nfnsquared

Ah... yes!! That is the million dollar question to which no one has provided conclusive proof....

Do you still really think that lower octane gas produces more carbon build up? Is it possible that you are mistakenly thinking that lower octane equates with lower quality gas (e.g. lower levels of/inferior detergent additives)?

At any rate, two different posters have made claims that lower octane gas produces more carbon build up. I just haven't ever seen or heard of this. Again, if anyone has such documentation, I'd love to see it.

1black_seven

iTrader: (2)

Lets beat this dead horse with another dead horse.

I use Seafoam once a year to clean my fuel system. I assume it helps avoid carbon buildup, I don't really know. I just pay for peace of mind that it works, like using manufacturer recommended grade gasoline.

alexb92

TLDR;

Just because you can't hear knock, doesn't mean it isn't happening.
The engineers say it's required for your car for a reason.
The pennies you save from pumping 87 is offset by the lower efficiency/power.

CL-S progression 01

iTrader: (2)

i have not put anything in my car but shell v power. I go out of my way to make sure it's the good stuff. I drive it all the time, mostly in the city and I start the thing 5+ times a day. Never once has it even hesitated to start.

I will also add I change my plugs every two years.

My mileage is actually better than as stated.

Moral of the story. Premium gas is more than just octane

nfnsquared

That's great. Nothing wrong with running V power. Shell is indeed a Top Tier distributor. But by your own account, there can be no moral to your story because you haven't made any comparison. Just saying...

anx1300c

iTrader: (2)

You guys that think running anything less than premium is going to "hurt" your car kill me. It's 95% marketing and it apparently works wonders! Upscale automakers always advocate premium fuel. Do you honestly thing it's perfectly fine to run the manufacturer recommended 87 octane in a 10.5:1 Accord, but somehow an 11:1 TL is going to self destruct on it? Half a point is miniscule at best.


And what about the J32 A2 in the 2G TL? Guess what? That was 10.5:1 and yet Acura advocated 91 octane. Amazing the TL needed premium at the same compression ratio the Accord only needed regular. And it's not like we're comparing MPI to direct injection, either.


Worse case scenario, you lose a couple horsepower. I personally only run 93, but I want full power.

Acura-OC

Just to add to your point

My other car 3.3 V6 10.8 compression requires 87 has 125K miles and on original spark plugs. Still runs as new.

Turbonut

iTrader: (1)

Many new cars have 11+ C.R. and the recommended fuel is regular.

And on it goes, next.........................

Jackass

If I am reading nfnsquard's posts correctly, he is mostly chasing the theory here, not the real world outcomes. "If" there is no knock, there is no difference between 87 and 91. This assumes no knock. He is trying to dig into the actual details and reasons behind it and ignore the advertising that has been done to make everyone always assume 91 is better. The real world has many many other variables to take into account which other posters have covered. If there is knock, then the computer compensates one way or another and there may be negative outcomes from there over time. Lots and lots of theory here....but none of us are internal combustion design engineers here. Many may be engineers, highly intelligent, or possibly idiots.....but we didn't design this engine nor the engine management computer.

Also to note on his discussion regarding carbon build-up....he is trying to point out that 87 or 91 or 93 has NOTHING at all to do with carbon build-up. The lack of detergents has to do with the build-up. You can run 87 octane the entire life of the vehicle with minimal buildup assuming there was enough detergent present in the 87 octane fuel that was used. Now what "usually" matters here on 87 vs 91 is that many stations do not put as much detergent in their 87 octane. That is where the Top Tier fuels come in since they are "supposed" to have the elevated levels of detergents/additives in all grades they sell.

nfnsquared

^^^^^ Yup

Majofo

It's not just CR that determines if an engine is predisposed to knock at a certain compression. That being said, maybe you can provide a list of cars that do.

nfnsquared

What else is in this equation besides CR and what is the relative impact of said design vs impact of CR? I was under the impression that CR is by far the largest factor in determining knock.

CrazyEights

iTrader: (1)

Timing, as for how relative it is, well it can be adjusted to compensate for knock, can it not?

Majofo

what?

Majofo

Octane and CR are the key components, but head design or piston surface are a part of it as well. Basically under high compression, the flow of the air and fuel compressed isn't linear. Areas where flow has more restriction will excite those molecules faster before equalizing. Take a bend in a pipe. The flow closest to the bend will have more restriction than the outer side of the bend. Also, if the piston surface develops a hot spot, that will assist in raising the activity of molecules around it pushing it closer to preignition.

CrazyEights

iTrader: (1)

MikeTC

Not to start a fight but just the facts.

Here is my experience with using 87 in all my cars with high compression engines requiring premium gas (no issue what so ever):

1. 1987 Mercedes 300E, 300K mi after 15 years of service (sold)
2. 2003 Honda Pilot, 100K mi after 8 yr of service (sold)
3. 2006 TL, 110K mi after 9 yr and running strong.
4. 2010 Honda Pilot, 65K mi after 5 yr and running strong.
5. 2015 Mercedes C300, fuel TBD but it's a turbo and still half tank left from dealer so it's a wait and see situation.

Est. total saving from using 87: $13,500

DMZ

1black_seven

iTrader: (2)

This thread is going to get trolled into oblivion. Can we just get the inevitable lock?

MikeTC

As long as people are civil and respect other’s opinions, I don’t see why lock it.

Majofo

With that logic..

575,000 miles.. let's say your avg was 20 mpg. and the avg differential between regular and premium is 30 cents which is conservative.. it's more like 15 cents over that time span. Considering the bulk of your miles are early on, it's closer to ten cents.. but lets get back to your logic.. that means you saved a maximum $8625. Unless you got 13 mpg or spent a 50 cents difference over the years, your estimate is

That's not even considering that the 300E CR is 9:1, which is fine for regular. If you really wanted an estimate of what you saved, 275k @ 20 mpg @ 20 cents = $2750.. if you estimate you might have seen a 2 mpg drop because timing was adjusted on 87, that's 1250 gallons more fuel. Depending on the price of fuel during that time, let's say ~$3.. that's over a thousand dollars wasted. Needless to say, but you didn't save as much as you think you did.

aIRpeACE

iTrader: (2)

very minor differences imo

MikeTC

I was just using $7 a week saving between all the years soit’s not the same as your calculation. The300E owner’s manual stated that premium gas is to be used. Since I don’t have your resources, I have noway of knowing that regular is fine but that’s what the owner’s manual says. I did not notice a different in MPG betweenregular and premium usage since I do monitor the MPG and if the car acts up before switching to regularon each car.

In my part of the woods, it’s about 34 cents this morning betweenregular and premium; some years higher and some lower but it's pretty close in price differences. Combined MPG for300E is 18, 2003 Pilot is 17, 2006 TL is 21 and 2010 Pilot is 18 but I do mostlycity so my average MPG is more like 16-17. The est.saving is about $10-12K give or take. Notas much but it’s enough for me since all the cars work asthey should.

screaminz28

iTrader: (1)

One thing everyone (on both sides of the argument) have failed to mention is HOW the engine determines its timing, and what effect that has on the engine's life.

No matter what anyone wants to believe, the statement made previously that, "if there is no knock, increased octane provides no benefit." End of story - you can't get around that. The goal is to use the lowest octane that prevents detonation. Octane is resistance to self ignition. Anything higher than what you need is wasteful and provides no performance gain.

This can be demonstrated in many boosted applications on E85 - the octane rating is so high, and the added fuel contributes to cooler cylinders allowing one to continue to increase timing well past MBT. I've seen instances of 10 or 15 degrees timing past MBT without knock on a boosted setup, with NO gain in power. Some people think that higher timing is better for some reason, but I'd say it is the opposite, to an extent. Higher timing means the engine is less efficient. Remember, timing is BTDC, so the higher the number, the earlier it is igniting before the piston reaches top dead center. In an ideal world, you'd wait until the cylinder was fully compressed before igniting it, or 0 degrees.

If you have a 1970s SBC with 8.5:1 N/A motor, running 93 will only empty your wallet faster, it won't provide any boost in performance, at all, ever. (If you add a 80mm turbo with 25 psi, that changes things a bit )

However, with the TL, and 11:1, the timing maps within it are already designed for MBT, which in most instances cannot be achieved with even the garbage 93 E10 that most people have access to. So, what happens? It knocks, the knock sensor pulls timing. What I have had trouble determining, (I think every tuner is in the same boat here) is how LONG/what algorithm does it use for adding timing back?

Subuarus have a well explained knock control strategy as well as 'timing recovery' strategy, so it's easy to figure out.

The TL on the other hand, may constantly be trying to add timing back, detecting knock, and then retarding timing. If that is the case, then running a lower octane fuel can decrease engine longevity.

Will running 87 octane in an 11:1 N/A motor with a knock sensor put a hole through a piston? No. Will it add unnecessary bearing wear from increased knock/detonation.

In that case, it would be wise to run the lowest octane available to prevent detonation, which in the case of the TL's programming, is 93.

nfnsquared

As I said, the key engine component is CR. Nothing else comes close AFAIK. Yes, piston design plays a small factor, but you also have to assume that the engineers of high CR engines design the pistons to minimize chances of detonation.

CrazyEights

iTrader: (1)

Careful, I was laughed at when I mentioned timing, apparently octane doesn't affect timing.

Yikes

Because people have been using the same arguments for years and years. To say threads like these are just beating a dead horse is the understatement of the century. The outcome is always the same: no one ever changes their opinion, and no one is ever able to convince anyone else of their position.

Most of us are set in our ways. There are those of us that want to use 93 octane because that's what it says in the owner's manual. There are other that want to use 87 octane because they don't really see the need to use 93.

You'll never convince me to put anything lower than 91 in my TL, and I'll never be able to convince you to use anything about 87. It is what it is.

We can dance around different scenarios and "what ifs" until the end of time, but at the end of the day in the real world, and engineering especially, there are no textbook scenarios or problems.

Especially by today's standards, vehicles are designed to operate within a very narrow margin. Most modern engines are engineered and tuned to maximize fuel economy and performance from the factory- the way the engineers designed it is usually the best it's going to get without modification. Deviate from the parameters of which it was designed to operate in, and your results aren't guaranteed.

Majofo

While it is a key factor, using the old baseline arc head geometry and flat piston design, you'd be on 110 octane to keep it running well at 11:1. The J seems to have been designed well to try to keep pressures uniform. The valley of the intake and exhaust side are flat and angled. The top of the piston flows with the head design to inhibit preignition. It's not optimal but it's not bad.

Mcesar84

the worst I've ever done to my TL is a 50/50 mix of 87 and 93.. some stations think it's acceptable to upcharge premium by $1.00 when you're in the middle of nowhere

08RLTech

what about kerosene... its cheaper, and sold at my local fuel station, so it must be ok for my engine. I think ill start using that instead... after all I graduated top of my GED (online) class and consider myself an expert of things and stuff. I didn't spend money on a luxury vehicle just to follow some lame engineers' opinions on how to fuel my vehicle based on facts and numbers and junk...
check and mate

Majofo

Just make sure the kerosene is top tier.

2012wagon

Curious in the 5 cars you mentioned, have you used premium too, to benchmark what the performance is, vs the 87?


I realize the Pilots aren't sports car, but curious if you lost anything in performance as well.


I personally put Premium, but I understand other's choices in putting something different.

Turbonut

iTrader: (1)

Not to put dent in your saving theory, the Pilot's don't require premium, they call for regular, but the others certainly do.

wackjum

I have a question I've been kicking around in my head for a few years now.

Don't flame me. I fully understand the concept of octane, compression ratio, etc. But here is my question:

Is the pressure in the cylinders the same regardless of load, or is it variable according to the throttle?

I would think that any throttle position less than WOT would mean that the cylinders aren't filling up all the way with a full charge of air/fuel.

If the engine requires premium octane in order for the fuel/air mixture to not spontaneously detonate when the cylinder pressure is at full design specs, the pressure must necessarily be less if the fuel/air mixture is decreased. Lower pressure means lower octane needed to resist detonation.

So the logical conclusion if all of this holds true is that if the car never sees full hard acceleration, it may never need higher octane gas.

Could somebody tell me why this would not be true? I could be fundamentally flawed on my understanding of how throttles work.


PS: I always use what the manual calls for. But this is a thought experiment.

DMZ

That's all you need to know! 'Nuff said.
.
.

polobunny

I believe this to be somewhat true, as long as you say "MAY" instead of "WILL NOT".

The problem with this train of thought is that even if you did not need higher octane gas in most situations, let's say there's an emergency situation where you need to accelerate quickly to not get in an accident or similar, would you enjoy your engine to trash itself? Would you enjoy if your engine got into limp mode by retarding timing and running the chance of getting in an accident?
Obviously the answer is no. Why some people want to take the chance with such important consequences, that I can't tell.

Acura-OC

I think there are different situations for detonations one is with high RPMs and another is with low RPMs. Try pushing a car from stand still position or keep pushing when it is rolling. Most of us do not floor it from stand still position, throttle could be at 35-45% position yet there will be detonation. Same if you are cruising at a slower speed on a higher gear with a lower RPMs that is when engine is more prone to detonation.
But it appears to me that the logic in this and other new cars build that way that if it pulled timing at certain load it will remember to pull timing during same circumstances for next XX time period or XX miles, I do not know which is it could be combination of both (only programming engineers know). Then it will keep trying to readjust itself to a norm. But I do not see any reason why would it need higher grade gas when engine is not under stress.
My flawed logic doesn't let me understand why would there be loss in MPG when you are cruising on a freeway when engine is not under stress.

nfnsquared

Same here. And I have driven over 10K highway miles in the last 8 years using 87 with no decrease in MPG. I just drove 800 highway miles this week on 87 and averaged 29 MPG on winter gas. I'm at 184K now.

MikeTC

I used premium on all my cars during the break-in period 500-1K mi, then I monitor if performance changed when regular is used. No differences in performance, MPG or long term reliablity issues but that just me.

Turbonut, you're correct, Pilots call for regular; my bad.

Majofo

This is a false assumption. Throttle and vacuum go together.. WOT is because at high RPM, vacuum drops as the scavenging process becomes almost laminar. Unless the head design is shit, valves don't seat right, blown rings, bent rods / bearings or there is an issue with the scavenging process, the CR doesn't change and is fairly uniform during the combustion cycle. Think about it, AF mix is drawn in under vacuum during the induction cycle, valves seal, AF mix is pressurized, then spark / combustion.

The volume change is uniform during this (from full volume to /11) so as long as the AF mix is uniform, which it should be unless there is an issue in the scavenging process, the pressurization of the AF mix remains the same. At very high RPM some roll-off might occur on some vehicles as the max efficiency has been reached. Anything more and your beyond spec, you lose power..

That being said, vacuum is relative to air pressure. When does that change? Temperature.. but primarily with altitude. So some of you mile high guys might get away with lower octane because the relative air density is less thus less likely to preignite. That's why you guys suffer power loss at high altitude.



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