How do I maximize MPG? from miles per hour
I've been so very lucky to have this incredible teaching opportunity come my way...I'll be teaching the children who travel with the Carson and Barnes circus...shortly, I'll be leaving Texas for Wyomi...
Forum Discussion
The 6.8 V-10 has an almost flat torque curve, 400-410 lb-ft from 1900 to 4000 RPM, in the tune used for the E-450. The 420 "peak" is just a little bump where exhaust tuning and the tuning of the high-rpm section of the intake manifold reinforce each other. Maximum engine efficiency (lowest specific fuel consumption) will be when producing maximum torque anywhere in this range, so it is not like you have to find a RPM sweet spot with the V-10, you just have to find a balance between using power to overcome drag, and covering ground. That's why MPH for best MPG might be very low, as there is no engine efficiency penalty for running the engine way below the torque "peak."
If you need to get up a hill, the 6.8 is almost as efficient producing 300 HP at 4000 as it is producing 250 at 2200, but if you let it run on up to 5000, it won't give you any more power and will use more fuel trying.
The E-450 tune for the 5.4 has a definite sweet spot 2100-2800 RPM, but torque doesn't fall off seriously until after 4000, where you have 95% of peak HP, and again you have another 1000 RPM with full power but less economy. The 5.4 has some of the same engine tuning tricks, and can be driven about the same as the 6.8.
I've not seen a torque curve for truck tunings of the 5.7, or even the 6.0 for the Express, but without variable valve timing or variable intake manifold lengths, you usually get a smooth round curve, where a relatively flat torque peak identifies the center of a range of maximum efficiency, and you have about 800 RPM range around that without much difference in torque. Ford's 4.6 and Chevy's 4.8 look like this. You can get quite a bit more power (up to 80% of peak) with a 800 RPM increase over peak torque RPM with little hit on efficiency, but torque will fall quite a bit, and specific fuel consumption go up, before you get to the RPM for peak HP, which might be close to 5000 for these smaller V-8s.
If you need to get up a hill, the 6.8 is almost as efficient producing 300 HP at 4000 as it is producing 250 at 2200, but if you let it run on up to 5000, it won't give you any more power and will use more fuel trying.
The E-450 tune for the 5.4 has a definite sweet spot 2100-2800 RPM, but torque doesn't fall off seriously until after 4000, where you have 95% of peak HP, and again you have another 1000 RPM with full power but less economy. The 5.4 has some of the same engine tuning tricks, and can be driven about the same as the 6.8.
I've not seen a torque curve for truck tunings of the 5.7, or even the 6.0 for the Express, but without variable valve timing or variable intake manifold lengths, you usually get a smooth round curve, where a relatively flat torque peak identifies the center of a range of maximum efficiency, and you have about 800 RPM range around that without much difference in torque. Ford's 4.6 and Chevy's 4.8 look like this. You can get quite a bit more power (up to 80% of peak) with a 800 RPM increase over peak torque RPM with little hit on efficiency, but torque will fall quite a bit, and specific fuel consumption go up, before you get to the RPM for peak HP, which might be close to 5000 for these smaller V-8s.
