So, we all know that each engine is designed to have a sweet spot that has peak performance and should be the most efficent. However, we also all know that high RPM's mean lower MPG. How does one make these two statements work?

 

Well, peak fuel efficiency should be achieved by a combination of going as slowly as you can safelyget away with, tires being properly inflated, a/c off, and use of cruise control. As you correctly mentioned, adding power detracts from this. The key, I think, is to travel at the slowest speed that's safe and practical. Air resistance KILLS efficiency disproportionally as speed increases. Use of the cruise control is probably the next biggest "helper" towards efficiency.

David

 

You forgot windows up, but hit most of the other points... as near asI can figure.

I have to say here, as (one of) the resident smart-asses, that when I saw the title of this thread I was about to answer 0 rpm's affords the best mileage.

Are we getting just a little bit silly over fuel mileage these days?
I am old enough to have lived through both gas "crisis" in the '70's and it never fails to amuse me how when prices are considered normal, or "cheap," how many people go out and buy their big-assed Cadillacs, Lincoln's, pick-up trucks and SUV's. But when gas prices are up suddenly, every one seems worried about mileage... even those that weren't before.
Sales for bigger vehicles go way down and the car companies and dealers suddenlyoffer deep discountincentives to sell them. Those that own these gas guzzlers are selling and trading them in at an alarming rate andusually at a loss.
I on the other hand, drive smaller, sportier, fuel efficient vehicles because I like them and always have.
Even w/my heavy right foot and sporting driving style manage to achieve 25-26 w/A/C and 27-28 w/o in my 3. How much better do you think it's going to get than that, and at what cost?

BTW: I have always heard that an engine is at it's most efficientat the crossover point (torque/horsepower) on a dyno graph. That's when it's breathing the best, properly filling the cylinder w/a correct, well mix of fuel to airand burning that fuel most efficiently.
That does not afford you the best fuel mileage however, but the engine is running at it's most efficient at that point.

 

Actually, Ididn't forget"windows up"...I chose not to include it. Per an SAE study, outlined in Road & Track magazine by their engineering editor Dennis Siminaitis, the drag that's created by open windows only starts to affect fuel economy once you're well into triple-digit speeds. Most of us are not cruising for any extended period of time at above-triple-digit speeds, so it's mostly a non-issue. They pointed out that, at normal highway speeds, the drag created by open windows is negligible at most. Whereas a/c, of course, taxes the engine directly.For me,all of this is gonna become little more than lip-service soon, because here in NCwe're onlyabout a month away from high-90s / high-humidity...my a/c will be on ROAR!!!

David

 

Here in Texas it's been at ornear 100* for the last week. My A/C ison ROAR even at 4AM!!
I am familiar w/Dennis Simanaitis (and his difficult-to-spell last name) and his articles.I was reading his work just this morning.Tech Tidbits is one of my favs in that mag... one of the first places I go w/a new issue.Been reading R&T for over 30 yrs now, but since we are getting "gas mileage silly" here....

Some of you may remember the VW BeetleTV adback in the '70's. They managed 80mpg from a std Beetle, but there was so little left of it (they stripped every body panel and amenity possible) that it wasn't practical to drive.

 

Hah, yes, he does have a tough last name! I was spelling it from memory, so sorry for the goof. I've been a R&T subscriber for about 26yrs, so you've got me beat by a little bit. My fave monthlyarticle is Side Glances by the fabulous Peter Egan.

David

 

I wasn't insulting your spelling. In fact his name had come up before in another correspondence. I thensaved it to my spell-checker dictionary, which in fact saved me frommisspelling it yet again in my last post. (<<< A suggestion.)
Ah... about 1970 or so I believe it wasI became interested in sports cars and asked for my first subscription as a holiday present... I think it was my birthday.

Most recently for me it's: PS > and interchangeablyTech Correspondence and/or Tidbits, or Peter Egan's Side Glances(can anyone have that many coincidences and experiences in his life?) Have you seen his most recent column about "The Red Car?"

 

I just got my new issue yesterday, but I'm not going to be able to crack it openuntil this evening. Side Glances will (as usual) be the first article that I read.

David

 

GOOD article about his parallels with "The red Car". Love that Egan!!

David