How to accelerate in P&G mode?

[sonyhome]

Originally Posted by dosco

A driving technique wherein you maintain an average speed - say 65 mph - by "pulsing" to 70 mph and then "gliding" (with the transmission in neutral) to 60 mph.

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)

[sonyhome]

Originally Posted by theholycow

I can tell you this is not universal. In my VW, injector duty cycle goes down when I go from 80% (maybe 70%, maybe 90%, my foot is just not that accurate) to WOT. I'm at a loss to explain it.

Also, note that the surge is barely perceptible, you really have to be looking for it, at least in my vehicles. It is gentler than, for example, the torque converter locking in my truck (which itself is almost impossible to feel).

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...

[theholycow]

Originally Posted by sonyhome

However, for the CRV, it seems there is no DFCO, unless the Scangauge is wrong. Downhill in "D", I see 0.8GPH used, and up if the grade is steeper and the engine RPMs go up. Shifting to "2" or "1" increases consumption too (slower speed higher RPMs, duh! and no DFCO?).

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!

Originally Posted by sonyhome

Could it be that the computer switches mode in WOT[...]

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

[sonyhome]

Originally Posted by theholycow

The ScanGauge has to guess/calculate fuel usage. It can't measure GPH. 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!

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?

[theholycow]

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.

[dosco]

Originally Posted by sonyhome

Aero mods are better I thing for highway MPGs. (yet to be proven for my CRV)

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.

[sonyhome]

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.

[palemelanesian]

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.

[sonyhome]

Originally Posted by PaleMelanesian

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

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:

One of the key elements behind the new Honda CRV’s excellent fuel economy is a 12 per cent lower drag coefficient. A significant part of that reduction is down to careful analysis of the air flow beneath the car. The use of strakes ahead of the front and rear wheels, cover panels beneath the cabin and a rear undercover decrease levels of turbulence.
The Honda CRV’s slippery body also keeps down wind noise, further helped by the curved shapes of the A-pillar cross section and door mirrors, and by using double seals around all the doors.

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)

[palemelanesian]

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