I know some of you are going to disagree and say I'm crazy, etc., but here goes.

I've experimented with regular (87 octane) gas in my RX for the last 2-1/2 months (approx. 3000 miles), and this is how it affects MY RDX (maybe not yours, but mine):

Mileage

I've seen very little if any difference in gas mileage between regular and premium fuel.

Engine Smoothness

Here is where it begins to show some difference. In small throttle transitions, such as when muddling along in stop and go traffic or making small changes in speed from coasting to throttle-on situations, there is a noticeable jerkiness that doesn't seem to be there with premium fuel. This makes smooth operation more difficult in these situations. It almost feels like there's some slack in the drivetrain.

My theory is that the extra octane value of premium fuel makes it produce power slightly more readily and the engine is better able to "smooth over" these small throttle transitions.

Transmission Smoothness

In normal acceleration (such as from a stoplight), the transmission shifts "harder" when running regular gasoline. It's as if the engine/transmission is straining a little bit to get to the next gear and has to slightly force the shift. This results in slightly "lumpy" operation - you can feel the shifts more so than when running premium fuel.

Here again, I think the engine's ability to smooth over small engine speed changes when using higher-octane fuel makes for a slightly smoother shift.

Combine this slight shift lumpiness with the engine smoothness lumpiness described above, and the vehicle just becomes a little harder to drive smoothly.


Now, if you always gun the engine and drag race other cars when you leave stoplights, you may not notice this. But in what I consider normal driving, I get smoother operation from premium (91 or 93 octane) gas.

This isn't a dramatic difference in driving dynamics, but if you're as sensitive to your vehicle's sounds and feel as I am, you'll notice it. And it didn't show up on my RDX right away - it was probably 3 or 4 tanks into the "test", so it takes a bit to show up.

Is it a big deal? Probably not for most owners. For me, it's noticeable enough that I'll switch back to premium every couple of tanks, or maybe just go back to premium altogether. This last tank of premium has smoothed things out again and I like the feeling.

Again - your RDX may be different. Or maybe you just haven't noticed it. If you like how yours is doing on regular gas, stick with it ... if you've noticed a little lumpiness in its operation, try some premium again.

Interesting theory....

your experimentation is a big DUH!!
the RDX has a high compression engine.
it needs the high octane!!

^ Justn...

Mike that was good experiment.

http://www.honda.ca/accord_sedan/specs
It's not a high compression engine by today's standards. I'd say more like average. 87 Octane for the Accord and 91 for the Acura when both have the same compression ratio? I know its been covered to death already.

direct injection, different mapped ECU, etc.
even if I did have a new accord, I'd still run premium.

I bet you would see better drive-ability with premium on the new accord, much like how Texas mike saw an improvement with his RDX

Mike_TX,

Thanks for your observations. I would have to say that my experience would seem to match yours. When I picked up my RDX a few weeks ago, I was surprised that the drivetrain didn't appear to behave as smoothly as it did during my test drive - very similar to your description. Initially, I chalked it up to switching from driving a Pilot to now driving an RDX, especially since I had to adjust to the way the electric power steering felt or didn't feel.

While there is no way for me to know what gasoline grade the dealer used for my first tank, I do know that the next few were 89 for one and 93 for the other two. Using the higher octane rating seemed to make the drivetrain operation smoother. The last two fill-ups have been 87. This week I started to notice the same drivetrain behavior that I had right after I picked it up from the dealer.

I'm leaning toward switching back to premium for the next tank to see if I can match your better results.

On the mileage side, there really hasn't been a noticeable difference - My average as reported by the car has been between 26.8-27.4.

Thanks, Techgirl. I freely admit that it might just be "my car", but give it a full tank or two before you make a firm decision about it. The ECU takes a little time to adjust itself (although the knock sensor is operational at all times), so you might not notice a difference immediately.

I know this is a sensitive topic (hence my tongue-in-cheek title), since some of the membership believes there is NO advantage at all to using premium fuel in spite of the mfr's recommendation. I had decided regular gas was fine until I started noticing this "lumpy" performance, and I'm now on the fence.

To restate, anyone perfectly happy using regular gas is encouraged to continue to do so - I'm merely reporting my own experience. :wink:

Put premium in your RDX. It will thank you everyday. And you will thank yourself after 75K miles or so (if you keep it that long).

After reading the threads about this, I tried 87 octane. I noticed the difference almost immediately. 93 for me.

No direct injection, just plain vanilla sequential port fuel injection.
The locality and quality of gas might be why Mike_TX is experiencing improved driveability with premium fuel. Being that it's Africa hot down there, the ECM is likely pulling timing to compensate for the high air inlet temps so premium would make sense.
His car runs better on premium so he uses premium.
My car runs fine on high quality Canadian regular grade and I and my car are good with that.
We can debate this till the cows come home and no one is going to win the argument.

^altitude also applies.
I'm not debating. =D i'm telling.

there's a whole of different factors, but the fact remains; premium is better for the car! better combustion! better mileage!
better everything.

go ahead and use canadian regular! if it saves you pennies, by all means keep doing what you're doing!

I have been switching back and forth between 87 and 93 every 3 tanks or so since I bought the car (that way the tank is less diluted with the leftover fuel). I'm currently on my 87 cycle. I also have logged every fill-up and type of gas and brand on fuelly.

http://www.fuelly.com/driver/dimcorner/rdx

My observations:
MPG is ALMOST a wash. I do get slightly better with 93 (maybe 1-2 mpg better). Smoothness it's about the same. If I do a blind test I don't think I will be able to notice the difference. I do about 1 fill-up every week. If I do 87 all year it should save me about 240 bucks a year, or 70% or a car payment.

I think short of getting an Acura engineer to comment on this or slapping the RDX on a dyno with 2 different gas grades we won't know for sure. All specs to me tell me that this is exactly the same motor from an Accord with very minimal changes. Maybe exhaust or intake restrictions changed a little. That also leads me to believe that the ECU map is going to be practically the same as well since the HP is the same.
If timing is pulled because of octane reduction then you should experience a noticeable drop in HP AND MPG.

Conclusion: Put whatever you want in your car as long as it's at least 87 and not diesel.

I used premium for the first 7500 miles and then switched to mid grade (89) and I've not seen any difference in the 4800 plus miles since switching to 89.

You guys need to do what I did: a blind test
Currently my wife drives the RDX to work with mostly 60/40 city-hwy.
All I do is fill up the tank and she drives without knowing anything about the gas. Current results: no change in mpg, avg at 23 mpg +/- .5 mpg.

My point is ---> 1.) the placebo factor must be eliminated. 2.) a good enough sampling must be made

Actions:
1. Let somebody else be the primary driver of your RDX
-- or -- Let somebody else fill the gas up for you without you knowing which octane (just tag it octane red vs blue)
2. Log the results (mpg, smoothness observations, average weather temp, out of ordinary driving routes) for the next 10-15 samplings

Only then, reveal what octane is being used for each sample and draw your conclusions.

***
Hopefully, your wife is a car person . If anything like mine, she will not even notice the difference between driving the CRV vs the RDX . If it has four wheels and starts with a twist of a key - that is all she cares.

Your RDX starts with a twist of a key?

I've used both hi test and regular and settled on the mid grade. Seems to work for me.

Mike_TX

When you title thread "I don't care what you say", do you read the replies?

Sure. Why? Or, better yet, why not?

I always think there might be someone who actually agrees with me.

Actually, I expected there to be a wave of disagreement, since some people seem to be convinced otherwise, but the difference in my car is enough that I thought it worthwhile to post it.

stay away from reg.. don't let the "I don't think I feel anything different" fool you.. stick with prem for optimal performance.

And.....once again, the 'premium' vs 'regular' designation rears its ugly head.

I believe Amoco super premium gas from the '70s to be an actual 'premium' fuel compared to the bargain brand 'regular's back then; but the current regulations and market have resulted in much higher quality fuels overall(and over all octane ratings). If somehow, 93 were a top-tier fuel and 87/89 remained a 'stock' fuel in terms of quality, we could accurately refer to 93 as 'premium'. As it is, 93 simply has a higher octane rating, not higher quality.

The terminology dies hard; but top-tier 87 is no less 'premium' than 91 or 93, just a different octane rating. YMMV(literally).

It usually retracts when no longer stimulated.

C'mon, Coach - that's just what it's called. Premium is the designation for the highest-octane gas a station sells - it's not necessarily a suggestion that there's anything particularly "premium" about it except for that.

That said, some oil companies DO still toss a packet of detergents and additives into their Premium fuel at the depot that isn't in their Regular gas. Maybe that can be said to make it more premium than lesser grades.

And if we get into strict definitions, "premium" means "more" (as in you pay more for Premium gas. )

Ain't that the truth! It's a full forty cents a gallon more around here for the past few weeks...and the overall prices are jumping in increments of 10/20 cents at a shot...funny game they're playing.

Oh, man. It wasn't that long ago that the increment between the grades of gas was 10 cents, but that crept to 12, then 13 then around here it jumped to 16 cents or more. So Premium costs at least 32 cents more than Regular.

As much as anything, I think it's for advertising purposes, since it looks good to put that (lower) Regular gas price on the big sign out front. If you run Premium you don't know what you're in for until you actually pull in, and they figure they have you hooked by then.

Regular gas here is about $3.12 and premium is about $3.42-$3.52 in the gas station. Minimum difference is 30 cents.

Funny thing is diesel is about 50 cents or more higher than 87 octane.

And everybody says Texas has low prices! We've been jumping between 3.29 and 3.49 for 87 for a while, with 93 running 35-40 cents more on average
I found yesterday a smaller difference ; but it was because their 87 was so high. Pulled in out of convenience and saw the 28 cent difference...the smallest I've seen in a couple of years. Again, the 87 price was darned high, but the 93 was close to other area stations(I have switched the C70 to 93 after having the Polestar tune installed in the early summer, so I'm not ANTI-93, I just don't run it in the RDX )

And Mike, I'm old enough to remember a two to five cent difference between grades back in the leaded/unleaded days! Wasn't uncommon to pull into the station and ask for two dollars worth of regular...oil checked and windshield cleaned at the same time! I honestly remember 19.9 cents a gallon at the Hess station growing up. I am REALLY getting old!

Yeah I had a twin turbo S4 and a RX7 before that so I'm not against 93 octane if it needs it.

I just saw the sign on the way to work for a gas station.
87 unleaded - 3.12
Diesel - 3.89!!!!

BTW, it was growing up in Columbia that provides those memories for me.

intersting reading, although they have RDX 2013-2014 in the "required" when we are not
http://www.edmunds.com/fuel-economy/...g-premium.html

Edmunds article says Premium costs "often as much as $4 per fill-up" more than regular, which isn't much compared to a couple of large coffees at most places. I'll stick with Premium in my Acuras.

I don't think the RDX will run on coffee, large or otherwise.

My RDX is a race car on premium, spins tires, pulls hard whenever, she's a spayed dog on regular, I will stick with premium at 20 cents more per gallon. She's worth it IMO.