What's wrong?

It's not normal that so many barchettas have stopped while driving through the mountains. It would be great if some Fiat engineer could spend some time thinking really hard about what my cause the problem and ... solve it.

I spoke with my father about it (he's very "car-technical") and he immediately thought about the vapour-lock (air-bubble in the fuel tube). But he also said that this was quite a common problem up to 10 years ago but with today's fuel-injection engines this almost never happens.

But the combination of low air-pressure (because of altitude) and high temperatures could lead to this problem. He also said that if the fuel tubes are too close to the engine (design fault) they may overheat causing a vapour-lock.

Maybe it's a combination of various factors. But I'm quite convinced that engine temperature and lower air-pressure have at least something to do with it. 

Low air-pressure you can only avoid by staying in the valley. But who wants to miss the sights of the Gran-Paradiso park? Wrong answer.

But you can adapt to a driving style that keeps your engine temperature relative low. While driving up the mountain behind some other barchettas last weekend I noticed that not everybody does that. So here's the next story. Keep reading. It's long and technical but once you understand it, driving becomes more fun.

Some theory: torque, revs and ... heat.

The power of an engine is the product of torque and number of revolutions. An increase of revs (push the gas-pedal) increases the power of the engine. Torque, however, is a characteristic of the engine which you can't influence. Torque is the power with which an axle turns. Assuming a constant speed (revs of the wheel axle stay the same), you need more torque to drive up the mountain than to drive on a flat road.

Torque for an engine is a given but is not always the same. With low revs, torque intends to be low. Torque goes up when revs increase BUT above a certain numbers of revs, torque decreases again. Modern engines are designed such that over a wide range of revs, as much torque as possible is available. 

Your Fiat dealer can show you a chart showing the relationship between torque and revs (torque curve) for the barchetta engine. You can roughly say that between 2600 and 5500 revs, torque is at an optimum level (with a peak around 4300 revs). 

Because torque is a given for an engine and you can only influence revs( with the throttle), they created something which is called a gear-box (you know that thing, don't you?). Remember, power is the product of torque and revs (torque * revs). Using cog-wheels you can change torque and revs of an axle as follows: assume the ingoing axle (from the engine) runs with X revs. Via cog-wheels, you can lower revs of the outgoing axle and consequently, the torque of this outgoing axle increases (the total power (torque * revs) stays the same for both ingoing and outcoming axle!).

If you use different cog-wheels, you can, for example, increase the revs on the outgoing axle but then torque will be lower. This is the whole concept of the gear-box. First gear results in high torque and low revs on the wheel axle, higher gears result in higher revs but lower torque. So to drive away from standing still or to drive up a mountian, when you need a lot of torque, you put the car in low gear (with low revs of the wheel axle).

"I know that" is what you think right now! Sure. But there's more to it. So keep reading.

Torque and revs have quite a bit to do with the temperature of your engine!?!

When an engine runs with very low revs, torque is low as well (see the Fiat chart). If you put your car in a situation that it needs a lot of torque (e.g. going up the mountain) while the engine can't deliver enough torque, the engine starts to overheat (basicly, if petrol is burnt, all the energy produced has to go somewhere, either as movement, heat, noise, etc. If the energy can't be converted to movement (because of low torque) heat is a good alternative).

Also, when an engine runs with high revs (and torque is at an optimum) but you don't really need it (the engine basicly over-delivers power while it can't "get rid of it"), it overheats as well! It's as if the engine runs idle (almost no load) so the produced energy doesn't fully get converted into movement and, alternatively, converts into heat.

Compare this with riding your bycicle up a mountain. If you put in high gear, it's extremely heavy, you almost don't make any progress while you get very hot and tired: all energy gets converted into heat and not into movement. When you put in low gear, it's extremely light, you peddle like crazy, still don't make a lot of progress and you again get hot and tired: still, all energy gets converted into heat and not into movement. You need to choose a gear that balances between how fast you have to peddle (revs) and how "heavy" it gets (torque).

So to keep the temperature of the engine low, you constantly need to make sure that the engine can convert all it's produced energy into movement and not into heat. This requires to choose a gear that keeps the engine revs within the limits of optimum torque (again, see Fiat chart).

Enough theory. Get into your car and let's drive up a mountain for some practice.

Driving in the mountains.

While driving up the mountain last Sunday, I noticed that the barchetta in front of me had a speed such that when I put my car in second gear, the engine ran with high revs while it wouldn't use all the power (it couldn't get rid of the energy). But putting it in third gear, the revs where too low (outside the range of optimum torque) such that the engine would heat up as well. In this case, you always loose. If you keep driving like this, your engine will ultimately overheat!

YOU NEED TO DRIVE AT A SPEED THAT ALLOWS THE ENGINE TO RUN AT A CERTAIN NUMBER OF REVS WHILE YOU EFFECTIVELY USE ALL THE TORQUE IT DELIVERS!!!!

So in the example of last Sunday, driving a little faster in third gear would have solved this. It would have increased revs so the engine would run within it's limits of optimum torque. Driving much slower in second gear would have solved the problem as well. But we were really going at a speed that was not in balance with the characteristics of the engine.

The right balance always depends on the situation but in the mountains is more limited than on a flat road! For example, it immediately changes when the road gets steaper. A rule of thump for the barchetta is that if you drive up a hill between 3-5%, you need at least 3000 revs to maintain the balance. If the hill gets steaper you will notice that the revs go down (the engine can't deliver enough torque to maintain the speed). If the revs drop below, let's say, 2700 revs, change to lower gear. Speed up to 3600 revs and shift back into higher gear and you'll end-up around 3000 revs again.

But NEVER EVER keep going in the same gear if the engine can't handle it. This is a mistake many people make. The car slows down because the road goes up, they react by pushing the throttle which helps a little bit, the car keeps slowing down, they push the throttle even further and on and on. The only thing that happens is the engine to overheat.

Also NEVER EVER drive up a mountain in a too low gear (1st and 2nd) with a screaming engine because the engine can't get rid of it's energy either. You can drive in 2nd gear but only slow.

I strongly believe that some of the problems we've seen in the weekend are a result of a "wrong" driving style. Now don't see this as a blaim on you. It all is quite complicated and when taking driving lessons, no-one will ever explain it to you.

But understanding the dynamics of an engine definitely helps to avoid problems. And it also makes driving more fun. Having to change gears all the time to find the right balance makes a very dynamic driving style which suits a sports-car. Much better than a base-ball cap does!

Next time when you are on the road, give it some thought and then ... practice. It's not theory only! You need to practice to learn and maintain a dynamic driving style using the optimum balance between engine torque & revs and gear.

And after a while, this becomes an automatic habit. In every situation, you will automatically use it's optimum capacity without having to think about it. And if you really get it right, you won't have to look at your clocks all the time because you'll most likely learn "to listen to the engine". You can hear when an engine runs at it's optimum.

Have fun,

Eric and Jonathan