Those of you that have scangauges can you share with me the criusing RPM's at 60, 70 and 80 MPH on flat terrain? Is there a rule of thumb on the freeway of instant MPG vs RPM, examples: 20 MPG Instant = 3500 RPM, and 25MPG= 3000 RPM. Not having a tachometer is something I miss greatly from my previous cars. I don't miss the mileage though. Thanks, John
The RPM varies according to load more than speed. Now you may think I'm being a smart allic or something, but "hills" you don't even know you're going up will affect the RPM. I've seen about 1500 RPM to 5000 RPM at 100 km/hr (about 62 MPH). Lower RPM almost always corresponds to better mileage, but you really can't control that in the Prius, other than just slowing down.
It's not so much the instantaneous MPG, it's the iMPG/MPH relationship. At highway speeds, keeping the iMPG at least half the vehicle speed generally should keep your RPM below 2400. I can't say what it is at higher ICE speeds. I try to avoid anything above that, and when I cross the 2400 threshold my focus is more on getting it back down than analyzing the instruments. Having said that, I finally have my CAN-View's data capture feature working. I'm at the river for the weekend, driving back tomorrow, and I expect to log the entire trip. After that I should have a better handle on the sustained relationship between iMPG, speed, and RPM at (close to) highway speeds. I plan to post my results in this thread. At slower speeds, RPM is about 2200 when iMPG > MPH/2. I made a chart earlier this week with CAN-View data from a segment of my commute: As you can see, the only time iMPG appears to drop below half the vehicle speed is when I pushed ICE speed over 2200 RPM. I say "appears" to drop, and iMPG has a question mark in the chart's title, because iMPG in the chart is calculated from some uncertain unit of fuel flow in CAN-View. Jay Groh (aka TheForce) and I have been working on trying to figure the right formula to convert the mystery units into gal/hr. I think he figured it out, but I plan to check it against real time data in my drive tomorrow to verify. Finally, back to your question, real-time visual monitoring of RPM suggests I generally can run 1600-1700 RPM pretty consistently on flat terrain at 60-70 MPH. That's something I'll be able to document better with my data capture, assuming I even get that fast.
Great info Jim. Really appreciate it. My lifetime mileage is 48.3 across a span of 6K miles (since Jan 1). If I keep the ICE under 2400 rpm's going up hills (sometimes hard to do thru the CA mountains) it should help me get above a 50MPG average by the end of the year. John
Thanks, John. Hope it helps. To help the hill-climbing, I try to get as much of a running start as possible. If a downhill precedes it, I use warp stealth whenever possible to capitalize on available kinetic energy. Then on the uphill I let speed decay as needed to keep it below 2400. All within safe and legal boundaries, BTW. Between driving technique and warm weather, 50 MPG should be a done deal for you soon. Good luck!
