We got to five and quit. At least in production engines. I've read it's because the valves take up area in the head and there are diminishing gains from that. But maybe there's someone trying to science it out?
We got to five and quit. At least in production engines. I've read it's because the valves take up area in the head and there are diminishing gains from that. But maybe there's someone trying to science it out?
Packaging and timing control.
Fiat and Audi played with 5valve heads. While anything beyond that may decrease valve area, I think you also start running into frictional losses as well
Diminishing returns. Which apparently actually starts at 4/cyl.
8 valves per cylinder works well, right?
Yamaha had 5 valve engines for like forever. I had one. An FZ1. Brilliant lump. Then they went back to 4.
I would think that 4 valves allows you to keep all your intake or exhaust valves inline with all bucket lifters for a DOHC setup which is a simpler valvetrain than having them staggered which would require different geometry lifters .
Edit: Looks like VW still manages to keep it simply with the 5V, although it is definitely more complex than 4v (split journal with more hardware at a minimum).
The almighty LS only has 2 valves.
/thread.
Patientzero said:The almighty LS only has 2 valves.
Which is why it doesn't breathe as well at high revs as 4- or 5-valve engines. :)
Given that something like 80% of the cars for sale today use 4 valve heads, I'd speculate that that's the sweet spot where you get the most VE gains with the least additional complexity. A directly-actuated, non-variable, 4-valve head (like the NA/NB Miata heads) is actually simpler and has fewer moving parts than a cam-in-block 2-valve pushrod motor.
Toyota and Ferrari also built 5-valve/cylinder designs in addition to the already-mentioned Audi, Fiat, and Yamaha. How many of those manufacturers stuck with the 5-valve design? How many went back to 4-valves? Hmmm...that might be the answer right there.
Want to blow your mind? Look into sleave valves.
mad_machine said:Fiat and Audi played with 5valve heads. While anything beyond that may decrease valve area, I think you also start running into frictional losses as well
The combustion space starts to look pretty bad, and it leaves less room for a fuel injector, which is why VWAG went back to 4v/cyl.
Everyone's pretty much settled on a narrow angle 4 valve head for optimal combustion and efficiency.
Something like the FreeValve that allows greater control of individual valves, is likely to have better benefits than adding more valves/hardware. I think that's the "next frontier" in valves. All of the control you could want with less hardware/smaller footprint:
-85829.jpg)
Would it surprise anybody that this picture above was a Yamaha? Ultimately they decided "That's too many valves, even for us."
In reply to MadScientistMatt :
When Yamaha says it's too many valves, it's too many valves.
I wonder where the minimal strength is for the combustion chamber vs valve quantity?
Maybe its worsening at 5 valves compares to 4 valves and since everyone is raising compression ratios...
Or its just a messy combustion with tightening emissions like previously stated
Can you get a VW 1.8t head to rev high? It seems even though they had 5v per cylinder, they didn't rev particularly high, but it also mainly came in the 1.8t turbo cars with the smallish k03. I recall there was a 20v n/a in europe and eurosport had an n/a build, but it was stolen a few years ago, trying to find out the details about that motor.
The real reason we haven't seen more valves is that most of the design and engineering effort that could be allocated towards this has instead been put into creating razors with as many blades as possible.
The Audi 2.7TT was an impressively smooth and powerful engine in its time with its 5 valves per cylinder. Also fairly efficient. 250 HP at 5800 RPM, 258 lb.ft. at 1850 RPM.
Valves are for chumps. 2 stroke is the way, the truth, and the light.
Also something something wankel something.
Cyclops cylinder head - 5 spark plugs, 151 valves.
STM317 said:Something like the FreeValve that allows greater control of individual valves, is likely to have better benefits than adding more valves/hardware. I think that's the "next frontier" in valves. All of the control you could want with less hardware/smaller footprint:
I have thought this as well, but im guessing there is a cost/complexity & licensing issue here.
The completely variable timing is interesting in that your lift profile can be almost on/off so you can maximize flow for a given valve size. Also interesting that you can just program EGR into the exhaust valves. And move between Otto and Atkinson cycles as needed.
noddaz said:Need something like this instead.
This guy's way ahead of you:
Has anyone tried non-round valves recently? A small number of huge crescent-shaped valves should flow well..
I think it can probably be summed up as having the law of diminishing returns applied.
How many valves in a modern F1 engine? I'm sure if there was a benefit to five or more, they'd use them.
You'll need to log in to post.
