ETA: According to the there’s a lot of loss to friction in the conventional valve train. Most of that would have to be in the cams. So I can see using individual actuators to reduce that, but it doesn’t sound economical.
I’m having trouble visualizing what you’re describing.
Well, most of the emissions problems come during acceleration-a engine operating at constant RPM would have fewer problems with unburned hydrocarbons emissions. It is very difficult to ensure 100% combstion when your engine is turning over 7000 RPM.
No, an engine operating at constant load will do that because its operation is steady state. An engine operating at a constant speed can have a wildly varying load and throttle positions.
Says who?
The problem with the cam phasing VVT on the GM OHV and Chrysler HEMI engines is that there is only one camshaft actuating both intake and exhaust valves, and you can’t phase intake and exhaust independently. Since the whole point of having variable valve opening is so that you can phase intake and exhaust in opposite directions, moving both of them in the same direction at once kind of defeats the purpose. The concentric cams on the Viper will allow independent intake and exhaust adjustments, but your OHV gas engine still suffered from the handicap of only having 2 valves per cylinder. Maybe they can go to a 4V design eventually like the new Ford diesels but that’s adding a lot of complexity to the valvetrain.
As it stands right now, FIAT Multiair essentially does everything you would want your electric valvetrain to do - infinitely vary both valve timing and lift on the fly, so that’s basically all you would need on a piston engine. The only roadblock right now is that the Multiair actuator system is too bulky to fit into the heads of small DOHC engines, the current applications are limited to SOHC, although they are said to be coming up with something for the new 2.4l in the Dodge Dart.
The real intriguing solution for me is to adapt FIAT Multiair into an OHV engine. Since these are mostly all big 90* V8s, space shouldn’t be an issue. Using a Multi air head powered by a single camshaft actuating a 4v OHV V8 would basically eliminate all of the above issues. Since these things mostly go into trucks with 100% profit margins they should easily be able to afford this. I was hoping for something like this with the new Viper, but I suppose neither “even moar power and torks” or “better fuel economy” were high on the priority list for the Viper redesign. A HEMI engine with infinitely variable valves should keep ye old iron block OHV engines going to a while yet.
Lolz
I had a 3V 4.6 Mustang that did the VVT thing. It felt like a 2 stroke. An aftermarket tune fixed it so that the powerband felt more flat.
Thank you for this. Since I read the response I have been scratching my head to figure out how you could advance one set of valves and retard the others on an OHV engine.
I absolutely believe you.
And no one cares what you think.
No need to do both sets of valves. Honda has had VTEC on their SOHC engines since 1995. It only adjusts the timing and lift on the intake valves. They must have seen some benefit to it because they kept it around in some form for a decade or so. I don’t know much about the variable valve timing on the R18, so I don’t know if it’s still intake-only.
You might want to tell that to the engineers at Volvo, BMW, Hyundai and several other car companies that use dual VVT systems. Anyway there is a huge difference between what Honda does and what GM is doing with VVT on a single camshaft.
GM advances or retards both the intake and exhaust together with no change in overlap. They have no choice, there is only 1 cam. With dual cams and a single VVT you can change the amount of overlap between intake and exhaust. This allows you more power in the midrange (intake) or a quicker cat light off (exhaust)
With dual VVTs you can do the above plus cool stuff like get EGR when needed just by moving the overlap, or a better idle.
Says me.Look at the fuel economy ratings when the engine is fully wound up-the flame front cannot initiate complete combustion at such engine speeds, so unburned hydrocarbons pour out the exhaust. Drive behind a car that is accelerating-see the cloud of smoke from it.
Honda also stuck with carburetors well past their “best by” date. Go look at the vacuum diagrams for the last CVCC engines.
Au contraire, mon frère.
Honda doesn’t use cam phasers in their SOHC engines, those have only the 2 stage variable timing and lift mechanism in the rocker arms. The benefit of cam phasing on a single camshaft engine are pretty limited, Ford has it on their SOHC V8s too. Does the Mercedes SOHC V12 have any kind of VVT at all? I suspect not.
are you saying it’s not expected that the engine will use more fuel at wide open throttle?
I’m not interested in what broken cars do. Hey- tell you what- here’s a video of a Mustang GT on a dynamometer, doing a full-throttle pull from 2000 rpm to redline.
please tell me where I can see the “cloud of smoke.”
second, here’s a video of some Formula 1 cars racing. Their engines redline at 19,000 rpm.
Where’s the smoke?
So, what are your thoughts on engines? Other than relation to dick size.
You’ll have to post some of those fuel economy ratings, and then tell where they came from. I’m not aware of any manufacturer who evaluates the fuel economy of a vehicle traveling at highway speed in second gear.
There’s absolutely no problem getting combustion done in time at high engine RPM. The turbulence generated by the intake process helps the combustion take place in a timely manner: the higher the RPM, the more turbulence there is at TDC, and so the more rapid the combustion, with the result that combustion duration measured in crank-angle degrees is actually fairly constant. It stretches out a just little at high RPM, which means you need to add some spark advance, but the end result is that combustion is still completed very early in the power stroke. If things were still burning when the exhaust valve opened (as you claim), you’d fry the valves in pretty short order. As proven in many racing applications (and in countless mass-produced street vehicles), there’s no problem producing shitloads of power at 7,000 RPM and beyond, even in large-bore engines.
An engine may be slightly less efficient at high RPM, but that’s largely due to mechanical friction (and throttling losses, if operating at something less than WOT). Manufacturers are OK with that, because again, you’re not intended to cruise for prolonged periods at 7,000 RPM. If you’re running the engine there, your goal is peak power, not peak economy. The same will be true of a pushrod V8 making peak power at 3000 RPM: you won’t cruise there, because that’s not its most efficient RPM. (I think big V8 engines - regardless of whether they redline at 7000 or 4000 RPM - typically cruise at less than 2000 RPM.)
And smoke coming from a vehicle at any RPM is indicative of a mechanical problem.
Well there is a grain of truth in it, engines that I’m familiar with typically will run richer when going full throttle under load, and go into “open loop” operation, to establish a margin of safety against detonation. But cars today aren’t really legally allowed to produce smoke when you hit the gas.