rv gas mileage

jplante4 wrote:

wa8yxm wrote:
Major differnce is the Triton, being a Ford, is a HIGH REV engine, producing the best power curve at a much higher RPM than the low-rev GM Vortec.

This may affect engine life,. but not so much MPG.

Physics says this isn't so. A higher RPM should burn more fuel. 460 cu in of air/fuel mixture going through the motor for every RPM, 15:1 air to fuel mixture indicates that higher RPM engines will use more fuel.

I had to explain this to a co-worker who bought her first car with a manual transmission. Her father told her to keep the revs high as possible. I explained that a lower RPM is fine. When she took mt advise, she commented that she was using less gas.

Partially correct. If comparing engines of equal displacement generating equal power, usually running a higher RPM will require lower manifold pressure, cause more pumping loss, and more frictional loss than running a lower RPM with higher manifold pressure. This is not true if the engine running at lower RPM is at or near Wide Open Throttle due to mixture enrichment at WOT.

Running at a lower manifold pressure (higher vacuum) means that although the engine may be spinning faster, because its sucking less air per rev due to the lower inlet pressure, it mixes less fuel in with the air. It's a slippery slope. Every engine has its sweet spots. Cam/valve timing and port configuration is very complicated and plays a big role in fuel economy.

Chum lee