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Old 09-08-2009, 02:57 PM   #1 (permalink)
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am i taking off too slow?

i try to keep vac above 10 inches but it feels like it just takes off better if i go down to about 4-5...anybody have any opinions or better yet, real numbers?

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Old 09-08-2009, 03:44 PM   #2 (permalink)
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It does not matter much as long as you are able to get it to shift at the lowest rpm possible.
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Old 09-08-2009, 04:08 PM   #3 (permalink)
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I've seen different numbers on this vacuum question. Some say 10 some lower like 6 or 7. The best P+G numbers are apparently at 75% throttle which is probably under 3.

I tested this on a couple of tanks. One where I throttled it up below 5 to speed then did steady state and the other where I "cat" footed up to speed at max 9 or 10 and there was only a small advantage to the "cat" footing. This was not a good enough test to see for sure but at least there wasn't a big difference.

Probably somewhere in between is good. I was surprised to see not much difference despite the "No jackrabbit starts" crap. As long as you are not wasting too much momentum, between 10 and 5 seems good.

I like to divide up the driving into

1) Create the kinetic energy efficiently under good BSFC and get up into the high gears fast.

2) Steady state and coast as much as possible.
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Last edited by orange4boy; 09-08-2009 at 04:12 PM.. Reason: Because P***y cats are banned :(
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Old 09-09-2009, 02:07 PM   #4 (permalink)
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The worst place to be for FE is to be hanging just below where it would shift up. So in some cases it is better to get your speed up faster.
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Old 09-09-2009, 05:52 PM   #5 (permalink)
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wish i had a SGII

might just have to settle for a TCC button and write EASY on it....
EASY BUTTON!!!!
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Old 09-10-2009, 04:07 PM   #6 (permalink)
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I really haven't noticed my acceleration style making any difference in FE. Seems to get swamped in the other variables. I have got mileage improvements by focusing on deceleration. I'd say use what ever acceleration works best with the traffic flow and concentrate on using less braking unless you really need to break an FE record
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Old 09-10-2009, 10:18 PM   #7 (permalink)
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bombloader and orange4boy raise good points: acceleration style, in the grand scheme of things is actually pretty insignificant compared to other driving techniques - like not wasting the momentum you've just created by heating up your brake pads right afterward.
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Old 09-10-2009, 11:06 PM   #8 (permalink)
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Quote:
Originally Posted by wagonman76 View Post
The worst place to be for FE is to be hanging just below where it would shift up. So in some cases it is better to get your speed up faster.
I'd agree for automatics, IMO the only good gear for FE is top gear with the converter locked, so I don't waste time getting there in my Neon. 1/3 to 1/2 throttle until 50mph then back off slightly so the converter locks is my technique. It also sometimes gives me some space from following traffic to glide without annoying people behind me.
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Old 09-10-2009, 11:35 PM   #9 (permalink)
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Where is the chart plotting the difference between mpg for varying degrees of acceleration? I have not found anything yet that shows this. I bet they cancel each other out to some extent.

Thinking out loud here and expanding on what MetroMPG said...

At the extremes of BSFC you have WOT and steady state cruise(SSC). The difference between these is where the meat of the gains (or tofu if you are vegetarian) is to be had in terms of FE. Hence the theory of P+G, where the pumping losses and engine friction losses from cruising are removed and replaced by short bursts of a more efficiently produced energy followed by coasting where aero and RR/bearing friction eat up the most of your energy.

When you accelerate from a stop, you are already producing energy much more efficiently than at SSC, like the pulse of a P+G. How much more efficiently seems to be not terribly important. Giver! Then coast all the way home.

The point is to preserve the momentum you have invested your acceleration into (by removing losses) and not create extra momentum to begin with. Slamming on the brakes can represent one of the biggest single losses of any one action. This is the subtle message left out of the "no jackrabbit starts" message. It should really read: Jack rabbit all you want, just don't waste the kinetic energy you've just created with your brakes.

1) Reduce parasitic losses
2) Don't waste momentum
3) highest gear, lowest speed.

As I write this I'm thinking about it and sorting these things out in my mind. It's not the easiest thing to express in a few words.
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Old 09-10-2009, 11:45 PM   #10 (permalink)
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Quote:
don't waste time getting there in my Neon. 1/3 to 1/2 throttle until 50mph then back off slightly so the converter locks is my technique. It also sometimes gives me some space from following traffic to glide without annoying people behind me.
I like this as well because people expect you to crawl away from an intersection if you've just cut your engine to avoid idling.

I think the Jackrabbit BS was started to turn people off of improving their mileage. Who wants to crawl off the line and who wants to be behind them?

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