Why doesn't Ferrari do 5 valves/cylinder anymore?

IMO 5 valves was always too much monkey motion for the perceived or realised benefits.
I think they did it more as a "we are different" move than for any performance advantage.
With a plug in the middle 4 valves fills the cylinder bore very nicely.

 

Efficiency

 

Two much heat and moving parts for too little benefit. That or Ferrari figured out how to out-flow a 5 valve head with 4 valves, which is probably possible. Also, with a pent-roof design combustion chamber I am wondering if the 5th valve caused an issue with combustion efficiency compared to 4 valves with true pent-roof

 

Does Audi still use 5 valves/cyl? I always thought my B5 S4 sounded great.

 

Search Yamaha on the net. I recall they had 5 valve heads before F car and they reverted to 4 valve.
My recollection was the center valve caused turbulance and as above they found the four valve to flow as well as the five. (Less valve train parts are also a benefit).

 

The Honda NR750 had 8 valve heads... brilliant engineering work there

 

Maserati built a prototype biturbo head in the early 80s which was 6 valves. Brilliant little engine actually. Lots of power with very little boost on that 2L - something like 290bhp IIRC.

 

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A) do 5 valve heads outflow 4-valve heads--yes
B) to 5-valve motors outperform 4-valve motors--no

The difference being that 5-vavle heads are very difficult to cool sufficiently.
Thus, while the flow is there to make more power, the hotter heads do not deliver to the bottom line (not to mention the expense.)

 

Good question and good responses from our mechanically oriented minds here.

 

The seat of the pants answer is: It's too much work for the payoff.

 

Doesn't the 4-valve 458 make about 125bhp per litre?

How much hp/cid can you reasonably expect?

 

I wonder why they didn't just make this a smallbore V8? Already had the valve, cams, crankshaft and connecting rods. Coole motor nonetheless. may have just been an engineering experiment even, who knows.

 

What do you think a 5 valve 355/360 would make with another 15 years of development?

 

That motor was designed to 'punish' the rules where only 4 cylinider (max) engines were allowed (in motorcycle racing), by making in essence a V-8 but with only 4 pistons.

Incidently, the rings for the pistons were hideously expensive to manufacture.

As to why they did not make a small V-8, I cannot say.

 

Learn something new everyday, did not know the reasoning behind this design and manufacture. Actually didn't even know it existed till today!

 

Purely a matter of speculation - but I think <>125 bhp/litre and 9,000 RPM would still be the limit today given other engineering considerations.

I kind of suspect that the 5 valves were felt to be a dead end by Ferrari when they went back to 4...it sure does not appear to have been a cost-saving measure.

 

I concur. Infact, I would question whether Maranello is familiar with the concept of cost cutting

 

Agreed--given stable or slowly reduced emission limits.

It seems to me that Ferrari can pretty much charge whatever they want to charge for engine stuff.

But, given that 4-valve motors are easier to cool and at least comensurate in power with the 5-valvers there did not seem to be much rational to continue 5-valvers when the new Maserati engine was being designed. {Remember the Maserati engine became the 430 engine with "significant" additional work.}

In any event, the 3 liter motor had been developed about as far as it could have been developed. The bore-to-bore spacing limited the bores to 85mm (since the 348 all they could do was to stroke it and reduce rotating and reciprocation masses). In order to play with the Porsche Turbos, Lamboghinis, LSn Corvettes, more cubes were mandatory.

 

This might help answer some of your questions.

http://world.honda.com/history/challenge/1979pistonengine/text/01.html

 

Just as a matter of interest - this was from a comparison test in a R&T back in the day -

The F355 Spider versus the Porsche 911 Carrera Targa:

Engines -
Ferrari: 5 Valve dohc NA v8 - 3496 cc. 375hp @ 8250 rpm, 268 lb.ft. @ 6000 rpm.
Porsche: 2 Valve sohc NA f6 - 3600 cc. 282hp @ 6300 rpm, 250 lb.ft. @ 5250 rpm.

Test weight - Ferrari, 3500lb - Porsche 3350lb.
Both cars were conventional 6-speed manuals.

Acceleration -
Ferrari: 0-30: 2.0 0-60: 5.3 0-80: 8.6 0-100 12.7 -- 1/4 mile 13.7 @ 104.5
Porsche: 0-30: 1.8 0-60: 5.2 0-80: 8.5 0-100 12.6 -- 1/4 mile 13.7 @ 103.5

Top speed: Ferrari 175mph, Porsche 171mph.
Fuel economy: Ferrari 16.1mpg, Porsche 23.9mpg

My conclusions? The Ferrari claimed almost 100hp and many more RPM than the Porsche - but gave away 100cc displacement and 150 lb. of weight. In spite of that, they are practically equal in performance - with the Porsche a little quicker below 100 mph, the Ferrari with a very slight advantage above 100 mph and 4 mph more top speed.

Remember - these were both state of the art cars for 1995/1996. However, the Porsche was the traditional SOHC Air-Cooled flat six with only two valves per cylinder and much less advertised horsepower. Which made me sort of question the Ferrari power claims at the time.

It also leaves me wondering just exactly how much that extra fifth valve was doing for the 355 - besides contributing to a list price almost double the 911. Maybe there is always just a little more to engineering than complicated specifications.

Disclaimer - YES, I do still own a 1996 993 Targa as my daily driver. However, I have nothing against the 355, and almost bought one before I found the Testarossa.

 

Those 355 numbers are a bit on the high side. Early ODBII car on a bad day?

 

The (rest of the) internet seems to think the 0-60 time is 4.6-4.7 seconds (M6) and the 1/4 mile time is 12.8-13.2

 

Very possibly - I believe this was published in 1996. But then, so would the Porsche have been...

(if it were a bad test day, I mean)