According to this article:

http://www.usatoday.com/money/autos/...1-accord_x.htm

Presumably this is true for the HAH as well, so does this mean that the car is good for 263 hp on premium.

I'm just itching to try it and see if it makes any difference, although I know it's not very "green."

Your comment that it is not green is right on.....Why is HP important (unless you run at the peak of the HP curve all the time)? Why is torque important unless you are constantly pushing for a better 0-60 elapsed time? Why then does it matter the impact of octane on performance? The real key is what really matters to driveability as you measure it (most of us by MPG). Sorry.....but I obviously do not understand where you are coming from.

Because ... sometimes it's just fun to put your right foot to the floor, feel yourself get pressed back into the seat and tear along the highway or some windy back road, which the abundance of power in the HAH allows for with ease. Another 10 hp and 10 ft-lbs would certainly help in that endeavour. Then when feeling slightly guilty about such wanton waste of fuel you can throttle back and still get 40 mpg + cruising sedately on the highway.

On the other hand, if the V-6 engine derates itself by retarding timing to avoid engine knock when using regular unleaded maybe it would be slightly more efficient using premium fuel instead of regular. This may be one of the few instances that premium actually does have a positive effect on fuel economy.

...maybe for the same reason some choose big roomy hybrid SUVs and avg. 26 when they could be getting around town in the same way in a cramped little Prius and averaging almost twice the mpg...having a smooth reving engine with lots of available power when you need it (or want it) is fun...it's the driving experience (which just happens to be greener), not just economical transportation.

With the extents engineers will go to get small gains in performance, I'm somewhat surprised that Honda would not advertize the "premium" horsepower ratings, as well as the ability to run on regular gas to save money as an option. 87 octane could still be listed as minimum reccomended, with a comment that 91 could be used for extra performance.

I expect that it would. On most engines buying the premium fuel is a waste of money as the compression is too low for the octane to matter anyway. Although from a sheer cost-benefit perspective I doubt any MPG benefit would be able to pay back the extra cost for the premium fuel, the ability to fill up with premium every once in a while for a performance boost would be great.

I agree, My old Integra GS-R was designed to do just this, along with most modern engines. It said in the manual that if fuel below an octane of 91 was used, the engine would retard timing, lowering performance and efficiency. If this were the case, why would Honda not take advantage of the potential for a higher FE numbers? I suspect that many mainstreem Accord buyers would be put off by the need for premium fuel.

Something does not sound right. High octane fuel is typically used for high compression engines, and is required to prevent pre-detonation. It is actually less combustable (more stable) than lower octane. Does anyone know what the compression ratio is for the Accord v6?

For the HAH, the extra '10' HP and '10' lb ft. would contribute to better fuel effeciency at all speeds. Yes, it would be noticable when you put your right foot into it, but for normal driving it would show up in MPG.

Compression ratio for the HAH V-6 is 10.5:1; that actually seems quite high.

10.5 to 1 - WOW! Thats surprising. In that case the Accord could definately benefit from higher octane. Are you sure about that Ratio? The LS2 Corvette is only a little higher (10.9:1) and it beats my LS1 Z28 (10:1). If you run either of those cars (Corvette or Camaro) on anything less than 93 your mileage craps out and the performance bogs.

Interesting!

I have my car registered on Honda's Ownerlink and the 10.5:1 compression ratio is reported in the technical info provided there.

I think I'm going to run a few tanks of premium (the extra cost is only about $3.20 per tank) and see if there's a noticeable difference.