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Old 04-30-2008, 09:11 AM   #21
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A grill block helps in several ways.
- Faster warmup time - a cold engine burns much more fuel.
- better aerodynamics
- warmer intake air - usually gives you better fuel economy.
See this post, click "my rides" for pictures of mine.

Some automatics are smoother shifting from N to D. My minivan's is rough - it revs up above 2,000 and then settles to 1500, so I rev-match to 1500 1/2 second before. Minimal fuel, maximium trans life.

Pulse & Glide - Neutral is a must. Leaving it in gear is completely wasting your time. Engine-off is even better, but only if your auto can be 4-wheel flat-towed (check the manual).
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Old 04-30-2008, 10:15 AM   #22
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Thanks for explaining the grill block. I figured it would affect aerodynamics, although I wasn't sure whether it would help or hinder; but I didn't think of the engine efficiency gains.

It's interesting to see where your comfort level and safety priorities are. Mine are quite the opposite. I would accept a rough N->D shift, considering that the torque converter is taking all the abuse and is made for such abuse; but I am totally not comfortable with (on a regular basis) shutting off my engine while driving in neutral...
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Old 04-30-2008, 10:39 AM   #23
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Thus, it seems like the only appropriate time to shift into neutral to save gas is when fully stopped at a red light. I guess you could also put it into Park? At the very least, you won't be using your tail lights.

I'll probably answer my own question, but can some one tell me why this is so?

In my own feeble mind the RPM's are lower when left in gear then when in Neutral, so how can it be using more fuel? Is it because it is under a load?
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Old 04-30-2008, 11:25 AM   #24
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On my minivan, it's already had the transmission replaced under warranty, and I hear this is the most common failure for this model. I'm being extra careful.

On my daily driver manual civic, it's already at 160,000 miles and still going strong, so I don't worry about wear. Safety - no power steering to begin with, and the brakes are good for several emergency applications before the boost runs out. I've played a lot with it on back roads and I know what the results are. If a situation does come up, I'm ready.
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Old 04-30-2008, 12:19 PM   #25
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Originally Posted by BBsGarage View Post
I'll probably answer my own question, but can some one tell me why this is so?

In my own feeble mind the RPM's are lower when left in gear then when in Neutral, so how can it be using more fuel? Is it because it is under a load?
You did answer your own question. RPM alone does not determine fuel usage. Load, power created, throttle position, air/fuel ratio, temperature, and some other variables I can't remember off the top of my head are all part of it.

I eagerly await my state tax refunds or my economic stimulus check so I can buy a ScanGauge II and just get a direct reading on fuel rate in gallons per hour...
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Old 04-30-2008, 12:29 PM   #26
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You did answer your own question. RPM alone does not determine fuel usage. Load, power created, throttle position, air/fuel ratio, temperature, and some other variables I can't remember off the top of my head are all part of it.

I eagerly await my state tax refunds or my economic stimulus check so I can buy a ScanGauge II and just get a direct reading on fuel rate in gallons per hour...

Just use this link for an explanation. It was exactly the info I needed.


http://www.autospeed.com/cms/A_110216/article.html
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Old 04-30-2008, 12:48 PM   #27
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Just use this link for an explanation. It was exactly the info I needed.

http://www.autospeed.com/cms/A_110216/article.html
Nice. That puts some additional science and math behind some of my own experiments and the theories that spawned them.

Also, it says something helps explain the efficiency of GM's gasoline direct injection V6 that's currently in the Cadillac CTS and will be in the new Camaro:
Quote:
Diesels, which we’ve not mentioned here, are much more efficient at low loads because they don’t have a throttle restriction in any type of driving – low loads are catered for by just reducing the fuel that’s injected.
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Old 04-30-2008, 09:09 PM   #28
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Well, I tried a few techniques today. I drove about 110 miles and...

-I followed a semi truck @ 70mph, 2-3 car lengths away for a good 30 of those miles. Didn't seem to help much.
-Drove only up to 70mph, most of the time at 65mph.
-Put it in Neutral with engine on for a few of the downhills. Seems to really help, especially if going less than 60mph. I think my engine likes to brake a lot for me.
-Went up to 70 on the uphills.
-Engine off Neutral (on my automatic!) twice. It was kinda scary. Found out I don't have power steering. Seemed to help, but not much more than engine on Neutral (but I wouldn't know...my speedometer was at 0 and I don't have a Scangauge).

So what's the final verdict on going up and down hills? It seems like when you go up a hill, you gain traction due to your going against gravity, so you use every bit of the gas you burn, as opposed to downhill where you go with gravity and possibly don't have as much grip, burning fuel and not transmitting all that power to the road.

Also, maybe the air you have to move is less when going uphill. After all, now there's less air under you as you go up (and more pavement under you), so air has to travel over you. When you go downhill, it seems that you'd be affected by both wind above and below, making you waste more gas going against the wind.
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Old 04-30-2008, 10:48 PM   #29
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FLAteam,

A couple of things not already mentioned unless I missed them...

Regular wheel alignments will help keep everything running true. Saves tyres as well as fuel.

Take out everything you are not using on that trip. Every pound costs fuel to transport so gut the car as far as you can.
Even taking out the street directory if you don't need it on that trip.

Good luck , Pete.
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Old 05-01-2008, 03:55 AM   #30
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You should have 100% traction/grip whether you're going up or downhill, under normal conditions. If you don't, you're either racing or you've got something very broken.

When you're going downhill, if you've got a modern engine and it's above 1000 rpm, it's using zero fuel. The only difference between coasting downhill in gear and coasting downhill in N with the engine shut off is that you'll gain a little more speed doing the latter, due to the road not having to turn the engine and operate the accesories. The energy used to recharge the battery after restarting is probably slightly less than the energy saved.

I disagree with your idea about aerodynamics. Your vehicle displaces exactly the same volume of air going up or down, has the same ground clearance and the same drag coefficient, and the same amount of pavement under it. Remember, the road's angle changes along with the vehicle's angle; so it's not like the vehicle pointed up will catch more air under and less air over or something like that.

Momentarily, when cresting the top of a hill or in the bottom of a valley, the vehicle's angle relative to the road changes, and at that point the balance of air going over vs. under changes momentarily; coming over the top, the bottom of the vehicle parachutes a bunch of extra air, while in the valley entering the uphill the ends of the vehicle are closer to the road and let less air under.
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