newteez

Good, info, the bottom line is we have to pay a little extra for the gas. All new cars in the luxury segment require premium fuel though, which makes me believe that there may be some kind of conspiracy going on. However I agree that for this particular engine and a car that is geared towards performance there is no reason to try a lower grade fuel in it. Plus as mentioned $200 per year isn't going to break the bank.

I only have been filling up with 93 octane fuel from Mobile, so maybe I am getting even more better performance...

JD

Lrpba300

Exactly! Just use the Premium. It's what it calls for!

DNPhotography

seriously, why do people buy luxury cars only to fill up on cheap gas. if you cant afford expensive gas dont buy an expensive car next time.

B18Ch1ck

If you can afford an Acura over a Honda, you can afford premium.

Even when I was a high school student, buying regular NEVER once crossed my mind.

Fishbulb

*snip*
"All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches." */Snip*

I find this section interesting. If a highly tuned and powerful car like a 911 turbo will not experience any mechanical problem running on regular fuel, I don't see what is so advanced about the RDX engine that would prevent it from doing the same.

c_hunter

Ah, those were the days of carefree youth and fuel grades. A time when the beer flowed like 93 octane Sunoco. Where beautiful women instinctively flocked like the salmon of Capistrano.

RSXster

What he might mean is that you can use 91 octane vs 93 since 93 isnt available everywhere.

You know what, go ahead and use 87 octane. Infact, put in diesel. Its your car, and you can deal with the results.

Everyone else, please continue to use 91+ octane as these are high compression engines which REQUIRE it. Detonation is not your friend, knock is not your friend.






Lrpba300, nice avatar! Chargers are going down!

Fishbulb

It wasn't my intention to provoke a rude response. I simply thought it was an interesting quote in context of the discussion.

SolidState

Why are people still confused about what octane of gas to use? It should be as well known as "smoking causes cancer" and "drinking and driving don't mix."

Lrpba300

I sure hope so! It's gonna be a tough game!

neo1738

Just for those with some doubt....look on the inside of the gas door. It does NOT say recommened, it says Premium Fuel ONLY.

Nothing but the best 93 octane for my baby.

CGTSX2004

iTrader: (1)

And without the context, that quote could be interpreted incorrectly.

The fact is that most premium luxury or sports cars/SUVs require premium fuel because their engines are calibrated to utilize the premium fuel to extract the best performance possible out of the motor. Yes you can use regular fuel, but at the cost of some performance (more noticeable on some cars than others).

Even Porsche's need to be able to run on regular when premium is not available. The knock sensors built into the engine are intended to minimize the potential damage that can occur due to engine knock. However, Porsche still recommends premium because it is what the engine is designed to run on. Extended use of regular fuel in place of premium may lead to problems with the motor.

So while your quote is interesting, it doesn't necessarily prove that you can use regular fuel on a consistent basis in a motor that requires premium.

RSXster

Hey, sorry for coming across like that. Its just that this whole thread is so frustrating. The manufacturer says use premium, the car has a turbo (aka high compression engine), and the car is around $40,000 and people are trying to save some $ at the pump.

IndyDaveS2K

This isn't exactly correct.

Turbocharged engines are NOT high compression engines; in fact the compression is deliberately lowered because of the turbo's boost. The RDX has a compression ratio of 8.8:1. The non-turbocharged MDX has an 11.0:1 ratio. Even the Honda CR-V has a higher compression ratio (9.7) than the RDX.

Fishbulb

Prove it. The Porsche fellow alludes to nothing of the kind, and for warranty reasons, they would be firm on that point if true.

I'll certainly concede some performance losses would occur, but I remain skeptical about the engine damage possibilities.

There is marketing involved here, just as much as engineering.

sasair

Prove it? I think it would be on you to prove that it wouldn't cause damage since you believe that it wouldn't.

Any smart person wouldn't risk it either way. I personally have witnessed what using non premium gas will do in an Acura non-turbo engine that required premium. It knocks like crazy. No, I didn't put non premium in my acura, but our company uses Acuras which get filled by various people who do not know to use premium. Service department says that it is the most common problem they see at the dealer.

crazymjb

Everything is NOT a conspiracy. Engine knocking is quite real in high compression and turbo engines especially. In order for the engine to compensate, it must detect it first. Knocking in turn destroys engine.

Law of transitive properties, Premium should be used where available for car that recommends or requires it.


Knock = Bad, Premium = no Knock(usually) No knock = good, premium = good

Seeing as the 911 has an 11.3:1 compression ratio it would be in your best interest to use at least 91 Octane fuel.

Mike

Fishbulb

And that's why today's modern engines employ a knock sensor, which detects it, as you mention. The only exception would be that of a supercharger, which could be a bit too quick for the sensor to compensate for.

I own a 1998 honda prelude, which specifies 91 octane or higher, which I bought new. I have religiously put in nothing but 87 octane since 20K on the odometer, not necessarily because I'm cheap, but because I couldn't notice a difference in how the car ran between each octane rating.

It has now just clocked over 250,000km, and has perfect compression, and recently ran a 15.4 at the strip, which is about average for the car brand new.

Mileage is unchanged etween 87 and 91.

I tend to believe the quotes from the engineers and experts in the article. The knock sensors on today's modern engines do a fine job of preventing engine damage, and the performance loss is hard to notice in most cases.

When I buy an RDX, I'll most likely start with 91, and eventually drop down to 89. If I don't notice any issues, then I'll continue with it. The oil companies make enough money already, thank you very much.

Fishbulb

On the contrary, I believe it would be on you to prove it since the Porsche engineers believe it wouldn't. I'm just quoting the article here.

jhwu

What is your reason to not use premium? Is it the cost or you feel that it doesn't matter?? Unlike your Prelude, higher octane gas will make a difference in a Turbo engine with regards to performance. So, since the car is tuned to get maximum hp and torque on 91 octanes, why do you want to lower your car's performance by using regular gas? Also, the knock sensors will retard the timing, but that may not lead to better fuel economy... who knows... maybe the engine is more efficient when it doesn' have to always compensate the timing for lower octane gas. With that, it makes saving 10 to 15 cents a little meaningless.

Anyways, I doubt your car will have too much problems w/ regular gas for normal driving experience, but for sure your performance will be handicapped a little. It's your choice. However, pay special attention to your engine once you start to use regular... listen carefully and if you hear any pinging or knocking, better put in better gas. Especially in high altitudes, climbing hills/mountains and in really hot weather... pay special attention to your engine. Just a friendly warning.

crazymjb

Fishbulb, its your car, do as you wish. Again, it is not a conspiracy. IMO, it is stupid, yes stupid, to not heed manufacturer fuel advisory, especially on a regular basis. This is not to say you couldn't get lucky with one of your cars, whether it be your driving habit or an engineer suggestion.

Also, as I will say again, knock sensors must detect knocking in order to cancel it, and their will be a drop in power. Also, there is no guarantee they will be fully effective. If you go to the 3G TL section their are threads about noticeable power losses due to compensation as well as engine knocking.

If anyone wants to calculate out the maximum effective compression ratio for the RDX IIRC it is close to 12:1. But of course, a conspiracy, lets use 89

Listen, I know you know everything about the octane ratings, engine compression, detonation, knock, and forced induction, but it is especially advisable to listen to the manufacturer and stick with premium. You spent 34-36K on car, why try to save a buck on something that could potentially damage your engine?

Edit: You don't need to be an engineer to know that it is a good idea to run premium in a Porsche, especially one under boost or high compression. If this helps at all, my physics teacher was a huge car buff, very cheap, and a master technician, and he said it would be insane to run anything lower than 91 in a car with an 11:1 compression ratio. How about this, go out and buy a Porsche, put in 87, and start pushing the engine to its limits.

Mike

sasair

What idiot would try to prove that it causes damage to the vehicle they just paid $35k for? Your thinking is messed up. I wish you the best of luck with your RDX and 87 octane. Who here cares about a quote from a Porsche engineer?

Fishbulb

I certainly have some respect for a Porsche engineer. I'd wager they know more on this subject than anyone who posts on this thread.

As I said, I'll use 89 in my RDX, and compare it to 91 for a time period. If I notice significant mileage or any performance/knocking issues, I'll stay with 91. I doubt that will be the case.

Anyhoo, different strokes, different folks. This is moving more from a debate regarding the points of the article, to personal suppositions.

schuchmn

It surprises me that the knock sensor of an Acura can't handle regular gas. But, of course, engine knock is the real-world test that unambiguously indicates a need for more octane. I haven't been following this thread from the beginning, but has anyone tried an tankful of regular in their RDX? I believe in being empirical, but not wth my car.

I never put regular in a car that calls for premium, but I did try the mid-grade gas on an '02 BMW (naturally aspirated) and a '95 SAAB 9000 (turbocharged). No knock but slightly lower mileage in both cases, which eliminated of some of the cost differential between plus and premium. In any event, I went back to premium.

CGTSX2004

iTrader: (1)

But what happens if the knock sensor fails or malfunctions?

Your case with the Prelude is more likely to be an outlier than it is to be within the norm. I have heard of several cases where knock sensors fail and the end result is ususally damaged valvetrains, bent rods, and even thrown bearings.

Nonetheless, do as you please as it is your car, but don't come crying to us if something happens to your car.

neo1738

I trust a honda engineer that helped design the HONDA engine more than a Porshe engineer talking about DIFFERENT engines. If the $200 a year in price is worth the price of a new engine go for it IMO. I'm not putting in anything but 91+

c_hunter

Even if the knock sensor detects the knocking properly, the result will be that the engine timing is retarded and engine output (and probably smoothness) will be reduced. Why bother paying for the RDX if you're going to handicap the engine performance? For a mere $80-100 savings a year?

My previous car recommended 91 octane, which I used. One time my wife put in regular gas and I noticed it right away (the engine performance prompted me to ask her, which is how I found out about the regular gas). The engine felt less peppy and throttle response was not good. The only thing the manufacturer noted on their website was a small (4HP) loss in peak horespower with reduced octane, and slightyl lower MPG. What they didn't say was that you felt a bigger difference through the whole power band, especially at low RPMs where we tend to be in everyday driving. After that experience, I fully appreciated the octane recommendation. If the engine mapping was optimized for a certain octane level, that's what I put in the car. I'm not interested in reduced performance for a 10 cent per gallon savings. For me that's $87 savings a year. Not worth it.

Brandon24pdx

I have lots of experience with turbocharged engines, and would highly not recommend running anything less than the highest octane offered in your area...usually 92 or 93 but as low as 91 in California. (for best performance and engine longevity).

For Turbo or supercharged engines, the higher the octane the better. On hot summer days, premium was sometimes not even good enough to keep the engines in some of my old cars running at max timing advance. (adding a couple gallons of 100-102 octane racing unleaded would make a big difference on track days)

Icealicy

Where would you find 100 or 102 octane gas? I have never seen that type of gas anywhere. Please inform. Lol. Thanks sexies, man. Lol.

Madison3

CITGO has 110 rating for racing: http://www.citgo.com/Products/FuelGa...ngGasoline.jsp

Or this: http://www.turboblue.com/typical.asp

RSXster

Well, ive seen Sunoco GT which is over 100. But that is rare, just go to the local track or your local tuner and they should have 100+. My tuner has a drum of 109 octane to tune for race gas which you would then get at the track.

happasaiyan

modern day "learning" ecu's have to LEARN. how do most people learn? they try things out.

your ecu will start with a baseline for ignition advance (timing) and learn up (attempt to apply more ignition advance). once it detects knock via the knock sensor, it will pull back advance. you could theoretically create an ecu that would run on 87oct through 116oct, but it would not be ideal. the baseline ignition advance curve will probably cater to 87oct and will be able to learn up to efficiently handle 93oct. the big problem occurs when you consistently use 93oct fuel and then fill up with 87oct. the knock sensor will detect the knock that WILL happen and it will pull advance back temporarily and make a note of it. then knock WILL occur AGAIN...and it will pull advance back temporarily and make a note of it. your overall ignition advance will not be sufficiently pulled back until a certain amount of time/severity/occurences.

the argument could then be made that "well if i just use 87oct all the time, i will never have the problem." that argument is wrong also. your ecu will always try to advance up to its maximum. over time, it will slow the advancements made to where it will detect small enough knock to not cause severe damage, but it will still try to advance.

happasaiyan

turbo engines have a relatively low STATIC compression. by definition, turbos and superchargers are COMPRESSORS. when running positive boost on an engine, you can ignore the static compression value, because the engine now has a higher dynamic compression value.

so in reality, your gas has to withstand the dynamic compression to supress knock...the static compression no longer matters.

happasaiyan

in turbocharged engines, the amount of fuel added per amount of air (air to fuel ratio, or AFR) can be modified to supress knock via cooling.

one of the causes for knock is if in cylinder temperatures get too hot. richening up the AFR (ie, lower number) will add more fuel and will essentially cool the in cylinder temperatures. this will help prevent knock.

some ecu's will richen up the mixture if it detects a lower octane fuel...and in the case of extreme knock situations, may even revert to a completely different (much richer) fuel map.

richer AFR = more fuel = lower mpg.

happasaiyan

take an STi, put anything less than 91 octane in it. floor it. listen to the knock.

some of the '04 STi's even knocked with 93oct! putting in higher grade gas ALWAYS got rid of the knock. granted that was an issue of a poorly mapped ECU, the fact remains the same- higher octane gas DOES resist knock better.

the ECU will account and adjust for the 89oct but it will knock doing so.

modern turbo cars are water and oil cooled. the design of modern turbo cars are such that when the car is turned off, there is a natural syphon that occurs where the hot coolant will rise to the top, and the cooler coolant will sink to the bottom...this will keep happening until the turbo and coolant are back to a normal temperature. no need for a turbo timer, but definately never a bad thing to cool it down...unless you dont like wasting gas (like me).

snorton48

Can't buy any better than 91 in San Francisco.

snorton48

What reason would Honda have in advising more expensive fuel if it's not needed. That's a negative marketing point, not a positive. I'd love to be able to use regular but I'm taking Honda's advice (requirement) and using hi-test.

gizsf

I can! If you need to find out where to get 113, let me know.

On a seperate note, Keep in mind that due to Cali laws, our gas is oxygenated to reduce pollution. This also makes it a bit weaker and causes many higher performance vehicles to ping. This is on top of the already lower 91 octane.

Lrpba300

You all keep talking about Cali. only having 91 octane. Well, Colorado is the same way, prob. due to the high altitude in most places. It's all I'll run b/c of the turbo type engine 7 that's what the Honda engineers advise!