Mazda K series engine VRIS fully explained

An explaination to VRIS for the Mazda K engine... Klde klze klg4 kl47 k8 etc

[markbrzezinski]

Correct me if I am wrong. My understanding of VRIS is the inlet valve is held open during the first third of the compression stroke. So air is pushed back into the inlet manifold. This is held in check by the "fast" flowing air from the throttle body side. This creates a pressure wave or pressure pocket of air for the next cylinder. It's a type of supercharging. But the air has to be travelling fast in the manifold otherwise the pulse will reverse the airflow at low RPM. Hence they only allow the air to travel down a small diameter tube at low RPM. As the RPM climbs more air is allowed in to feed the beast and this resonance pressure wave effect has less of a benifit but still there to a degree. Interestingly even though a KF is two litres it actually is only about 1.8 litres given the lose of stroke but supercharged. Given the power being produce in naturally aspirated form using this manifold and greater duration inlet cam timing, the supercharging effect must be significant. I can't think of a 1.8 litre engine that produces 180hp with a standard restrictive air cleaner and compromised cast exhaust manifolds held back by a streetable cam.

[playk]

The idea here is to have plenty of air at all times. Which is the basic system. The additional vris valves will take advantage of increased positive air pressure within the intake system and open in order to take that pressure and create a high volume forced air/fuel mixture into the system. It is a momentary 'burst' as the increase air pressure is relieved into the combustion system. That's my understanding anyway. Why not have them open all the time you might ask?... That would negate the increased air pressure which we want to take advantage of for a high rev (set to 4500rpm) intake influx of air/fuel.

[Goeiuuh]

Thanks for the explanation! I always wondered though, why can't they be opened up all the time to let more air in constantly?

[brx]

Most Mazdas have an earlier version of this system. My brothers 1986 626 LX has the boost around 4K RPMs. Most of the time if you put an aftermarket intake on this earlier version of VRIS. The system will not work anymore. So just do a drop in air filter or leave stock. Do all you other power mods first so you can tell how much this system works. I am not sure if the Skyactiv engines use this tech.

[CarShed]

i wonder, why they use vacuum if they can use electromagnetic coil activators for flaps? = faster response, less parts :)

[tmac]

If it was open all the time you would loose low end torque