"Porpoising" for better mpg

[68 Suburban]

Ok, I have the result of my initial test. I went 156 miles on 8.08 gallons of gas. That comes out to 19.3 mpg in the city. So I guess it does work. It is a pain at first, but you kind of get use to it.

So for this test, yes it did work!

[Stout72]

I still have yet to read what this "porpoising" actually is, and how it applies to trucks (moreso than go carts). WTF?

[68 Suburban]

Ok, Ok....lol

Before I get started I want to say that this was an EXPERIMENT, and I am not suggesting in any way that this is something that people should, or should not be doing.

Porpoising is a driving technique. The way porposing was explained to me, it is best/easiest done with a stick shift vehicle. Since I have an automatic, and I did not want to do it to the degree that was explained to me, I would say I have been doing a "modified porpoising" technique.

It is a technique that I feel is more benificial while driving in the city, than it would be on the highway.

Basically you are more conscience of your driving situaltion. When you are coming up to a red, or changing light you shift in to neutral and let your vehicle coast, instead of holding the excellerator until you get to the light and then braking. You also try to time the lights with this technique.

Also while driving you will coast in neutral while you are driving. When you are behind someone, instead of holding the gas, you shift to neutral and coast. I am pretty lucky because my burb coast real well. To increase the coasting of your vehicle, they tell you to increase your tire preasure, make sure your brakes do not drag excessively, etc.....

If the speed limit is 35, I would gradually get up to 45mph, then shift to neutral and cost down to 35, etc..... Now in the city this is not really that hard to do. I would never consider doing it on the highway.

I think the main way I was using it was by fore seeing what was coming up ahead of me. If I knew that if I contined to drive normally while I was coming up to a light, just to have to put on the brakes to stop. I would just shift to neutral and coast then stop, instead of waisting that little bit of energy. You find yourself reading the light situation by looking at thinks like the crosswalk signal flashing, etc... A lot of time I would find that I was still coasting when the light would turn green. Then I would just drop it into drive and go.

It is hard to explain, but it is not as much of a pain in the butt as it seems. It almost starts to become second nature. I will say one thing, if you have someone else in the car, they do seem to get annoyed

My conclusions?

Well I have only done it for one fill up and I did see a pretty good increase in mileage for my city driving. I actually gained 5-6 mpg.

Will I continue to porpoise? Im not sure. It did start to become second nature after doing it a while. Kind of like using your turn signal. One you get into the habbit you really don't have to think what you are doing. I think if I do continue to use this method, it will be an even more modified version. I think I would cut out the coasting with out reason (45 down to 35 back up to 45 etc.), but I think the coasting to stop lights, behind cars, etc... I might continue to try.

This obviously would not be for everyone, but I wanted to try it out to see if it really could work.

[ChevLoRay]

Specifically, 1973...I worked with a guy who had a '65 Falcon Futura 2-dr hardtop. It has a 170CID/Stickshift. He thought he'd see what kind of mileage he could get out of it, since gas was approaching 60-cents/gallon (first Arab oil embargo). He pumped his tires up to the max, I believe he had 40-lbs of air in them. He installed a vacuum guage...then, he used it as he drove. The federales had already dropped the speed limit to 55 on the interstates, so his planned trip didn't particularly hinder the traffic. He drove with the vacuum guage, keeping the vacuum as high as possible, which he noted allowed him to drive about 45mph. For the trip that he took, which was close to 200 miles, he got almost 41mpg. Some of the tricks included shifting to neutral and coasting, when possible. Minimal idling time.

Free-wheeling, is the process of coasting in neutral. Some states have laws against doing it when descending a hill. Some automobiles in the 20's and up to the early 50's, featured the ability to "free-wheel".

Shifting to neutral is something to consider, when driving a standard, to save some wear and tear on the clutch and release bearing, as well as the pressure plate. I do this, but I watch the lights, too, in my Celica. It becomes a habit, and I don't care if you ride with me and get nervous because of it. Your option is to walk.

I wouldn't have called it porpoising, tho.

[68 Suburban]

ChevLoRay
hehe, like I said, I considered it a modified "porpoising" technique. I took the parts that I felt like I could do. The original version that I read, called for a stick shift, and turning off the engine and coasting! Then putting the key back to "run" and dumping th clutch when you want to start the car up again! Seem like a real pain in the butt With an automatic, you would have to physically start the vehicle each time. Yeah right! Not to mention the damage you would eventially cause to the automatic trans because the pump would not be pumping oil through the trans when the engine was off.

[Project1970]

I'd give it a shot...but 98% of my driving is I-10 between Phoenix and Tucson. No chance for coasting there.

My dad told me about a trick one of his friends did (with my dad riding shotgun nonetheless) on a run between the two back when my dad was going to the University of Arizona...

He drafted a semi.

My dad said he had the vacuum gauge pegged almost the entire way. Not exactly the smartest idea, though.

[Locutus]

Originally posted by Project1970
I'd give it a shot...but 98% of my driving is I-10 between Phoenix and Tucson. No chance for coasting there.

My dad told me about a trick one of his friends did (with my dad riding shotgun nonetheless) on a run between the two back when my dad was going to the University of Arizona...

He drafted a semi.

My dad said he had the vacuum gauge pegged almost the entire way. Not exactly the smartest idea, though.

I have done that before. On long hiway runs it does work. It reduces your air resitance considerably. Truckers don't like it they can't see you. It not as dangerous as you might think. You can get close enough to draft a semi and still have enough room to stop. You can stop much quicker than a loaded semi. The down side is the wind you are avoiding from the front will beat you up from the sides.

[jku72]

I deducted that this porposing is speeding up and then coasting, in an attempt to gain better mileage. Especially with a carburated vehichle, this just wont work. Acceleration uses much more fuel than steady running, and even while coasting fuel is being consumed. Due to the fundemental fact that you cant get somthing from nothing, and that resistance to change in motion, as well as other rolling resistances, it just does not add up. In fact, it has been documented time and again that the best mileage come from slowly accelaerating, then maintaining a constant speed, and when stopping, coast down well in advance, eg roll down instead of braking.
If you get good mileage porposing, you could get better mileage feather footing it and driving steady.
However, if you had one of the new electric cars, then yes, then coasting then uses no gas at all, and perhaps in the long run, some form of porposing could be beneficial.

[68 Suburban]

jku72, like I said, I don't know how this would work on the highway, but doing what I did in the city, I went from 13-14 mpg to 19 mpg. I don't know how all the feather foot driving in the city would get you that?

The part I used is just the coasting where I did not have to use the acceleration to make up the lost speed in the true "porpoising" technique.

Example: I see a light changing a 1/2 mile ahead, I shifted to neutral and costed to the light. A lot of the time I would still be costing at a good clip when the light changed and I would just drop it down to drive and continue.

Now on the other hand, I could have kept the gas depressed and continued up to the light to apply the brakes and stop, then I would have to accelerate to get back up to speed. This would include the acceleration I would have to do to make up for the energy lost to braking.

That is how it worked for me. I agree, I don't see much benifit in slowing down to just speed up to make up the lost momentum when there was no reason to slow down. But what I did was to minimize the loss of energy by using my momentum instead of my gas pedal when slowing down was not controlable.

[ebfabman]

I agree with what jku72 says....."If you get good mileage porposing, you could get better mileage feather footing it and driving steady. "

I'm sure some will not agree, but one of the easiest ways to drive the steady posted limit, I've found over the years, is to not use the rear view mirriors unless you are going to change lanes or you hear an emergency vehicle. WHY? Because people always drive on the rear bumper of the car in front of them. It becomes very hard to drive a steady speed with someone driving all up your back side.
I just tilt the rear view mirror up as if the vehicle behind me has thier brights on..........I can still see whats behind me but when the driver of the vehicle behind me figures I can't see him in the rear view he either slows down or drives around me.


Sorry for anyone who's been driving behind me

[Hotrod70C10]

lol! i've been shifting into neutral coming up to lights since I started to drive a whole 5 1/2 years. I didn't even think of it saving gas or having a name. that's kinda funny

[Long Knight]

How does this work if your engine runs so rough you have to drive with both feet in an automatic just to keep it running?

[jku72]

I usually live away from town, but for the past 2 months I have been in Bakersfield CAlifornia on business, so i got a good dose of city driving. I noticed that many of the drivers here do what '68 suburban' says that many people do, that is race from one light to the next. I did this at first, because I was trying to do as the locals do. Well, I soon got sick of this, and discovered somthing pretty important, that is that driving fast and waiting at lights got me to work no faster than just driving slow the whole way. I also have come up with the theory that traffic lights are timed based on speed limits. When I drive just under the speed limit, I rarely have to stop for a red light, they seem to come in sequence. I guess this also proves the theory that you always get red lights when you are in a hurry. My mileage on the rental car I drive got way better when I drove slow, and my time to work stayed the same.
68 suburban talked about coasting up to lights, well, I call that feather footing it. I dont take it into nuetral, but i dont ram the brakes either. My goal is to never have to apply brakes, by anticipating stops. On the highway, I use cruise control, but a better method would be as somebody else said, drive by vacuum. If you know your torque peak, and have a tach, then the best place to be is in high gear, at the torque peak.
I think porposing is more influenced by some people paying attention to how they drive, and deliberate attempts to get better mileage, more than the 'slowing and accelerating' does. I could be wrong of course.

[Shane]

is "porpoising" kinda like "waxing your dolphin?"

[72CustomCamper]

OK, now we all know what porpoising is!

Thanx 68 Suburban for finally unveiling the mystery!

My $.02:

I think that driving for max vacuum is probably just as effective and isn't illegal in some states (...going into neutral while rolling).

But we all throw a pair 'o' pennies every chance we get!

Oh well, i'm happy with 9 mpg...

Now could someone tell me why my right rear tire is so worn out?!

[68 Suburban]

Just out of curiousity, how would a cop know you were in nuetral?

[O'l Buck]

Now I get it.......been doing it for years........but not a real good idea with a Peterbilt grossing 80,000 lbs on interstate in Wyoming.....87 in a 75 isn't a cheap ticket.......the trooper wouldn't buy my "jake's wouldn't hold it" story.

[~72'Pete~]

yall are smoking LOL

[smokekiki]

You can porpoise all you want,but you are a fool if you draft a truck.If you ever drove truck you would know. I blew a rear inner trailer tire.The tread seperated on a virgin tire,trailer was 2 month old,went under the honda drafting me,honda thru gaurdrail,driver taken to hospital. I installed 100 watt "back-up"lights in the rear bumper panel.At night someone tailgating would get a warning to back off,if this didn't work I would light them up.I also didn't let other trucks run to close to my rear. If you can't run out front don't follow. The back of my trailer had a Killer Cat license plate.750hp cat,950hp with propane injection,built by Great Lakes,backed by a 6&4 trans set.

[O'l Buck]

Man, that sounds like a heck of a power unit. I drove truck for 5 years, most of them were powered with tuned up Cummins BCII's, only had 1 Cat. My Favorite Cummins was a 74 KW with a 475 Twin turbo that was dumping about 500 to the ground and a 15spd with the gears flipped for taller tall and shorter low. I agree totally with the "gator toss" thing..........a cap can do ALOT of damage in a short time.

How'd you like the 6x4?......I've heard good things about the 5x4, and have driven a couple of 4x4's and I think 2 sticks rock.......not just anyone can drive a 2 stick.

[>X<]

can someone please explain what "driving for max vacuum"?

[smokekiki]

Iloved that set up.I did a lot of heavy haul.It had the grunt to get it moving with plenty left over for the hills.Great Lakes diesel did the rebuild for me.They do them just like any hi-pro rebuild.heads are ported,pistons are coated,rotating assembly is balanced.What a difference a balancing does to a diesel.add a swietzer turbo and the propane injection,which acts like nitrous in a gas engine,and your ready to haul. I had this in a 1987 Marmon.A normal out of frame rebuild was close to $8000,this rebuild was $12000,not bad for a double in horses. A friend of mine has a 78 KW extended hood with a 475 twin turbo with an allison trans.That truck will run!

[Project1970]

I think driving for max vacuum is getting into high gear and then trying to keep the vacuum gauge pegged (basically, most RPM's at the least throttle).

[72CustomCamper]

Some cars in the 70's (and 80's I think) had a vacuum gauge right on the dash. Some of them were labeled "Fuel Economy". Basically, the more you mashed the throttle, the more the vacuum as read by the gauge would drop. On the "Fuel Economy" gauge, this corresponded to "Poor" fuel economy.

A running engine creates a serious vacuum in the intake plenum (on the order of 17-21 inches of Hg). When you open the throttle, this vacuum is what "sucks" the air fuel mixture into the cylinders. The vacuum as measured by a gauge attached to the intake but not in the carburetor's flowpath and will indicate a drop in vacuum as the throttle plates open.

Bottom line...

A drop in vacuum is somewhat proportional to throttle position which is somewhat inversely proprtional to fuel mileage!

= low gauge vacuum = bad mpg = bald right rear tire

[Hooter]

I'm with the majority when I say, what the **** is Porpoising?