valves? Anybody? Anybody actually pay for a walnut shell blasting on their intake valves?

Make it up. Pretend to be a Subaru tech with 85 years of experience and a pristine employment record. I don't care. Just demonstrate that you understand the full topic at hand.

[Injector cleaner is great for your direct injector nozzles. I use it every other oil change. It will do piss all for the intake valves , which is where carbon buildup should be your biggest concern, given the history of DI engines. Toyota uses dual injection - port and direct - to fix this problem and keep valves clean. Also, do not discount that your ECU "learns" how you drive and adjusts your throttle map accordingly. It does so with efficiency, not performance, in mind, since Subaru's CAFE average is approaching godawful with these inefficient pancake engines. Products like Pedal Commander claim to be able to fool your ECU into behaving more predictably.]

[fourD2]

I would not call the Legacy XT fuel efficiency "godawful".  To my knowledge it has the best MPG of any midsize (non-hybrid) AWD sedan.  An added bonus is, despite being turbo-charged, it takes regular gas.  Most 4 cyl turbo engines require premium.  

[dohturdima]

I wouldn't be too concerned about carbon buildup and oil burn in a Japanese engine, whcih is deliberately designed to for longevity rather than performance-first (vs Germans, which burn oil and contribute to carbon buildup). Just change oil as recommended and add a Techtron or similar every other change. 

[MoleMan]

22 hours ago, dohturdima said:

I wouldn't be too concerned about carbon buildup and oil burn in a Japanese engine, whcih is deliberately designed to for longevity rather than performance-first (vs Germans, which burn oil and contribute to carbon buildup). Just change oil as recommended and add a Techtron or similar every other change. 

Correct.  However it depends on the manufacturer.  Toyota has the D4S. The difference is you have both DI and PI so the Carbon issue is not even a worry.  With everyone going to DI without PI the carbon issue in some engines is become problematic.  However not really seeing it in any engine from Toyota.  BMW had an issue with carbon and seems to have curbed it. And Audi has had DI for years and so many older 2.0s running around.  Only manufacturer that seems to have major issues is Hyundai and Kia.

The main issue with DI only cars is no matter what gas or cleaner you use it will never get rid of all the carbon. The reason for this is the fuel is ignited before it reaches the top of the cylinder. This is why D4S is a great system because the PI injects the fuel so it retards the carbon build up.

Only real way is do do a soak with SeaFoam or similar and even then it won't get all the carbon out.  And the method for doing that I would never recommend to someone who is not experienced. 

This is why I try to avoid DI engines all together.  But it's sorta like trying to find a non CVT car these days not to many options.

[Dantvballcoach]

On 12/24/2023 at 11:51 AM, blusubado said:

I didnt Google crap, this is what's being taught at schools like UTI where i went to. you use the fuel that the manufacturer has tuned the engine for. so let's not be presumption as if you know me. lets stick to the facts of the subject and keep our opinions to ourselves 

THIS^^^

[MoleMan]

On 12/24/2023 at 10:51 AM, blusubado said:

I didnt Google crap, this is what's being taught at schools like UTI where i went to. you use the fuel that the manufacturer has tuned the engine for. so let's not be presumption as if you know me. lets stick to the facts of the subject and keep our opinions to ourselves 

Yes and no. It's a recommendation.

While most people stick to the recommendation some do not.  

On my daily I am using 91 ethanol free. Manufacturer spec is 87 Octane cheapo gas.  Mileage gains on highway jumped from 42 to 46 at 80.  Even better when reduced speed.

I mean to be nitpicky you can fill a diesel tank with Jet A.  It works and has no issues running.

 

I will say in my 3.6 I see no difference between cheapo 87 or 91. Always returns 28 on the highway like clockwork. No more no less 

Now with our Lexus if you do not use 91 and put a lower grade the engine pings and runs like crap.  Could be a product of the D4S or cold weather. But clears up when at -temps with 91 as Toyota recommended.

 

[MarkInAustin]

I am almost 81 and a product of an earlier and simpler age.  It remains true that lower octane gasoline ignites more readily and thus in a higher compression engine pre-ignites [knocks] more readily.  But the electronic control of timing in our now computerized engines changes the simple calculation, I think.

The car will run well on the prescribed octane.  If it runs better on higher octane than on the prescribed octane that would have to be either a timing issue, now computer controlled and not subject to manually advancing the distributor, or a product of altitude - Houston driving requires slightly different octane than Santa Fe driving for the same result [unless the computer has also controlled the density of the air charge - IDK about this - someone here probably does].

 

For those too young to remember, there was a time when you could advance the spark by rotating the distributor, say by an extra five degrees before top dead center, switch to high octane gasoline, which would ignite only from spark and never compression, and gain significant HP.  Advancing spark while using low octane gas was a recipe for knock, in those days.

 

Finally, carbon buildup can raise compression!  An older engine used to be subject to knock because of it.  I wonder if the DGI engines will begin to act this way.

I suspect, but do not know from either experimentation or engineering analysis, that a catch can would limit carbon buildup in a DGI engine.

All your comments from experience or actual analysis are welcomed by me, anyway.

 

Edited April 20 by MarkInAustin
fixed typo

[MoleMan]

On 4/20/2024 at 9:18 AM, MarkInAustin said:

I am almost 81 and a product of an earlier and simpler age.  It remains true that lower octane gasoline ignites more readily and thus in a higher compression engine pre-ignites [knocks] more readily.  But the electronic control of timing in our now computerized engines changes the simple calculation, I think.

The car will run well on the prescribed octane.  If it runs better on higher octane than on the prescribed octane that would have to be either a timing issue, now computer controlled and not subject to manually advancing the distributor, or a product of altitude - Houston driving requires slightly different octane than Santa Fe driving for the same result [unless the computer has also controlled the density of the air charge - IDK about this - someone here probably does].

 

For those too young to remember, there was a time when you could advance the spark by rotating the distributor, say by an extra five degrees before top dead center, switch to high octane gasoline, which would ignite only from spark and never compression, and gain significant HP.  Advancing spark while using low octane gas was a recipe for knock, in those days.

 

Finally, carbon buildup can raise compression!  An older engine used to be subject to knock because of it.  I wonder if the DGI engines will begin to act this way.

I suspect, but do not know from either experimentation or engineering analysis, that a catch can would limit carbon buildup in a DGI engine.

All your comments from experience or actual analysis are welcomed by me, anyway.

 

Ok.

 

In a nutshell.  I avoid DI engines like the plague.  You will always have carbon build up because the fuel does not get to the piston it ignites before. While technically more efficient it creates the carbon build up issue.  An acception to this for my is the Toyota 4DS system. You have DI and Port Injection so you don't get the carbon build up issues.

Now the issue here is most all manufactures are going to DI.  To me that is gonna cause a lot of engine replacements after the ten year mark.  

To your question. No. No way to prevent the carbon build up in a DI engines. Once again the fuel is not igniting as normal in the cylinder. It's igniting at the top of the cylinder and not hitting the piston.  It basically ignites when the injector sprays the fuel in a more efficient way.  So regardless of fuel grade used it will still keep building after time.  

Yeah you can use certain chemicals to remove the carbon. But this generally involves putting the chemicals into the spark plug holes(which is a pain in the rear on boxer engine) and doing a "soak" overnight etc.. several videos of this are on YouTube. So you can see for yourself.  Most are being done on Civics which are Port Injection but still a few DI videos are to be found.

A catch can will do nothing to prevent carbon build up.  As far as your fuel question.  Remember Santa Fe will have lower octane then Houston due to the altitude difference.  Most Subarus run fine on regular gas.  In fact I have used 91 ethanol free, 91 regular, and plan crap gas in my 3.6.  results all the same as far as mileage.  And yes 91 is the highest grade due to the altitude I live at. This would be equivalent to 93 in Texas.  Only exception is on the Turbos which I believe need premium.

I would do some research especially on DI more. You will see that some manufacturers have found the problem and have tried to fix it or make the carbon build up better.  While others manufacturers just go a step further and put a port inject in to alleviate the issue all together(Toyota). Now Subaru being partially owned by Toyota I would hope would have something similar to 4DS but I am not familiar or can speak for it as I simply do not know on the 7th gens.

Maybe someone can chime in on that.