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Titanium valves in the YZ426
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Posted by: Joe Turner---------------------

I think I understand why Yamaha put titanium valves in the 250F because of it's higher redline, but what I don't really understand is why they would put them in the YZ426 and the WR426. I've never heard of people having problems with valves in the older YZFs. Anybody have any insight on this?

Thanks.

Posted by: steve125---------------------

Joe, I believe it works like this: Lighter valves use lighter springs(tension); therefore, less valve train drag (wear),less drag equals better response at all rpm's!

[This message has been edited by steve125 (edited 01-01-2001).]

Posted by: Rich Rohrich---------------------

That's certainly a secondary advantage, but if you think about it there is a much better reason to go to ultra light valve train components when you aren't planning on raising the peak rpm, like in the 426. There are lots of smart guys floating around here, anybody want to take a shot at this ? http://dirtrider.net/ubb2/smile.gif

Posted by: CRGuy---------------------

Throttle response
the lighter the parts n there the faster they can move. Lets say normaly it takes five seconds to rev to 11,000 rpm on the 426 and with the lighter parts it will take Four and seven tenths of a second to get there.
The result is to make more two smoke guys get a four becuase of the quick throttle response like a Two smoke But less maintance and the EPA bieng Happy.
My 2 cents

Posted by: Rich Rohrich---------------------

That's basically the point Steve was making, but I don't believe that is the main reason behind switch. Anybody else have a theory?

Posted by: steve125---------------------

I'm reaching,would it allow for longer intake and exhaust duration,by having an advanced cam profile,due to faster acting valves? Rich if this is wrong how "bout" some hints. http://dirtrider.net/ubb2/confused.gif

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by steve125:
how "bout" some hints. http://dirtrider.net/ubb2/confused.gif

OK, think about ways you can maximize torque over a broad range without paying a major penalty somewhere.

Posted by: steve125---------------------

Here i go again,the valves ability to transfer heat quicker,especially the intakes,would allow for a cooler intake charge (denser)this would then raise the torque curve. Im' cringing on that one!

Posted by: Saratoga---------------------

The lighter titanium weight allows the motor to move the valves up and down faster. As the number of times the valves open and close increase more horsepower/output is generated. The faster gas moves in and exhaust moves out the more torque the crank generates to the rear wheel.

Posted by: WWR---------------------

Rich,
did the compression ratio also go up this year?

The only other reason I see for the change, besides weight, would be durability.

Are we getting any closer?

Paul

Posted by: Vic---------------------

Paul- Weight is the reason. The question is, "What benefit will the lighter weight provide."

Could it be that the lighter valve train requires less power to drive it? http://dirtrider.net/ubb2/smile.gif

[This message has been edited by Vic (edited 01-01-2001).]

Posted by: steve125---------------------

Vic, i think your answer is the same as my first reply. Let's see we have covered,friction,weight,heat transfer,and duration.HMMM Rich what are you thinking?

Posted by: Rich Rohrich---------------------

Torque is to a large degree a function of cylinder filling. When you look at a torque graph you are essentially looking at a cylinder-filling (volumetric efficiency) graph. In relative terms two strokes have huge ports that open and close very quickly. Four strokes on the other hand have tiny valves (especially in the YZF series) that open and close very slowly. If you want to improve cylinder filling you have a number of choices:
- Tune the intake and exhaust waves (lengths and diameters) very sharply to a specific rpm. This works exceptionally well but only over a very narrow rpm range. Outside of that rpm range the wave tuning disrupts cylinder filling and causes a torque trough.
- You can increase the TIME available to fill the cylinder by increasing the intake valve open (cam) duration. That works well at high rpm, but leaves the valves open too long at lower rpm and again disrupts cylinder filling and causes a torque trough.
- We can increase the valve AREA with larger valves, but you again push the torque peak rpm up with this approach as well as running into space and cooling problems.
But AREA is the key here. Yamaha's initial approach to this problem was to use the 5-valve design, which provides greater valve area at low valve lifts than a comparable 4-valve design. The smaller lighter valves that come with the 5-valve design also allow them to open the valves faster which provides more flow area over a longer period of time. It's my belief that valve AREA is their reason in going to Ti valves.

You can't instantly open a valve in a four-stroke. The camshaft has an intricately designed opening and closing ramp to ease the valve off its seat and back on again. This cycle has to be repeated hundreds of thousands of times for each hour of running. So as a cam designer you have to balance opening the valve as quickly as possible (high valve acceleration rates) versus long term reliability. Keep in mind that until the valve is well off of it's seat, it's nothing but a hindrance to flow. The trickest port in the world can't flow worth a lick till the valve is up off its seat and out of the way. To expose the maximum valve area for the longest period of time designers try to accelerate the valve off it's seat as quickly as possible, but you can only accelerate the valve so fast before you can no longer control it's mass. If you can't control the valve reliability suffers in a hurry. The greater the mass the harder it is to control. Going to three intake valves instead of two gives you the advantages of additional low lift area, as well as lower valve mass that can be accelerated at a higher rate increasing the time that the area is available. It's a win win situation. By changing the valves from steel to Titanium, the cam designer is given a huge advantage. He can accelerate the valve much faster and fill the cylinder much quicker without the drawbacks of some of the other approaches. Torque goes up across the board.

I know the magazines are telling people that the valve springs are lighter so the frictional losses are reduced and providing a torque increase and quicker revs. The frictional losses associated with springs are small compared to the advantages to be gained by improved cylinder filling. When you consider how light the valve springs in the YZF are to start with the delta becomes even smaller. As we've pointed out so many times out here, the magazine guys are living in their own little world http://dirtrider.net/ubb2/smile.gif

So by now a bunch of you are thinking, why should I believe you? Well you shouldn't blindly trust me, but unlike the magazine guys I have the opportunity to qualify my theory http://dirtrider.net/ubb2/smile.gif As soon as the new cam is available I'm going to run a cam analysis (acceleration, jerk, etc) on the new 426 cam versus the old cam. We'll know in short order what's up. Stay tuned.

Posted by: Shaw520---------------------

Rich, are you saying you're gonna run the new cam with on the older steel valves ?

Posted by: Rich Rohrich---------------------

Initially I'll just run the cams on the "Cam Doctor" analysis hardware and I'll look at the characteristics of the two. If I find what I'm expecting too then I'll do some math and figure out if running the new cam is feasible with the steel valves. It should prove interesting either way http://dirtrider.net/ubb2/smile.gif

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by fastkevin:
The ti valves are used to allow it to spin up faster.

I guess that remains to be seen http://dirtrider.net/ubb2/smile.gif

Posted by: steve125---------------------

Rich i really enjoyed this,challenge us again sometime,it's the best way to learn!

Posted by: Vic---------------------

It will be interesting to see how different the new cam is.

Posted by: BOOMER---------------------

first i like to say Rich's comments are true-to some degree. but if the valve diameter is the same as steel valves-you DONT get more valve area. the only advantage to a ti setup is reaching peak horsepower by reducing the time to do so & the ability to reduce parasitic losses thru the valvetrain. the down side is berelium material is used for the seats to cushion the ti valve. it wears fast & the average dirt bike rider isnt going to want to have a valve job cut & the valves replaced a few times a season-(if he wants top maintain peak performance) I have been building drag & roadrace engines (i was chief engine builder for a factory support Yamaha team-& i race an owo1 yzf) since 87. i have used & made ti valves in a variety of applications. the advatages are VERY SMALL. I doubt if my dyno will show a difference with the new 426. But it is a wonderful marketing gimmick for yamaha to use "new titanium valves!" (our dealers need the service work!) i am very pro Yamaha-i have stuck by their 5 valve genesis design since its birth-but with a large combustion chamber inherit with 5 valves you can build the motor 2 ways- 1. increase cylinder pressure via compression & cam timing etc. for good acceleration. 2. lower compression & spread the cams' timing for better topend over rev & peak horsepower-at the expense of lowend acceleration. the ti valves are going to allow a engine built to accelerate(dirt bike) to rev higher-but with no real big power gain.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by BOOMER:
first i like to say Rich's comments are true-to some degree. but if the valve diameter is the same as steel valves-you DONT get more valve area.

If you increase the opening rate of the valve the effective valve area under the curve plotted against time IS increased. You are correct that the static area is the same given the same lap diameter.

Quote:

Originally posted by BOOMER:
the only advantage to a ti setup is reaching peak horsepower by reducing the time to do so & the ability to reduce parasitic losses thru the valvetrain.

If you follow the published research on frictional losses you'll see that there is very little evidence to support that claim.

Quote:

Originally posted by BOOMER:
the ti valves are going to allow a engine built to accelerate(dirt bike) to rev higher-but with no real big power gain.

The original YZ400F had a very small (by current design standards) valve area to piston area ratio . When Yamaha increased the bore to 95mm in building the 426 they didn't increase the valve area so the ratio is even smaller which obviously lowers the torque peak rpm and limits the need to rev the engine. It's unlikely given the lack of valve area to support high rpm running that Yamaha went to Ti valves in an effort to increase the peak rpm. The cylinder head in it's current configuration can't feed the engine adequately to support higher rpm without major changes. A more aggressive cam profile is a fairly inexpensive and expedient way to update the engine without incurring non-reoccurring engineering costs. The volumes of data they have from their superbike racing efforts will quickly tell them how fast they can open the valves for a given valvetrain mass, with only minimal pre-production testing. All in all it's a pretty smart move and buys them some time while they work on the new engine design. Although I wouldn't be foolish enough to discount the marketing aspect of the whole thing.

Posted by: MXN4FUN---------------------

Rich, are you saying the advantage of titanium valves minute unless coupled with a cam. Greater performance gains are yet to be noticed until different duration cams are used. Does GYT have something up its sleeve? " A little knowledge is a dangerous thing" Said by someone wiser then I.

Posted by: Dirthead---------------------

If doing a comparison between a steel valve and a ti valve using equal spring pressures, the ti one will close more quickly than the steel. The ti one will then be less prone to "floating" under the equal conditions.

Consequently if you can then use lower valve seating pressure (i.e. softer valve springs) to accomplish equal peak rpm characteristics, you have effectively decreased friction in the valve train and increased horsepower at the crank.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by Dirthead:
If doing a comparison between a steel valve and a ti valve using equal spring pressures, the ti one will close more quickly than the steel.

The valve seating velocity is still controlled by the cam profile regardless of the material used. The lower mass of Ti parts simply allows the designer to exploit the advantages via a different profile.

Quote:

Originally posted by Dirthead:
Consequently if you can then use lower valve seating pressure (i.e. softer valve springs) to accomplish equal peak rpm characteristics, you have effectively decreased friction in the valve train and increased horsepower at the crank.

That's the popular explanation and in theory it's correct, but in practice the advantages in a design like the Yamaha seem to be grossly overstated. It's an easy concept to grasp so it's the first one that the magazine guys jumped on, but I think you'll find that they are incorrect again http://dirtrider.net/ubb2/smile.gif
I'd be happy to provide some research sources if you guys want to dig into this deeper.

Quote:

Originally posted by MXN4FUN:
Rich, are you saying the advantage of titanium valves minute unless coupled with a cam.

That pretty much sums it up. The advantages aren't likely to be great enough to justify the expense if their isn't a corresponding change in cam profile or a need to increase peak rpm. Whether or not the return on investment is worthwhile from a marketing standpoint is a question best left to someone other than me. http://dirtrider.net/ubb2/smile.gif

Posted by: rick#3---------------------

Rich,
You made a comment "All in all it's a pretty smart move and buys them some time while they work on the new engine design" is Yamaha working on a new engine for the YZF?

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by rick#3:
is Yamaha working on a new engine for the YZF?

Yep

Posted by: SFO---------------------

Ti valves do not nessecitate the use of Berylium copper seats.
There are a few seat materiasl that are softer than the valve face and will suffice.
We used to manufacture Amco 45 ( 5%Ni Bronze)seats just for this purpose.
The reality of Ti valves requiring a unique(to them) cam profile is true, at least to justify and exploit their lightness.
They also become more corrosion resistant at higher heats than a comparable Stainless valve.
This heat resistance/stability also offers the cam designer more leeway in that the valve can spend more time off of the seat flowing air, than on the seat getting rid of heat.
The spring pressure thing, though a real consideration, I consider a wash.
I was taught to consider valve springs like a capacitor.
What they take to compress they put back in to the cam on the backside of the profile, minus the frictional losses.
My one question is how come laminar flow is not adressed in the flow equation.
The divergent cone/laminar flow makes single port/valve setups attractive.
The friction of more actual port/wall area is a consideration that perhaps is not part of this discusion, is worth note.

Posted by: motopuffs---------------------

most of you already know this, but when we say "titanium" this is actually a slang term for "titanium alloy". Titanium, by itself, wouldn't make a very good valve. It is alloyed with other elements (such as aluminum, vanadium, molybedenum, etc.) to produce a strong part.

ok, the titanium valve can run at a higher temp. What is the heat transfer coef. compared with stainless steel? Stainless steel has a relatively poor heat transfer coef., about half that of carbon steel.

someone mentioned that the titanium valve would close faster...it would only close faster with a more aggresive cam profile.

Does the spring actually return all of its energy to the cam (minus friction), even at high rpms? The cam is "running away " from the valve or rocker, even though they are still in contact.

Honda uses 2 titanium valves because they need the room in the head, and smaller springs allow this.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by motopuffs
Honda uses 2 titanium valves because they need the room in the head, and smaller springs allow this.

How did you come to that conclusion?

Posted by: holeshot---------------------

I thought Honda used titanium on the intakes because they are larger than the exhausts. This would bring the weight of the titanium intakes and the steel exhausts close to the same, giving them roughly the same rev, cam profile and spring tension limitations.

In short, maybe Honda thought making the smaller exhaust valves out of titanium would be a waste, because performance would be first limited by the larger intakes.

Edit above - exhaust was switched with intake - must start posting more carefully.

Posted by: motopuffs---------------------

and I quote:
"lightweight valves help create a high-revving engine, but with the CRF450R the primary focus was on saving space. A lighter valve permits the use of a smaller valve spring, which takes up less space so the camshaft can be set lower for a more compact engine..."
Red Rider Magazine (The Official Publication of the Honda Rider's Club of America)

Rich, you really didn't think I was smart enough to just figure that out on my own, did you?

Posted by: holeshot---------------------

So, the primary reason that Honda used titanium for the intake valves was so that they could set the intake cam a fraction of an inch lower (taking less space), and performance was really just a secondary issue?

Hmmmmmmmmm :think

Posted by: SFO---------------------

Even if you don't know whos shoes the dog doo is on, you still smell it.
I am not sure who stepped in it but I smell it.
Could it be corporate kaka?
So this thing is shim under bucket on the intake side and rockers on the exhaust valve?
I have a hard time imagining that Honda used Ti intakes to put the cam center line down.
It seems like if you have x for cam lift there is x above the valve guide/seal detail.
How is a smaller spring changing anything?
They would have to shorten the guide and sink the whole package into the head to drop the cam centerline.
something seems off here...

Posted by: MXN4FUN---------------------

Is it possible that Honda uses titanium intake valves for the purpose of reducing spring pressure? They want to have a longer duration of valve opening coupled with a steep closure angle on the cam lobe. By lessening the force needed to close the valve it limits wear on the seat by not creating as much valve seat pressure. Just a guess. Take it easy on me Rich. That's why I ride'em not design'em.

Posted by: smb_racing---------------------

I thought the reason yamaha used titanium valves (in comparison to steel) was a durability issue. Gunmakers use Titanium firing pins due to an ability to heat treat the metal more efficiently and for more shear strength. The firing pin in a gun has to be able to withstand a high shock and stress as would the valve face on an intake or exhaust valve due to the compression of the fuel/air explosion. Any viable information to my thought :think ?

Posted by: kevkon---------------------

Interesting thread

I am not too familiar with the YZF internals, but I was curious to know if Yamahas valve weight reduction efforts extend to the retainers, keepers, and buckets(lifters)?

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by MXN4FUN
Is it possible that Honda uses titanium intake valves for the purpose of reducing spring pressure? They want to have a longer duration of valve opening coupled with a steep closure angle on the cam lobe. By lessening the force needed to close the valve it limits wear on the seat by not creating as much valve seat pressure.

High spring pressures certainly accelerate wear, but it's my belief that cam dynamics and controlling the valves are much higher priorities in a high rpm engine.

No offense Moto but like SFO, I won't be putting too much stock in the "engineering information" gleaned from a marketing publication. Once a cynic always a cynic

Posted by: motopuffs---------------------

Yea, I hear you Rich, didn't mean to treat it like gospel, I guess it's just a press release.

Regarding the comment on firing pins made from titanium alloy, I think it is pretty safe to say that titanium is MORE DIFFICULT to heat treat than steel. This is a generalization, but think of how common heat treatment of tool and other steels is compared to titanium. More people are familiar with it.

Solution treatment and age hardening of titanium alloys must be performed with better control over time and temperature when compared to most common steels.

Posted by: SFO---------------------

I disassembled the head on my Ti valve 426 today.
Some observations...
The seats and guides both appear to be cast iron, there is not a hint of copper hue in either one.
It appears as if they are relying on the valve coating for abrasion resistance in the guide.
After 15-20 rides everything looks good. The valve faces have erroded naught and the face width is .040" for the valve contact patch.
The guide interface feels good as well.
The oem intake valves are backcut @ about 30 degrees for about .300".
The outer intake valves both had carbon build up on the back sides of the valve faces, the center intake is clean as a whistle.
Both outer intake ports had spooge/carbon build up about .375" back from the seat.
Thick gummy tarlike stuff, I have yet to find a way to remove it without scoring the valve coating.
I will try leaving them in solvent for a while. I relented and used a standard abrasives wheel (Buff and Blend 12") to polish the valves and radius the frontside.
I blended the seats on the intake side and where the throats were bored the short turn had a pretty sharp edge on it too that I worked out.
It appears that you could bore the throats an additional .080" but that might make future valve jobs challenging.
Buffed out the cumbustion chamber and radiused the sharp edges on the swirl enhancers (AKA TSCC anyone?)Per Rich's suggestion...
Reminded me of the first head I saw that Pierre DesRoches had done while he worked for Jerry Branch.
The chambers were fully organic not a sharp edge in sight. It was fun working at a Drag bike shop, you never knew what was in those cardboard boxes upstairs untill you peeled 'em open.
BTW, Yamaha chose to use steel retainers, a detail I thought funny if they were really going for lightness...
Can't wait to get my 450 big bore back from Eric and bolt it back together...
My local dealer sells Arrow pipes, the one for the 426 looks like it has a long (longer than most) silencer. I think the europeen stuff might be quieter. Maybe I am just wishing for too much, quiet, light, well made, better performance?
The Ti version with a carbon fiber silencer is 600.00 retail.
I never would have imagined I would think that that was cheap.
Let me know what y'all think about the intake spooge.
The guide seals seemed fine, I suspect it is a cam timing/overlap thing.
Bill

Posted by: HiG4s---------------------

Question, do the Ti valved engines cams have a faster rise rate? I thought that the limiting factor on non-roller cam engines was the angle of attack of the leading edge of the cam lobe against the valve actuator (Shim, push rod, what ever).

Posted by: SFO---------------------

The rise rate question will be answered as soon as Rich drops my cams into his camdoktor.
Limitations of design being answered with Ti... Now that is a different question.
Sure the angle of incedence is a factor, but just make the base circle bigger and then you will have a less severe tangent angle.
Acceleration (I believe in this case) is a function of mass and the ability to control it.
The bucket size /lift relationship on this motor is still conservative enough that the cam lobe is not reaching over to the edge of the bucket.

Posted by: SFO---------------------

I was thinking that perhaps the burned on carbon on the outer intake valves was a sign of the reversion noted in another thread.
The intakes aren't closed before the flame front hits them.
Why just the outers I asked myself?
Then I remembered the early 80's suzuki 4cyl 4valvers. The book would have you set the carbs pulling higher vacuum on the outer cylinders due to a longer intake tract.
So I think that the outer intakes have a longer path, and the center valve has a higher velocity so the charge coming out of the center valve is pushing harder than the outers giving the valve time to close before the flame front hits it.
I can just see it now...The valves racing to their seats before the critical moment.
With three intake cam lobes I would think you could grind a cam to equalize the velocity diferences of the port design, adjusting the outers against the inner...
Or, put smaller valves in the outers and smaller seats to bring the outside velocity up.
Maybe a 3 intake valve head should be treated as a single intake with boost ports.
I remember a thread about air injection and its merits boosting efficiency...
How about the 3 intakes closing and opening at different times to induce swirl?
I think I have been doing too much metal finishing lately...
The aluminum dust is having an effect.

Posted by: Rich Rohrich---------------------

This is a good thread and is worth bringing back up to the top.

Posted by: Boozer---------------------

Rich, i have a stupid question that has been bothering me for a while. Why are the exhaust valves smaller than the intake valves in almost all 4 valve engines. And in five valve heads, why is there always 3 intake and 2 exhaust? Please give me one of your in depth answers. Thanks. Oh, and im new here and was wondering what it is you do, and your educational backround.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by Boozer
Why are the exhaust valves smaller than the intake valves in almost all 4 valve engines.

im new here and was wondering what it is you do, and your educational backround.

Exhaust flow generally is designed to be in the 65-80 % range of intake flow. Exhaust valves open when the cylinder pressure is very high on the combustion chamber side, and very low (atmospheric) on the pipe side. So as you can see it is very easy to get exhaust gases to flow at the moment of initial valve open. The intake valve is in the opposite situation . The carb and intake port will only see atmospheric pressure while the cylinder pressure is high due to compression as the piston is rising towards TDC. The intake needs all the help it can get to flow in the right direction so additional valve area is the key. This is the main advantage of 5-valve versus 4-valve engines greater effective valve area at low valve lifts. If the exhaust flow and intake flow were matched it would tend to overscavenge and draw fresh charge into the exhaust system during valve overlap. A certain amount of that is necessary for high rpm power but too much of it just kills power. Balancing cylinder head flow and cam timing is the real key to making four-strokes work

There is lots more to it than I've outlined here, but we'll get to that at a later time.

My job? Well my paycheck says Senior/Analyst Engineer Nuclear Applications, so I guess that's what I do when I'm not asleep at my desk working on a transfer to corporate malcontent.

As for my education, I read a book ONCE long ago

Posted by: biglou---------------------

Rich, my dad was a Senior Systems Analyst for 40+ years. I think he was around when they invented the computer, but (swear to God) I had to go over and change the channel on the VCR from "AUX" to "03" two nights ago so the parents could record their movies! Kids, ya gotta lov'em.

Posted by: Rich Rohrich---------------------

My dad fixes his car with an AMEX gold card and his entire house blinks 12:00 so I figure I'm probably adopted

Posted by: rick#3---------------------

Hi Rich, to put it simply is Yamaha's 5 valve head an advantage over a 4 valve design or is it more for marketing. If so what are the advantages and disadvantages to both designs.

Thanks

Posted by: Rich Rohrich---------------------

Rick it's not hype it's more of a design philosophy.
The output of an engine is pretty much proportional to the average intake valve effective area. When you look at a 5-valve versus a 4-valve engine with the same bore size a 5-valve engine can have an intake valve head area 5% smaller and still have an approximately 10% greater average intake valve effective area than the 4-valve engine. The additional effective area can improve flow and tumble compared to the 4-valve. To get the same effective valve area in a 4-valve engine the bore usually needs to be increased by 3-5% .

As an example the YZF444 (97mm bore) engines I'm building have less intake valve head area than the new CRF450 but similar effective valve area. Both have big flat torque curves that peak well below the redline. Breathing is everything, and if you can get the same air flow through smaller passages you can keep velocity high and improve response and combustion efficiency. Increasing the valve head area generally moves the torque peak to a higher rpm.

Given the fact that the piston area is fixed, the BMEP value will directly relate to torque regardless of the engine speed. With similar engine designs the additional valve area of the 5-valve cylinder head can obtain fairly high Volumetric Efficiency (V.E) values even at lower engine speeds.

A basic indicator looks like:
BMEP = Compression Ratio * 14.697 (perfect sea level pressure) * V.E.

So if you can make the engine breathe and improve the V.E without having to spin the life out of the motor it will have a nice flat torque curve, which as far as I can tell is what ultimately gets those lap times down.
...well that and riding like McGrath

Posted by: cp380sx---------------------

To put it simply, the greater the total intake valve circumference the higher potential VE.

Three smaller valves may have the same head area as two larger valves but they will out flow the two larger valves because of a larger area under the valves at full lift.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by cp380sx
Three smaller valves may have the same head area as two larger valves but they will out flow the two larger valves because of a larger area under the valves at full lift.

The effective area under the curve (before total lift) is where the advantages are realized with most 5-valve designs. At full lift you'll tend to see similar total flow, and in many cases an advantage for the 4-valve designs. It's one of the reasons you rarely see 5-valves used in engines where maximum output is a priority and the HP peak is set at very high rpm.

The Yamaha R6 600cc streetbike is a good example of this. 5-valve engines represent good trade offs for high torque applications like MX, but it's far from an engineering panecea.

Posted by: cp380sx---------------------

I think that's more because of dynamics of the airflow and port design. The center valve has to deal with a lot of turbulance. The 5 valve Ferrari engines have some of the highest VE ratios in the auto industry so I think there is more potential there.

Posted by: rick#3---------------------

Very interesting Rich thanks. Is their any true to a 5 valve head creating more heat. If I remember correctly I read an article regarding building a superbike with an older Yamaha 5 valve and one of the issues they said was the extremely large radiator required.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by cp380sx
I think that's more because of dynamics of the airflow and port design. The center valve has to deal with a lot of turbulance.

The center valve in the Yamaha design sees the cleanest flow and straighest shot from port to combustion chamber so even though turbulent flow is a way of life in high speed engines the center valve tends to be one of the quietest areas in these cylinder heads. It's interesting to see the difference in deposits on the back of the center and outer valves in these engines after you get some time on them. As you watch the airflow exiting the center valve you see the flow over a greater number of degrees of the total valve head.

Quote:

Originally posted by cp380sx
The 5 valve Ferrari engines have some of the highest VE ratios in the auto industry so I think there is more potential there.

If memory serves correctly Ferrari abandoned the 5-valve concept for F1 use about the same time that the Yamaha/Judd engine dropped it. The tradeoffs at high rpm and 15mm valve lifts were apparently greater than the potential advantages.

For lower speed high torque work like street engines I agree it shows huge promise.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by rick#3
Very interesting Rich thanks. Is their any true to a 5 valve head creating more heat. If I remember correctly I read an article regarding building a superbike with an older Yamaha 5 valve and one of the issues they said was the extremely large radiator required.

Lots of horsepower equals lots of heat. No getting around it

Posted by: cp380sx---------------------

I was referring to Ferrari's production engines(ie. 360 and 550) which still utilize 5 valves.

As you indicated turbulence is a way of life in any 4 stroke engine and shrouding of the valves is another. Obviously the center valve will have the highest flow rates because of it's central location but it's cylinder filling capabilities will be compromised because of it's adjacency to the other intake valves and their charges. If you were able to delay the opening of the side intakes and give the center intake a headstart by opening first some efficiencies and low end torque might be obtained. The 426 could use some low end. The best thing would be variable valve timing but it comes at a price.

Posted by: Humai---------------------

Quote:

Originally posted by cp380sx
The 426 could use some low end.

Compared to what?

I suggest if you compare the YZ4xx to any other four-stroke under 520cc you will be hard pressed to find another engine with markedly superior torque characteristics at operating revs, including "low end".

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by cp380sx
Obviously the center valve will have the highest flow rates because of it's central location but it's cylinder filling capabilities will be compromised because of it's adjacency to the other intake valves and their charges.

I haven't seen the Ferrari design but that's not the case with the Yamaha design. My testing has shown the outer vales are subject to a greater degree of shrouding then the center valve. It's been my experience that making the center valve work to it's maximum potential is one of the real keys to making real power with this engine.

Posted by: cp380sx---------------------

Quote:

Originally posted by Humai

Compared to what?

I suggest if you compare the YZ4xx to any other four-stroke under 520cc you will be hard pressed to find another engine with markedly superior torque characteristics at operating revs, including "low end".

I don't know it for a fact, but I've read a number of tests on the new CRF450. All have stated that it has much better low end torque than the 426. It's a well known fact that multivalve engines sacrafice low end torque for high rpm HP. Variable valve timing is the key to having your cake and eating it too.

Posted by: Humai---------------------

Quote:

Originally posted by cp380sx

Variable valve timing is the key to having your cake and eating it too.

Amen to that! Given its efforts in the car world, I would put money on Honda being the first one to release that technology to the dirtbike world too.

Posted by: jake949---------------------

Rich what did you find out about the cam profiles? Did the cams get updated when they got the new Ti valves?

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Titanium valves in the YZ426

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