For me P&G works better in the city with my DelSol car. My CR-V slows down too fast doing P&G on highway. Aero mods are better I thing for highway MPGs. (yet to be proven for my CRV)

Could it be that the computer switches mode in WOT, and computes the optimal duty cycle for acceleration, whereas at 80% it does what you tell it and runs too rich without returning any benefits in improved acceleration? (by too rich I means spend too much gas for no extra return, not spitting out unburned gas)

I'll try to look for that surge on my Del Sol. 875RPM is darn close to idle, no suprise there...

The ScanGauge has to guess/calculate fuel usage. It can't measure GPH, there's nothing in the OBDII standard for that. I assume that it guesses based on O2 sensor reading combined with MAF, but if so then it's probably correct and your Honda has no DFCO. I have a hard time believing there's no DFCO on the CRV!

Could be. I don't know, but I hope to find out eventually.

How can the SG compute MPG reliably and not be able to compute GPH? If what you say is true, then MPG results would be way off when coasting downhill (hard to prove, try downhill coasting for a full tank! LOL). People report that the SG should display "9999" in DFCO, right?

Well is there DFCO for other slush-box A/T vehicles in general?

My slushbox GMC has DFCO, though it's not very useful -- it only comes on after ~10 seconds of non-DFCO engine braking (which uses lots of gas).

The inability to measure GPH is the main weakness that has held me back from getting a SG. That inability is confirmed, I'm 100% sure that OBDII and the SG does not support fuel rate measurement (though I'd still love to be proved wrong), and that the SG calculates it. I asked and researched a lot (here and elsewhere) until I was sure of it.

I don't think aero mods are *bad*, but I wouldn't put much stock in aero mods drastically reducing your fuel consumption. I recently did some calculations and found with a coefficient of drag of 0.28 the power consumed by drag at about 65 mph (assuming a standard atmosphere at 70 degrees F) is something like 16 hp.

Side note: assuming a coefficient of rolling resistance of 0.030, I calculated the power consumed by rolling resistance as something like 30 hp(!!).

Anyways, using P&G and some very mild aero mods (upper grill block) I have been able to hit up to 45 mpg. I'm not convinced that any single (or even a bunch of) aero mod would improve my mileage as drastically as implementing P&G.

I recently turned a buddy on to P&G and he has been hitting 50 and 60 mpg in his VW TDI.

Hollycow,

If DFCO activates after 10s, I would've seen it by now if it is either visible with the SG, or can be felt by the driver... Maybe rigging the DIY fuel rate monitor with the SG could help detect if the SG is lying...

Dosco,

I didn't mean P&G is not usefull on highway. I don't really know.

However, for my Gen'2 AT CR-V application I feel there's a lot of roll resistance and I suspect a lot of power lost thorugh aero at 75MPH: The drag coef. must be higher (like 0.30 maybe?) and the surface bigger too. I can't pump the tires much because of tire specs and SUV roll safety. All I know is P&G for an AT CRV on highway doesn't seem that feasible. Slows down too fast.

16HP on air friction sounds quite low. But then again power dissipation must be squared with speed or something, which would explain why a 120HP car can't go much past than 120MPH.

According to this link, the CR-V has a cd of .5! That's huge, combined with it's larger area.

P&G works on the highway, but still the slower the better, unless you drive an aerocivic. 45-60 P&G has given me 75mpg over 150 miles. Steady 65mph cruise gives me about 45mpg on that same segment.

and aerodynamic drag is proportional to the CUBE of velocity.

You might be quoting the coef for the Gen'1 CR-V (online mentions an unconfirmed 0.44). The Gen'2 can't be that high. Looking online, people quote 0.34... The Gen'3 CR-V Cx is quoted as 12% less than previously which would mean 0.30 or 0.29...

Gen'3 data:
Gen'1: Cd 0.44, Up to 2001, boxy, smaller size
Gen'2: Cd 0.34, 2002-2006, more rounded, still boxy, bigger size
Gen'3: Cd 0.30, 2007 & up, very curvy body, probably less space inside now

If diesel was available in the US, the CR-V would sell with the 2.2L iCDTi engine and get 48.7MPG HW (Gen'2) and 49.6 HW (Gen 3)

I dunno. That's just the first search result I found, and it doesn't look very reputable.

I'm pretty sure this is exactly true, but I want to add something to help people not get confused.

There are scantools that mechanics use, that plug into your OBDII port and report a lot of things. Some of the scantools report injector data. This seems to contradict what you said, but not really. I believe the folks who made the scantool paid a licensing fee to one or more car makers, and were given data about the proprietary method that maker uses to report injector data via the OBD port.

In other words, the data is not part of the OBDII standard, and therefore it's not easy to get at, even though it does exist, on some cars.

I think Scangauge decided to not to try to get at the data that way, presumably because it would have been difficult and added expense to the product. Maybe a lot of expense. I wouldn't be surprised if the car makers demand a licensing fee on a per-unit basis.

A lot of cd data is here:

https://web.archive.org/web/200412040...rmayf/tbls.htm

I don't see the CRV, but maybe there's some similar vehicle, to make a comparison.

You are most likely correct. It seems extremely expensive to get manufacturers' proprietary stuff like that.

And, here's proof that the SG definitely calculates/guesses fuel rate:

[QUOTE=monroe74;106420]A lot of cd data is here:

https://web.archive.org/web/200412040...rmayf/tbls.htm
QUOTE]

Cool!
The Del Sol has a Cd of 0.42, but tiny frontal area. Could work on that!

The Ford Explorer has a Cd of 0.45, in line with what I found floating around for a Gen'1 CR-V, reported above.

How do you figure that?

drag = 1/2 rho Cd S V^2

rho = air density

Cd = drag coefficient

S = area

V = velocity

In metric system:

rho: kg/m3
S: m2
V: m/s

Therefore drag = kg.m/s2 Are these the right units?

https://upload.wikimedia.org/math/7/2...e3a20cb4b5.png
https://upload.wikimedia.org/math/1/d...54d626ea78.png

The small v is just a unit vector that points the direction of movement in 3D space, doesn't change our computation for our application, rho=1.293 kg/m3. A means area, same as S (for surface) above.

from https://en.wikipedia.org/wiki/Drag_%28physics%29

Bottom line: 2X speed = 4X drag force, 3X = 9X force etc. Squared indeed. However, the power dissipated seems to be cubed... but you have to take into account the total time to travel a fixed distance, to figure out your net energy cost (you cube but then you actually go faster on that distance). Argh help.

BTW:

If you know the drag % of the underbody (or the wheels), and the drag of an air dam, you could tell if adding an air dam is likely to provide any benefits (increasing the frontal surface S, aka A, but reduces Cd by some amount)...

Yes, if I'd pulled my head out of my arse I would have taken the next step and calculated the work equation. Pale is correct. I'm a dullard. D'oh.


I think it's a bit more complicated than that, since the drag is a function of the entire body, and the interactions between the components is not linear. But I think your point has merit....

Time to wake up this thread.
 

So I did a P&G experiment on my comute:

- Commute: 3 miles one way, with lights, 35PMH limit surface streets, return often with 1.5miles highway (next exit) and lights & stop sign. Night twice a week, drive to the gym, about 10 miles R/T surface street.

Experiment result

- Old method: Fast acceleration from light, 1st/2nd/3rd then coast down, 3rd or 4rth gear short pulse, then glide. Result is accelerations are short followed by long glides. Shifting usualy around 2500RPMs.

Result: 35MPG over 338 miles

- New method: Slow acceleration from light, 1st/2nd/3rd/4rth/5th, fast shifting to stay below 1500rpms, but anemic acceleration. I don't really do WOT acceleration, but my foot is pretty heavy after the 1st gear. End result is I spend more time accelerating than coasting.

Result: 35.22MPG over 191 miles

Bottom line:
Seems like both techniques work about the same in terms of fuel economy. However the new method supposedly with better MPGs is harder to drive I find because the car is less responsive. I am more likely to miss a light.

I wonder if I should try one run with normal driving, no P&G. I wonder if I'd fall back sub 30 or not, with somewhat controlled driving conditions. City EPA for my car is 25MPG (new rating) so I'm 40% overjust from P&G and some awareness of lights.