I've started data logging in the Durango more steady than I was over the last few days and have been getting some interesting data. It's no wonder this thing gets such low mileage, it revs low and doesn't use much of the engine's power at all.
A snapshot of the middle portion of my trip yields the following(average in bold):
58 mph (42mph)
1610 rpm (1219 rpm)
21% calculated load (not absolute throttle position) (8.7%)
33 degrees of spark advance (34 degrees)
201 degrees F coolant temp
111 degrees F intake air temp (38 degrees ambient this morning)
Distance: 13.2 miles Time:~25 minutes
The simple removal of the cold air snorkel on the stock air box was good for a lot of temperature rise it turns out(a good 50+ degrees).
Even steady cruise in this thing is next to nothing. For example, calculated load at idle is 4% and to keep 40-42mph on the way to the freeway on the first leg of the trip I logged a load of 6% under steady cruise and 17% to get up to that speed. My peak load for the whole trip was 33% @ 2232 rpm to get up to highway speed relatively quickly to merge so I could get into the far left lane before traffic got backed up at the next exit on the right.
A hybrid system in this thing would have to hold a fair amount of energy though. This is a vehicle that weighs a hair under 5k pounds with nothing in it and is equipped with an engine that makes 230 horsepower at 4,000 rpm and 330 pounds of torque at 3,200.
Now, in regards to the smaller engine, the 3.9L V6 this thing was available with made 175 horsepower at 4,800 and 230 pounds at 3,200 and is EPA rated 13/17 vs the 5.9L V8 at 11/15. It's roughly a 33% decrease in displacement/power for a ~15% increase in economy.
The energy density quoted by EPA for their accumulators is 50 KW seconds per gallon. I would think a 10 gallon accumulator would give you something like 650 HP seconds of energy. Remember this is available instantly, you dont have to wait for your engine to rev up.
It takes about 17 revolutions of your wheels to panic stop in 130 feet in your truck at 60 MPH. Thats about 4-5 seconds.
The UPS delivery vehicles in operation weight 26,000 pounds gross and have 83 gallons of hydraulic fluid to operate their systems, thats 5 times the mass of your truck, so it works out to about 16 gallons of hydraulic fluid instead of my quoted 10. Of course the size shrinks proportionately to the pressure.
Now consider you have the accumulator energy added to you engines max power it you really want blistering acceleration. Put a 2.5 liter Gayle Banks built 200 plus horsepower diesel engine in your truck. That power can be added to your stored accumulator energy, at the instant you begin to deplete the maximum accumulator pressure.
The same engine can loaf along at 1 gal per hour fuel consumption producing enough power for your truck to maintain about 45-50 MPH, higher with some real aero work, maybe 55-60 MPH.
0-60 in 5 seconds and 50 MPG combined sounding good?