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northboundtrain 06-23-2007 08:55 PM

Easy 25% Increase
 
I just filled up today and found my city driving has improved from 32-33 mpg up to 40+ mpg. This is pretty much all attributable to pulse and glide driving, with the gliding in neutral not eoc. This is not at all extreme p & g, rather, I just use every opportunity to coast, like on slight downhill grades or rolling up to a red light. Someone following me would hardly notice. I'm pretty amazed at the improvement.

One thing to be careful of though: I was coming down out of the mountains one day, coasting a lot obviously and using the brakes to slow down for curves. I thought I was going easy on the brakes and giving them plenty of time to cool off, but then I pulled over 'cause the kids were fighting in the backseat, and I could smell the brakes. I checked the rotors and they were blue from the heat. So now I'm careful to use the engine for braking on long grades.

cfg83 06-24-2007 01:20 AM

northboundtrain -

Quote:

Originally Posted by northboundtrain (Post 60440)
I just filled up today and found my city driving has improved from 32-33 mpg up to 40+ mpg. This is pretty much all attributable to pulse and glide driving, with the gliding in neutral not eoc. This is not at all extreme p & g, rather, I just use every opportunity to coast, like on slight downhill grades or rolling up to a red light. Someone following me would hardly notice. I'm pretty amazed at the improvement.

One thing to be careful of though: I was coming down out of the mountains one day, coasting a lot obviously and using the brakes to slow down for curves. I thought I was going easy on the brakes and giving them plenty of time to cool off, but then I pulled over 'cause the kids were fighting in the backseat, and I could smell the brakes. I checked the rotors and they were blue from the heat. So now I'm careful to use the engine for braking on long grades.

Yeah, depending on the circumstances, and especially when coming down a steep grade from the mountains, I use engine braking for safety reasons.

Sometimes what looks like a hypermiling oppurtunity isn't :( .

CarloSW2

parasonic 06-24-2007 06:57 AM

Your motor is still probably running air, so you likely ARE hypermiling if you aren't pressing the accelerator.

cfg83 06-24-2007 09:43 AM

parasonic -

Quote:

Originally Posted by parasonic (Post 60464)
Your motor is still probably running air, so you likely ARE hypermiling if you aren't pressing the accelerator.

Yes, but I should have wrote more. The gas used to go uphill is not optimized going back downhill. That is to say, on a gentle grade with no curves, I can get the energy back and maybe be able to EOC without speeding up. On a curvy-steep downgrade, the additional braking is "energy lost", and the gear braking, at least in my car, still uses gas because of the higher revs and the fact that my car does not go into complete fuel-shutoff (this is what my ScanGauge shows me).

northboundtrain -

The next time you EOC, can you report your instant MPG? Also, the next time you use engine braking (in gear, foot off the accelerator), can you report your instant MPG? That will tell us if your car is using complete fuel shutoff or not.

CarloSW2

baddog671 06-24-2007 10:40 AM

Im sure there is some kind of brake cooling ram air for your brakes since its a VW and they have a nice aftermarket line-up. Might lower FE a bit but look cool and keep your brakes cooler.

northboundtrain 06-24-2007 12:28 PM

Quote:

Originally Posted by cfg83 (Post 60478)
northboundtrain -

The next time you EOC, can you report your instant MPG? Also, the next time you use engine braking (in gear, foot off the accelerator), can you report your instant MPG? That will tell us if your car is using complete fuel shutoff or not.

My car is mechanically controlled, no computer. So I believe that means that the scangauge is not an option. I don't exactly know how the injection pump works with regard to idling versus coasting in gear, but I suspect it pumps more fuel when it's in gear because the revs are much higher.

Snax 06-25-2007 06:03 AM

What about engine off coasting in gear? This is an effective way for most EFI based manuals to engine brake. I'm not sure how well that would work out with the VW injection however.

I used to do that all of the time in my hillclimb car when descending. Due to the amount of heat buildup, it also helped to cool the motor down to a more reasonable level. (I could touch the turbine side of the turbo after a 2 mile descent.) Of course that brings up the question of efficiency on restarting since the cooling effect might result in higher initial consumption to warm up again.

northboundtrain 06-25-2007 06:41 AM

Quote:

Originally Posted by Snax (Post 60610)
What about engine off coasting in gear?

I'm not sure about that. It might work, but if the engine is turning, then the injection pump is still being driven by the timing belt. I could install a separate kill switch for the pump (that's how you turn the engine off), but if the engine is still driving the pump, I'm not sure if it would continue pumping fuel or not. Also the pump is lubricated with fuel, so if it were spinning, but not pumping, I wonder whether it would be getting the necessary lubrication.

The internal workings of injection pumps are pretty mysterious to most of us shade tree mechanics, since they require very specialized and expensive equipment to work on. We just send them out to be rebuilt/fixed.

rvanengen 06-25-2007 06:44 AM

Wouldn't the 0% throttle position in the diesel be almost no injected fuel at an engine speed above idle since it doesn't need to care about lean burn or keeping a 14:1 air:fuel? I would think it certainly would be absolutely no worse than simple idling, but likely better.

northboundtrain 06-25-2007 06:54 PM

Quote:

Originally Posted by rvanengen (Post 60618)
Wouldn't the 0% throttle position in the diesel be almost no injected fuel at an engine speed above idle since it doesn't need to care about lean burn or keeping a 14:1 air:fuel? I would think it certainly would be absolutely no worse than simple idling, but likely better.

I think you're right, and I think that's why I have seen such a huge improvement with a relatively small change in driving style (all my p&g is in neutral with the engine idling). Diesels are much more efficient at idle for the reason you mentioned -- they can run as lean as possible without overheating the cylinders.


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