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Old 08-03-2010, 06:59 PM   #1 (permalink)
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Going up steep hills- downshift or floor it?

Hey all, I'm new here, and have been lurking for a while and finally made an account. My ride is a 1995 Audi A6 Quattro- 2.8L V6, AWD, 5 spd manual, 185K miles. Anyway after applying a few hypermiling techniques, I managed to get 31MPG out of my last fillup, which I don't think is too shabby.

Anyways, on to my question. I live in a rural area in Ohio, and usually can travel on relatively flat roads. However sometimes I am forced to travel on a very hilly/curvy road- and by hilly, I mean REALLY steep hills, which is the basis of my question. On a couple of the downhills, I go down in 4th in order to be going slow enough to make the corners at the bottom (avoiding brakes). Going back up hills, I try to gain as much speed as possible before starting up the incline. Anyways, my question is, on the really steep uphills, is it more beneficial for my FE to leave it in 5th, and put the accelerator to the floor in order to make it to the top (usually at/around 30MPH at the top), or downshift to 4th or 3rd and not have to put the pedal to the floor?

I would get a ScanGauge and test for myself, but...I'm 17 years old and don't have a job, so I don't exactly have $150 laying around for one...yet, though.

I would appreciate any input...thanks a lot

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Old 08-03-2010, 07:23 PM   #2 (permalink)
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generally, staying in the highest gear is best. I also live in a very hilly part of the country, and I do have a scanguage. But I don't have the fortune to have a stick, so flooring it would cause it to downshift. But I do know in the instances I do end up having to downshift, the mpg goes down instantly. Generally, if i see a hill coming I try to build up as much momoentum as I need (and is legal and safe, of course) so i don't have to downshift.

I wouldn't floor it though. A modern engine will richen the mixture as a self preservation technique at wide open throttle, so stay away from that. Give her 80% or so, and keep it in 5th as long as possible.
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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 08-03-2010, 10:12 PM   #3 (permalink)
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I find in my 2.2L Camry that it's better to change to 4th, as there isn't a huge amount of torque. I change my shifting point (steep inner city hills - such fun) so I stay between 2000-3000rpm, rather than my normal 1000-2200rpm, if my revs go below 2k I don't have enough torque to keep the same speed, so I have to floor it to stay the same speed vs half throttle in 4th to speed up slightly.
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Old 08-03-2010, 10:18 PM   #4 (permalink)
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I've been wondering the same thing and I'm guessing it varies somewhat from car to car and only something like a Scangauge or vacuum gauge can give you the real answer. When I'm on the hilly roads near my house with not a lot of other people around I'll build up an extra 10 or 20mph going down hill and bleed it off on the way back up the other one. But what happens if you get stuck at a stop light at the bottom of a hill? I dunno, time, and some equipment will eventually give me the answer.
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Old 08-03-2010, 10:26 PM   #5 (permalink)
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I'm planning on getting a scangauge for the Sonata, but my Camry is Australian built, and has an OBD-II port that isn't actually OBD-II (sigh). I'm considering a vacuum gauge, but we might be selling the car soon (my mom owns it), so I don't wanna be adding weird (in most people's minds) gauges to it.

I'm working on the logic that for sustained throttle position, less is always better. I think it's more for accelerating where low-rpm high-throttle and high-rpm lower-throttle comes becomes relavent, 'cos you aren't going to be accelerating for minutes at a time (I sure hope not, anyway).
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Old 08-04-2010, 03:22 AM   #6 (permalink)
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For those with low powered cars like my Geo Metro, flooring and downshifting is the only option. I have to do this for 1 hill on my way home from work. I'll start at 40 MPH at the base of the hill in 4th and be in 3rd doing 30 by the top if I'm lucky.
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Old 08-04-2010, 08:29 AM   #7 (permalink)
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In a manual car its always best to (almost) floor it. As Shadetree said, 80% is good. You don't want to get fuel enrichment.
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Old 08-04-2010, 10:41 AM   #8 (permalink)
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Agreed. Top gear and 80% throttle.

Autospeed - Brake Specific Fuel Consumption

Aim for the red zone.
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Old 08-04-2010, 11:15 PM   #9 (permalink)
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Thanks for all the responses Next time I'm on that road, I'll give it 80% acceleration in 5th until I absolutely have to shift. Hopefully I can get a ScanGauge in the near future so I can get actual numbers.
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Old 08-05-2010, 02:47 AM   #10 (permalink)
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Many cars have a place in the throttle that feels heaver. Using my MPGuino I can see when I go past that point the fuel mileage drops significantly. it drops linearly with the pedal from ~24 to 20 coming up to the stiff point then straight to 16 or less after the heavy point. I find that a slight acceleration up to about 10 over before the hill allows me to decelerate a little less going up the hill as the engine spends more time closer to where it makes more power.

If you have to down shift keeping the engine loaded is good. Pick a gear where you can keep about that 80% without slowing "too much".

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