What is variable valve timing?

[imported_Truenofan]

i understand that there is a more fuel efficient timing set. but what im saying is that the second set kicks in a such ridiculously high rpms that it makes it almost useless for normal driving on the streets. on most. i don't know about others. but im pretty sure the honda vtec and i-vtec system kick in pretty high.

 

[natto fire]

Well, I give up.

I thought I had explained VTEC the best I could.

And your sig explains nothing except that NA can't match forced induction. Only an idiot would think otherwise. It should be noted that Formula one engines can achieve a sort of "fake" forced induction, in that they can achieve over 100% volumetric efficiency.

I skimmed through the article (it actually explained too much that kept an experienced tech bored) and yes, the rocker arm pivoting techs such as BMW's VANOS, the newest Nissan, and Audi tech is superior, and was trying to show the difference between cam-phasing and cam-shifting, which was covered in the article, but I digress.

 

[spidey07]

Originally posted by: Truenofan
i understand that there is a more fuel efficient timing set. but what im saying is that the second set kicks in a such ridiculously high rpms that it makes it almost useless for normal driving on the streets. on most. i don't know about others. but im pretty sure the honda vtec and i-vtec system kick in pretty high.

I think you are severely misinformed and have not read the article nor listened to the points raised regarding fuel economy, consumption, power and engine/cam design. Nor do I believe you have driven such vehicles or understand.

You would be mistaken and misinformed. I drive a 2004 TL and can barely feel "when the VTEC kicks in yo!", but what I can feel and document (I'm not going to goole for you) is the fuel economy and brickwall torque curve. Honda's approach (as referenced in the article) is not the best-just their version, but the page is a really good read for those interested in one of the most revolutionary concepts of the last 15 years.

If you would please read the article maybe you would understand the advantages of variable valve technology?

*read* NOT JUST VTEC

 

[spidey07]

Originally posted by: Captain Howdy
Well, I give up.

I thought I had explained VTEC the best I could.

And your sig explains nothing except that NA can't match forced induction. Only an idiot would think otherwise. It should be noted that Formula one engines can achieve a sort of "fake" forced induction, in that they can achieve over 100% volumetric efficiency.

I skimmed through the article (it actually explained too much that kept an experienced tech bored) and yes, the rocker arm pivoting techs such as BMW's VANOS, the newest Nissan, and Audi tech is superior, and was trying to show the difference between cam-phasing and cam-shifting, which was covered in the article, but I digress.

Don't give up. You very clearly clarified my understanding of honda's approach.

To your point we would both have a hard time making heads or tails of an F1 motor. I've seen them dissected and cross sectioned in person. I can barely identify the basic parts.

 

[natto fire]

Originally posted by: spidey07
Don't give up. You very clearly clarified my understanding of honda's approach.

To your point we would both have a hard time making heads or tails of an F1 motor. I've seen them dissected and cross sectioned in person. I can barely identify the basic parts.

Thank you.

I thought you seem genuinely interested and were getting it. To draw on the last part of your approach, it comes in clear as crystal once you have dissected the beast itself. I know I had a hard time understanding VTEC until I took apart both a B17A1 and B18C1 head and looked at it close hand. I am just that type of learner, hands on is definitely best for me. Some people can read a book or article and know exactly how something works, and hey, I congratulate them. I was trying to convey what I learned from personally taking apart these cylinder heads, and I know I am not perfect at giving directions or explanations.

Like you, I cannot even pretend to understand how formula one engines can use the exhaust to achieve a sort of forced induction. I would drool over the idea of even being able to hand disassemble one, but have come to terms with the fact that I probably never will.

To be honest, I could care less what people's opinions of VTEC, or any engine for that matter, are. I always have my personal beliefs of mechanical beauties or blunders. No one can take that away from me, and I am not trying to force "gearheadism" on anyone. At the same time, if you cannot appreciate every triumph or tribulation in the pursuit of power in the wild history of the internal combustion engine, then you are not truly a gearhead in my vernacular of the word. Which again is fine, there are plenty of people that claim to be gearheads but will only appreciate a car that is made in a certain place or have a certain powertrain. Everyone is entitled to their opinion, just like in racism. However, just like racism, there will be more open minded people that will reject all that crap and see the beauty of automobiles as they are. Lets face it, the ICE is on it's way out and should be respected in all shapes and forms before, and after, it is written to the history books.

While that is probably an extreme analogy and might not even happen in my lifetime, there is no doubt it is inevitable. Hell, I bet there were people that thought that because of refinement after refinement to the carburetor that it would last forever, but look how that turned out. The point is technology is always progressing, whether or not certain vocal minorities want it to.

 

[timxpx]

Originally posted by: Truenofan
i understand that there is a more fuel efficient timing set. but what im saying is that the second set kicks in a such ridiculously high rpms that it makes it almost useless for normal driving on the streets. on most. i don't know about others. but im pretty sure the honda vtec and i-vtec system kick in pretty high.

sure, it kicks in pretty high. my car hits lift at ~5800rpm until i redline at ~8100rpm.

however, i don't find it useless, especially since on weekdays i drive anywhere from 54 (minimum round trip work commute) to 87 miles daily, which is all mostly highway driving.

if i really really need to accelerate on a highway on-ramp, i'll down shift, hit lift, and my car feels a little more spirited. if i need to keep accelerating, i'll take it to redline, up shift, and the pin will drop right back to 5800rpm... still in lift. i can still keep going at my cars peak power range without waiting to rev back up, but at this point, i'm at highway speeds and my car's alter ego gets put away and i have the whole low end of the power band to be an average daily driver...

think of it as power on tap i guess?

---

also, shouldn't the line in your sig be "vtec - all the lag of a turbo, none of the boost... it's like waiting for bad sex" ?

if you check out steveox's thread somewhere on here - he's turboing a matrix xrs. it's the 2zz-ge VVT-Li toyota engine that's very similar to my civic engine. it's another high compression, high revving car with lift engagement around ~6100 rpm and staying happy until about 8k. it's the same engine that puts smiles on lotus drivers' faces! that thing will be a beast with boost + lift!*

who says the two technologies can't play nice?

*after reading this back, i should clarify that i am in no way comparing a toyota matrix to a lotus. just pointing out that this things got potential!

---

oh and going back to the article in the op... so *thats* why it feels so smooth when my friend drives like a maniac in his 330xi

 

[spidey07]

Originally posted by: Captain Howdy

Originally posted by: spidey07
Don't give up. You very clearly clarified my understanding of honda's approach.

To your point we would both have a hard time making heads or tails of an F1 motor. I've seen them dissected and cross sectioned in person. I can barely identify the basic parts.

Thank you.

I thought you seem genuinely interested and were getting it. To draw on the last part of your approach, it comes in clear as crystal once you have dissected the beast itself. I know I had a hard time understanding VTEC until I took apart both a B17A1 and B18C1 head and looked at it close hand. I am just that type of learner, hands on is definitely best for me. Some people can read a book or article and know exactly how something works, and hey, I congratulate them. I was trying to convey what I learned from personally taking apart these cylinder heads, and I know I am not perfect at giving directions or explanations.

Like you, I cannot even pretend to understand how formula one engines can use the exhaust to achieve a sort of forced induction. I would drool over the idea of even being able to hand disassemble one, but have come to terms with the fact that I probably never will.

To be honest, I could care less what people's opinions of VTEC, or any engine for that matter, are. I always have my personal beliefs of mechanical beauties or blunders. No one can take that away from me, and I am not trying to force "gearheadism" on anyone. At the same time, if you cannot appreciate every triumph or tribulation in the pursuit of power in the wild history of the internal combustion engine, then you are not truly a gearhead in my vernacular of the word. Which again is fine, there are plenty of people that claim to be gearheads but will only appreciate a car that is made in a certain place or have a certain powertrain. Everyone is entitled to their opinion, just like in racism. However, just like racism, there will be more open minded people that will reject all that crap and see the beauty of automobiles as they are. Lets face it, the ICE is on it's way out and should be respected in all shapes and forms before, and after, it is written to the history books.

While that is probably an extreme analogy and might not even happen in my lifetime, there is no doubt it is inevitable. Hell, I bet there were people that thought that because of refinement after refinement to the carburetor that it would last forever, but look how that turned out. The point is technology is always progressing, whether or not certain vocal minorities want it to.

Given your knowledge I think you would be freaked out by an F1 motor. I'm not a true gearhead nor do I do it for a living, but I would think I could identify a head/cam/piston or ya know...maybe the crankshaft? so small, so powerful.

 

[jagec]

Originally posted by: Truenofan
i understand that there is a more fuel efficient timing set. but what im saying is that the second set kicks in a such ridiculously high rpms that it makes it almost useless for normal driving on the streets. on most. i don't know about others. but im pretty sure the honda vtec and i-vtec system kick in pretty high.

If it wasn't for that second set, the "economy cam" would be less optimized for low-RPM driving. Variable valve technology helps both the bottom end and the top end, but using more appropriate cam profiles for both. So even if you drive like Grandma and never get near redline, you are still enjoying the benefits of VTEC. It's true that you could swap out the cam for a more economical one and do just as well as the VTEC engine, but then you HAVE to drive like Grandma.

You're telling me you NEVER hit redline on the streets? Come on now.

 

[imported_Tick]

Great post OP.

*dreams of servo-actuated valves*

 

[jagec]

Originally posted by: Tick
Great post OP.

*dreams of servo-actuated valves*

F1 has pneumatic valves IIRC. Not sure how they deal with timing, though.

 

[LTC8K6]

Yeah, F1 has had pneumatic valves for a while now. Springs were too slow for the high revs, iirc.

 

[Howard]

Originally posted by: LTC8K6
Yeah, F1 has had pneumatic valves for a while now. Springs were too slow for the high revs, iirc.

They had pneumatic springs, not actuation (well, the "on" part, anyway). Not sure about the current engines but past engines used camshafts.

 

[Howard]

Originally posted by: Captain Howdy

Originally posted by: spidey07
Don't give up. You very clearly clarified my understanding of honda's approach.

To your point we would both have a hard time making heads or tails of an F1 motor. I've seen them dissected and cross sectioned in person. I can barely identify the basic parts.

Like you, I cannot even pretend to understand how formula one engines can use the exhaust to achieve a sort of forced induction.

It's likely the fact that the exhaust is tuned (at certain RPM ranges) to flow extremely well, such that the inertia of the air flowing into the cylinder continues to assist the "pile up" once the intake valve is closed (at higher speeds the intake and exhaust valves are both open momentarily after the power stroke). Or it could be something else...

 

[LTC8K6]

In F1 they are very secretive about what they are running.

 

[natto fire]

Originally posted by: Howard

Originally posted by: Captain Howdy

Originally posted by: spidey07
Don't give up. You very clearly clarified my understanding of honda's approach.

To your point we would both have a hard time making heads or tails of an F1 motor. I've seen them dissected and cross sectioned in person. I can barely identify the basic parts.

Like you, I cannot even pretend to understand how formula one engines can use the exhaust to achieve a sort of forced induction.

It's likely the fact that the exhaust is tuned (at certain RPM ranges) to flow extremely well, such that the inertia of the air flowing into the cylinder continues to assist the "pile up" once the intake valve is closed (at higher speeds the intake and exhaust valves are both open momentarily after the power stroke). Or it could be something else...

Yeah, I assumed that as well, as the exhaust stroke is really the only place they would be able to extract reasonable waste energy to assist induction. Hell, turbochargers already do it, but those being barred from F1 those wise engineers found another way to use exhaust pulses to their advantage. VTEC technology was born of this same idea, but back then, almost 17 years ago, they did not have it locked down perfectly.

Even with that, I believe they are only getting around 130% volumetric efficiency, which is pretty impressive considering they are only allowed to use NA, but still cannot even come close to VE numbers using more traditional forced induction methods.

 

[Howard]

Why do you think it's only the exhaust which can increase VE over 100%?

 

[spidey07]

Originally posted by: Howard
Why do you think it's only the exhaust which can increase VE over 100%?

I would guess it might be similar to how tuned pipes work on 2 stroke motors?

I've heard them run before up close and personal and there is a discernible "singing" to the exhaust. Plus there's been videos out there and the exhaust runs super hot so probably shape could create a vacuum or low pressure? The exhaust glows red hot in some kind of expansion chamber.

 

[Howard]

No, you mistook my question. The intake obviously has a hand as well.

 

[Eli]

Text

 

[Howard]

You've posted that before.

 

[natto fire]

Originally posted by: Howard
Why do you think it's only the exhaust which can increase VE over 100%?

Because the atmospheric pressure is a set value. You cannot create more energy from nothing. Yeah, the intake tract could be made perfect, but that would still only yield 100% VE. You need to take energy from something else to increase VE over 100%.

 

[Howard]

What does atmospheric pressure have to do with anything? If you can get the intake flowing fast enough into the cylinders (be it reinforced by pressure waves - e.g. variable length intakes), you can have the air stack-up inside the cylinder and therefore increase the mass inside.

 

[imported_Truenofan]

I'm just asking, how often do you really need that vvt in the city. where most driving is done. how often do you really need that second set of cams? are they really that important? if they were never put in the engine in the first place, would you really mind them not being there? all in all its really just marketing the way i look at it and how Honda/Toyota seem to bloat its effects onto they're cars.(I dont hate the people who use it for daily drivers)
your vtec shouldn't kick in for cruising, it probably switches back to your fuel efficient cams which it uses more often than the advanced timing ones. i know in all honesty, i wouldn't notice the 6-ports(n/a rotary version of vvt) on my engine not being there. but i suppose the "power on tap" is always a good though. its always there, always optional if you need it on demand. yes its useful is what I'm saying, but only to a point. its not a be all end all, best system of the world, its just those systems cost far more to mass produce, and are far more complicated.

You're telling me you NEVER hit redline on the streets? Come on now.

no, i have never brought my car up to redline on the streets. i have no need to. the only place i will bring my car up to redline, is on a empty road where there is nobody behind me, and nobody in front of me. not in regular traffic or in cities. even when I'm entering the highway, i only redline it in first, then i shift normally to second, ect... only to break the carbon lose in my engine. no more, no less.

be it reinforced by pressure waves - e.g. variable length intakes

go ahead and get a dynamic intake manifold for your car, that works efficiently. you'll be hard pressed to find them, and if you do, they're quite more expensive than your normal intake and vtec system since it has to be integrated into your ecu/timing, ask some people who have just ITB's and how hard it is to tune them properly.

 

[jagec]

Originally posted by: Truenofan

i have never brought my car up to redline on the streets.

i will bring my car up to redline...on a empty road

when I'm entering the highway, i only redline it in first

 

[DivideBYZero]

Originally posted by: jagec

Originally posted by: spidey07

Originally posted by: Howard
Audi's Valvelift system seems to be the best one out so far.

http://youtube.com/watch?v=4AQgiAulFcM
http://youtube.com/watch?v=7NTP4quytTI

Excellent! Thank you. I thought that's how VTEC worked. The cam, with two sets of lobes is shifted along it's axis. Looks pretty slick and not as mechanically complicated as i once thought.

-edit-
I see. The cam itself isn't shifted, just the lobes. VERY interesting. Makes sense.

That's the Audi system, not the Honda system. IIRC the Honda system doesn't move the lobes at all, it just locks together different rocker arms to transfer the motion of different lobes.

Originally posted by: BouZouki
What about BMW's double VANOS.

They actually managed to eliminate the butterfly, so they get my vote.

Nah, not with Double Vanos. Valvetronic is without the butterfly, IIRC. My Double Vanos has SIX butterflies.