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Old 03-15-2004, 10:39 PM   #31
R34RB30DETTV
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Originally Posted by USAF-Sergeant
I couldn't agree more with the above list. Not to concerned with VTEC as I think it is nothing more the variable timing used to increase economy. I could be wrong and it wouldn't be the first time. If I'm right... I think its funny how certian generations think VTEC is some kinda high performance design.
i hate to say it, but the VTEC system is a high performance system, although you are right about it being a fuel saving idea too..i will explain it in greater detail at some other time. is it ok Vwhobo/bav/SJ (moderators generally?) if i post something on the VTEC system? its about 2000 words long and i should confess that it is not my own work, but it is very informative and useful..
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Old 03-15-2004, 10:45 PM   #32
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Originally Posted by R34RB30DETTV
i hate to say it, but the VTEC system is a high performance system, although you are right about it being a fuel saving idea too..i will explain it in greater detail at some other time. is it ok Vwhobo/bav/SJ (moderators generally?) if i post something on the VTEC system? its about 2000 words long and i should confess that it is not my own work, but it is very informative and useful..

Make sure you give credit to the author...but if you could, just post a link if you can...makes it easier IMO.
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Old 03-15-2004, 10:54 PM   #33
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sorry, i only got the writing, can't remember the website...! "The engineer Giovanni Torazza, at Fiat, conceived and developed a valve operating mechanism that does everything to ensure that the engine should combine the best features of the most rabid and most restricted of conventional types.

The essence of the Fiat Torazza engine comes from early developments announced in 1970 by General Motors who had been experimenting with intake valve throttling. Here, the pivoting rocker levers of an otherwise fairly conventional pushrod engine were given movable fulcra enabling the intake valve lift to be varied. The object was to correct the cyclic variations of cylinder pressure suffered by a conventional engine digesting very weak mixtures. By minimising the vavle lift so as to create the smallest possible opening for the load applied, and thus maintain the full pressure drop across the port, the velocity of the incoming charge is kept up to the speed of sound. The droplets of petrol passing through the port undergo almost explosive atomisation in these circumstances, resulting in fast and consisten combustion immediately after ignition, even when the engine is running lean at part load.

The object, as might have been guessed from the date of the announcement, was to reduce toxic emissions in the exhaust. Torazza took the idea further, arguing that the possibility of changing both intake and exhaust valve opening duration and lift as a function of speed and load must be even more attractive. The essential mechanical features were an oscillating cam driven by an eccentric and connecting rod, and finger follower in an arc swung from the cam's centre of oscilllation, timing and lift were altered simultaneously - lower lift and softer timing in one direction, higher lift and sportier timing in the other. The typical valve opening variation in lift amounting to 37 per cent. Control was effected hyraulically through a three dimensional cam moved axially in response to engine speed and radially to inlet manifold depression.

The snag encountered by General Motors with their intake valve throttling was that in light-load running, when valve lift was very small, despite the high airflow velocity across the seat there was not enough movement upstream in the induction tract to support the droplets of fuel sprayed by the carburettor jet or conventional injector nozzles. This objection could be overcome by the truly atomised mist produced by Petrol Injection Limited as a more acceptable successor to their earlier Tecalemit-Jackson equipment. However, engineer Torazza has not reported any such difficulties, on the contrary finding no increase in the engine's tendency to detonation despite evidence of a leaning out of the mixture. This he thought might be due to an improved mixing of fuel and air downstream from the carburettor, as well as to the higher gas velocities across the valve opening annulus.

The experimental results verified by Fiat for the Torazza engine are wholly encouraging. An increase of bmep of over 30 per cent is realised at low speeds, drooping to 5 per cent at high engine speed where the size of the inlet and exhaust passages is the controlling factor. We should bear in mind that the conventional engine with which it was compared was camshafted for optimum performance in a regime between 60 per cent and 90 per cent of maximum power speed. It is worth mentioning that the whole arrangement was simply superimposed on normally-produced four-cylinder Fiat car engines, in one case with inclined opposed valves in the standard hemispherical combustion chamber, and in the other with in-line valves in the standard wedge type combustion chamber.

Other points to note were that the specific fuel consumption was improved and that valve gear noise was no greater than in the standard production engines. No abnormal vibrational fatigue was observed in the valve springs or the kinematic system, nor any abnormal wear in any enigne component after 600 hours testing, much of which was at maximum power and at overspeed.

Inevitably such mechanism is more costly than the normal arrangement because of a greater number of components demand more production operations and more complex assembly. A study of the torque characteristics of the engine make it clear, however, that if the unit is designed ab initio for this variable timing system, the increased cost may be compensated by the better performance and the possibility of reducing the engine displacement or, more probably, the number of transmission ratios and thus the overall weight of the power train. There are more possibilities inherent in the system, notably that of obtaining better mixture homogeneity through valve throttling at part-load and an internal exhaust gas recirculation by means of negative valve overlap. Moreover, some of the characteristics offered by this variable valve-gear may be of value not only in competition engines but also in the diesel and multifuel field: chief of the attractions is the possibility of increasing the engine's breathing capacity and turbulence throughout its speed and load range, and the possible improvements when starting at cranking speed."

Honda has improved on Torazza's original idea in the 20 years between his engine, and VTEC. VTEC varies the lift and timing by having two sets of rocker arms. The first operates directly on the valve, riding on the lower lift cam lobes. The second set ride on the higher duration lobes. In order to engage the higher lift a set of pins lock the first and second sets of rockers together forcing them to operate on the higher lift lobes. Although the engagement is mechanical, the pins are operated by a hydraulic selunoid. This is activated by the engine's computer which measures oil pressure, engine tempature, throttle postion, and many other things. When the engine is cold, VTEC will not engage to avoid potentially damaging the engine parts.
...and there we have the VTEC system.. hope that was helpful and informative.. and i give credit to the author, who ever you may be..
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Old 03-15-2004, 11:20 PM   #34
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whoa thats some long shizzle.
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Old 03-15-2004, 11:23 PM   #35
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Originally Posted by SuperJew
whoa thats some long shizzle.
don't say i didn't warn you... well, actually, you could really... (because this is my 50th post am i only a new or a bie now?)
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Old 03-15-2004, 11:24 PM   #36
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Originally Posted by R34RB30DETTV
don't say i didn't warn you... well, actually, you could really...

2000 words is actually less than I expected.
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Old 03-15-2004, 11:28 PM   #37
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Originally Posted by BavarianWheels
2000 words is actually less than I expected.
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yeah, sry, it was in bigger text in my word document and took up nearly 6 pages, and going by the rough estimation of 300 words/page i thought 2000 words was a good estimate.. how wrong we can be..
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Old 03-16-2004, 01:12 AM   #38
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Question Thanks for the info

Thanks man. When someone types all that for my benefit, its doesn't go un-appreciated. It appears to be similar to what Ford is doing with the new Mustang ( ) and the VVT design. Again, I could be wrong. I think the VVT was also used on the 5.4-litre V8 F-150's.

New question..... SORRY!!! I'm really trying to learn as I am extremely intrested in all this technology.

I'm trying to read how the VTEC compares to the VVT. I get to reading it and my head gets overloaded. Can you explain (in laymans terms) how these systems compare? Being the loyal American car lover that I am, is Ford's design a big improvement over the VTEC? I must confess, I swell a little with pride when I hear that the Big 3 have come out with technology superior to that of the import companies. Yep, I'm a VERY proud American.

Quote:
Originally Posted by Car&Driver

The base 4.6-liter V-8 now features an aluminum block and receives the SOHC 3-valve aluminum cylinder heads and variable-cam-timing mechanism from the new Ford F-150s 5.4-liter V-8. Engineers have squeezed more airflow efficiency from the heads, in part with a computer-controlled intake flap that varies the port sizes with engine speed. At low speeds the flaps constrict the passages to create a venturi effect and induce turbulence for better charge mixing. At higher speeds they open wide to let past the rushing atmosphere.

Thanks again.
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Old 03-16-2004, 11:02 AM   #39
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Originally Posted by USAF-Sergeant
Thanks man. When someone types all that for my benefit, its doesn't go un-appreciated. It appears to be similar to what Ford is doing with the new Mustang ( ) and the VVT design. Again, I could be wrong. I think the VVT was also used on the 5.4-litre V8 F-150's.

New question..... SORRY!!! I'm really trying to learn as I am extremely intrested in all this technology.

I'm trying to read how the VTEC compares to the VVT. I get to reading it and my head gets overloaded. Can you explain (in laymans terms) how these systems compare? Being the loyal American car lover that I am, is Ford's design a big improvement over the VTEC? I must confess, I swell a little with pride when I hear that the Big 3 have come out with technology superior to that of the import companies. Yep, I'm a VERY proud American.

Thanks again.


You don't have to apologize, we're all here to learn and asking is the best way.. I think, I may very well be mistaken but i believe that the system is to improve the atomization (mixing) of the fuel at lower engine speeds to improve (smooth) the idling of the engine. When the airflow through the induction manifold is slowed down due to low engine speeds the air does not have such turbulence and so the fuel does not atomize so well, so by creating this restriction the same amount of air is moving through a smaller gap and so it speeds up (much like rapids in a river), now when the fuel is introduced to this faster flowing stream of air the atomization is greatly improved. if you want to see the two diffrent systems (VTEC Vs VVT) go to this link. http://www.billzilla.org/vvtvtec.htm - i hope that answers your question.
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Old 03-16-2004, 11:00 PM   #40
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Thanks Sam.

I appreciate it. I hate soundeing like a dumbass but I also can't stand poeple who talk about shit they know nothing about, just to hear themselves speak. I figure if I'm going to add any to these threads, I might as well be knowledgeable. Thanks again.
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Old 03-16-2004, 11:11 PM   #41
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Originally Posted by USAF-Sergeant
I appreciate it. I hate soundeing like a dumbass but I also can't stand poeple who talk about shit they know nothing about, just to hear themselves speak. I figure if I'm going to add any to these threads, I might as well be knowledgeable. Thanks again.
yeah, i know how you feel about ppl talking shit. don't worry about feeling like a dumbass, just offer what knowlage you can and i'm sure it will be appreciated and as for learning more, i'm in my final year studying automotive engineering and yet i still feel like i know nothing.. .. glad i could be of help, any more questions don't hesitate to ask..
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Old 03-18-2004, 10:30 PM   #42
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I must confess, I stole it from Lectroid. LOL

ALRIGHT you avatar thief I'm proud that you took it It's as much yours as it is mine. My youngest brother is in the Air Force and just received the SNCO of the year award. Be smart, be safe.
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Old 03-18-2004, 10:39 PM   #43
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ALRIGHT you avatar thief I'm proud that you took it It's as much yours as it is mine. My youngest brother is in the Air Force and just received the SNCO of the year award. Be smart, be safe.
Not to deflate your pride or anything, but... I also won SNCO of the year along with NCO of the year (twice) and Airman of the year. That just proves they'll give it away to anybody.
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Old 03-18-2004, 10:45 PM   #44
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Not to deflate your pride or anything, but... I also won SNCO of the year along with NCO of the year (twice) and Airman of the year. That just proves they'll give it away to anybody.

And you are saying that didn't make you or your family proud? I know better /don't jerk my chain.
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Old 03-18-2004, 10:53 PM   #45
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And you are saying that didn't make you or your family proud? I know better /don't jerk my chain.
It was something that went with the territory. I would have been much happier doing my job instead of winning awards. In my case I was the poster boy for the non-politically correct, we're here to fly jets and kill things types. Sort of the anti-award winner. I can't say I wasn't proud but unlike most people who win them I never persued the awards.
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