Just as a data point...
http://www.fuelly.com/driver/dimcorner/s4
My S4 takes premium only and in the past 6 years of ownership I used $10,774 worth of gas for it. I consumed 3,205 gallons of premium in that time and it comes out to about $3.36/gal. Regular in this area is about $0.40 less so estimate $2.96/gal over that time and we are looking at almost $1,290 of gas money saved. Granted that car averaged about 22mpg vs the RDX of about 26 but it is still a chunk of change I rather spend on something else more useful to me like tennis strings or a new video game or something more useful to me.

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

If you believe that having premium is the way to go then by all means keep doing it but you can't come with an argument of "well if you can afford a $35k car..." I dont go around telling people that buy $5,000 watches (or even $50) that their current phone that they already have tells the time just as well. This car isn't exactly an exotic, it's got a J35Z2 Honda Accord motor pushing the same power.

 

First, the engine is *not* tuned for premium. It's tuned for regular. I've confirmed this with multiple Acura service techs at my dealership, including the service manager.

Second, it's not about affordability. It's about opportunity cost and utility. If I spend $200 of my income on higher octane gasoline, that's $200 of my income that I can't spend on something else. I'm not going to get any utility out of higher octane gasoline on an engine that doesn't require it, and I'm not going to get any utility out of paying oil companies more than I need to. I'm pretty sure they're OK without my charity. I'd rather take that $200 and spend it on Blackhawks tickets or a dinner out as both of those would deliver me far more utility than spending $200 on higher octane gas.

Lastly it comes down to whether I believe that using lower octane gasoline will lead to a higher repair cost in the future than what I spend on gas over time. Frankly, I simply have no reason to believe that. The engine isn't a high compression engine, requiring premium. It doesn't have a supercharger. It doesn't have a turbo charger. Overall, there's just not statistically significant evidence to support the theory that higher octane gas has an impact on engine longevity.

In the end, if spending extra money on gas makes you feel good about yourself, then great do it, but don't make some assumption that everybody has the same personal utility curve for more expensive gasoline just because they bought the same vehicle you did.

 

So you talked to a service manager and two techs that told you what you wanted to hear.
The RDX is no different than my Mustang in that it is optimized to perform best with premium but will also run on regular.
I've tried regular in both of my vehicles and the results are the same. The ECM commands less timing and the vehicle makes less power.

 

I like how you assume you know what I wanted to hear with zero context around it. Obvious troll is obvious.

However, for the benefit of anyone else reading, the reason I asked multiple techs was because the sales guy was the original one to say it, and I wanted to make sure anything a sales guy told me was correct. So, again, what I *wanted* to hear is what the *correct* thing to do was. I phrased it very carefully that I did not care either way I just wanted to do what was right, not necessarily what was cheap. The service team all said that there would be no adverse effects of using regular and they were assured this by the manufacturing technicians during their training on the vehicle just before it was released.

Again, if paying more for gas makes you feel good, then by all means pay more for gas. I'm not telling anyone that wants to pay for high octane not to do so, but I am telling you gas snobs to stop telling everyone else how to spend their money.

 

Umm, I have to object, too. If the engine isn't tuned for Premium, why would Acura recommend it? In actual fact, it IS tuned for Premium, but will adjust the timing to accept lower-octane gasoline.

What I think you got is semantics. The service people you spoke to are trying to say the engine will tolerate other than Premium. But it IS optimized for Premium, so to me that means "tuned" for Premium. And tuned for Premium doesn't mean Premium is all it will take.

 

It's not optimized for premium. I specifically asked that. The question was not "will it work if I put regular in anyway?" They specifically stated the only reason it has that label is because they printed the owners manuals before they finished engine testing and they weren't going to go back and change it. There's also the marketing stigma that comes with it in that you get people (like many posting here) who assume it's not luxury enough if it doesn't recommend premium.

There also a difference between recommended and required. The TL says premium is required, but the TL will certainly adjust accordingly if you put regular in. The RDX doesn't even bother to say "required" and says "recommended" instead. If you choose to believe that the label is truly there for technical reasons and there are no other motives or marketing-think behind putting that there, that's certainly your prerogative, but I don't agree. I believe if Acura really thought the vehicle was best served by high octane, then they would have put on a "required" label just like on the TL.

I believe my service techs that the engine is tested and tuned for regular. I've been going to the same dealership for eight years and they've never led me astray. If you want to choose to believe it's tuned for premium, then by all means, but I simply don't agree.

 

I get the impression that it's similar to what Ford had done with their engines. They actually post different HP ratings if premium is used versus regular. Maybe the Acura engine puts out a few more HP when premium is used. However, I don't think unless you are drag racing at every stoplight that the average driver would even notice it. A guy that has a Ford Mustang GT and a RDX is probably a more aggressive driver and may notice the difference.

 

I'll just say that if you choose to believe the manual was printed before the engine was tested, then "by all means" ... but I choose to believe that's pure hogwash and I don't believe your guys.

I also choose to believe they put "Premium Fuel Recommended" in the manual specifically because they DID test the engine, and determined it will perform fine with Regular gas, but will perform BETTER with Premium. If they hadn't finished testing the engine, they would have taken the safe and easy route and given it the same "Required" caution they give the TL. Changes to this engine from the version in the TL (such as 10.5:1 compression ratio vs. 11.2) simply permit more leeway in the fuel used.

But we've beaten this to death, and you have your opinion and I have mine. So I think it's time to let this go.

 

My proof: testimony of service technicians from one of the busiest and best reputation Acura dealerships in a major metropolitan area.

Your proof: a sticker.

Until you have more than a piece of paper with adhesive backing to prove that high octane fuel does something for the RDX other than make its owner feel warm and fuzzy, the only thing that's hogwash is premium making a difference.

 

I sure don’t want to get in the middle of this argument, since neither side is 100 % correct. Back in “the old days”, if they really “tuned” the engine for premium, then you would be having pinging under a variety of driving conditions. In fact, years ago, anything over 9.5:1 would be said to require “hi test” and if “regular” was used you would probably hear pinging under anything above moderate acceleration. However, since that time even the way they calculate octane has changed. Today it is calculate by averaging the “motor method” (knock index under load) by the "research method” (this test is performed on a free running engine, not under a load). Because the free running research method produces higher octane numbers, the rating you see at the pump is an average of the two methods.



It’s interesting to note that the Acura manual doesn’t even say which method they’re referring to. It’s poorly stated as best. Since today’s 87 “pump octane” is equal to 91 RON, it can cause confusion (even though I will assume they’re referring to the “average method”, which by law requires any gas labeled as “Premium” or “Hi Test” to have a minimum of 91 pump octane. Because of today’s engine’s ability to advance or retard timing electronically, controlled by computer, as long as the octane used is within the engine’s ability to retard or advance its spark with the octane used, there is absolutely NO ADVANTAGE in using a higher octane gas. If the octane gas you use is within the electronic adjustment range, you should experience NO INCREASE in power, unless one of the engine’s sensors or its computer is malfunctioning. However, some people watch the Chevron cartoon that pushes their gas with “invigorate” and believe it will invigorate their car. For those people I say, if it makes you feel better to flush your money down Chevron’s (or Exxon’s) toilet, knock yourself out. There are worse things in some brand’s gas that is just as important as using high octane gas. In the end, if you’re paranoid, then when you get to a half tank, take turns filling it with premium one time and regular the next.

 

I've had plenty of more powerful vehicles before maturing a bit and going the Acura route. If there was a significant difference in performance between fuel use, I'd likely notice. I also specifically asked if it would make a horsepower difference and was told no.

I'd say it's more likely that the premium recommendation exists solely to scratch the back of the oil companies, which every auto manufacturer does to a varying extent. Honda, for example, recommends the "top tier" companies, meanwhile Ford recommends BP. Those are recommendations also, but your vehicle isn't going to perform differently from using those fuels. It's just marking dollars and kickbacks hard at work, and if I had to bet money it's the same thing with the premium recommendation.

 

Whatever makes you happy, singlecoilpickup. That's what's important.

 

Guys .. y'all are fussin about nutin.

Is the the 10.5:1 compression ratio optimal for premium gas use (relative to other Acura non DI engines)? --> No
Does the ECU optimize the ignition timing map for premium vs regular? --> Yes

I've made the switch and now use regular and under light use there is zero performance difference, but I'd bet under a dyno comparison (WOT acceleration) the premium fuel does make a difference.

Inverse case --> my former 2003 Honda Accord (J30A4): no manual or spec confirms any advantage of using premium, but a Honda engineer and dyno confirmed that using premium allows up to 10hp more (again; this is WOT acceleration)

Did I use premium in my Accord? No .. Do I use premium in my RDX? No
Simply put, my daily driving habits do not realize the performance gain offerred by premium gas over regular, so why pay more?

 

You Texas guys are the best at puttin' it all into perspective.

 

We're not "fussin", we're discussin!

 

I wonder if I could put these lyrics in a country song

 

I even doubt it's tuned for Premium.
It's the same engine than a 2012 Accord V6 that runs on regular.
It also gets the same HP and TQ (I consider +/- 2hp or tq a wash). Why would the same engine with same compression need to be tuned for Premium specifically to get the exact same HP?

I'm going to see if I can find a drag racing app and see if I can do a 0-60 comparo between premium and regular and do a few runs to test.

 

Riddle me this, y'all...
Different marques tell the same story about how the ECU or the man behind the curtain can detect knock and make timing adjustments almost instantaneously; however, they always state it can take more than a tankful of 'different' octane fuel to give noticeable results.

Wut up wid dat?

 

I'm guessing because not everyone waits for the tank to run dry before filling up. Even if you fill up when the light comes on you have about 2 gallons (maybe more) left in there. Lets say someone fills in when they reach 3/4 empty and has about 5 gallons left in there and they throw in 10. You now just mixed 5 gal of 93 and 10 of 87 so you are about 89 grade or so. I might take you another fill up to wash it out a bit more but you still will be a little above 87. People's definition of a tankful for the non-enthusiast (like my mom) can just mean a fill-up, and she doesn't wait for the light to come on to fill it up either.

 

Right on!

 

I guess the answer to this discussion is Acura is in bed with the oil companies who want you to pay more for gas. There is no other logical reason, so all of you who want to put regular in do so because it does not matter to me. I will continue to get raped and put in premium because to me, if Acura recommends it there is probably a good reason. Until an Acura Engineer comes on here to tell us why premium is recommended or not, I will continue with premium. I would think Acura would be more than happy to say you could use regular for more fuel savings.

 

LOL-Sometimes it can be as simple as giving naïve people what they're expecting. Despite some "luxury" deficiencies, Honda slapped on an Acura badge and calls the RDX a "luxury vehicle". They reinforce it by telling prospective purchasers that it uses "premium" fuel. Yet, it appears to be so similar to the engine (and as far as I can determine, uses the same cam shaft and other parts that might change the fuel requirements) used in the Honda Pilot.

The Pilot: 250@5700rpm - Torque 253@4800rpm
The RDX: 273@6200rpm - Torque 251@5000rpm

Compare the two! I would really like to see them both on a dynamometer, with the RDX and Pilot both running Regular fuel and then Premium fuel. I'm certain that after you saw what they're doing, if given the choice between having the engine with the Pilot's specs using Regular Fuel or the RDX specs using Premium Fuel, you would choose the Pilot's engine. And, I'm willing to bet that in a blind test you couldn't tell ANY difference....if there IS ANY.

In the end, they're just giving the fans what they expect.

 

I think the pilot uses a J35A9 vs the J35Z2 of the RDX
The J35Z2 is used in the 2008-2012 Accord V6 Automatic as well as the RDX (Not sure what other Honda uses it)

2008-2012 Accord Regular gas
271@6000rpm - 254@5000rpm

Like I mentioned before, it's the same HP as the RDX on the cheaper gas. The accord even has the 3 mode VCM. If the RDX was tuned for premium I would expect a increase in HP but as you can see there isn't any.

As another example the Mazda CX-5 compression ratio in Europe is 14:1 vs here in the US of 13:1. Reason was the fuel quality and Mazda probably didn't think it would be a good idea to say that their economy car is the best in gas mileage, but you REQUIRE premium. So they lowered the compression (different piston) and lost a little bit of HP. In the UK the 2.0 cx-5 makes 162hp vs 155hp in the US. Putting premium in the US CX-5 does nothing since the ECU won't advance timing.

Premium gas won't hurt the car. Maybe it has some extra detergents that regular doesn't. I don't think that premium has any benefit other than possible cleaning detergents over regular. Does anyone has more proof than "the manual says so" or "All previous Acura's used premium" to justify premium? I showed some engine specs and engine codes as well as my own MPG calculations. In the end you have to remember that Acura is only a luxury division in North America of Honda. It's a Honda engine and unless the same engine shows more HP or TQ then there should be no change in tune from whatever Honda they took the engine out of.

BTW in my mom's MX-5 you do notice a HP difference as well as a small (1-2mpg) difference. I feel no difference in the RDX.

 

I know it's fashionable these days to hate corporations, and oil companies in particular, but I think it's silly to suggest Acura is in bed with Exxon and Valero and Shell. I guess you figure they get a kickback for every gallon of premium gas sold.

And the suggestion that they recommend premium to make customers feel like it's a more high-end vehicle strikes me as equally silly. In these days of high gas prices and environmental awareness, it would actually HELP sales to be able to advertise that the RDX will run on regular gas. Having to use premium doesn't make a car "nice" or "luxurious" - having to buy gas for your car is a necessary evil, and being able to tell your customers they can use a lower-priced fuel is a plus, not a negative!

I figure this thread has run its course and stopped providing useful info.

 

Do you account for the differences in intake and exhaust when you consider these two engines to be identically tuned? Why does one engine have to spin faster to produce peak HP? It would seem there are some differences, maybe not seat of the pants differences, but actual mechanical and tuning ones.

 

I agree that this "has run its course" the subject of regular versus premium is discussed on multiple threads here. Bottom line it is only "recomended" not "required" as on most of the other Acura models specify. Do whatever you want, posting is unlikely to change anyones opinion if they have read all the posts on all the threads......

 

Of course you do have to consider the differences.
But 2HP over 200rpm could be just that, maybe an extra bend in the exhaust or smaller panel filter. Point is that on other cars a drop from 93 to 87 octane is closer to a 10hp-15hp decrease. It's noticeable.

I do agree that people will make their own minds. I just did not agree when people spit out the whole "$35k" car issue so I replied with some backup data. No skin off my back, I own stock in Exxon ....

Hey wait a minute...

YES EVERYONE SHOULD FILL UP WITH PREMIUM!!!!

 

You make the case pretty well with your statements above. The only thing I see that's "silly" is that they would even offer a car requiring premium fuel when they already offer essentially the same engine that doesn't require it. I view that as nothing more than sticking it to the "luxury" car buyer. There is nothing else anyone can say that could change that marketing/engineering blunder.

P.S. - The reference in the manual to the "top tier" fuel companies is nonsense. However, for those that want believe it, it REQUIRES those companies to use the SAME ADDITIVES across their ENTIRE gas offerings. So even if you buy regular 87 octane, you're getting the same level of additives as the person who buys premium. So next time you're passing your favorite station around midnight and see an unmarked tanker filling their tanks, you can wonder if that load had the "top tier" additives (let alone the right octane).

 

I thought that the 2010 Accord 6MT saw a HP increase with 93 on a dyno somewhere. Maybe a dyno result would say 3-4 HP increase with the RDX? which wouldnt be noticeable to me.

I think I read that on some accord forum a few years ago.

 

Exactly. I really doubt that the average driver could notice the difference. As far as marketing goes, that's one of the first things the salesman told me when I was looking at the RDX, "You can use Regular, no problem". The dealer Owner said the same thing during an orientation for new owners at the dealership. Acura owner manual says 87 octane will not damage your engine. So IMHO use what you want as long as it's at least 87 or above. If you notice the difference in the kind of driving you do then pay more. If not, pay less and don't worry about it.

 

I just bought a 2013 RDX AWD with Tech. Have been battling the same issue on what gas to put.

So far I have filled up the gas 4 times. 3 times it was 89 and just yesterday I put 93 from shell. I was planning on putting 89 but one of the patients I saw yesterday is a "master tech" for Honda and said it's very important to put 91 or better gas in the RDX...So I went ahead and put 93 yesterday..After reading all these posts, I think I am going to go back to 89

He also said that I should put synthetic oil and change the oil every 5000 miles and not always look at the maint. indicator...

What do you guys think?

 

Also, the Honda master tech said that if I don't put the "recommended" gas in the car, it's possible that the catalytic converter would go bad at 100k-150k miles


Off topic question: My car is brand new and every time I take my foot off the brake pedal I hear the clunk/thumping sound.

It was like that even when I test drove a few different cars like the Q5, another RDX, X3

Why is that?

As a matter of fact my 2011 Honda Accord does that too..especially if I am driving it for the first time in a given day.

 

You can always just send a sample of the oil to blackstone labs for analysis. My dealer has a schedule to keep in order to maintain their warranty (don't have to do it at the dealer, but have to have proof of maintenance). I would probably do at least a synthetic blend on the RDX. If it were up to me, probably would change between 6k to 8k miles.

Catalytic dying is usually caused by overly rich mixture getting to the cat. Mostly caused by faulty O2 or dumping too much fuel per cylinder. I don't think the octane will affect it since I believe IF there is any change due the fuel the ignition timing would be the variable factor.

Thump, I dunno, I do't have a thump.

 

^^ The debate about which fuel to use will live on forever, so don't expect to get a clear cut answer. Do what makes you feel better, because at the end of the day, it is your money, your vehicle and your piece of mind

For me, I don't see the advantage of putting anything different than premium, but that is because I can afford it, I don't see the conspiracy factor and like to sleep at night knowing I don't put a fuel with ethanol in it, and give my babies the best there is to offer. I don't do cheap beer for myself, why would I treat my babies any differently

 

So in your area, 93 octane fuel do not contain any ethanol? I was under the assumption that there is up to 10% ethanol in any octane rating. In Florida, unless the station claims ethanol free(for boat and their fiberglass gas tank), there is up to 10% ethanol in any octane rating.

 

It may be different in Canada, but in the US it all has ethanol whether it's high octane or not.

 

Yeah all the regular gas stations here (unless specified) contain up to 10% ethanol regardless of octane.

I can afford premium too (my S4 drank it for the last 6 years) but since I believe it can take 87 with no issue I rather put that in and pocket enough in difference for an extra 4 tanks of gas per year vs premium. Or buy me a new badminton racquet to go with my other 7

 

You need to get your foot checked.

Bazinga

 

Yep...the only way to avoid ethanol around here is to find a marine dealer. All the 'normal' stations have ethanol in all octane grades.

Dim, I've strung rackets for almost 4 decades and fortunately, only ONE was a badminton bat. Thank goodness!

 

I guess I'm used to badminton racquets . I'm playing tennis now (just started last year) and a full poly job is not joke! That string just doesn't want to work with you! Weaving poly is harder for me than weaving a badminton racquet!