If you’re reading this, chances are, you are a performance enthusiast. That means you aren’t afraid to push your engine to its rev limiter on occasion, be it in competition, or simply for personal entertainment. In that vein, you have probably also heard a huge number of wives’ tales about how to properly break-in, maintain, and care for your engine, with varying degrees of truth behind them.
One of those old standards was something referred to as the “Italian Tuneup,” where you would take your car out onto the highway, and make a pull (or two or three, we’re not here to judge) to the rev-limiter. The idea behind doing this is that it would clear out the carbon buildup in various parts of your engine and “clean it up.”
Our friend Jason Fenske, from Engineering Explained, has a penchant for taking fairly simple ideas – like the Italian Tuneup – and diving incredibly deep into the science (or lack thereof) behind the theory, and we absolutely love him for it. Especially when he ends up finding actual published scientific papers on the theories behind something that is more of a colloquial practice, than an industry standard.
A Scientific Look at the Italian Tuneup
First, Fenske defines what someone is actually trying to accomplish by “cleaning out” the engine with high-load pulls to redline. “The idea behind [the Italian Tuneup] is that whether you drive your car a bunch or not much, the EGR and PCV systems recycle oil particulates through the engine, and that will eventually lead to carbon buildup,” explains Fenske.
“You go out on the highway, make a few pulls, get the engine high up into the RPM range with load, and that gets the deposits so hot that it breaks them up and runs them through the engine. That’s the basic idea.”
While that sounds like a reasonable and logical plan, Fenske is a scientist, so he needs hard data to satisfy his curiosity. So he outlined the points he was curious about: 1. At what temperatures do carbon deposits form? 2. Is there actually a temperature at which carbon deposits break down? 3. Do engines get hot enough to actually break down the deposits?
How Deposits Form
Before you can understand how to defeat the buildup of carbon deposits, you must first understand how they are formed. Since internal temperature seemed to be the focus of the theory, Fenske focused on that, himself.
“I found a research paper that says the deposits start to form around 195°C (383°F) to about 290°C (554°F). The peak there was at 200°C (392°F), which is the sweet spot for the carbon deposits to form and react with the metal surface, bonding to it,” Fenske says.
“Below 190°C (374°F) and it’s too cold for that to happen, and if you get above 290°C (554°F) it’s too hot for the molecules to bond with the metal and each other. So from a deposit standpoint, you don’t want the [engine components affected by carbon buildup] to be in that range.”
Killing Carbon with Fire
With the “Goldilocks Zone” for the formation of carbon build clearly defined, the next step is to see if there is a temperature which eliminates already-formed carbon deposits.
“I found another paper which found that starting at about 325°C (617°F), you can really start to remove carbon deposits,” Fenske shares. “It’s hot enough that it will break the deposits apart from both the metal surface and each other. Also, in that range, the deposits wouldn’t form in the first place.”
Forgive us; the next paragraph is going to be nerdy, as we explain what’s happening at that magical 325°C point. “In a reaction called decarboxylation, the temperature is so great, that the carbon molecules are ripped out of the compound molecules,” says Fenske.
With those carbon molecules removed from the compound, the carbon deposits’ structure is upset and crumbles like a Jenga tower after you pull out the wrong wooden piece. “That causes deposits to detach and disintegrate and then get hopefully get blown out the exhaust, and not back into the PCV or EGR system,” says Fenske.
Getting Up To Temperature
Now the real question becomes, can you get the surfaces of the buildup-prone components to that magical decarboxylation temperature safely and reliably by simply making a full-load pull, up to your rev limiter on the highway. Once again, Fenske found a paper addressing that.
“According to another paper, the surface of a piston in [normal operation] gets to 280-300°C (536-572°F), peaking at the center of the piston face and declining, the closer to the cylinder wall you get, as the cylinder walls are being liquid-cooled,” shares Fenske.
“In that temperature range, you shouldn’t have carbon deposits forming all that much, because you are above the forming temperatures. As far as the cleaning out deposits, it does seem like, if you were to push the engine hard, you could raise the temperature of the piston face by 25 degrees or so fairly easily.”
With that little bit of information, it does seem like there may be some validity to the Italian Tuneup idea. However, that is just the data on the face of the piston. The key offender in performance-reducing carbon buildup is the intake valves. For that, Fenske found – you guessed it – another research paper.
“The first study I found looks at a port-injected engine, which means you have fuel spraying over that intake valve and producing a cooling effect,” Fenske says of the first paper relating to intake valves. “That study saw that both the side of the intake valve that was hit by the fuel and the side shielded from the fuel spray ranged from 170-190°C (338-374°F), which is actually below where you have carbon deposits start forming.”
However, those temperatures were not recorded under performance parameters, and the temperatures rose into the Goldilocks Zone when pushed. “Running the engine in a high-RPM, high-load condition, the research team was able to get the intake valves up to about 272°C (521°F),” Fenske shares. “Of course in a port injection engine, you also have that fuel spray onto the valves, which is washing off those deposit precursors so they don’t attach in the first place, along with the detergents in the fuel specifically aimed at breaking down the deposits that have formed on the valve.”
As is to be expected, direct-injection engines, which don’t have the cooling, cleaning fuel spray, are more prone to carbon buildup, and surprisingly, an Italian Tuneup exacerbates the problem, rather than helping alleviate it. “I found another study on a direct injection engine and that was unfortunate news,” says Fenske. “They saw a correlation between engine load and deposit formation. Basically, the more load the engine was under, the more deposits that formed.”
Rev It Out
So to answer the question posed at the beginning of the article, Fenske only has a non-committal, “It depends.” As you can see from the data he’s compiled, it seems that a good, hard workout for the engine can keep carbon from building up on the face of the pistons, and that exhaust valves are pretty exempt from worry no matter what.
However, when it comes to the intake valves, it appears that hard use may actually have the opposite effect, putting them into the heat zone where carbon buildup forms. That means that on a port injection engine, fuel additives – whether gotten at the pump pre-blended in the fuel or as a supplemental fuel treatment – are probably a more effective solution to prevent carbon buildup than revving the snot out of your engine.
Fenske also points out that generally a single pull to redline on the highway probably won’t increase component temperature enough to make a difference. “Old sayings like, ‘A Redline a day will keep the carbon away,’ aren’t really accurate,” concludes Fenske. “If you’re trying to get rid of carbon deposits through temperature, you’ll probably have better luck through sustained load like at a track day.”
One final nail in the coffin in the overall theory of hard driving as a substitute for proper engine maintenance is this thought from Fenske: “Running your engine hard will create more blow-by, which puts more carbon into the system through the PCV, and creates more potential for the carbon deposits.”