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-   -   Geo drivers, please help me get a few things straight. (https://ecomodder.com/forum/showthread.php/geo-drivers-please-help-me-get-few-things-5302.html)

lyd 09-28-2008 10:48 PM

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.

MetroMPG 09-28-2008 11:29 PM

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).

bbjsw10 09-28-2008 11:47 PM

Quote:

Originally Posted by MetroMPG (Post 64054)
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.

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

lyd 09-28-2008 11:48 PM

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

lyd 09-29-2008 12:08 AM

Quote:

Originally Posted by MetroMPG (Post 64054)
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.

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. ;-)

99metro 09-29-2008 11:18 AM

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.

MetroMPG 09-29-2008 12:15 PM

Quote:

Originally Posted by bbjsw10 (Post 64059)
When you do this do you shift to 5th as soon as possible, like skip a couple if you are going 30-35mph?

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

lyd 09-29-2008 03:13 PM

Quote:

Originally Posted by MetroMPG (Post 64105)
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?

MetroMPG 09-29-2008 04:19 PM

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.

lyd 09-29-2008 04:38 PM

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.


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