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

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

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

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

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

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

quote:

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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

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quote:

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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.

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Thats how i understood it

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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that all there is to VTEC: When the ECU detects a certain RPM a solenoid controlled valve allows the oil pressure to flow?

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quote:

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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.

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You live and learn

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.........

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.

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.

I've read that the Toyota 2zzge also uses a version of this type of vvt...is that right?

Fletch,

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.

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.

quote:

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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

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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]

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:

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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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Forget Megajolt go with the new Emerald K2 ECU http://www.emeraldm3d.com. They already have base maps for most V-Tec Engines.

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]

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]

This web site has given me many happy hours at 'work' Thanks for all your contributions.
Just to add to the VTEC thread according to a Honda brochure the Civic Type R has i-VTEC and to quote 'Add Variable Timing Control to match inlet-valve opening to the engine load even more precisely. Bring on more power and torque lower down, so there's a smooth progression right across the rev range, instead of a sudden peak at the top end'.
My interpretation is that they have added variable timing to the inlet camshaft in addition to the slow and high speed cams for both the inlet and exhaust valves.
VTEC was described back in the October 91 issue of the defunct magazine Car Design & Technology
Can't beat a good V8 but can't afford the petrol.

The K2 ecu is about £350 with a base map installed. If you then want/require a RR session then you looking at another £200 or so, this with someone who knows about engine mapping.
I don't think the megajolt system will able to control the V-Tec system in the correct manor ie for engine reliability.
Why change the way/method of V-Tec engagement from the way Honda designed it in the first place.
Having now had quite a bit of experience of V-Tec with my F20C engine, best solution is to go for an Emerald/AEM15 (Gems) ecu just because they have base maps. Building a map from scratch is a real pain and almost impossible without a RR and good knowledge of this type of thing. What sort of price do you think it would cost just in RR time alone without a bse map, more that 3/500 I can tell you.


[Edited on 4/5/05 by atomic]

James, im planning on using Megasquirt II when its out, on my Turbod VTEC.

I cant see that the basic mapping will be particularly challenging, as I have read the maps off of the ROM in the stock ECU. So I plan to start with those, and some basic turbo multipliers and take it from there. Hopefully I wont blow the engine up, but if I do I have a spare

I think the Honda VTEC system is very good, you?ve got to hand it to them, the engine I have, from 1990 produces 170PS if used with the JDM ECU, that?s not bad for a 1.6L engine!

I have had my turbo manifold made up so I can run several turbos, either the MHI TD04 from a WRX STI using a special funnel (plan a) a T3 or a T4.

I keep meaning to put a website up but I haven?t got round to it yet. I have put a couple of pics in my gallery now though.

Scott.

quote:

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Originally posted by ned
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]

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Supercharing is a better option for the V-Tec engines. There are server of the new generation superchargers which use a turbocharger housing and turbine but are belt driven of the crank which can used.

MonkeyHunter, how have you read the maps from the stock ecu?..
Depending on the ecu, you may have another option, which would be to send the ecu to Hondata (http://www.hondata.com)and get the mod which allow you to remap the ecu at will.

hmm , lotus had an offering of a hydraulic system before the japs got into it !! - porsche alters thetiming of cams by adjusting the tension in the cam chain .

i think if you use MsnS youll have an output for controlling the solenoid , hell just needs to be an rpm controlled switch - which will only operate within certain parameters that you can program into the software , eh ?

Megasquirt is as good as GEMs since gems has only one fuel map to play with and can accept knock sense and does boost control - its just a case of figuring it out - you do need to get a wideband sensor definitely - mine was £230 for everything including controller .

the only downside for MS is the customer back up - altho the chap im dealing with is starting to do it professionally so its getting better .

Emerald = £380 incl flying lead loom, base map, software etc etc = bargain in my book. Depends how much of a price tag you put on time +hassle.

Atomic