Variable length intake runners

[beef_bourito]

Just wondering if anyone knew about this. I've looked online and couldn't find a whole lot of information. Does anyone know of cars that have these (either race cars or street cars) I only know of one, the Mazda 787b. Also, does anyone know of any drawbacks to variable length intakes?

btw i'm talking about continuously variable intake runners, not the ones that have two different ones and a valve that opens up the shorter one at a cartain rpm.

[KiwiBacon]

Check out an Australian car called the Ford Falcon.
I think the later versions of it's 4 litre straight six feature them. But I haven't seen them myself.

[Moppie]

The Honda Integra VTi-R/GSR/SiR fitted with the B18c had variable intake runners, as did the 6cyl M3 BMW's.
I believe Porsche use or used it in various 911 models, and Mercedes use it somewhere to.

[UncleBob]

most variable intake systems use a butterfly in the intake track that opens up to longer/shorter runners. Its not a true variable intake, but has a similar effect. There is dozens and dozens of cars that use this type of systems

I don't know of any *true* variable intake track systems on cars, but there's a few motorcycles that have used it. Such as the Honda RC30, RC45, and the suzuki R6 (very recent models). But these are very short velocity stack-style setups

[beef_bourito]

so far i've only found one road vehicle that has variable length intake runners that make the runners longer rather than just open up a new set. the yamaha R1 has that but it moves between two set positions, it's not constantly changing or at least constantly changing between two set rpm's.

it doesn't seem as though anyone has come up with a system that has continuously variable intake runners and i'm starting to wonder why. to me it seemed rather simple, you have equations telling you what length they need to be for a set rpm, motors of some sort that move the runners out and in to make them that length. of course i'm talking about a simplified intake where you have individual throttle bodies and no complex intake of any sort but there've got to be ways to work around that too. hell if you had it designed for racing and you wanted it to be very precise, you could adjust it for temperature, humidity, etc. on race day.

it doesn't even seem as though it would be very expensive to implement in small quantities for race applications or sports cars.

[curtis73]

Any time you're asking a flexible joint to compensate for constantly changing vacuum variables, plus move a runner around, the reliability goes out the window. I think that's why you don't see it on production cars. Some cars have trouble with intake gaskets after 50k miles. They are tightly sandwiched gaskets, but they fail from thermal changes and the constant (thousands of times per minute) radical pressure changes.

[UncleBob]

I think the conclusion you can draw from how little infinite-variable intakes have been attempted, that its not worth the hassle. Small gains for the level of complexity