Tried my first P&G today
 

Had to drive 200 kms, lots of highway and some city. That's almost half my tank so I decided to P&G, filled up at the end, and got 54 MPG which is pretty much normal for me (drafting or driving slow). :(

On the highways I was running late, so I was pulsing to 70mph and gliding to around 55mph. It wasn't going well. My pulses were almost longer than my glides. I decelerated pretty fast as soon as I clutched in. I think there is too much air resistance at that speed, and my tires probably ought to be overinflated.

Later on I was pulsing to around 35-50 mph and gliding down depending on the speed of traffic and limits, and it was much much smoother. I could easily glide twice as long as my pulses. I suspect I made up for a lot of the MPG at this stage, since my gauge was going down faster than normal to begin with.

Advice?

Also, today on the highway I pissed off an ambulance who was driving behind me (only 1 lane). I would speed up to 110, and he speeds up to the same, then I glide down and he's right on my tail, then suddenly I would pull ahead and repeat. Then I saw him flashing his brights in my mirror. Finally he got an opportunity to pass me, so he went ahead and started driving 50mph in front of me, glaring at me from the side mirror. So I just P&G at a lower speed until he lost interest and drove away. :)

Sweet little car. I see them in a whole new light since joining this forum. I'll bet you'll get more out of it if you invest in a gauge. Can the 1991 Metro use an UltraGauge or Scangauge? The precision of your pulses would improve, probably yielding more efficiency.

Definitely consider the fact that resistance and drag factors become more of a factor at faster speeds. Personally I try not to drive faster than 65 at the top of a pulse. Wind resistance on the car is just greater. I also would consider only 10mph arcs at highway speeds. I only say it because that is what I am doing and getting lovely results (68.4 on my 22 mile freeway leg today without slip-streaming or anything besides 55-65 mph P&G, engine on).

On the annoyed ambulance driver (pretty funny it's an ambulance!)... Why not just encourage a pass? Glide down to a much slower pace, hew close to the shoulder side of the lane, and flag the driver by... saves you headaches. There are lots of ways to do it. We get really focused on our performance driving, so if we're not careful we're kinda like street drag-racers: the drag is different but the lack of consideration for others is the same. I have pissed-off some folks behind me without even trying, and later had to realize I could have just let 'em by. :thumbup: so... simple... :)

How long does it take you to coast from 65 to 55 mph? I have a 99 Coupe and it seems to take about 5-8 seconds which looks like it's too quick?

When I wrote that 55/65 thing above it was summer, and I had a 4" airdam, 80% grill blocks, and partial rear wheel skirts. My tires were pumped up high too (10+ psi over sidewall). Assuming no wind or slope I'm sure I got significantly longer glides than you are describing, but I never timed it. Also, with the engine on and with my WAI I find the 75%-80% load pulse and sudden closing of the throttle during engine-on glides makes the car run leaner.

My little car doesn't do well as far as P&G is concerned. It just slows far too quickly due to rotten aerodynamics. But the biggest problem - apart from being an automatic - is that it only has 3 gears...

It's sweet-spot seems to be around 2500 rpm, where I am only doing 40mph. Fine around-town, but not much good on the open road.

My big diesel (manual), just runs and runs when you coast. According to the Ultraguage, it is giving me an indicated 78mpg (imp) at a steady 60mph and not much less at 70mph

Doing the 7 miles into town - which is slightly downhill - I can easily get about 100mpg (imp) if I P&G (engine on)

I attempted pulse and glide also for the first time on Saturday

3/4 throttle acceleration in 5th gear from 2000-3000 RPM (50mph - 70mph) then glide in neutral and repeat. Did that for about two hours solid on the motorway (uk highway) and got about 58.6mpg vs 48.4 official value which I feel isn't quite high enough considering how I was driving. I don't know if my way was the right way though... I feel the engine was using too much during the glides to make a big difference and it took too long to get upto 70 again.

My car is a 1.8 rover 200 k-series, tyres pumped to 36PSI (2 above normal). Using a cone filter but not HAI yet, air temps at the filter were about 10 degrees according to my meter (diy MPGuino that I've made which includes a temp sensor).

I did definately notice the difference when I found myself a lovely tanker to sit behind, my glides lasted much much longer, the air must make a huge difference.

When you say 3/4 throttle do you mean throttle position? Because I usually need only somewhere in the 20s% throttle ... the goal is "3/4" or more properly somewhere around 75% load (not the same as throttle). What instrumentation are you using?

Yes I meant a throttle position of 3/4, as in the pedal three quarters of the way to the floor. Is this not right?

I'm not using anything except the fuel usage monitor I've made with an arduino. I want to fit a vacuum gauge but haven't yet, is that what I need?

48.4 official HIGHWAY value, or combined cycle value ?

What does it return at a steady 60 mph ?

3/4 throttle would be about right - you want to load the engine properly to get the best BSFC during the accelerations.

Not shutting the engine down during the glide of course reduces the effectiveness of the P&G technique.


Tankers aren't even the best to shelter behind.
The air swirls in around the bottom of the tank.

Square trucks or busses are the best.

Thanks for that :)

Yes it is 48.4 highway, not combined. In the UK we refer to that as extra-urban :P

I did sit behind a big square truck for a fair while but after he left the tanker was the next best thing. Weren't as many around on the road as I'd hoped for lol.

After reading about my engine management system it appears the injectors are always live and the ECU pulses the injectors to earth to trigger them. Could I therefore have them on a switch inside the car that I can activate to connect the injectors directly to battery live so as to effectively disable them?

Then on a glide I could flick the switch to effectively stop any fuel from being injected but keep all electronics going, then turn the injectors back on again for the next pulse.

Eventually I would work to automate this somehow, but would this work for the moment? Also should I be aiming to do 50-60 rather than 50-70mph? Thanks! :)