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Old 12-17-2008, 12:19 PM   #3 (permalink)
mobilerik's Avatar
Join Date: Nov 2008
Location: San Diego, CA
Posts: 108

rik's prerunner - '03 Toyota Tacoma Prerunner Double Cab TRD 4A
90 day: 29.68 mpg (US)
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How to Calculate Your Optimal "Pulse-to-Glide Ratio"

Calculating your Optimal "Pulse-to-Glide Ratio" depends on your GPH during acceleration and glide.

For instance, Pulse in the Prerunner uses between 3.5-4.5gph. Idle during Glide uses about .35-.45gph. I want to compare that to DWL at 52mph, which uses in the vicinity of 1.3gph.

For those who want to see how to compute this:
  • P&G Gas Used = PulseRate x PulseTime + GlideRate x GlideTime
  • DWL Gas Used = DWLrate x DWLtime

Plug in your averages:
You'll need to choose a cycle time to compare, ex. 5 second pulse and 10 second glide = 15 total seconds.
  • P&G gas used = 4.0 gph x 5 sec + .4 gph x 10 sec = 20 + 4 = 24
  • DWL Gas Used = 1.3 gph x 15 sec = 19.5
So you can see that using a 5 to 10 pulse-to-glide ratio (or 1 to 2) is not fuel-efficient for me. It turns out that I can break even around a 4 to 9 ratio, and I try to shoot for 4 to 10 or 5 to 12. If I don't think I can get a 10 second glide out of it, I won't bother. Of course your numbers will be much different. Mine reflect the difficulty of accelerating and coasting in a 3600 pound brick.

You can of course use the same formulas to find ratios for any variations of P&G. For example, sometimes I use DWL at a throttle position too low to hold speed, then gas just enough to continue the cycle. This only works for me if I can limit gassing to about 1-2 seconds to get a 20-30 second slow deceleration out of it... which generally only succeeds for me downhill. If you're in a small car, your ratios will be much more favorable.

NOTE for those bothered by units of measurement: You don't need to convert to "hours" to make the above calculation useful. The final units you'll be comparing are technically "gal/3600" -- it's just scaled. You can think of the above as telling you how much gas you'll use if you do 3600 P&G cycles.

Also note: These calculations also don't take into account any other losses during a P&G cycle. For example, rev-matching. As it is, my Tacoma automatically rev-matches coming out of Neutral Glide. It's awesome. But if I'm aborting the glide at too low a speed, it'll sometimes miss overdrive, and I have to give it a "panic pulse" to get overdrive back. If I wasn't "panicking" I could probably read the GPH of the extra pulse and add that in as well.

Last edited by mobilerik; 12-17-2008 at 06:02 PM..
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