Ferrari uses belt driven cams?

[SparkyJJO]

Take your pick:

Timing belts do not require a lubrication supply making them simpler to engineer and manufacture.

Timing belts transmit much less shock and vibration to the valvetrain.

Timing belts are quieter.

Timing belts have MUCH less stretch than chains which makes maintaining tension simpler (in fact, most belts require no active tensioner at all).

Timing belts are lighter.

Timing belts suffer fewer frictional losses.

ZV

The whole noise, shock, vibration, stretch, weight, and losses are all at best just slight differences and do not beat the overall robustness of a chain. Chains typically last the lifetime of the vehicle and almost never need any servicing or even second thought. It isn't like they are making a racket or beating up your valve train or anything. If they were, my Dad's old Camry wouldn't have made it to 300k miles :hmm:

If you have an interference engine the last thing I want to rely on is the belt. I know people who have had broken or jumped belts. My brother's Toyota has had two broken belts due to something about it attracting rodents (google "sienna mice" it is rather amusing). A friend's Honda broke a belt which resulted in engine destruction.

Besides, having a "quiet" belt vs a "noisy" chain on a louder performance vehicle is rather a moot point

I'm still trying to figure out how a rubber (mostly) belt doesn't stretch, but a steel chain does I'm not denying chains stretch, but however much they do seems to be very little given typically they never need changing on most cars.

Timing chain >>>>>>> timing belt

 

[pcgeek11]

I agree. Given a choice I will take a chain over a belt any day.

 

[Zenmervolt]

I'm still trying to figure out how a rubber (mostly) belt doesn't stretch, but a steel chain does I'm not denying chains stretch, but however much they do seems to be very little given typically they never need changing on most cars.

Timing chain >>>>>>> timing belt

Actually, while the belts have a rubber coating, the actual core is usually either kevlar or, more recently, carbon fiber. That's why they don't stretch.

And chains stretch significantly, as anyone with a chain-driven motorcycle knows. The reason that you don't need to change a timing chain on most cars (within the normal vehicle service life anyway) is because the active tensioners are designed to be able to take up a lot of slack.

The tensioners for chains also are typically not gears but rather simply plastic pads that press against the chain to take up slack. (See this picture.) These plastic tensioners definitely do NOT have an unlimited service life and do fail. They are wear items and need to be repalced eventually. Because the chain runs against the tensioner pad all the time, it also contributes additional frictional losses.

The reduced valvetrain "shock" (admittedly more like vibration than shock) is more important at higher RPM (less transmitted vibration means more precise control over timing). Similarly, the lighter weight and lower frictional losses are important in performance applications.

I agree with you that a timing chain is generally a better option from the owner's perspective assuming that the chief concern is keeping a vehicle for several hundred thousand miles with as little maintenance as possible, but there truly are valid engineering reasons to choose a belt over a chain in certain situations.

ZV