mpg on my 340
Once again I'll post my 2000 Dakota R/T 5.9 CC Mileage.
At 60 MPH 2000 RPM through the O/D effective final drive of 2.8x (3.92x.73) EVIC says 17 MPG.
At 50 MPH 1650 RPM EVIC says 23 MPG.
EVIC verified by actual math to be within .5 MPG over three full tanks.
So no, peak torque is not peak MPG.
If peak torque was the place to cruise at,our powerful street sbms would be cruising at between 3700ish and 4500ish,I think.And you have proved the Mpg to Rpm relationship.
Peak torque is more important for your rotor tiller.
I have had good results with gearing for peak vacuum when in neutral. If it vacuum-peaks at 2200, I would consider that about the lowest fuel-efficient cruise rpm. A similar engine that vacuum-peaks at 1400 will usually get better fuel mileage than the one that peaks at 2200. I proved this with my engine, by having run it with 3 different cams from 270 to 292 advertised durations. The Scr was adjusted with each, to keep the Dcr within about a quarter point. The final drive ratios were adjusted with each, to work with the peak-vacuum. The cruise fuel-mileage varied widely. Of course the 292 was the worst, and the 270 was the best.The AirGap, and Eddies, stayed on all of them.As to cruising,Nothing else was changed except the cams and the final drives, and occasionally the carb. With the 270cam,I also experimented with many different final drives. At one point I was down to 1.53 (2.76 x .71 x .78). this made 85mph = 1700, and 65 = 1300. This cam could pull phenomenal mpgs.It also had a ton of torque. More than the other two,especially the 292. This 270cam was pretty happy with a starter gear around 10.0/1. It loved 11/1. Now, 12/1 was just too low,and the 13.28 (3.09 x 4.30s) was wild and ridiculously low and that rear was not in there very long. And while 9/1 was acceptable in most cases, the 11/1 was the favorite.
In case you are wondering, these are the chunks I tried;2.73/2.94/3.23/3.55/3.91/4.10/4.30/4.86/5.13. Eventually; the 5.13s spit out two teeth,the 4.10s I traded away for the 3.55s,the 3.91s got noisy and I was unable to re-adjust it quieter so I junked 'em,and the 4.30s are now sold.This is now going on 17 years since I started. (I still have the 4.86s;any takers?) The various engines have also been tried with trannys having lows of 2.47/2.66/3.09.
--My favorite will always be the 270cam with the 3.09-o/d box,3.55s, and the GearVendor splitter. This was an extremely nice combo, for every conceivable driving circumstance..This thing vacuum-peaked very low,and was quite happy with; a 1.97 final drive,and a 10.97 starter.It cruised at about 1600Rs, having vacuum-peaked a little earlier.
--I would still be driving this combo, except the cam dropped 2 lobes when they took the ZDDP out of the oil.It would be most excellent with my final gearing as it is today; 3.09-1.92-1.40-1.09-.78od, and split %s of 62-73-78-71 into od.
