Naw, by then the polar ice caps will have totally melted and there won't be any land left.

http://i140.photobucket.com/albums/r22/LetMeIn_2007/Waterworld.jpg


Mike, I was planning on towing up to Alum creek until I stepped on one of my hulls and heard a lovely crunching sound. Unless I can find a cheap pair of hulls I'll be laying resin and glass this weekend.

double post.

Anyway, nobody has answered my other question about cruise control related to gas mileage. Do you get better gas mileage with it or without it?

And is it important or not to keep your rpm's down as much as possible?

Since our Odyssey has automatic transmission, if it is on cruise control, it keeps shifting up and down a lot. If it is NOT on cruise control, I try to prevent that from happening, so I can keep the rpm's low. But Rick says that would be bad, because I might be causing the engine to lug, which would be bad for mileage.

Any opinions (or facts) about those things?

no facts, just experiences: Same thing happens with our minivan, lots of up and down shifting, especially at overpasses and bridges, where it might downshift 2 or 3 gears...instinctively I believe that has to hurt mileage, and I believe that it doesn't do any good to the transmission either....my solution is to take it off cruise control when I see an overpass or hill coming up, putting the cruise back on on the downhill. I am pretty sure that my mileage improved after starting to do that. In my little car (Mazda Protege5) I use cruise all the time because it has a manual transmission, I just keep an eye on the RPM's on hills and downshift if the RPM really drop off.

Agree completely with Jake! I drive frequently in Europe, and the Autobahn thing is hugely overblown, since there are speedlimits virtually everywhere, and automatic speed enforcement radar cameras (ticket comes in the mail...). The truck issue is huge, especially if they start overtaking each other when their build-in speed regulators are off by 1 or 2 km/h....here you go driving along at the speedlimit for cars (135 km/h in France for instance), and you come up to two trucks passing each other at 80km/h and thereby blocking all lanes....hair-raising (and even worse where there are no speed limits)! And they take at least a couple of minutes passing each other, causing traffic pile-ups everywhere!

That depends on how good you are at working your speed. On flat level ground where the throttle won't be changing at all then there is no advantage to using your foot. On hills where you can speed up a bit going down the hill, and also let off a bit going up the hill then there is something to be gained.


It varies engine to engine. If you can get a dyno graph showing where your engine is making the most power that is where where the engine is most effiecent, but even then it may use more fuel then you want. A dyno sheet will show you at what rpm it starts making power at. Some where between where it stops flat-lining and where peaks out will be best. Kinda vague I know, but if you are trying to keep it below 2000 rpm, and the engine isn't starting to come alive until 2300rpm then you aren't gaining anything. I had a little Dodge car with a V6 that got better mileage in top gear at 75 than at 60 just because it wasn't working in an effecient rpm range.



Automatic transmissions will sometimes make use of the torque converter slipping to keep the engine in the effiecent range. In the case of getting as much power to the ground as possible a little bit of slippage is also good as you get a sort of multiplication in torque because of it slipping. I don't honestly know why, and mechanical engineer could chime in on that. There is a very fine line where that actually works though. Honda probably spent a fair amount of effort to keep it in that rpm range and that is why it is shifting. Nowdays the valve bodies are all controlled by the computer.

Get a graph showing at what rpm your engine is making HP/TQ at. There is also a diminishing return where the engine may be making better use of the fuel, but you are pushing so much air that it negates the gain in efficiency. My diesel pickup gets stupid good mileage at 1200 rpm, but I'm only doing less than 40mph in 6th gear.

I used to haul everything too, however I now travel light and buy in when something is needed. Would you do the same at $10 per gallon?

A snail carries its home on its back too, and look how fast they go!!!


Cheshirecatman

I think in most cases, driving with the cruise control turned on is better for the gas mileage. The car is going to get better mileage the closer it stays to a constant speed and rpm, so cruise control is better in that respect. However, if you're driving through a lot of hills and causing the transmission to shift a lot the engine rpms are going to be all over the place which is inefficient - remember, nature prefers to resist change. You may be able to reduce the amount of shifting by changing your speed slightly or by turning off the overdrive.

As far as shooting for minimum rpms, this is not necessarily the most efficient. As was previously stated, each engine has a maximum efficiency point where horsepower and torque are maximized. Just a guess, but it's probably best just to cruise somewhere between 2000 and 3000 rpm.

sm

Just my opinion, but if I'm a young guy hoping to enjoy the first summer that I have a job, I would seriously look at cats instead of a jet ski or boat; everything seems to fit.

Mary, I had deja vu on your cruise control question...sorry sm, I agree with Karl on this one, anywhere but flat highway cruise is not as efficient.

I've driven in Ireland, Spain and France (on the Superhighway). IMO, overall European drivers are much better than American drivers. On the superhighway differences in speed of various vehicles were marked (guessing up to 30 mph). It didn't take long to figure out you had better pay attention if you wanted to use the left (passing) lane. Turn indicators and headlights are used extensively for signaling the other drivers of intentions. They use the passing lane just for that and get right back over in the right lane, and do it ONLY when passing will not impede (slow down) the progress the faster, overtaking cars from behind. Works great once you know "the rules" and everyone seems to abide by them. I've never seen anything like this on US interstates. How many times have you encountered one car (with cruise on) going 72 that's passing another car (with cruise on) that's going 71?

Just think of poor Larry Ellison, his boat takes about 160000(!) gallons of fuel, at the Dutch price of $1.90 a liter or $7,22 a gallon (3.8ltr) makes for a hefty bill of $1.155.200.
That is money he wont be able to spend on his new 90ft AC multimonster.


(We will not even think about how much fuel goes into this 162m (530ft) giga yacht :



About the autobahn speeds, the place where I drive on a regular basis is so quiet that I can set cruise control at 185km/h (115mph) (My car wont go any faster!) and just leave it for an hour and a half and maybe pass a few cars and the occasional truck now and then.

Most annoying thing in the world. Or when they go 45 in the left lane.

In my econo brick, I see the best economy in the center lane doing 65. I then use the left lane for passing and get right back.

Cruise is not efficient on hills. I've devised a system using a dash mounted adjustable vacuum regulator on my cruise control's vacuum actuator (the device that uses engine vacuum to pull the throttle cable) in my RV so I can limit the amount of throttle that the cruise control applies to climb a hill (if it works, I'll do the same thing in my truck). I haven't implemented it yet, but I expect it will help make the cruise control more efficient. Since I'm pretty much the slowest thing out there anyway in the RV (besides really loaded up trucks), I really don't care if I speed up and slow down.

sounds like something to patent

I doubt it - it's a $50 vacuum regulator that will keep the maximum throttle to an adjustable limit so I can prevent it from "flooring it" going up hills with something in tow. Then again though, I bet some people would buy that as a kit huh?

The closed loop control systems that cruise controls use are pretty dumb and there are undoubtedly a lot of advances that could be made to make cruise controls more efficient. HOWEVER, I don't think the world would stand for cruise controls that speed up and slow down. I get frustrated enough when someone slows down when they start to pass a big truck and block a lane and I can't imagine a freeway full of cars that slow down going up hills at different rates mixed in with cars that maintain steady speed. Talk about road rage!

Jake

kit form maybe... depending. it isn't like you would want the car to slow down to 30 in a 70!
When I was towing the 31 the truck would obviously not like going up hills and of course downshift then roar to try to keep the same speed. I always slowed down heading up hills because if not, you might as well pour the gas out the window.

Check this out http://money.cnn.com/2008/05/01/news/international/usgas_price/index.htm?section=money_mostpopular

All we have to do is all move to Venezuela. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Exactly! I can't stand it when my RV downshifts to climb a hill. I would rather it slow from 65 to 55 like the heavily loaded trucks do anyway. This way, I'll have a knob on the dash that I can limit maximum throttle and keep it just off the kick-down switch but keep it rolling up a hill. Once back on the downside, the cruise control will maintain a controlled re-acceleration back up to the set speed and hold it there until the next hill.

Jake,
Folks have been doing a similar mod on turbo cars for years. I have a manual boost controller on my daily driver and for $40 now have 13psi max boost instead of only 8. Hasn't helped mileage any, tho... <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

Same with my pickup. Instead of 21psi, I get 32 psi now.
For those with turbo'd vehicles a boost gauge is an excellent way to tell exactly how much fuel you are pouring into an engine.