Geo drivers, please help me get a few things straight.
 

I've been reading these forums pretty voraciously for about three weeks now, and while I have learned tons, my head is spinning a bit with some of the technique info. So much seems to be contradictory at first glance, and a lot of it has continued to seem that way after many repeat glances. ;-)

Please, just tell me if this statement is correct, as a summation of all the many things I have read:

I want to be accelerating as quickly as possible, shifting at peak torque (3300 rpm), until I hit cruising speed, at which point I want to keep the vac guage above 10.

If that's correct so far, as far is it goes, then I have a couple of initial questions:

- What am I trying maintain on the vac during that "quick as possible" acceleration? It drops to 0 pretty fast.

- Keeping the vac gauge above 10 seems to result in my frequently going well below the speed limit. Even a moderate incline scrubs me down to 50 or 45 mph pretty quickly, and slightly steeper ones have me dropping below 45 and down shifting to 4th gear. Is this pretty normal?


Clearly, I need to get that boarduino and other bits ordered to get more feed back than the vac-n-tach setup is giving me, but I'd a appreciate a little help in the meantime. I cranked out a couple hundred miles of 48mpg just vaguely trying to go slower, use high gears, and shut the car off to coast once in a while. Now that I am all equipped with new knowledge and instrumentation I feel like I'm doing much worse and have been all over the place in the way I'm driving. I need to get centered on an approach again.

I can't tell you exactly how much throttle to use when accelerating, except to say my own technique has me shifting below that 3300 RPM mark the BSFC chart suggests is optimal for the non-XFi engine.

I'm more likely to shift around 2800-3000 RPM simply because I don't like winding the engine out, even if it is a bit more efficient.

That said...

If there's any chance you're going to have to brake or otherwise slow down shortly after accelerating in this manner, don't do it. Just accelerate gently and upshift as early as you can. Braking after brisk accel is about the worst thing you can do. (The best thing, speaking only of efficiency, is to shut the engine off and coast after accelerating - Pulse & Glide).

Re: the vac gauge, I've never used one in my car, but you're effectively describing "DWL" (Driving with Load), which I do regularly when highway driving (I've moved away from extended P&G cycles on the open highway). And the answer to your question is "yes" it's pretty normal for your speed to fall off on even modest inclines if you've picked a relatively low load target (e.g. inches of hg or instant MPG on the MPGuino or ScanGauge).

When you do this do you shift to 5th as soon as possible, like skip a couple if you are going 30-35mph?

'Kay, that helps a lot, thanks. I just needed someone to reassure me that I hadn't gone completely off the rails. ;-)

I've been driving this car for years, and have generally shifted at 4k as a minimum when trying to accelerate at a decent rate. Freeway on-ramps and such I'd wind it out almost to 5k.

It took an act of will to start shifting in the low 2k's these past weeks. ;-)

I am using moderate acceleration, shifting at around 2000 - 2500 or so. I sometimes shift earlier if I am going downhill, so this RPM varies on terrain. The idea is to use the least amount of horsepower I can. I do my best to stay in 5th gear going up hills, and generally either slowly decelerate, coast, or at least try to maintain 35 mph up the long ones if I am out in the back roads by myself. I have also limited my top speed to 55 mph. But that is me - still a work in progress.

I am trying to work on a theory of P&G while shifting through the gears. In other words, every time you shift up and put in the clutch to shift to the next gear, allow the car to drop 5 mph before engaging the clutch again to accelerate. It's kind of a patience issue on my part to do this - and it depends on what traffic is behind me. Again, a work in progress.

Yep, if I'm going to drive with load after accelerating.

I've been trying this today, accelerating briskly up to 55 then DWL from there. Thing is, I'm dropping back to 45mph early and often anyway. Then, following a DWL strategy, I'm slooowly regaining 55 on the next flat or downhill, keeping the vac guage at 10.

Seems like I should either give it more gas to maintain speed on the uphills, which would be closer to the whole 3300 under load thing, or drop even further in speed on the uphills and then accelerate briskly again.

Any thoughts ok which might be better?

You're basically describing a "pulse and bleed" strategy, and I don't think it works. (At least I've never been able to come out ahead the few times I've tried it.)

I think a strong "pulse" (accelerating briskly, near peak BSFC, up to speed) will only pay off if you maintain a high mpg for a long time afterwards, or if you plan to immediately follow it by a glide, and rinse/repeat.

That makes sense. I guess I'll go back to my slow acceleration, except where I know I am going to have an EOC coming up. I haven't been doing that systematically (EOC I mean) but have been taking advantage when really good opportunities present themselves, like long downhills or steadily decreasing speed limits coming into towns.

Get to your highest gear as quickly as you can but without using much gas. This is trial and error to find. In a Lite car that should be easy. Pulsing hills works but if done the right way. Not all vehicles are Equal..
The fact that Every hill should have a peak works in my area well. I don't increase much fuel before the incline but I do increase speed, about 5 to 10mph "a Hair more of Pedal" almost to the point of going up it. Once Your climbing Let off your pedal but keep your foot at your Max MPG speed which ever that maybe, 43 45 47 etc. Hold your pedal just like if you were on flat land. A Tach makes it Easier to find. You should loose speed climbing, and once at the peak let off your pedal.
This works the best for my Heavy 6000lb van which loves gaining speed downhill because of all the LBS pushing it down the hill. A slight down slope it will increase speed.

Well, in my Geo "a hair more pedal" does not increase speed on an incline, even a gentle one. At 10 on the vac guage I am just barely maintaining 55mph on level, open road. Holding it there on the frequent gentle slopes I encounter on the Wisconsin County Hwys I'm driving most will drop me 45mph, and on the slightly steeper ones I drop below that quickly. On those I'll downshift to 4th while still holding 10 on the vac and wind up cresting sometimes as low as 35mph.

Holding speed on the upslopes requires dropping to 4 or 5 on the vac, and acceleration requires 2 or less. I have not been doing that except where traffic makes it unavoidable.

On the downsides I'll either hold at 10 to get back up to the 50-55 range if another upslope is coming, or back off closer to 15 and gradually creep up to that same range if it looks flat ahead. Once I am out on the flat things settle back down to around 10 on the vac to hold speed, just.

I have been EOC where I can, mostly as I come into towns where the speed limit is dropping gradually 55-45-30-25, or where I am approaching a turn from one highway onto another.

No idea if any of this is most efficient, but seems to be the best I can do until I get the real-time MPG data going.

Re-reading what I have written above, it sounds like I am going for 55mph as my target, and I guess you could say I am, but the way it all works out DWL I am spending a lot more time around 45mph than I am at 55. This doesn't bother me -- the short runs I make on these local highways are perfect for driving a slower average speed, as it is hardly going to change my total trip time at all-- but it definitely bothers the hell out of traffic behind me on these 2-lanes, so I am a little concerned about that. There are many easy passing zones and plenty of openings to use them, but it seems to really piss some people off to have to do so, however easy it may be. The 30 or 40 seconds they get held up behind me waiting for the next passing opportunity is apparently extremely frustrating to them. Thats the root of my at least trying to hit 55 (which is still too slow for everybody, but I'm not going to apologize for driving the posted limit) rather than just outright driving 45, which I could maintain much more easily in this terrain.