James
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| posted on 29/4/05 at 05:47 PM |
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V-Tec: How does it work?
V-Tec: How does it work
I'm curious as to how the Honda V-Tec system works.
I've done some investigation online and it appears to be this (simplified):
extra cams/valves are activated at a certain preset RPM.
they are activated by oil pressure. At the preset RPM the ECU activates a solenoid valve that permits oil flow down auxilary oil galleries. It's
this oil pressure that allows the extra cams to activate the valves.
Is it really this simple?
Does anyone know of anyone successfully running a V-TEC with Megasquirt/jolt?
Thanks,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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zilspeed
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| posted on 29/4/05 at 06:04 PM |
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Think of a conventional 16 valve head where there are two cam lobes to operate two inlet valves - these are operated by rockers.
Now imagine a third cam lobe in between these other two which has a different profile. This lobe has half of a rocker which follows the cam but
does nothing else because it has no valve to lift.
At a preset point, this follower is locked to the follower at either side thereby overriding the two other cam lobes and forcing the vlaves to be
operated by this third cam lobe which has different timing/duration. That's why you hear a Vtec engine going onto the wild cam profile.
Quite simple really.
The Rover system is much more elegant because it allows an infinitely variable transition between valve timing and does not depend on a third cam
lobe. It also does away with the notice jump as the valve timing changes because it all happens without a preset change.
Mild merges into wild giving low grunt and high end power 
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bigbriglasgow
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| posted on 29/4/05 at 06:35 PM |
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Oh yea john,
i noticed you tearing by that s2000 type r the other night with that better rover engine of yours!
Te he he
Brian
coz its a bit of an animal
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zilspeed
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| posted on 29/4/05 at 06:41 PM |
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Now now....
I don't have VVC.
All I was saying that it's a more advanced system than the original Vtec.
Then again - Hondas don't like blowing head gaskets as often as Rovers.
P.S. Have you seen this ?
Not mine....
GTM Rossa K3 on ebay
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bigbriglasgow
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| posted on 29/4/05 at 06:48 PM |
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Te he he just kiddin
Bloody hell that looks like a nice car but unfortunatly i am selling all my toys for a house so not for me i am affraid!
Nice with the soft top!! buy it zil and sell it again once you canabilise the best of both for 1 great car
cheers
Brian
coz its a bit of an animal
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Dale
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| posted on 29/4/05 at 06:48 PM |
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Some aftermarket cam pullies can be made/used that start at a certain position and then as rmp increase to a certain amount the pullies internals
allow it to shift to new setting.
Dale
Thanks
Dale
my 14 and11 year old boys 22
and 19 now want to drive but have to be 25 before insurance will allow. Finally on the road
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zilspeed
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| posted on 29/4/05 at 06:56 PM |
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quote:
Originally posted by bigbriglasgow
Te he he just kiddin
Bloody hell that looks like a nice car but unfortunatly i am selling all my toys for a house so not for me i am affraid!
Nice with the soft top!! buy it zil and sell it again once you canabilise the best of both for 1 great car
cheers
Brian
Getting a brand new hood Brian.
Unfortunately it's errr £590.
Still - it's a work of art compared to most. Can be put up or taken down from the driver's seat. Unlike a seven hood which is like putting
up a cheap tent 
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James
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| posted on 29/4/05 at 06:56 PM |
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quote:
Originally posted by zilspeed
Think of a conventional 16 valve head where there are two cam lobes to operate two inlet valves - these are operated by rockers.
Now imagine a third cam lobe in between these other two which has a different profile. This lobe has half of a rocker which follows the cam but
does nothing else because it has no valve to lift.
At a preset point, this follower is locked to the follower at either side thereby overriding the two other cam lobes and forcing the vlaves to be
operated by this third cam lobe which has different timing/duration. That's why you hear a Vtec engine going onto the wild cam profile.
Cheers but I know that bit!
Maybe I simplified my understanding a little too much!
My point is:
Is that all there is to VTEC: When the ECU detects a certain RPM a solenoid controlled valve allows the oil pressure to flow?
It just seems too simple for something I keep being told is really complicated!
Cheers,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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phelpsa
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| posted on 29/4/05 at 07:14 PM |
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Thats how i understood it
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Bob C
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| posted on 29/4/05 at 08:14 PM |
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MG VVC only alters cam timing, VTEC gives a whole new profile as well as timing so it's a far superior system. The 'hot' cam is
bigger everywhere than the 'mild' ones (opens before, wider and closes later) so it completely takes over when the oil driven pin goes
home.
The stock VTEC that I saw a dyno plot from was tuned to give a big shove when the hot cam came in. This is purely marketing overrriding engineering -
there's no need. If the 'hot' cam took over at lower rpm there would be no torque step and a smoother (better) overall result.
With your own ECU you can switch over as you like!
Bob
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chrisf
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| posted on 29/4/05 at 08:37 PM |
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quote:
that all there is to VTEC: When the ECU detects a certain RPM a solenoid controlled valve allows the oil pressure to flow?
No, it is a bit more complicated than that. A list of conditions must be met before the VTEC engages. An RPM threshold must be crossed while the
throttle must be buried in the floor and I think certain temperature conditions must not be exceeded (it won’t engage if the air is hot enough to
cause pinging).
You can tune the VTEC point to engage lower, but sometime that can be detrimental. IIRC, VTEC engagement occurs around 6.5k RPM. If you lower it too
much, the VTEC will engage but you will not have the air velocity to feed the beast. In this case, it will act as most 4 cylinder cars with hot cams:
it will bog.
It’s fiddly work best done on a dyno.
--HTH, Chris
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clbarclay
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| posted on 29/4/05 at 09:42 PM |
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quote:
Originally posted by Bob C
If the 'hot' cam took over at lower rpm there would be no torque step and a smoother (better) overall result.
From my experiuance even on a mild cam there can be quite a step. For a standard engine, the 1.6 honda in my brother's rover 216, there is a
very noticeable steps from mild to hyper active at 3500rpm when the cam comes on.
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zilspeed
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| posted on 30/4/05 at 08:09 AM |
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You live and learn
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Dave Bailey
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| posted on 30/4/05 at 08:40 AM |
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Anyone know how the Ford st170 system works. This too has a solenoid in the head but I have heard that it is only the exhaust timing that
changes.........
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smart51
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| posted on 30/4/05 at 10:45 AM |
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most VVC systems anly alter the exhaust timing. many do it by "simply" advancing or retarding the cam timing with respect to the rest of
the engine. This is superior to VTEC in that the exhaust vale timing is controlled to be correct over a wide range of RPM as it is continuously
variable. It works at low and medium RPM as well as high.
The VTEC system just changes between two cam profiles so there are only two points in the RPM range where the timing is correct. VTEC also
"loses" a couple pf revs where the cams are swapping over. The only advantage of VTEC is that it also controls valve lift. Don't
give VTECa hard time though, it was the first variable valve system developed.
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ned
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| posted on 30/4/05 at 11:15 AM |
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just to add the i-vtec system as used on the k20a (civic type r engine), not sure on the s2000 unit. anyway, i-vtec also has two paths in the inlet
manifold, a long and short path to the cylinder head. believe its operated by a roller barrel assembly that is actgivated under certain engine
conditions, this can realise improvements in torque i gather due to effectively changing the length of the inlet tract. another variable to add to the
equation/mapping procedure 
Ned.
beware, I've got yellow skin
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thekafer
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| posted on 30/4/05 at 10:06 PM |
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I've read that the Toyota 2zzge also uses a version of this type of vvt...is that right?
Fletch,
I'd rather have a bottle in front of me than a frontal labotomy...
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NS Dev
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| posted on 1/5/05 at 09:27 AM |
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Just a quick addition, the BMW system also shifts the timing (like most systems) by hydraulically moving the chainwheel relative to the cam. The ECU
controls the hydraulics.
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britishtrident
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| posted on 1/5/05 at 02:12 PM |
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Alfa had a very simple system that worked by a simple hydraulics in the centre of one of the cam sprockets --- at a preset rpm a simple spring
loaded centrafugal valve open and operated the hydraulics.
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britishtrident
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| posted on 1/5/05 at 02:22 PM |
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quote:
Originally posted by Bob C
MG VVC only alters cam timing, VTEC gives a whole new profile as well as timing so it's a far superior system. The 'hot' cam is
bigger everywhere than the 'mild' ones (opens before, wider and closes later) so it completely takes over when the oil driven pin goes
home.
The stock VTEC that I saw a dyno plot from was tuned to give a big shove when the hot cam came in. This is purely marketing overrriding engineering -
there's no need. If the 'hot' cam took over at lower rpm there would be no torque step and a smoother (better) overall result.
With your own ECU you can switch over as you like!
Bob
Honda had a major problem in that the small capacity older engines had sweet fa low speed torquebut the power came in wih a bump at at 4,000 rpm ,
while the larger capacity Honda units weren't a ball of fire at low speed either and at 4000 just made a lot more noise without delivering the
goods.
Although Honda engines are ultra reliable and sit behind one myself I don't rate them highly in the performance stakes as I get the impression
Honda power figures are a bit inflated compared to those claimed for Rover or Ford engines.
From my own experience on the old Lotus Twincam on L2 cams just altering the overlap a few degrees is enough it has a major effect on driveability.
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NS Dev
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| posted on 2/5/05 at 07:14 AM |
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hmmmmmmmm, have you driven anything with an s2000 engine in it????
I have (mum's s2000 and a grasstrack special with one in!!) and 240hp certainly makes these shift! The rolling road doesn't lie either!
(well.....I suppose it can to a degree but..........)
[Edited on 2/5/05 by NS Dev]
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paulf
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| posted on 2/5/05 at 09:07 AM |
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From the replies it sounds as if this would be possible using a megajolt and its programmable outputs , but do the engines turn in the correct
direction?
what would be a suitable donor?
Paul.
quote:
Originally posted by James
[Cheers but I know that bit!
Maybe I simplified my understanding a little too much!
My point is:
Is that all there is to VTEC: When the ECU detects a certain RPM a solenoid controlled valve allows the oil pressure to flow?
It just seems too simple for something I keep being told is really complicated!
Cheers,
James
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atomic
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| posted on 3/5/05 at 10:44 AM |
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Forget Megajolt go with the new Emerald K2 ECU http://www.emeraldm3d.com. They already have base maps for most V-Tec Engines.
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James
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| posted on 3/5/05 at 03:17 PM |
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And at a mere £550 for the ECU (alone?) I can see why that wouldn't be the way I'd go!
Can anyone tell me why MS wouldn't be up to the job? I can't find any info from anyone who has actually used one on a V-Tec but I also
can't find out why the hell not!
Cheers,
James
[Edited on 3/5/05 by James]
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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ned
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| posted on 3/5/05 at 09:22 PM |
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james,
probably because if you can find a few grand for an engine, wjhy skimp a couple of hundred for an ems?
and also you spend the money on the engine, build you megajob and then blow up the engine, what a fool you would feel.....
Ned.
ps thats assuming you even managed to hook up all the sensors and get it mapped yourself, how many engines have you mapped? remind me please oh and
let us know when you find a rolling road that'll do your megajob too
[Edited on 3/5/05 by ned]
beware, I've got yellow skin
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