Agreed…but that Air is brief and honestly nothing compared to being wet with even cooler fuel and quenched rapidly and repeatedly. The absence of that fuel is a Huge thing to be deleting in my opinion. Id say the cooling effect of fuel and air is multiple TIMES more effective than air alone…and not just half…definitely a factor of some multiple…
“But isnt hotter better for no carbon to build?”
Consider where the carbon is coming from.
Non-gaseous “stuff” is coming in with the air on each intake stroke.
Fine droplets of motor oil, unburned & partly burned fuel droplets from the PCV & EGR systems.
Some of these droplets can’t follow the curving air flow around the valve so they land on the back side of the valve.
Plus hopefully insignificant amount of oil coming down from the valve guide.
So these form a film that “cooks” into a sludge and eventually into carbon if the valve temp is ~300-500F.
The carbon itself needs ~600-800 to burn off and apparently intake valves don’t get that hot, at least on the back side.
Heat is also lost through the valve stem.
Plus the intake valve guide is going to be cooler than the exhaust guide.
No idea if it’s true, but Mazda claims to have reduced intake valve deposits on their DI engines by increasing valve temps above 400C. From what I can tell, exhaust valve temps are typically 700-800C:
“To eliminate the problem of intake valve deposits that plague current direct gasoline injection engines, the engineers at Mazda determined that deposits are formed when intake valve temperatures fall below 400 degrees C. Measures were taken so that the intake valve would operate above this point to reduce deposit formation.”
This Hyundai video shows fuel injected both while the intake valves are open and another shot after they’re closed:
Top tier additives (at least theoretically) have a chance to get to the backsides of the intakes.
I guess it’s also possible for some additive to become part of the blow-by which makes its way back to the intakes via the PCV system.
I have two cars with the same engine (Sonata and Tucson). Based on the Hyundai forums, carbon buildup is not common. One of mine has 40K miles and so far all is well, but that is too early. I am using Synthetic oil with 5K intervals and Shell gas.
Between CVT and dual clutch transmissions, DI, Turbo, I am running out of options/cars that run on the simpler technology of the past. These were just good deals and could not pass them up. Might be in for a lesson hard learned.
My 2014 Mazda6 with the SkyActiv engine is GDI. I have over 50,000 miles and no issues at all. I use gasoline from stations with frequent fuel deliveries and the oil has only been changed at the dealer (mostly because they do it for free with my regular maintenance). My purchase of the Mazda SkyActiv technology was a leap of faith but also a calculated risk. I wanted high gas mileage but the following were items I would NOT consider to achieve that: diesels, hybrids, CVTs, and eco modes that shut off the engine at stoplights.
Buying a car comes down to what you DON’T want as much as what you want. I think GDI is no different than advances we have seen in the past. Who amongst us really wants a carbureted car with an actual distributor (including condenser and points)? Other than nostalgia I don’t miss many old technologies at all. GDI is all about raising compression to increase fuel economy. In five years it will be as meaningless in car advertising and buying as “rack and pinion steering” and “bucket seats”.
GM and Ford solved the problem by avoiding soot formation that leads to carbon deposits. Proper EGR design, injector location and angle, and injection timing work for them. Cadillac’s GDI V6 used in the CTS is in more than 200,000 cars with no documented cases of excessive carbon build-up. Ford tore down an Ecoboost at an auto show in front of an audience. It had 160,000 abusive miles on it, and there were only light carbon deposits. Read about it here:
Thanks for the link, great article. Of all the new technology I’d rather avoid, DI is at the bottom of the list, if the carmaker isn’t having problems. Mazdas will get a serious look next time I’m car shopping.
^^ Nobody asked me but I will answer anyway 
The CVT concerns me most. It is annoying to drive one, it is expensive to fix them too and the gas mileage benefit for me is really minuscule.
I guess I could live with a Turbo, but then if I need power, I would rather have a bigger engine and not wait for the turbo to kick in. I still consider the Turbo’s a bit concerning over the long run.
As far as the Hyundai GDI, I have read that the valve openings are adjusted as such that on start up it helps with the cleaning. Only time will tell. As you all know, I also have an 05 Camry and even though so far it has not given me trouble, that engine is known to have issues with the bolts on the cylinder head. So, I Guess, anything you buy could be trouble one way or another.
Just because an ominous tsb exists, does not necessarily mean that problem will happen with your car
But me, I’d rather buy a car where such tsbs do not exist in the first place
Mind you, I’m talking about buying used cars
And I have absolutely NO problems with the idea of paying $20 or $25 to log onto the factory website to search for such things
Information is a commodity, and I have no problem forking over money so that I can get the latest potential dirt on some car
@db4690 - Yes, I’ll take GDI, but would rather avoid CVT (more because of the way it drives), and turbocharging (mostly because many of the turbo cars don’t make their EPA targets).
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@db4690 - Yes, I’ll take GDI, but would rather avoid CVT (more because of the way it drives), and turbocharging (mostly because many of the turbo cars don’t make their EPA targets).
Actually, I like the way a CVT drives. You have all the power you need at any speed, or you can operate with minimal RPMs.
Can loook stuff up if needed but it seems in some newer models the newer transmisissions are a source of trouble, one example from consumer reports
This year, Acura becomes the latest brand to see its overall predicted-reliability ranking drop sharply (down 7 places from last year) due to problems with in-car electronics and transmissions for its newest RLX and TLX sedans. CR has already seen these trouble areas drag down overall scores for Ford, Nissan, Fiat-Chrysler and others. “We’ve seen a number of brands struggle with new transmission technology,” said Jake Fisher, Consumer Reports’ Director of Automotive Testing. “Whether it’s a complex system such as a dual-clutch gearbox, a continuously variable transmission, or one with eight or nine speeds. Many vehicles require repair and replacements because of rough shifting among the gears and slipping CVT belts.”
Not all new-generation transmissions are troublesome. Audi and BMW have created reliable dual-clutch transmissions, while the CVTs in Honda and Toyota hybrids have been strong performers.
The one automatic transmission that was more annoying than the Nissan CVT, was the Ford Focus Dual clutch transmission. It is supposed to shift like a manual, the problem is it shifts like someone who does not know how to shift a manual is driving it. Somehow, the Prius transmission did not bother me, but that was a short test drive, so I am not sure how it will feel if I wanted to merge on a fwy.
The one automatic transmission that was more annoying than the Nissan CVT, was the Ford Focus Dual clutch transmission.
My brother rented one for 2 weeks a few months ago. He said the DCT worked great.
@insightful Might had been the ones I drove (2 different ones). Esp when taking off from standing, I would have to push the gas pedal. For a few seconds nothing would happen and then it would slam in gear.
“Somehow, the Prius transmission did not bother me”
The Prius (and other hybrids with the Toyota Synergy Drive) vary the effective ratio by electrical means, not mechanical.
A whole different ball game.
I posted some time ago the idea of using the TSD without storage (batteries) instead of a mechanical automatic/CVT.
Instead of multiple gears and clutches, or belts, chains (kinky!), cones etc. there would be one planetary gearset and two electric motor/generators.
Didn’t get much love on that one.