legacycentral bbs

So really how much of a power gain can be expected by running higher octane fuel?

Say premium fuel as opposed to regular? 93 octane?

Will the butt dyno notice a difference here?

Octane boosters....is that a big help?

Thanks for any help,
Brad

I'm not really sure how much HP can be gained by running higher octane fuel but it will help reduce detonation. Putting higher octane in a car designed for a lower grade can actually hinder performance much as putting lower octance in a car meant for a higher octane will. As far as I'm concerned, most octane boosters are just hype.

Subaru_Nation555 wrote:Putting higher octane in a car designed for a lower grade can actually hinder performance much as putting lower octance in a car meant for a higher octane will.

Truer words were never spoken (or written )

My Legacy seriously felt like it was always driving with the brakes on with 93 octane. It has more power and runs better on 89 octane.

Remember, the more octane the gas has, the more energy is required to burn it. High-CR or forced-induction cars have that extra energy to burn the high-test. Regular engines designed for around-town use don't have that extra energy and therefore only have to work harder to burn high-test.

Higher octane allows you to run the engine with more timing than you would with a lower octane. So unless your experiencing pinging or knock, it's not really going to make a difference. The tendency of preignition in an engine is given by its octane number. The lower the number, the greater the tendency to knock.The two standards are heptane which has a value of zero and isooctane which has a value of 100.

There's a little misinformation in this thread.

Octane is mostly a measure of how compressable the gas is before it ignites itself. (knocks) This is the aki (anti knock index) which is the average of two other ratings which acronyms ive completely forgotten, but they're knock indices for idle and under load situations. Modern cars can adjust their ignition timing to make optimal use of varying qualities of gasoline automatically. This is done by advancing the timing, which increases cyl pressures. Of course there's a limit to how far the ecu can advance timing, but it allows some flexibility.

On a old car where ignition timing is not controlled by an ecu, there is no benefit to putting in better gas, in fact its worse since the gas is not near its max compression. This wouldnt be true if the old car had been re-timed to use higher octane gas.

Running a lower than reccomended octane gas in a modern turbo car is easily accounted for by the ecu, it pulls timing and boost, a modern na car pulls timing, and a mechanically timed car will ping. Either way, your performance is gonna suffer, and your engine could suffer if its mechanical and not correctly tuned.

Lower octane gas does provide for better low end power because of the nature of its explosion, and similarly won't be found as reccomended fuel in a high revving car.

Octane rating has almost nothing to do with how rich you need to be; the best engines require stoich 14.7:1 in all conditions.

Octane booster says it will raise a tank of gas 2-3 points. That's 91 raised to 91.3. Toluene is a better answer.

Appologies for anything incorrect, i did this off the top of my head at 1 am.

The difference is not in the amount of energy contained by the gas. It will be virtually the same energy per gallon regardless of the octane rating. The higher octane rating gas self-detonates (explodes without a spark) at a higher pressure, but when burned releases the same amount of energy as low octane. In fact candle wax has amost the exact same energy per gallon as gasoline - same type of bonds, but longer molecules that don't ignite as easily.

So both low and high octane contain the same energy. To get the absolute most out of the explosion, however, it has to be timed at exactly the right part of the piston stroke. If the explosion is early, before the spark plug fires, as happens during detonation, the piston is still on the way up on the compression stroke, and that slaps the piston and conrod very hard, a very bad thing. This also wastes energy.

The proper octane rating allows the ECU the fullest tuning latitude, mostly by changing the timing of the spark in relation to the piston stroke. the manufacturer makes the ECU maps with a certain octane rating or range in mind. If you ignore these recomendations, you limit the ability of the ECU to adjust and MAY lose power and mileage.

Plenty of articles have been written about this. The better the car, the LESS is will matter if you run lower octane. On certain cars when the ECU can't fully adjust, or high-performance cars requiring 91+ octane, the use of 89 or 87 will hurt a little. the numbers seem to be a few percent power loss, and at worst a couple MPG lost.

As for better low-end power with lower octane, or no benefit to using higher octane in non-ECU cars, NOPE and NOPE. It is the most benefit to using high octane in non-ECU cars, or poorly tuned cars, as they have no ability or poor ability to pull timing, and thus avoid detonation. Especially true if running lean as well.

note that I didn't say anything about reformulated gas (RFG). That has a lot of stuff in it that isn't gas at all, so doesn't burn with the same energy. It has 2-3% less energy per gallon.

Also shitty gas can hurt.

Neither of these things is the octane rating, just how much gas is in your gas. Stuff that isn't gas almost invariably has less energy, ethanol, oxygenates, etc.

professor wrote: As for better low-end power with lower octane, or no benefit to using higher octane in non-ECU cars, NOPE and NOPE. It is the most benefit to using high octane in non-ECU cars, or poorly tuned cars, as they have no ability or poor ability to pull timing, and thus avoid detonation. Especially true if running lean as well.

scottzg wrote:This wouldnt be true if the old car had been re-timed to use higher octane gas.

Just so we're on the same page.


But you're right about no better mid range from lower grade gas, i dont know what i was thinking last night.

So how come I noticed a difference in acceleration and top end power running premium gas in my 92 SS?
I believe it was 91 octane, and I dumped several bottles of octane booster in there.
Granted, this was the night before my engine seized due to ALL my oil leaking out at once.

Your ecu advanced the timing and ran full boost.

I think a better question is, why weren't you running premium gas in your car to begin with?

Alright, well because I am a poor bastard haha.
But yes, the premium gas really woke up my car.

it let you run 9 psi instead of 6 once it realized it had premium gas again.

Perhaps all your oil seals were only used to 6 psi and the sudden increase in pressure confused and bewildered them.

Lower octane gas has more energy than high octane. The additives used to raise octane have less energy than the gas they are mixed with.

I can't fathom running anything but 92 in my car. The difference when you fill up is only a few bucks. That $2 will be spent without thinking on coke and candy bar.

I will agree with Todd...


It's better to feed the SS than my stomach!



Although the SS is a very hungry child sometimes

I agree.

Which is why I'm glad that I have someone else paying for his feeding right now.......

The latest Sportcompact magazine has a good article on octane boosters.

Just get the 92-93 rating stuff and skip the boosters. ( unless you want to add toluene)

Unless you can get the 100 stuff