Okay, just want to have a little fun here without starting a war.

When I first joined GH back in February the HCHII was hanging at 45 mpg in the COMPARE forum. Then it ticked up to 46. Somebody must have posted some new tanks, because today I notice it ticked up to 47 mpg (rounded up).

The PriusII is now a "mature" automobile, having gone through a couple of summers and winters. I wouldn't expect it's mileage average to change much, though I admit I haven't been watching it carefully. It's currently at 48 mpg (rounded up).

The HCHII, on the other hand, is just coming into its first summer, following lots of winter driving.

So, what do you think? Will the HCHII catch the PriusII, or will the Prius surge ahead? Do I dare ask if HCH has the potential to pass it?

Or, an alternate question if you're not in the mood for wagering; what do you think the potential for the HCHII is in the mileage database? The Prius?

Toast I agree that summer will raise the HCH2 while as you say the Prius is mature so summer will have less impact. The gap may be too much to overcome. The Prius has a pretty good lead.

I can single-handedly increase the gap! I just finished a round-trip drive San Diego <-> Phoenix at speeds usually between 82 and 88 mph, and I have to say, this car gets ludicrously bad mileage (for a car of this type) when going anything above 80; I haven't calculated the final trip mileage but it's likely around 33 mpg. The car's weak engine just could not keep up, especially when scaling some steep mountains where I had to floor it at 6000 rpm just to maintain 70 mph. Also, the steering is very wobbly and nervewracking above 80.

Although my recent oil change might be partly responsible; since I plan to trade the car in soon, I just used official Honda 0W20 oil, which is mineral crap.

Wow, well, good luck with your TCH. I'm sure the larger engine will serve you better above 80 mph. I don't think Honda had 80+ in mind when they designed the civic....

Yeah they clearly didn't. The 93-hp engine is very efficient in low-load situations (i.e. cruising at 65 mph or below) but its efficiency lowers dramatically as load increases, like with high-speed cruising... more powerful engines don't suffer as dramatically. Plus the TCH has Toyota's HSD which I find superior anyway (even the 76-hp-ICE Prius does well at 80+ mph) so we'll see. It'll definitely be interesting to compare.

i think the hch.ii will catch the prius. i don't think it will surpass.

i think the potential for the prius will stay right around where it is at 47.5mpg. i think the potential for the hch.ii will be right about the same as the prius, maybe a little less.

I think the HCHI will soon uptick to ~57 mpg, rounded. Maybe 56. We'll catch you yet, Prii.

Pretty much every car gets bad gas mileage above 80 MPH. That is a pointless comparison, IMO. I am skeptical that the Prius will do that much better at such high speeds, especially going over mountains and maintaining 70+. Probably the Insight would do the best, simply due to aerodynamics and the fact it is so light. But still, why drive in a non-fuel efficient manner and then complain about bad gas mileage?

Also, while a more powerful engine may do better at high speeds, they do worse at low speeds, so the trade-off is most likely going to be for the worse. People with the HAH seem to be struggling to get 30+ MPG in the first place, so in that light your mileage numbers don't look that bad.

Try it and see. There are some places where Priuses can be rented, or a dealer might have a demo available.

As for your low speed allegation, that also is false. Wayne Gerdes owned an Insight and hypermiled it to 92.5 mpg, but he hypermiled a Prius to ~110 mpg.

His point is that the relative mileage at that speed is bad. While I generally won't drive as fast as 88, there are times when driving 78-80 is just a lot more practical than driving 60. An example is with long road trips with multipel peopel. It's worth an extra $5 in gas to save an hour of driving time in my opinion. When you're only driving 4 miles on the freeway though, it's probably not worth accelerating all the way up to 80 and braking back down, as the time savings would be minimal. Faster cruising speed is defintiely a major plus on very long drives though.

While the extra aerodynamic drag is there no matter what, meaning absolute MPG will never be as good as driving slower, good engineering can reduce a lot of the powertrain waste associated with those speeds in certain engine designs. In the case of the Civic, the engine is actaulyl pushed out of its fairly narrow efficient powerband, making it achieve worse mileage than even some non-hybrids of similar size, driven in similar ways. This is also I believe why things like accessories, better handling tires, and other modifications have a much more pronounced effect on hybrids than non-hybrids.

This is why I think someone should come out with a turbocharged miller cycle hybrid that is tuned for better highway mileage. Boost pressure could be designed to kick in mostly at 2000rpm+, and the electric motors could be used to mask the acceleration lag. Things like the transmission, the turbo, and the electrics could all be controlled to save gas in the city, while still providing a more powerful, sustained engine load on the freeway without needing to rev the engine as fast.

Also, the Camry hybrid from all indiciation seems to be a very good balance between engine and electric power as well, as most magazine tests that have driven it in side-by-side tests have shown it achieves only a couple MPG lower than the Civic Hybrid, much closer to EPA, despite being a much larger car with much higher peak power. The Toyota HSD design can also minimize the larger engine's low-speed inefficiency by shutting it off more and using more electrics, and still benefit from the slightly larger engine size on the freeway. The V6 used on the Accord however is probably a bit too much engine for that car, by comparison.