Acura tunes the vehicle for it. Some people argue that it's "safe" to run the cheaper stuff... But at a minimum you will not get the same performance, and at worst you could affect the longevity of the engine.
Now for other vehicles where the manufacture recommends regular... Just run regular. They won't benefit from a higher octane. But when the manufacturer specifies premium, heed their advice.
Your car does not even have an Option...
Open your fuel door look at the sticker on it:
USE PREMIUM FUEL ONLY... I mean, Seriously! There isn´t a bigger hint that the one the manufacturer of your vehicle printed on it.. Literally the people who made that engine and entire vehicle drivetrain specifies to use Premium Gas ONLY.
The only ones that should be asking this question is the ones using a 3rd gen MDX that has Regular as an Option.
Personally, I run only premium around town or any time I'm in any real mountains. OTOH, I am OK with running regular during long, flat cross-country trips where the engine is never operating anywhere near the conditions that will require maximum power. I came to this conclusion by looking at the ignition advance while driving a given (high) speed on a flat, windless interstate, running the end of a tank of premium. I then pulled in and filled up with regular, and checked again in a few miles (after any residual premium in the tank and fuel lines would be replaced with regular. A quick check of the ignition timing (using my phone and the Torque Pro app) showed the same advance, indicating to me that the engine hadn't had to retard the timing to compensate for the lower-octane fuel during that particular scenario. I don't worry about hurting the engine, since even if I do push it, it's got smart enough systems to retard the timing to prevent detonation. This gamble is well worth it to me since I average over 20,000 miles of interstate driving a year, and the difference in fuel cost is HUGE. In the few years since I've owned the car, this has probably saved me $1500-2000, which would cover a host of problems (which haven't happened, of course). I'm not saying that everyone should run regular, but just what I've experienced with my own vehicle.
As a side note, those who use regular around town or when driving anything but interstate style probably end up getting poorer gas mileage (because of the adjustment the engine computer does), which will offset at least some of the savings from cheaper gas.
We should have two forum stickies. One that says "Premium fuel only" and one that says "It's okay to use regular". You aren't going to change people's minds, so simply click on the one that sides with your belief.
With that being said, here is my opinion from the Gospel of Mark: Regular 87 here on my '04 and 230k miles, 17 mpg around town/22 hwy. I don't notice a difference in acceleration because it is a freaking SUV, not a sports car. And I always get clean oil reports from Blackstone showing no unusual wear of any of the metals , so I know the engine should be good for another 100k+ miles.
Folks, the 2003-2006 has the same compression ratio as the Honda, and the 2001-2002 is even the identical engine used in the 2004-2007 Saturn Vue, all of which do not require premium. If you are towing or climbing steep grades, use premium. Otherwise, you will most likely be fine using either. The engine will take care of itself.
2004 PILOT LX EX
ENGINE Type: SOHC 24-Valve, VTEC V-6
Displacement (liters) 3.5
Displacement (liters) 3.5
Horsepower @ rpm (SAE net) 240 @ 5400
Torque (lb.-ft. @ rpm) 242 @ 4500
Compression Ratio 10.0:1
Valve Train: SOHC 24-Valve 3-Rocker VTEC™ n
Fuel System: Multi-Point Fuel Injection n
Ignition System: Electronic w/Immobilizer n
tl;dr - Do your own research. Don't just ask questions and listen to other people's uneducated opinions. Look for facts and proof and formulate your own opinion based on those facts and your own experience. I have made my choice, and my oil analysis reports show me that my choice is fine for my vehicle: https://drive.google.com/open?id=0B7qpoUIBLY38Y0NIZUxfNkprcU0
BTW, here is what other respectable automotive sources say:
With all of that being said, I will also include this article from a Ford engineer. He has a good point that a lot of it depends on the vehicle. For me, I have found that the MDX engine and my driving style while in that MDX has no problems with 87 octane and no impact to fuel economy (unless I am going to tow or travel to the mountains). My 1994 BMW e36, on the other hand, is more susceptible to knock and I can hear it for a split second before the computer kicks in when I am starting off on an incline or climbing a hill, so I run 93. Of course I also hit WOT in that car and frankly enjoy hearing the engine/exhaust sound made at 6500 RPM lol.