Fast or Slow Acceleration? Test Results

[oldtamiyaphile]

Originally Posted by nuverde

My finding was that for my car, accelerating slowly up to 65mph and cruising for a short amount of time until I reached the one mile mark used LESS FUEL than accelerating quickly and then spending more time cruising at 65mph (until the one mile mark).

What you've actually discovered is that driving at a lower average speed burns less fuel. That was never in debate.

[Cobb]

I demand a retest!!! Can you add 2 entries? 1 for the rpm below vtec engagement and just above it? Vtec engagement is 2500 rpms+- a few conditions, right?

Run Data:

Acceleration Run 1 Run 2 Run 3 Run 4 Avg. MPG Avg. Gallons Used
Slow (~1800rpm) 28.6 27 28.4 26.6 27.65 0.036
Med. (~3300rpm) 24.9 23.2 25.2 24.43 0.041
Fast (5000+ rpm) 19.9 21.3 21.1 20.77 0.048

[nuverde]

Actually, the more I learn, the more I am convinced that trying to isolate a single variable for testing is beyond my patience. The engine in this civic (R18a) has a vtec that is kinda backwards from what we are used to thinking. In short, between 1000 and 3500 rpm, low cams may be engaged, IF the conditions are right for fuel economy. See http://asia.vtec.net/Engines/RiVTEC/ for lots of details. Cool stuff.

Between that, the CVT and ECON mode, the car is doing a ton of mpg optimization in real time. This car is made for MPG. If you want a 'performance' Civic, you get the Si, with traditional vtec.

[Cobb]

The insights and I believe HCH the switch over point is 2500 rpms. Thats assuming the car is warmed up and its not floored. Otherwise it will engage it at lower rpms. I think for the SI its much higher like 4800-5700 rpms.

It seemed you got a testing method, so I didnt think it would be any trouble to test that as its something I wondered if using the lower end of vtec or the upper end of the stock grind gave better mpg. You know cam profile 1 vs 2.

[oldtamiyaphile]

Originally Posted by Cobb

Run Data:

Acceleration Run 1 Run 2 Run 3 Run 4 Avg. MPG Avg. Gallons Used
Slow (~1800rpm) 28.6 27 28.4 26.6 27.65 0.036
Med. (~3300rpm) 24.9 23.2 25.2 24.43 0.041
Fast (5000+ rpm) 19.9 21.3 21.1 20.77 0.048

I would argue that 1800rpm isn't 'slow' acceleration, that's actually probably around BSFC. The argument for accelerating 'fast' isn't to rev to 5000+ RPM, its' actually to use high loads to accelerate.

We know more RPM will use more fuel.

The real issue is shifting at the same RPM but varying the throttle opening. I've always found heavy foot low rpm (~2000) to work the best (carb, EFI, petrol, diesel, NA, or turbo it's always worked). Most people trying to save fuel are afraid of using the accelerator when they shouldn't. Although light throttle doesn't 'waste' fuel, if you can move faster for no economy penalty you might as well. I think this point would bring hypermilling to the interest of a lot more people too.