Mr Incredible

So, by what you are saying, performance is all about the timing table and has nothing to do with an increase in octane.

By that logic, 89 octane will perform no better than 87 octane as long as the timing tables are the same. For that matter, as long as the timing table is not switched, anything higher than 87 will not perform any better.

Likewise, 91 will act the same as 92, 93, or 94 octane...no measurable increase in power. I don't see how that could be a true assumption.

As for an increase in mileage due only to increased octane, without a performance gain? With no other changes an increase in mileage is automatically an improvement in performance. Maybe even measurable by dyno?

I'm no expert with timing tables or tuning, nor do I have years of experience with them. But it seems to me, all things being the same, that an increase in octane within the parameters required for operation of any internal combustion engine will produce more power...up to the point where it doesn't.

Timing being the same, 89 will produce more power than 87 octane. 93 will produce more power than 91.

I hope my assumptions of your statement are correct and my own expressions are clear. It's early yet and I'm not sure I've had enough coffee for in-depth thought.

ChocoTaco369

seafoam is great stuff. in my old 3.4L, i put some in at 75,000 miles and smoked out the pike in blue smoke for a quarter mile. cars were slamming on their brakes and everything. everyone at my buddy's dad's shop were cracking up. some random guy making a tire delivery commented "that kid's got issues."

ChocoTaco369

it's a myth. the minimum is all needed. any increase in mileage, if any (it's not proven) is so small, it's unmeasureable to the point that it's not worth the extra nickel a gallon. all power gains are the "placebo effect." people expect more power so they feel more power. octane is something that if you use less, you lose power and mileage but use more and see nothing. just use the necessary and no more.

the only way you'll see benefits is if you have your ECU tuned for it.

Mr Incredible

I'm sorry, but that just doesn't make sense. If it works one way, it works the other way. Incorrect oversimplification.

$.02

jmm98LS1

iTrader: (28)

Let's put this to rest, mmmmk?......

Octane: There is NO ADDITIONAL ENERGY in 93 octane over 87 octane....none.....period. As the octane rating of fuel goes up, the energy required to light the air/fuel mixture goes up, making the burn more controllable. The energy produced from the mixture combusting does not go up.

Timing: The ls1 is programmed from the factory with timing tables to run on 91 octane fuel. The values in the high octane table are optimal for 91 octane. If 93 is in the tank, the pcm will not add more timing.....the values in the high octane table is as high as they go....period. You will not make any more power with 93 octane, or 100 octane for that matter, unless the high octane table values are increased.

There are knock sensors in the motor. If they detect any knock (for example, if you put 87 octane in the tank), they will pull timing from the values in the high octane table until the knock is supressed. If this happens enough, the pcm will switch to the low octane table, which carries spark values low enough to safely run on 87 octane fuel without spark knock. The pcm will continue to try to switch back to the high octane table as long as knock isn't detected, so for example once the 87 octane we put in the tank is gone and we've driven with 91 for few driving cycles it will default back to the high octane table.

What does all this mean? You'll make less power with 85, 87, 89 octane than you would with 91, because the pcm pulls timing when spark knock is detected--not because there's less energy in lower octane fuel.
You will make the same power with 92, 93, 94, 100 that you will with 91. Of course, this is assuming you are detecting zero spark knock with 91 octane. If you, for some reason, are getting spark knock with 91 (could happen in extremely high temps/humidity) then higher octane fuel will keep timing from being pulled and produce more power. Clear as mud?

ChocoTaco369

never said anything about energy. you only need the minimum for octane. your car won't run better on 93 than 91, assuming it doesn't ping on 91, but it could run like **** on 87 or 89. since it only dictates how fast fuel is being burnt, as long as it's enough to keep detonation from happening, that's all you need. 93 is not >91 unless your car pings on 91. 87 and 89 may not be a good idea as the general does not recommend them.

ChocoTaco369

nope. wrong. you only need the minimum to suppress detonation. it's not a power adder.

Mr Incredible

I disagree, but thanks anyway.

N4cer

iTrader: (11)

I'll agree with you here. Totally. I was just disagreeing with a car "getting used to" the type of fuel.
And also with the whole "91 will ping the same as 93". Which you clearly refute in your own argument above, making yourself clear.

ChocoTaco369

all i was saying was that while it may be bad to run 87 or 89 octane as it is not recommended for our engine, using 93 octane DOES NOT necessarily mean that it'll postpone detonation longer than 91 octane will, assuming detonation will occur in the future of your engine's life. your ping could develop at exactly the same time if you use 93 or 91, but we'll never know for sure. i recommend using 91 because if the ping ever does occur, you have a cushion to fall back on (you can use 93). if your ping develops while you're using 93, you're in trouble.

Mike02Z

iTrader: (13)

I agree that you will make no more power on 93 than 91. I also think any additional mileage or power that people think they get on 93 is in their minds. I further think that running 87 on a stock tune is not a smart idea as the stock PCM was programmed around using 91.

I also think that if you feel better running 93 go ahead, it's your car and at an additional 5 cents per gallon we're talking 65 cents more per tank so who gives a ****?? Certainly not worth getting upset over it.

jmm98LS1

iTrader: (28)

Sorry man it's the truth, whether you like it or not.




I just don't get why you assume that every engine is going to start pinging eventually.....you act as though it's an unavoidable disease that motors catch as they age.
I've run a small block chevy into the ground with upwards of 300,000 miles running nothing but 87 octane gas and it never "developed ping". I eventually pulled the motor because it leaked down about as fast as it could build compression (rings were totally shot) and it burned over a quart of oil every 1k miles.....no pre-detonation of any kind. Where do you get this presumption that pinging is just a fact of running an engine over time?

Glad to see we're straight on the use of octane though.

blkbird

iTrader: (28)

All I know is that my car ran like crap with anything below 91 octane.....

ChocoTaco369

yes, i just quoted myself. key word there is "assuming." the whole time, we have been assuming ping is inevitable. i never said you yourself would ever get it. hopefully you will never get it. i'd never want an LS1 to suffer

MrDude_1

iTrader: (4)

thats because your engine is designed for premium.
when you put something below 91 in it (assuming you arnt at high elevation), it pings.
the knock sensors detect this, and the car pulls ALOT of timing.

if this continues, the computer reverts to the low octane table.. this table is not very efficient, and will pull enough power out that you can feel a diff.

Zick

iTrader: (18)

You just said that at some point in time if the engine does not blow up it will develope ping. This statement would include every person in the world who drives a car.

ChocoTaco369

yes, meaning if the engine never ever ever dies. it HAS to eventually develop ping, it just may take a million miles. assuming you wait til ping starts. it has to at some point. it's just like saying if the only thing able to fail in the engine were the pushrods, at some point the engine would HAVE to fail due to the pushrods, it just may take a long long long time. i'm just assuming nothing can go wrong but ping. this makes pinging inevitable. the reason why i'm saying it may never happen in real life is because this is a completely unrealistic scenario, it's hypothetical just to illustrate a point.

Mr Incredible

http://en.wikipedia.org/wiki/Octane_rating

Pertinent entries:

"It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation (pre-ignition = engine knock) as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.

A simple explanation is the carbon bonds contain more energy than hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content. "

"Using high octane fuel for an engine makes a difference when the engine is producing its maximum power. This will occur when the intake manifold has no air restriction and is running at minimum vacuum. Depending on the engine design, this particular circumstance can be anywhere along the RPM range, but is usually easy to pin-point if you can examine a print-out of the power-output (torque values) of an engine. On a typical high-rev'ving motorcycle engine, for example, the maximum power occurs at a point where the movements of the intake and exhaust valves are timed in such a way to maximize the compression loading of the cylinder; although the cylinder is already rising at the time the intake valve closes, the forward speed of the charge coming into the cylinder is high enough to continue to load the air-fuel mixture in.

When this occurs, if a fuel with below recommended octane is used, then the engine will knock. Modern engines have anti-knock provisions built into the control systems and this is usually achieved by dynamically de-tuning the engine while under load by increasing the fuel-air mixture and retarding the spark. Here is a white paper that gives an example: http://dinancars.com/whitepapersFile.asp?ID=9 . In this example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). "

ChocoTaco369

it doesn't create more power. it's a tradeoff. it contains more energy but since it burns slower it negates it. please, dyno YOUR car with 91 octane then 93 octane on the same day, same temperature, same conditions. see if it makes more power. you'll be disappointed.

what does that car tested on that site recommend? does it require 93 octane? find that out, i'm too lazy to read all this. your car will lose power if you give it less octane than needed, but more octane shouldn't show more power.

this has been tested over and over recently due to the gas price increases. what "wikipedia" says doesn't mean it holds in real life applications.

Mr Incredible

In this example the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp).

So you're saying that switching back from 91 to 93 in the same test/engine will not regain the lost power?