Archimedes screw throttle

[johnmyster]

That's the same "two intake settings" vtec setup that my '98 accord used. Mine used it for additional power/torque. They're using it to have a "low load efficiency" setting with drive by wire throttle control.

I thought the "i" in i-vtec stood for infinite. Looks like it stands for something else.

[dcb]

Hmm, it says they retard the intake timing and open the throttle more. Hmm...

I know some modders advance the valve timing to move the torque band lower. Hmm... I guess it would be a pretty efficient detuning to retard the intake cam. I might have to try it on the bike and see...

[tasdrouille]

With careful valve timing pumping losses can be reduced by 80% at low loads. No wonder recent engines have CVVT.

As far as the throttle plate in concerned, it's designed to restrict flow so I don't see the point of improving it's aerodynamics.

[metromizer]

There are many improvements made on the 'throttle blade' opening over the years, from 'rolling cylinder with an oval hole' on this Aurora indy car engine (shown), to some single and double guillitine types, an iris type, and double opposing blade design I've seen. A friend's sponsor applied for a patent on one he's used/using on his 4 cylinder in-line Ford USAC midget. They are mostly useful in some types of race engines, ones where part-throttle acceleration and low end torque for exiting a turn are useful. But the only engines I've seen them on are one throttle per cylinder (no plenum type intake tracts). I am thinking that a plenum is busy enough, load of turbulence but the ports and intake runners 'straighten out' the air flow after the throttle on a plenum design.

Still, I think about this stuff too. What if you had a 'revolver' type throttle body design. Where, like a revolver pistol, the correct venturi size was quickly rotated into position for optimum venturi diameter for a given engine load?

If you think about GM's XFi, where they used a slightly smaller throttle body than a standard Metro, there must be something to be gained (I assume GM wouldn't have bothered if there weren't mpg gains to be had for specifically the XFi modle of Metro)

enough of my rambling...

[Johnny Mullet]

I actually would have to side with Frank Lee on this one.

A restriction is a restriction.

[ronarprfct]

I believe intake turbulence is a problem because it increases pumping losses. I had read that the partially opened throttle caused inefficiency due to the work done sucking air into the engine. I would think lowered turbulence in the intake stream would lower pumping losses.

[johnmyster]

That's not what the term "pumping loss" refers to.

[dcb]

Just grabbing the first numbers I can find, a chevy 305 at idle:
assuming: 75 cubic feet of air per minute at 20 inches of vacuum

(75 cfm) = 2160 cubic inches per second

imagining a 1" square piston in a suitable "cylinder", it can lift 20 lbs, 2160 inches in one second. I figure that is about 6.54 horsepower in pumping losses at idle across the throttle plate. (1 hp = 550 foot*lbs/second)

[MechEngVT]

metro, I always thought a really cool throttle would be a sphincter. Lacking anything else to call it that's how I envision it...an idealized convergent-divergent nozzle (i.e. a venturi) that can smoothly and continuously change the area of the minimum opening to vary the mass flow through the nozzle. Haven't quite worked out the practical aspects of that yet.

Ron, I don't think your idea was taken as offensive. It's just an idea. We can discuss and debate it if you wish, but I *am* a mechanical engineer and in product development ideas only make it to fruition if there is a reasonable tradeoff of performance gained to effort expended on development. I think what folks have tried to establish is that there's no "100 mpg carburetor" and that any throttling device improvements are pulling off-the-wall concepts out chasing a gnat's-ass potential improvement. That's a recipe for "little to gain, lots of effort to gain it" and while there may in fact be some gain there (doubtful in this specific instance) it isn't worth chasing.

[johnmyster]

Originally Posted by dcb

imagining a 1" square piston in a suitable "cylinder", it can lift 20 lbs

20 inches of mercury isn't anything close to 20 psi. 20 inches is (ballpark) 2/3 of an atmosphere, so roughly 10 psi.