How to Accelerate?

[bbjsw10]

I have started accelerating differently, I was taking off at 10in. hg. now I have began to take on in first shift to second at like 5 mph, and 2nd-4th about 4-5in. hg.

I have an A/Fuel ratio gauge and at this position of throttle it stays a lil more on the lean side.(I have been listening for spark knock none what so ever) If I give it any more throttle than this it goes into opem loop and stays pegged at rich. It kinda has a little sweet spot right there at about 40-50% throttle, it is a very small area I have to watch A/F gauge very closely or it goes rich. I can't move my foot more than 1/8" or I lose this spot. I also must shift about 2200-2500 rpm to stay in this fuel reading. Maybe it is the Xfi ecu has a different map.

This should in theory reduce my pumping loss of the engine by not "bogging" it down at the lower throttle position. I guess only time will tell on this method I hope it does do what I am thinking it will. Another added benefit of this is that I reach cruising speed in 5th about 5-10 seconds sooner, which is probably the most efficient speed for this car 35mph in 5th.

[99metro]

This might get lost in this thread, BUT I have been playing with acceleration techniques the past couple of days. Just watching the Scangauge, I played with slow acceleration versus fast acceleration. Not a whole lot of difference either way. The end result ends up being close to the same by the time I get to the next stop sign 4 miles down the road.

Then I tried something different. If I accelerate in first gear, push the clutch in and neutral coast down 5mph, then shift to second, accelerate, push the clutch in, neutral coast down 5 mph and continue up through the gears like this, I found I only lost about 1/2 of the MPG than If I went throught he gears normally. I don't have the data as evidence since I am fairly busy driving, but I encourage anyone to verify this if you have octopus hands!

In other words, if you graphed my acceleration speed it would look like a saw blade, vice looking like plateaus, if that makes any sense.

[99metro]

That might not have sounded clear.

Accelerate in first gear to 15 mph, shift to second keeping the clutch in, but don't accelerate or pull the clutch out til you drop down to 10mph, then accelerate in second to 25mph, clutch-in coast to 20, third gear accelerate to 35, clutch-in coast down to 30, 4th to 45, clutch-in to 40, then 5th as needed to P&G speed.

Clearer? Hope so...

[aerohead]

Originally Posted by PA32R

I'd love to see both of those articles. I've posted quite a few times on this subject and brought up an issue that HAS to play into the optimization question: the adding of kinetic energy. The fuel burned (and not wasted as heat, friction, etc.) goes to two things: overcoming the total resistive force (externally, these are aerodynamic drag and rolling resistance) and adding kinetic energy (we'll ignore potential energy by assuming level ground). It's quite easy to show that to add the kinetic energy to get the vehicle mass up to, say, 55 m.p.h., all else being equal, accelerating 1/2 as fast will get you twice as far in the process of adding that kinetic energy. This argues for the slowest possible rate of acceleration. But the m.p.g. as a function of m.p.h. curve and the engine map argue for a different protocol. I haven't yet concluded how to optimize these conflicting factors.

I found the papers last night,set them out,and like a dumb---,left 'em on the desk as I left the house for town.I'll bring 'em next time.Sorry!

[PA32R]

Originally Posted by aerohead

I found the papers last night,set them out,and like a dumb---,left 'em on the desk as I left the house for town.I'll bring 'em next time.Sorry!

Cool, I'll be looking forward to it, Thanks

[tasdrouille]

I did some test runs accelerating from 70 to 90 km/h in 5th which I logged with vag-com in my TDI. I logged RPM, load and injected quantity.

The logs appeared to agree with the bsfc map. But more logging to test more operating points will be necessary to prove it without a doubt.

[aerohead]

Originally Posted by PA32R

Cool, I'll be looking forward to it, Thanks

Papers: SAE Paper 770418 "An Analytical Study of Transmission Modifications as Related to Vehicle Performance and Fuel Economy",Engineering Staff General Motors Corp.--------------------------------------- within the body of the text they mention" a performance level of 13.5 seconds to accelerate from 0-60 mph will be assumed as being the vehicle requirement.This requirement was set forth by the Office of Air Programs of the Environmental Protection Agency in 1972 for several powertrain investigations."------------------------------- SAE Paper 730790 " Passenger Car Fuel Economy-Trends and Influencing Factors,by U.S.EPA.--------------------------------- within the text,they make mention" The effect on urban fuel economy due to a change in driver habits(approximated by changing the acceleration rates for the cycle driven) resulted in the following: doubling the nominal acceleration of 6 ft/s-squared to 12 ft/s squared resulted in approximately a 6% fuel economy penalty,while halving the acceleration to 3 ft/s-squared resulted in approximately an 8% gain in fuel economy.It can be seen that a more sedate approach to acceleration by the driver will improve his fuel economy."----------------------------- SAE # 750954 by GM shows a graph of mpg vs acceleration rate,slowing accel from 0-60 in 11-secs,to 0-60 in 13.5-secs,reduced consumption 1-gallon over a hundred miles for a 2800-pound car with a 228-cu in engine.------------------------------ SAE # 740620--------------------- a 1924 Chevy achieves 164-mpg,doing burn and coast (pulse and glide,momentum driving) by accelerating at WOT in high gear,from 3mph to 15mph,then coasting with engine off down to 3 mph.It took 6-cycles to cover a level mile,at 0.16 miles/cycle.1959 Opel achieved 376 mpg doing same thing.

[pumafeet10]

i decided to come back to this post and was reading a lot of things you /\/\/\ posted

This last post has me a bit confused,

[jonr]

You always want to run at best BSFC until this causes speed to be so high that friction losses become a major issue.

[2000mc]

1959 Opel achieved 376 mpg... thats frickin awesome, too bad avg speed was slower than most bicyclists.