Whether gas or diesel, there are limitations due to the nature of the reciprocating engine. I'm not sure technology could overcome the shortcomings. If cost is an issue, forget it. The exhaust gases coming out of an engine are pretty hot and represent a huge amount of unused energy. That's why stationary power plants use the exhaust gases to preheat the combustion air. Even then, the 300 degree air going out the stack represents a good bit of unused energy. Right now, we don't have a good way of recovering that energy in mobile applications.

At theoretical best, a 10:1 compression ratio gas engine could be about 60% efficient, and that's it. I think current gas engines are about 20% efficient, so your typical 15 mpg truck would have to double its efficiency to get to 30 mpg. That's a huge gain - I don't think it's likely we'll get there with reciprocating engines, unless cost isn't an issue, and even then I'm skeptical. Emissions requirements make it tougher because higher temperatures mean higher efficiencies but also higher NOx.

By the way, one of the reasons diesels get better mileage is because there is about 10-12% more energy in a gallon of diesel compared to a gallon of gas.

 

It will be done... 10-30 years??? If we all don't switch to hybrid vehicles, -which is probably the way it will get done. Today as close as you will get is variable displacement diesel, turbocharger with aux supercharger. Pure physics raises it's ugly head with weight and thermodynamics tho...

Big old HEAVY cars in the mid 60's got 20+ mpg, of course they were simple without many frills. They also did not have today's aerodynamics either. Big steel bricks on skinny tires.

 

And one of the reasons cars of even half the weight and a 6 cylinder motor get the same gas mileage, thats because they run so many accesories.

 

I had a 68 Plymouth with a 318 that would make 21+mpg depending on weather conditions. It had AC and a radio...

 

That's why I think the Cadillac idea was so cool - shut down all those cylinders when you're cruising. I think it has potential.

XXL

 

There is a truck from a company in Japan who do not get much business over here, Daihatsu, who have a forward control pickup truck, half ton, that gets 36mpg.. They have a much smaller truck that gets 45 mpg. Both are diesels.

Theo

 

How about a 429 block with direct fuel injection that gets over 60 mpg? I have seen, inspected, and driven this animal in an old Lincoln Towncar body. The fuel was ethanol and methane mix. It had no problem smoking the back tires, had no throttle body- open intake manifold like a diesel, and if you were enterprizing you could make your own fuel at home. It was also a zero emmission engine. It now belongs to - who else- an oil company that has to remain unnamed. Yes, the technology is out there but the money machines aren't going to let you have it.

 

Don't by chance remember any specs or could do any sketches could ya?

 

I had a Nissan 1/4T PU, that got 30Mpg. But it wouldn't pull the cookies out of a girl scout's hands.
I had a Dodge D-50 Diesel that got 25-29 mpg and I pulled a 3000# boat with it on occasion. I still would like to have that little pu.
I really think the American Mfg'rs would have a 30Mpg pu if it was possible. I think that's what the new emissions demand in 2007.

 

That's darn good mileage for a 250!! I'm lucky to get 18 on the highway in my 150. What did you do to get it? The only things I know to do are to drive conservatively, drop the tailgate on road trips, use K&N filter and customize the exhaust system...

I once tried to figure out how long it would take for my K&N filter to pay for itself in gas mileage. It would take about a year and a half assuming a ten percent improvement in mileage. Of course, the added acceleration makes it hard to be coservative!!

I also buy into the conspiracy theaory that oil companies keep that technology away from john q public because that would be tantamount to slaughtering the goose that lays the golden eggs. Also, if they did allow the auto makers to reease that technology, they would be forced to sharply raise the price of fuel- afterall, they are trying to make a profit, too.

 

You would be surprised at how much oil is really in the earth. More than enough to supply everything we do at this current pace, until the chlorine hits the gene pool.

 

The EPA ratings are 19 city and 29 highway.

 

Ok, now, theoretically - if I was the oil company, I would design, perfect, and patent this technology so I could reap the rewards. Rather than clinging on to the aging technology we currently have, hoping that nobody comes out with something better, I'd beat my competitors to the punch, and control the future.

Then again, I'm not a billionaire oil tycoon, so what do I know?

XXL

 

Honda redesigned a chebby 350 in the 70s and it got under a full load something in the neighborhood of 30mpg. They were looking at it for the trucks, the oil companies shot it down.

 

well, it appears that the oil companiesare never going to allow us to use the technology, So, I guess the question is: what is the closest you can get to 30MPG without spending your life savings? I didn't buy my truck for the mileage- knew it was going to be low, so 20-23 MPG would be great for me!.