xpolosp0rtx

hey, always been kind of a lurker until my parents bought me a tsx ...
just a quick question on gas. i know the manual recommends premium gas and i told my dad that and he refuses to buy premium... he says that it's just some marketing ploy. i don't mind getting premium, but the thing is we will be sharing this car and i can't stop him from putting regular gas in it. i already tried speaking with him and even though the manual and dealership both recommend premium higher-octane gas, he refuses to listen.

i have two questions:
1) how much is this going to matter? will using regular seriously affect the car?
2) if so, is there any way i can offset any negative effects that could come of this? my friend was saying something about something you can add to the engine/fuel ...

i've tried convincing him otherwise and it looks like there's no way ...

thanks in advance ..

Dan Martin

The ECU will retard the engine timing to cope with the lower octane. You'll lose power and your mileage will suffer.

xpolosp0rtx

hmm ... and no way of counteracting it?

Dan Martin

You can get octane additives that you just dump in your gas tank. It should do the job but it's pretty expensive to do it regularly.

Eeyore

If you are thinking of octane boost additive, I would recommend not going this route. Modern engines such as the one in the TSX are meant to run on premium regular gas (ie no additives). Who know what very high octane levels will do to the engine or various emission sensors. Probably nothing good. Besides, if you use octane boost, the octane level in the fuel will always be changing since it sounds like you'd be the only one putting it in.

My suggestion -- every time you take the car, go fill it up with 93 or 94 octane. Then forget about what your Dad does, the car will be fine.

Dan Martin

xpolosp0rtx

oh, okay good ... i was under the impression that using a high-octane wouldn't balance out the lower-octane gas my dad would be putting... gotcha, thanks.

JTso

iTrader: (2)

Just keep the tank full with premium, so your dad doesn't need to go fill gas. Problem solved!

n3ok318

iTrader: (1)

i filled up with 87 couple times, no problemo

o_nate

Here in NJ, it's illegal to pump your own gas. Once when I was getting gas and the tank was already half full, and I noticed that the attendant had hit the button for regular gas, even though I told him premium. So I told him, and he stopped the pump, rang me up, then filled the rest with premium. Since then I always check to make sure they hit the button for premium.

Jim Holloman

> he says that it's just some marketing ploy

I can assure you that it is not a marketing ploy. If it was, then aircraft like the Cesna C-152 would have been using 90 octane rather than 110 octane when it was available. And, race cars would be using street gas. Want to guess where many race cars get their gas -- at the airport. Why, because it has higher octane. In fact, in some states, it is illegal to fill a car with gas from a pump used to fill aircraft. Why? Because it can make a car go!

Why does you father want to use 87 octane in an engine designed for 91 octane? It will not save any money. The difference is price is offset by a loss of mileage. The TSX will retard the timing to compensate for the lower octane and the power, as well as the mileage, will drop. I have tried this in two other vehicles. I found that in both cases, the drop in mileage offset the difference in price of the gas. Higher octane means slower combustion; resulting in greater power; especially if the engine is designed to take advantage of higher octane. If it were not for the need for higher octane, then we would never have had lead (a toxic metal) in our gasoline, nor the expensive additives that have replaced lead (some that can be harmful to engines).

I hate to say it, but you father is not fully informed when it comes to gasoline. And, it sounds like he has little interest in expanding his level of knowledge. I had a father that burned up an automatic transmission because he believed that anti-freeze wasn't desired during the Summer months. He flushed out a radiator a half-dozen times in an effort to keep a car from boiling over -- but refused to add anti-freese during the Summer; it was an unnecessary expense. He was so set on it that he would drain the radiator in April (antifreeze included) and put in fresh water.

DEVO

higher octane does not mean greater power... hate to rain on your parade.

an engine with higher compression ratio can generate more power if using gas that will combust at the right time... i.e. higher octane gas.

Jim Holloman

Given a fixed spark timing, both low octane and high octane will combust (ignite) at the same time in reference to crankshaft position. It is the speed of combustion that is the difference. I have used both regular and high octane in two vehicles that had no adjustment of spark advance other than RPM's (flyweight on a distributor). In both case, the high octane produced better mileage. That indicated, at least to me, that the higher octane fuel was producing more power -- with power being synonymous with energy in this context.

It is also my understanding that a primary reason diesel produces more energy, and thus better gas mileage, than gasoline is because it has a slower rate of combustion. To witness the difference in the speed of combustion, throw a match on a puddle of gasoline and then thow a match on a puddle of diesel. On second thought, that experiement is NOT RECOMMENDED when it comes to the gasoline.

Boosting the octane of gasoline makes it a little more like diesel. If I recall correctly, the term octane directly relates to the "speed of combustion". Someone correct me if I am wrong.

Having a slower rate of combustion allows the spark timing to be more advanced, resulting in more effective use of the pressure produced without causing value pinging or engine knock. But, even on a engine that makes no adjustment in spark advance for higher octane the mileage can increase.

MrChad

No offense to your dad or anyone in specific, but if you pay $27k for a TSX and are too cheap to use the recommended gas, WTF!

Buy an Accord then, it's a fricken couple bucks per fill up.

God, the Prius was made for folks that horde pennies over gas.

Putting cheap gas in the TSX is spending a dollar to save pennies.

You could always do a mpg study to show him the proofs in the pudding.

It's 4cyl TSX not an ubber utte, it's not like you're blowing through the 93 octane good stuff either?

sauceman

Wrong. Diesel has a higher calorfic value. For the same volume, diesel contains more energy, so it is more efficient. This is why you have a better mileage with diesels.

Diesel also has among things, a higher flash point, so it is less prone to explosion than gas.

In this you are right that it is a slower combustion fuel. It has the advantage to withstand very well high engine pressures, allowing it to reach a very efficient burn.

DEVO

I can tell you right now that if I put 93 octane gas in my honda civic hybrid I will not get an increase in gas mileage and will get the opposite effect. Again... match the octane to what your engine was designed for, for the best results in mileage.

There are studies of this done where putting higher octane gas in a car that didn't require it, and showed that the car's performance suffered along with gas mileage. I'm sure you can do a google search to find this.

Dan Martin

From the horse's mouth:
http://www.shell.ca/code/motoring/en...es/octane.html

kaikai114

I went with 87 once and got a feel of the car. Throttle response is so much retarded and the car is less willing to climb up to higher rpm (also works harder to get up there). Engine doesnt run as smooth when rev'd high. After doing a similar drive (half freeway/half local), with 87 I got a 24 miles/gallon. Wherever I usually get 27-28 miles/gallon with 91 premium.

-K

ClutchPerformer

Actually, you get better mileage in a Diesel engine mostly because you don't put in as much fuel per cycle.

But you are right that the energy density is greater with Diesel fuel. It's because there's more Carbon-Hydrogen bonds to break (and release energy) since the molecules are bigger than iso-octane.

ClutchPerformer

Corrected.

Do your experiment with the gas on the floor. The 87 puddle will burn at the same rate as the 93 puddle.

JonDeutsch

In the Philadelphia region, I am only given 3 choices of octane:

87, 89, 93.

So far, I've been going with 93, but as you know, the prices are skyrocketing and I'm just wondering what the performance hit would be (and mileage hit) for 89 vs. 93?

And why can't I get 91???

Jon

jlukja

Jon,
My guess is that you will not see a significant enough performance and economy gain from using 93 to justify the additional cost of 93 over the 89. I know its a PITA but you could refil at 1/2 tank alternating between 89 and 93. Otherwise, I'd go with 89.

ClutchPerformer

I wouldn't use 89. The 91 is a minimum number, so 93 won't hurt you in any way. The 89 will, though (through spark retard and decreased power). I have the same problem, and I use 93.

rifleman

Someone attributed the the unavailibilty of 91 in the Delaware Valley area to altitude--everything is sea-level. Can you get 91 in the Poconos? So in an engine that specifically calls for 91, is the greater risk in putting in a little lower or a little higher octane--neither of which is recommended for the TSX. Or do you split the difference and fill up half the time with 89 and the other half with 93? So far I've been putting in all 93, but am aware of the reports that using a higher octane than called for in an engine is as bad in its own way as using lower. A good question for Acura 800 people or my local service rep-whom I haven't had the pleasure of meeting yet.

osubuckeye98

The TSX has a high compression engine so it needs fuel with the ability to withstand premature detonation. Why does the TSX have a high compression engine? The engineers say a V6 was not a good fit for the TSX chassis, so in order for the TSX engine to produce similar power to a V6 with less cylinders, it must use more pressure in the combustion chamber (cylinder). Higher compression means more power. Higher pressures also means the fuel/air mixture in the combustion chamber must be resilient to spontaneous ignition, which results in loss of power because the four stroke cycle of our beloved internal combustion engine is now out of balance. There are a variety of ways to do this, but for the TSX, using higher octane fuel is the answer.

Gasoline's octane rating is it's ability to withstand premature detonation and is derived from a comparison with a similar mixture of heptane and isooctane. Heptane is extremely volitile and doesn't like compression while isooctane is very stable. So on a scale of 100, 93 grade gasoline is equivalent to a mixture of 93% isooctane and 7% heptane. This mixture is a lot less likely to ignite spontaneously than one with 87% isooctane and 13% heptane. The compression ratio of the TSX engine requires you to use gasoline that is more resilient to premature ignition.

You can still use low octane gasoline, however you will lose both mpg and performance because the engine is now operating outside of its optimum parameters. Low octane gasoline causes knocking and knocking causes internal engine damage over time.

So does higher octane gas mean more power? better gas mileage? Absolutely...but only if you are running a high-compression engine. It's useless in normal-compression engines.

Sorry about the long post...

lamster

I can understand how putting lower-grade gas in the TSX will result into poorer mileage and performance, but do you have any proof about this "internal engine damage" statement? What kind of damage are we talking about here?

DEVO

because you live in area near sea level... lot's of oxygen in the air... you will find 91 octane stations the further inland you move... the reason being that at higher altitudes there is less air... no need to further retard combustion (the atmoshpere is helping because of lack of air).

DEVO

in order to maximize the power output of the engine you cannot have pre-detonation (pinging). with lower octane gas that is extactly what happens in an engine with high compression ratio. in order to not predetonate, the engine needs gasoline with higher octane to retard detonation as much as possible.

DEVO

if you are confused.... keep reading this post over and over and over and over and over... until it sinks in. this is all that needs to be said on the matter.

DEVO

91 is rare to find at sea level stations... you will find more 93 then 91. the further inland (higher altitudes)... the lower the octane rating.

MrChad

The 91 min is set solely for states like Cali with strict emissions where 91 is the highest available grade.

ClutchPerformer

Yes!

DEVO

i suspect it's not an emission related reason for having 91... but more to do with cali being in area where you can end up at high altitudes within a 100 miles.

ClutchPerformer

Warning: This answer is complicated!

Still with me? OK. So knock is an auto-ignition (meaning not sparked) of the fuel/air mixture. It causes high frequency pressure variations in the cylinder. Pressure variations can also be interpreted as sounds (by your ear), thus you can HEAR knocking in your engine (it's a pinging/panging sound like if you were to hit the side of your block with a small hammer).

So let's talk about the gases in the engine really quick. Hydrocarbons burn at temperatures on the order of 2000K (2273C). Quick! What's the melting point of Iron/Aluminum? (what most blocks/heads are made of)

Answer:
Iron: 1538C
Aluminum: 1675C

So the combusting gases are hotter than the melting point of the materials your engine is made of!

So why doesn't the whole thing just melt? Well there's many reasons, but the main one is that based on fluid dynamics, there's a "thermal boundary layer" between the walls of your cylinder/piston crown/head and the hot gases inside. In this layer, there's a temperature gradient (a gradient is a variation in space) from the hot to cold gases. The bigger the boundary layer, the lower the gradient, and the slower temperatures change from hot to cold as you get closer to the walls.

Now, the heat transfer to your metal surfaces is directly based on this temperature gradient. A higher gradient >> more heat transfer at same temperatures. So you WANT low gradients and big boundary layers so that ALL of the heat from those way-too-hot gases doesn't get to your block/piston/head.

So where does knock come into play? To put it simply, the pressure variations that come with knock "scrub" the boundary layers off of everything they come in contact with. From the previous discussion, you can imagine that the lack of a sufficient boundary layer means a high temperature gradient between the gases and the walls, and thus a LOT more heat transfer to the walls.

So what does it all mean? The engine is designed to run normally, and under normal conditions, the boundary layer is thick enough that your engine isn't in danger of melting. When you run outside of those normal conditions, you have higher than normal heat transfer to the metal and you run the risk of heating it up too much. If you've ever seen a "burnt" piston, you'll know what I mean.

It's cool stuff. Kinda scary, too. But one or two knocks won't kill you. This usually happens over a long period of time since knock sensors usually catch it after only one knock. If something really goes wrong (or your knock sensor goes) and your engine is continuously knocking then you'll go down quick.

Make sense?

MrChad

No the 91oct max is for emissions. Other states besides Cali have altitude.

JonDeutsch

So, if altitude is a reason for not having 91 in my region, then is 89 eqiv to 91 at my altitude?

aascsm

I agree!!!!!!

osubuckeye98

Digesting Clutch's explanation, knock is caused by a few factors:

1) Improper spark plug timing
2) Fuel octane rating does not match the engine's compression ratio
3) Excessive carbon deposits ignite the fuel/air mixture

The above factors cause the fuel to detonate in an uncontrolled fashion. These sudden/random explosions generate violent shock waves that vibrate the engine and cause the temperatures of the combustion chamber to rise to very high levels. If you let this phenomenon continue, you will cause both thermal and frictional damage to the cylinders, pistons and valves of your engine.

Think about it this way...you have a perfectly machined cylinder with a piston in it that goes up and down smoothly (very little friction), giving you the power to out run the all squirrels in your neighborhood. We all know that friction is the force that works against another. So let's say the squirrels install a small hammer that "knocks" the side of the cylinder, causing it to vibrate alot. Now all the sudden those vibrations cause friction between the piston and the inside cylinder wall. This extra friction not only slows the piston down, but also creates heat. Your one cylinder engine is no longer running smooth (efficiently). The extra heat and friction will eventually wear out both the piston and the cylinder. In the end the squirrels catch up to you.

Per others in this thread, the engine damage takes place over a prolonged period of time. However the ECU in the TSX engine is smart enough to adjust its operating parameters to compensate for the low octane rated gasoline. So you can run low octane gas, but then you will post a thread here complaining about how your TSX can't outrun the Geo Metro a couple doors down.

High performance engines are feats of engineering designed to very tight specifications (they squeeze every ounce of efficiency out of the engine). The higher the engine performance (output), the closer the operating specs (input) must be, the less room for error.

The most efficient engines burn fuel at very high temperatures very quickly. Cool running engines waste fuel (not completely burned) and mar performance and are therefore not as efficient. However the trade off for the high performace engines is that they must run very close to the knock limit (keeping the combustion smooth instead of chaotic). Remember, high performance engines run at very tight specifications, so that means you have to have a very accurate fuel/air mixture, timing and compression.

In the end, to get the most out of your TSX, use high octane fuel.

DEVO

no