ChrismanTSX

Sauceman and Clutch, many thanks for all this info. I had read a few things about the topic of premium gas, and how a high performance, high-compression ratio, engine requires its use, but your detailed explanations were amazing. I even managed to convince my wife to fill up with 91!


Chris

Anthony Nalli

That was one of the most helpful and best explained posts I've read on any forum. Thank you for it.

Anthony

4x4ord

I own three TSX's and use regular fuel in all of them. I have not been able to measure any difference in fuel economy between regular and premium. There are four reasons why I don't use premium.
1. I live at a little higher altitude (about 3000 ft) so even under conditions where the engine is run at low rpm and WOT the amount of air being drawn into the cylinder is reduced due to the lower atmospheric pressure. Therefor even though the TSX has a higher compression ratio the cylinder pressure is not as high as it would be at sea level.
2. My cars are not driven hard. The throttle plate is seldom wide open so again even though the compression ratio of the engine is high the throttle plate is restricting the amount of a/f being drawn into the cylinder so again the cylinder pressure is not nearly as high as it would be under WOT conditions.
3. The engine has knock sensors to protect it from detonation in the event that I was driving the car in a manner that promotes detonation.
4. I could not measure any difference at all in fuel economy switching fuel so I believe running premium is a complete waste of money.

redpoint

I have been running 87 PON in my TSX for 2 years for the same reasons you listed, except I am near sea-level. No noticeable change in fuel economy, although it has improved over time as I get more familiar with the car and my commute. I also have an oil analysis done after every oil change and have not had anything abnormal show up.

DuckDodgers

Regular fuel, if you don't push the engine, will normally be easily compensated for by your ECU. After a lot of miles, the chances of the ECU becoming unable to compensate are much larger and uncorrected knocking, if you don't notice it, WILL destroy your engine. You pays your money and you takes your chances.

nj2pa2nc

Still running excellent after 151,000 miles on majority regular gas. I drive conservatively, mostly highway. I keep up on all its maintenance.

andrewcjduong

I believe it's your car, you can run whatever you want in it. Manufacture recommends 91 Octane, you aren't required to follow it. In the end, if the car wears out prematurely, it's your fault.

I drive my car hard so I choose to fill 91. It's a habit and an expense so I really don't mind it. Every car I've driven has required 91 so I'm use to it.

Simba91102

I agree, it's personal choice. But since (I assume) Honda knows more about the car's needs than I do (or anyone here), I'll continue to use what they recommend. Plus, gas is so expensive now, the cost of the upgrade is negligible (on a percentage basis). Plus...., am I the only one here who is really sick of this conversation? Can't we just agree to disagree on who or what came first, the chicken or the egg?

redpoint

You are concerned with premature wear and drive hard. These 2 ideas appear to be at odds with each other.

I will say that if I drove hard regularly then I would use 91 PON. Then again, if I wanted to accelerate quickly I would have got a turbo-charged or 6 cylinder car.

andrewcjduong

I'm not concerned about premature wear. I'm concerned about performance lose with lower octane gas use. If I cared about premature wear then I wouldn't have my car slammed and my wheels wouldn't be wearing out every year or two.

I've come to an understanding that in order to drive a nice car (at least I think our cars are nice. Hope you do as well), you have to pay the price. If I wanted cheap fuel efficient vehicle, I'd drive a corolla.

CoquiTSX

+1 for 7 yrs.

CJams

Through the entire 187,000 miles on my TSX I've found a noticable difference between 87 and 91 octane. The main difference is the length of time between stopping for gass. If I fill with 87 I get about 325miles out of a tank. If I fill with 91octane I get above 400 miles from the tank and have done above 500 miles per tank a couple of times. I dont feel any difference between the way the car runs on either gas, but I can tell if I have to get gas 1-3 days sonner than normal when i run 87. Oh yeah, still on stock plugs too.

StealthTSX

Both the above posts show lack of understanding of mechanical compression ratio of the TSX K24 engine plus ECU firmware strategy with respect to knock sensors.

DuckDodgers

We await your explaination, StealthTSX.

nj2pa2nc

+1

CoquiTSX

You must do a lot of city driving since I have never got less than 400+ miles from every tank of gas (~15+ gal- 87 octane). I can get 500+ on mostly highway every time.

redpoint

Fair enough.

My butt dyno may not be calibrated because I didn't find a performance difference between the grades of fuel, but I wouldn't be surprised if others do notice a difference. Part of my butt dyno calibration problem is that I only mash the skinny pedal once every 3 months or so. I actually did purchase the TSX as a commuter car, but I appreciate the sharp handling, good fuel economy, and silky smooth gearbox.

It seems like my car took several tanks of gas to "learn" what fuel I was using. I vaguely recall getting lower fuel economy when I first switched to 87 PON, but then it went right back to where it was with 92. I've slowly improved my mpg throughout the 3 years I've had her.

I've said it before, but the TSX isn't the highest compression engine that is capable of running 87 PON. My CBR600 has a 12:1 ratio and the owners manual lists 87 as the proper fuel.

Heck, the TSX manual states that it's okay to use 87, but that 92 is recommended. If I raced the car then I would run 92. Unfortunately it's all public roads between my house and work. Then again, if there were a race track between my house and work, I would take Lafawnda (my Honda CBR) to work, burning 87 octane all the way. The performance of the TSX, while better than the typical car, is utterly rubbish when compared to a $3000 motorcycle.

CJams

Mostly City driving now. But when I hit the highway for long commutes every day I could tell the difference for sure. Now in the city I hope to get 400 no matter what. Average speed is like25mph now... blows

StealthTSX

The question you are asking is like asking me "How do computers work"??
Where do I start with trying to explain that or explain compression ratio in a gas engine or ECU strategy?

In an another discussion, it was said that the Honda engineers recommend using very thin engine oil (eg. 0-W20) these days so that is the best oil to run.
A bit of research shows that recommendation for very thin engine oil is actually to try to increase the fuel economy and not for engine longevity.
The engineer's recommendations are compromised.

In this discussion, it was mentioned that the Honda engineers have recommended 91 Octane or better.
Why would the engineers do that? Why not recommend 87 Octane? It would help sell more TSX's as it would be cheaper to drive.

In this case the Honda engineers have not compromised their recommendations. The TSX engine does have a high compression ratio. It is designed and requires 91 Octane fuel to achieve it's peak fuel economy and peak power.
Running 87 Octane will not hurt the engine no matter how long you run it.
The TSX engine has knock sensors that are constantly monitoring for engine knock. Once it senses engine knock, the ECU retards timing, which reduces power and fuel economy.
The TSX ECU does not adjust to 87 octane fuel. It always has the timing to spec until knock is sensed.

For anyone running the Hondata reflash on their K24 TSX, they should DEFINITELY run 91+ octane.
The Hondata reflash has the stock TSX engine ignition timing even more advanced than stock.

DuckDodgers

And, of course, the ability to retard timing is limited...

And, the need to retard timing is caused by pre-ignition...

And, the use of 87 octane fuel, which has minimal detergent additives (just enough to meet government standards), often results in engine deposits...

And, engine deposits increase pre-ignition...

And, increased pre-ignition require more retarding of timing...

Thus the ECU will eventually run into a situation where it cannot retard timing sufficent to prevent pre-ignition...

Hence, my statement.

I have NEVER said that the ECU adjusts to 87 octane, only that the engine will produce less power under load due to the ECU having to retard timing more often because of the lowered knock resistance. That's why I say that depending on your driving habits, you may be able to run 87 octance, but you risk eventually having a car that has an engine that can no longer perform anywhere close to it's design limits due to the risk of pre-ignition that the ECU cannot prevent. The same is true of buying cheap 91+ octane and never running any cleaner through your system, as the cheaper brands of gas run lower detergent packages.

Vintage

Great thread. I like everything about the TSX. Exactly the question I am considering before I purchase one.

CoquiTSX

Not according to the Top Tier Gas:

"The deposit control performance of unleaded gasoline conforming to section 1 of this document shall be met at the retail level in all grades of gasoline sold by a fuel company in all marketing areas of a selected nation."

Higher octane does not mean higher additives.

The additive concentration is suppose to be the same in all grades.

StealthTSX

^^Exactly. Premium or more expensive gasoline has no more additives or is no more cleaner than cheaper regular gasoline.

DuckDodgers

Now, now StealthTSX, that's an incorrect generalization.

1) The quote refers to Top Tier gas ONLY. (List below)

USA Canada, 76 Stations, Chevron Canada, Aloha Petroleum, Esso, Chevron, Petro-Canada, Conoco, Shell Canada, CountryMark, Entec Stations, Exxon, Hawaii Fueling Network (HFN), Holiday Stationstores, Inc., Kwik Trip / Kwik Star, MFA Oil Co., Mileage Stations, Mobil, Ohana Fuels, Phillips 66, Quik Trip, Rebel Oil, Road Ranger, Severson Oil, Shell, Texaco, Tri-Par Oil Co., U.S. Oil

Also note that they agree to provide AT LEAST the Top Tier standard of detergent in all grades, not "just". A number of producers use more detergent additives in their high grades of fuel.

2) In other stations, the Federal standard is a minimum, and well below what most experts recommend.


For example, read the story here ( http://www.abcactionnews.com/dpp/new...ssions-mileage ) and note that the same brands gasoline has MORE detergent in premium than in regular...even in the Top Tier brands.

Again, you can elect to use cheaper, lower octance gas, but in the long run your engine will probably suffer. If you are going to sell you TSX before 100k or more, who knows.

Simba91102

I would caution against drawing conclusions from this thread. The wisdom (or lack of) using gasoline with an octane rating (in the US) of less that 91 has been a long, ongoing discussion here. Naturally, there seems to be two camps; those that use regular (87 octane) on a regular basis, and those that don't. Honda recommends 91 by the way. And also naturally, there's no real consensus. But remember that it's all opinion, all personal preference, and pretty much zero fact based conclusions. As with many things in connection with our cars, we all think we're right (which is kind of like saying that 70% of all students were above average). We like to talk about it, though I doubt we get many converts to either position.

Now, to throw a little fuel on the fire; I will add that there is a statement in the owner's manual that came in my recently acquired 010 that leave less doubt of Honda's more recent position on the subject. It clearly states that regular use of gasoline with and octane rating (in the US) of less than 91 may result in damage to the engine. I don't remember if that's in the owner's manual for the first gen cars. I'm only the messenger....

nj2pa2nc

According to the owners manual (pg. 228) of my 06 tsx, it states Use of a gasoline with a pump octane number less than 87 can lead to engine damage.

WheelMcCoy

But was that fuel 87 octane, or 91?

I have a 2012 TSX Wagon, and checking the manual, page 221:
That said, the Acura service guy told me 87 octane is ok once in a while. But 91 octane will get you the rated mpg and bhp whereas 87 will give you less of both. He added that prolonged use of 87 could lead to engine deposits.

I use 91 when I can, but most gas stations only offer 93.

DuckDodgers

Wheel, the octane numbers for premium (and sometimes regular, for that matter) vary around the country. Some states require a 92-93 octane for premium, while some say 91 is fine. 89 and 87 are the common regular and plus octanes. However, due to altitude, regular can be 86 octane in Lubbock or 85 octane in Denver...and it works the same as 87 octane at sea-level.

Remember how they get the various grades of gasoline. The tanker pumps two grades of fuel into two tanks...one is the minimum grade (regular, we'll call it 87) and the other is pure premium 9we'll call it 93). Then they mix the two fuels to make the other grades...so mid-grade/plus/89 fuel is two gallons of 87 and one gallon of 93. In other places it might be one and one (87 and 91). If you do the math, the station always makes more money on mid-grade in Texas, because of the two to one mix and the fact that mid-grade is priced halfway between the two extremes versus the proper one third of the way.

Gebby16

I got the hondata reflash for my 06 tsx auto trans... running lower octane gas reduced my gas mileage pretty significantly. on the same ~100 mile stretch of road, I averaged only 27-28 mpg with lower octane gas, but I got 32-33 with 91 octane.

I originally thought that the reflash had lowered my gas mileage, but I did the reflash immediately after buying the car and didn't realize how important higher octane gas was! If I understand correctly, the reflash slightly leans out the a/f mixture, advances timings, and changes vtec and redline points. I did not think this would reduce mpgs, but rather it should improve it due to the leaner a/f mixture and it *should* be running more efficiently. Turns out, I was just giving it the wrong gas and not taking advantage of the advanced timings anyway.

tl;dr - I have noticed better mpg and should get better power with 91 octane, and will be buying it from now on.

nmike101

I have an 08 TSX with about 60k miles.
I've tracked my gas mileage on Fuelly for about a year and a half (same user name if you want to view it). I find that I get the best economy with 89 octane. I note the octane for the next tank in the notes section if I'm changing. I've tested 87, 89, 93 and 91 without ethanol. I normally fill up at Mobil or Sunoco. The one time I was near a Shell and filled up with 93 V-Power my gas mileage was noticably better, but there are no Shell stations near me. I drive "spirited" regularly, and I don't notice a performance difference by changing octane.
I also thought Honda revised the requirements for the TSX a few years after it's release to say it no longer REQUIRED premium, but only recommended it.

redpoint

Post #66 describes what the '06 manual states. "Use of a gasoline with a pump octane number less than 87 can lead to engine damage." This implies that use of an octane of 87 or greater does not lead to engine damage.

I've run 87 PON for 3 years now and get 30mpg. Just recently I changed to 92 PON just to see if I can improve MPG. Based on the past 2 tanks of 92, my MPG hasn't changed one bit. Engine smoothness has ever so slightly improved when running low RPM (<2500) and high throttle (>90% load). I'll give 92 a couple more tanks and then will likely switch back to 87, or possibly 89.

Since premium costs 5% more than regular, I expect to see a 5% improvement in fuel economy, otherwise I can't justify its use.

csmaan12

Well damn, after reading this, I feel like I should start looking for gas stations that sell 91. I myself fill up at Shell with their 93 V-Power and as nmike101 said, since I switched to Shell my gas mileage did noticeably go up with it. More so than when I used to fill up at Citgo with 93.

Trip computer would usually average 20.3-22.7 with any other gas. With Shell I usually see 22.4-24.7. This is mostly city driving, on the highway I've only done one long trip which resulted in 36mpg (with pretty much 0 traffic, and going 75mph with CC).


I can't seem to find stations that offer 91 though .

speedingbulletl

According to edmunds it says " premium " not plus or mid grade

http://www.edmunds.com/acura/tsx/200...res-specs.html

speedingbulletl

Every Sunoco I been to has one

aldohe

I just purchased an '04 TSX ATX this month with 145,000 miles. The previous owner only used 87 octane for about the last 6 to 9 years. I drove it about 80 miles from Austin to San Antonio and did notice any knocking or issues with acceleration.

When I had to fill up I used Shell 93 and will continue to use Premium 91 or greater because I want to follow the manual and because of the age and mileage of the car.

I know that they did have to replace one of the mufflers about a year ago don't know if that was because of the wear on the emissions due to the lower grade gas.

I am going to take it into the shop next week to have a full inspection on it and I will post back on a different thread the results.

Glad to be part of this HOF thread!

elsaic15

i almost always use premium, have only used regular about 5 times in 4 years. I never really noticed any difference

2FRESHTL

premium the way to go cant be cheap on gas!!!

WheelMcCoy

Some interesting reading related to this thread:

http://www.roadandtrack.com/go/news/...DM_panelHeader

I mostly use 91 or 93 octane in my 2012 TSX Wagon.

Timmy18

Just for the record.. My TSX has roughly 112K on it, and we got it used in 08 with around 74K on it ( If I remember correctly). Since then we haven't really used 91. i don't usually fill the car up but when I do I use 87 most the time. I'm sure my parents use the same thing. It's the cheapest and we aren't the richest.

The car runs fine. Smooth and strong. Granted there is a difference in performance. I noticed that after we would take the car in to the dealer for service and they would fill it up with 91. A few days later after all the 87 was gone (or well mixed in and diluted with 91) you could tell the car got a little more peppy. With in a week or so (still a quarter tank of 91 left from Acura) the car's ECU had adjusted fully and the car felt totally different. Not so much that it made it feel sluggish on 87, but so much that you can notice it.

I know its been mentioned before, but Honda's ECU's are CONSTANTLY re learning and adjusting to our driving habits and the environment around them.

I'm positive the TSX will be best on 91+ but it's perfectly fine with anything as low as 87. (I wouldn't go lower, some places offer 83 and even 81!). It might be slightly rough for a few days (if you've been spoiling it with 91 all its life) the ECU will be a little upset with the sudden change if quality but will make adjustments as needed.

Acura and Honda wouldn't send a car out with the possibly of it getting a lower fuel octane level required leaving it to just blow the engine or damage it.

No doubt about it damaging the engine in some way. The higher compression and lower oct fuel cause a accelerated build up of carbon deposit on the cylinders and valves. The result is lower fuel economy and power form the ECU, but also slightly more chances of wear and tear by the carbon falling off and scoring the cylinders. but I've been feeding my TSX with 87 for 5 years and no telling what the owner before us feed it, and its running fine. No CEL's ever.

if you read my post about a rough idle, its due to a vacuum leak, which I believe has been found and fixed.

aldohe

FYI - Got my car back from shop. No issues.