Thread: 55 MPH rearing it UGLY head again?

Tweet

Originally Posted by willowbilly3

There is a lot more to mileage than the speed, as we can see from the posts. However if you have a car specific built to a lower speed then it should get better mileage at the lower speed. Sure everyone wants to keep driving fast, we are in a hurry. Maybe we should run a 55 lane on the service road and just open up the interstate like the old autobahn. Then you could be part of the carnage or not. Already the metros are kind of that way. We never go near Dallas during peak traffic because you know that you will be setting still for 2 hours while they spatula someone off the road. Might as well go the secondary roads through the small towns and enjoy it.

That's what I'm doing when I take my '65 Rambler to the Syracuse Nationals..It does not have enough go power for me to comfortably get on the on ramps of the interstates.. So I'm taking all secondary roads, going to take over 2hrs more than it does to take the interstates with a car capable of 75 MPH. but it will be a nice ride thru the countryside

I don't think anyone here is in favor of a mandated 55 mph speed limit...but maybe if we all slowed down 5 or 10 mph and conserved just that much gas it would help. Certainly not a cure all, but the way I look at it your either part of the solution or part of the problem.... The interstates in South Dakota can be cruised most all day any day at 80 with no fear of a ticket... I CHOOSE to do my cruising on them at 62 to 65 mph for the simple reason that it uses less fuel.... In the Bonneville, that's just a shade under 2000 RPM....

I guess it's a matter of personal choice. If you must drive at or over the speed limit to save the XX minutes per day and don't care that it costs you extra in $$$$ for fuel, then just do it..... I guess my life isn't so fast paced that 10 or 15 minutes per day is any kind of deal at all.... Relax, enjoy the drive!!!! Driving on a public highway is not a competitive sport, after all......

In CT our posted speed limit is still 55. Minimum is 45. That said average traffic (yes most state police too) speed is 60-65. But there are still those in a big hurry who drive 80+. I pretty much drive 60 in the wagon. 65 in the wifes Monte. Under 70 your pretty safe from getting a ticket depending the time of month. But most cops are pretty cool here and understand traffic flow under certain situations. Lots of work zones here too. Seems they are forever redoing the roads here and there the speed drops to 45. Fines are doubled in work zones here. Rightfully so as there has been quite a few deaths of the state roadworkers being hit by oncomming traffic in posted work zones. State Police as well while on a routine traffic or breakdown stop. I-95 is not a fun place to hang. There are a few breaks further upstate where posted limit is 65 for short while. But most of the state is a posted 55. I've had people pass me in the breakdown lanes just to get around me and flip me off while doing so like I'm the jerk in their way. LOL!!!!

IC2 wrote:

There is a 'sweet spot' for most vehicles

I agree with you Dave. Several weeks ago I decided to put my life at risk by slowing down going to and from work on the interstate. Normally the first 30 miles would be covered at about 80-83 mph, so in the interest of saving fuel and money, I slowed it down to 65 - 70. Other than nearly getting run over by the majority of the SUV and PU drivers, I found that my mpg had actually dropped from about 28 mpg to 26 mpg at the slower speed. I know in theory it shouldn't have, but it did.

I might not return to the 80+ plus speed, put I am sure as hell giving up on the 65 speed. Think I might try the 70 - 75 range next.

Guess I don't understand how fuel mileage will improve as the rpm increases....... More rpm requires more fuel, that's how an engine works.

how about somthing smarter for the govt to regulate... mandate cars be produced with cruise control.. that increases gas mialage on most newer vehicles.. my mom has an '02 Concorde w/ the 3.5 V6.. gets 30 MPG on the highway with cruise, 26 w/o

I think if the flippin' government would get the heck out of the automotive industry, as well as many others, things would be much better!!!! Granted, they should set pollutant standards, and maybe even CAFE fuel mileage...other then that, we'd do a heck of a lot better without them...

Originally Posted by Dave Severson

Guess I don't understand how fuel mileage will improve as the rpm increases....... More rpm requires more fuel, that's how an engine works.

I know Dave, it seems bassackwards, but at 45 my daily gets 21-22 mpg (built in fuel monitor) at 55 I get 23-24, and at 65 it jumps to 26, sometimes 27 on cool nights. I have counted the shifts, and mine pops into overdrive 4th at 42 mph, so that isn't a factor. Maybe the converter locks up at higher rpms or something, or maybe it just has a sweet spot.

I have had a flowscan fuel monitor on a few of my boats, they are extremely accurate. My one boat would get optimum fuel economy at 3200 rpms, and would fall off below or above that number. That has something to do with planing speed probably, so maybe the same thing happens in cars, with wind resistance, tire resistance, etc??

Don

on or off plane in a boat is easy to understand...but not revs in a car.... It simply takes more fuel to sustain a higher rpm once you are in the cruise mode, be it EFI or a carb.. Exception being like the Caddy system that cuts out cylinders and turns off injectors in the cruise mode.....

Still don't understand it.... too many variable on mpg anyway in a daily commute... but I just can't see how fuel flow rate would decrease with an increase in rpm??????

Originally Posted by Dave Severson

Guess I don't understand how fuel mileage will improve as the rpm increases....... More rpm requires more fuel, that's how an engine works.

I think you have to keep a certain rpm to maintain a combination of functions in the most efficient range. Port velocities would be a biggy. Also their are rhythms ( for lack of a better word) like the harmonics or frequency that everything has, even buildings. I think an engine would have better efficiency if it was operating at the optimal rhythm.
Remember the old economy meters< They were a vacuum gauge and an engine should get it's best mileage when cruised at the highest vacuum reading.

"....Guess I don't understand how fuel mileage will improve as the rpm increases ...."

Come on Dave every engine has a sweet spot. Too slow and the engine is lugging and much above that and the mileage also goes down. In the case of my Mustang and Plymouth with the cams in them the sweet spot is 2100 and 2600 respectively (a lot more cam in the HEMI). The tires and gears put that put those ranges at 75 MPH.

Back when the 55 MPH speedlimit first went into effect there was almost nothing out there with an overdrive and the gear ratios were relatively deep compared to today. Most of us were turning our engines over 3000 RPM at highway speeds. Nowdays 75 is often under 2000 RPM on many cars.

Houston seems to be slowing down on its own.
I drive 65 (the speed limit) and WAS being passed all the time.
Now more and more people are driving at that rate.