Idea for a VVT/VTEC engine in a truck...

[ClarkB]

My experience looking at trucks in America is that if you want a truck with the ability to pull a boat or trailer you will never have a truck that gets decent gas mileage. Even if you only need the power to pull your boat to the lake twice a year you live with the below average gas mileage for the rest of year. Chevy is claiming 20 mpg with their newest trucks which is OK, but nothing to get excited about.

I doubt I'm the first one with this idea, but I haven't heard it anywhere else, so I'm curious what you guys think about it. A truck manufacturer could make a truck engine with two cam lobes utilizing a VTEC/VVT style system (I'm not sure what the correct term actually is, but I'm speaking of one where two very different cam lobes are used similar to Honda's VTEC system). The difference would be that one cam lobe would be used exclusively for towing or hauling heavy loads. The other cam lobe would be more tame and aimed at increasing efficiency while at cruising speeds.

Along with this a different gear could be built into the transfer case to coincide with purposes of the different cam lobes. Possibly a 4.1-4.3 for towing and 3.5-3.9 for cruising/economy mode. Any thoughts?

Clark

 

[mstrjon32]

I've never seen a case where VTEC or VVT improved economy, usually you get a little more performance, but economy figures stay about the same or go down. At least back when you could get Honda products in VTEC and non-VTEC models, the VTEC models always got worse mileage than the non-VTEC models.

Plus, I think the different cam profile makes a bigger difference at higher RPM, most 'trucks-for-towing' cruise around in the 1500-2500 RPM range. I think they're buying themselves more economy with the displacement on demand than they would be with low-RPM VVT, but I could be wrong.

 

[oilyriser]

The quasi-atkinson cycle can be done with cam timing, by leaving the intake open for a very long time, so the charge backs up into the manifold instead of having to use the throttle to restrict flow. This reduces torque a lot, but gives better efficiency.

 

[Max_Wander]

Well, it's not just valve timing that affects torque. Peripherals such as the intake manifold, port design etc affect torque. As for the idea of VTEC being used for a truck manufacturer, well Honda put a patent on the dowel-pin activated "VTEC", so all other manufacturers were left to devise their own VVT/lift methods. Not many realise it's benefit. Two cam profiles would make less sense on a engine with a 4500-5500rpm rev range, and beyond 5500rpm rev range would be useless in a truck, no one is going to wind out a peaky truck engine. So the only thing you're gonna get VTEC on is the on the Odyssey pickup with the 3.5L

 

[CharBaby]

Clark,
Well, the 4.2L inline 6 used in the Chevrolet Trailblazer/GMC Envoy has VTEC although I don't think this is quite what your talking about. Im sure that you were talking about full size trucks with V8's. I do have friends that tow small boats(between 26 & 32 ft) with their Trailblazer/Envoy and like them better for towing than their privious Toyota 4 Runners/Nissan Pathfinder/Jeep Grand Cherokee(when comparing 6 cyl's). And the fuel economy isn't too bad for everyday family use. They tow their boats to the marina and then leave them there all Summer and then pull them back out during the Fall for winterizing and Winter storage on their own property.

 

[biomed_eng_2000]

Anything with variable valve timing and lift will have a similar or superiour effect compared with VTECH with only two lobes.

BMWs variable valve lift and timing is so versitle and advanced that those engines don't even need a throttle body...it just reduces the valve lift when you want to decelerate and increases the valve lift when you want to accelerate.

 

[Tosh]

Diesel.

 

[glennc]

All those tricks increase efficiency, but the gains are incremental. Not that I'm not for them.

It seems to me though that the reasons those trucks get mediocre mileage is that they are heavy body-on-frame designs and that the competition has given us more and more power rather than more and more economy, because that is what sells the vehicles.

As for efficiency, if you can get 20mpg from a three-ton barn door going down the road at today's speeds then that's pretty darn good.

And if you go a step down in size/work ability, to a crossover type SUV or even a minivan, the improvement in mileage isn't really that great.

 

[bdcardinal]

the ford's have variable cam timing in the F150, 250 and 350's that have the 3v motors. not much help in gas mileage though.

 

[Steve S]

Too heavy.

 

[swalve]

Originally Posted By: ClarkB
Along with this a different gear could be built into the transfer case to coincide with purposes of the different cam lobes. Possibly a 4.1-4.3 for towing and 3.5-3.9 for cruising/economy mode. Any thoughts?

Clark


Yes, I think gearing would have to be integral in such a system. Maybe a six speed automatic transmission with a relatively wide gearing range. In economy mode it would use 2-6, and in towing mode it would use 1-5. Then the variable cam could be tuned to the engine dynamics and requirements at the various RPMs.

The question would be, is it worth it? Would gains be worth the tradeoff in cost and complexity?

 

[ClarkB]

Tosh - I agree that diesel is the way to go, however I don't see that happening state-side very soon. I wish it would happen but I'm not holding my breath.

I don't buy the argument that trucks are too heavy to get better gas mileage. There are V10 trucks out there that get 9mpg and there are V6 trucks that can get 20-22mpg. Should we just accept it that trucks can only get into the low 20's because they are too heavy? And if they are too heavy, why doesn't the V10 get better mileage? Shouldn't it be able to sling the weight of a truck around easier, especially with cylinder shut-down systems? Weight is merely one loss of fuel economy in today's vehicles.

I don't think that this would be too difficult or expensive to implement. Look at Honda's Odyssey. They have put significant development into cylinder shut-down technology and VTEC systems for a couple of MPGs. Considering the number of trucks out there that drive around every day with nothing in the back and nothing being towed, I think this system would have the ability to get 25mpg in an otherwise normal half-ton truck on long trips.

I was just curious what most thought of such an idea. I can see that it is poorly understood by many and that there would be some extreme doubt for many owners of actual real-world returns of mileage.

Clark

 

[BuickGN]

No matter how you slice it, it takes a certain amount of power to push a heavy vehicle with the aerodynamics of a brick. Doesn't matter if you have the V6 or V10, it will only make a little difference in the same car cruising down the freeway.

Once you start dipping into the extra power of the V10 or V8, gas mileage will be noticably worse.

 

[ekpolk]

Originally Posted By: Tosh
Diesel.


A great choice -- if you're OK with ponying up the extra $7-grand or so that the diesel engine costs over the comparable gassers. At least this is the case in the Chevrolet/GMC offerings. It's right there in the "build your own" subsection of Chevrolet.com and GMC.com.

The diesel trucks are a great choice for a specific mission (heavy hauling where the economics justify the investment, or if you just like diesel and don't mind paying). What baffles me is how people hammer on other technologies for their added costs (hybrid comes quickly to mind...), but somehow, we overlook the $7k cost delta between a diesel P/U and a similar gasser.

 

[tom slick]

Ag tractor companies such as caterpillar have developed technologies for increased power or economy depending on conditions, one of which was a variable valve timing arrangement.

 

[Duffman77]

The Deal with valve events is that they are targeted to an engine RPM for a given set of Intake and Exhaust ports. The reason you are not seeing VVT on trucks is that the cam timing is all geared for towing. Incedently this low RPM focus is also good for economy. VVT would only increase the higher RPM potential on these engines which would really only add complexity for what really is only a work vehicle, and has an already good power to weight ratio in unladen operation.