Indications Vtec indicator for 1.8

[pjr]

VVT-i (Toyota) is some sort of variable valve timing and some of the Zetec (Ford)engines also have variable timing (not sure if they all do - my Puma with the 1.7 Yamaha designed Zetec engine did, and my Mazda 3 which had basically a 2.0 Ford engine also had some sort of variable timing).

Don't know if the implementation is the same as Honda's Vtec system. I was sceptical of Honda's claims for the performance of a 2.0 with the fuel economy of a 1.6 (for the 1.8 i-Vtec engine), but having driven it for over a year I can believe the claims. Civic is certainly as quick as my 2.0 Mazda was, but with far better fuel economy, and much lower emissions.

[Unknownsoldier]

I agree, I had always been skeptical, but my Grandfather had the greatest faith in Honda engines and always swore they were the best.... so I gave them a try and I absolutely love the engine.... it's a superb bit of technology.

Tom

[JonTypeS]

Whats wrong with the lovely orange lights we already have?

[lloeki]

how K20 vtec engine works:

imagine you're walking. you breathe a certain rhythm. when you'll be running, the rhythm will raise, but try to keep the same quantity of air coming in, you'll soon choke. the best way is to take deeper and longer (relative to length of a cycle) breathings.

so to achieve maximum power, the higher the rpm, the bigger the ratio valve opened/closed on one cycle must be.
else the engine does not receive enough air/fuel, and does not give all the power it could. on dohc it also acts on the exhaust valves, so that all the burnt components can be released. on sohc the exhaus timing would be fixed.

below a fixed RPM, intake valves and exhaust valves timing is fixed, giving fuel economy.
above a fixed rpm, the intake valves lift long enough for the engine to breathe correctly, and exhaust ones to exhale correctly. what's more (at least on the most recent ones like the K20Z4) the timing is not always the same depending on the zone you're in once vtec has kicked in. previous vtec were all-or-nothing, while recent ones are more progressive (that is, the more rpm, the more it breathes), and are also linked to other parameters like gas pedal position.

why doesn't it takes place all the way from 0 to redline? because there are technical limitations like risk of damages when vtec kicks in when not under load (I suppose that's why at a stop you can't rev past vtec)

this is usually what vtec refers to, and what (dual) vvti and other variable valve timing of sorts are made by other manufacturers (10~20 years after honda)

how R18A vtec works:

as the goal is not the same, this behaves totally different although, of course, this is also about valve timing. here we're on a sohc so only the intake cams are handled. upon intake opening, the piston goes down, pumping air/fuel into the chamber. on a usual engine, once it reaches down point, the intake valve closes, and we go into compression phase as the piston goes up. this way we get the full displacement of the engine. not so with this vtec eco technology. the intake valve stays open past the lowest point into the compression phase, pushing back some of the mixture into the intake manifold, up to a point. the intake valve then closes partway up and the compression takes place. this effectively diminishes engine displacement.

this way the R18A is able to simulate a 1.6L engine. the timing at which the intake valve closed is dependent on rpm and gas pedal. the more fuel you inject, the more it has to be compressed. so this can only be achieved under light loads and at low rpms (well, low relative to a honda engine! seriously, do you know many sohc engines that rev up to 7k?). why low rpms? because the 'default' cam position is good for high rpm, like a classic vtec.

so, what about the green leds? well, they could very well represent this valve timing: the more green lights are on, the more the displacement is reduced. and as this is of course directly linked to fuel consumption it will be hard to tell them apart...

[GHGH]

Thanks! That was a introduction to the vtec techs so even I understood it.

[equinoxe]

Hmmm... now i really understand. This was very enlightening, thanks lloeki.

[Nick7]

As for VTEC (on DOHC) does not engage on low RPM - simply because you would lose power.
Reason is air speed when entering chamber, ability to disperse fuel, etc, etc..

For example, on older cars people sometimes used some tools, like VAFC, to change VTEC crossover point.
Best way to find when is best position for crossover point is with dyno.
First make a run without VTEC engaging.
Than make a run with VTEC engaged way too low (3000 rpm as example).
Than you compare two graphs and see where power crosses, and you find ideal VTEC crossover point (usually in 5000-5500rpm range).