Gasoline octane?

[kwren]

I suppose the general consensus is that the higher octane gasoline is better to burn in our SVX's. What does the higher octane do that is different than the regular?
What could result in maybe mixing half a tank of each instead of a full tank of one or the other?

Anyone know?
Thanks,
Keith

[lilbrudder]

higher octane = less ping and knocking = ME

i always use 91 fuel but just recently started adding octane boosters, my engine has been noticeably smoother and quieter.

[lilbrudder]

higher octane = less ping and knocking = ME

i always use 91 fuel but just recently started adding octane boosters, my engine has been noticeably smoother and quieter.

[Hocrest]

Premium is not "better" than regular. It has a higher octane and it burns less easily.

On higher compression engines like ours, the higher detonation temperature of premium helps to prevent pre-ignition.

[lilbrudder]

^oops, sorry. my web sux here!

[kwren]

Originally Posted by Hocrest

Premium is not "better" than regular. It has a higher octane and it burns less easily.

On higher compression engines like ours, the higher detonation temperature of premium helps to prevent pre-ignition.

mean the higher octane actually burns slower?

Thanks,
Keith

[dragoontwo]

Originally Posted by kwren

mean the higher octane actually burns slower?

Yes. 1234567890

[lechnoid]

Fuel's octane rating measure it's ability to reduce knock. The higher the octane fuel, the slower and more controlled the burn is. Running fuel with too high of a rating (without proper tuning) will have you running rich and leave more unburnt fuel going into the exhaust. This can lead to premature catalytic converter failure.

This discussion does bring up an interesting point though. What is the recommended octane rating for the SVX? I know it says mid-grade, but what octane that is depends on what part of the country you're in. I lived in Nevada for 3 years. Out there, premium was 91 octane. In Minnesota, premium is 93 and sometimes 94, with the 94 usually being 10% ethanol.

Additive octane boosters are generally bad. Generally being about 98% of the time. If you're paying less than $40-50 for a bottle of it, likelihood is that it is wearing away at your fuel pump and injectors because of what is used to make it. Same goes for over the counter injector cleaners.

Instead just avoid going to the cheapest gas station in town and go to one of the more expensive, bigger named places. In general, their fuel will be cleaner, have better additives (from the refinery, not the parts store), be more stable, and have more accurate octane ratings. Also, go to the busier gas stations, as they get fresh refills more regularly. Gas loses octane as it sits, but that's usually over longer times, but also the holding tanks collect moisture inside through condensation over the course of a day's warming/cooling cycle. The more days the gas sits, the more water you'll end up with in it.

I think I'll get off my fuel soap box now and go have a bowl of Lucky Charms.

[dcarrb]

Originally Posted by lilbrudder

i always use 91 fuel but just recently started adding octane boosters, my engine has been noticeably smoother and quieter.

This would concern me. My cars start enthusiastically, idle contentedly and run strong, and I run a mix of grades from the cheapest joint in town.

Fuel additives, injector cleaners, octane boosters and other high-priced magic potions are marketed specifically to separate money from your wallet. Most may "work" in some respect, a few may not, but the thing is, you don't need a one of 'em.

Does anybody still make a lead substitute for old engines designed to burn leaded gas? That would be an exception to the additive rule.

dcb

[Ownbot]

I have been told that the higher octane gas just has more impurities so It will ignite at a higher temp, thus being more "dirty" and not as good for your engine as a lower octane "cleaner" fuel.

[Subix]

Originally Posted by Ownbot

I have been told that the higher octane gas just has more impurities so It will ignite at a higher temp, thus being more "dirty" and not as good for your engine as a lower octane "cleaner" fuel.

The only impure thing about premium gas is the price tag associated with it.

[oab_au]

Originally Posted by lechnoid

Fuel's octane rating measure it's ability to reduce knock. The higher the octane fuel, the slower and more controlled the burn is. Running fuel with too high of a rating (without proper tuning) will have you running rich and leave more unburnt fuel going into the exhaust. This can lead to premature catalytic converter failure.

.

There is no different in the burn speed of 92 octane to 98 octane. The only difference is in the 'flash point' of the fuel. This is the temp/pressure that the fuel can stand before it will self-ignite. A higher octane can stand a higher combustion chamber temp/pressure, before it will self-ignite/detonate.
It won't make it run rich or hurt the cats.

Harvey.

[kwren]

Originally Posted by oab_au

There is no different in the burn speed of 92 octane to 98 octane. The only difference is in the 'flash point' of the fuel. This is the temp/pressure that the fuel can stand before it will self-ignite. A higher octane can stand a higher combustion chamber temp/pressure, before it will self-ignite/detonate.
It won't make it run rich or hurt the cats.

Harvey.

There was different octanes in fuel before there were any "cats"

People on the USAF that stole airplane gas would burn the valves on their car because the burn speed was too slow.

[crazyhorse]

Originally Posted by kwren

There was different octanes in fuel before there were any "cats"

People on the USAF that stole airplane gas would burn the valves on their car because the burn speed was too slow.

The valves would burn due to the increased combustion temps and pressures that the higher octane brings. (Because of the slow burn) Add in the fact that the old US stuff didn't have hardened valve seats, and you have a recipe for destruction.

The other thing to remember is that back then "regular" was 110 octane.
AvGas could have been upwards of 200 octane!

Modern AvGas is 100-130 octane, depending on air/fuel mixture. It's not rated the same, so a direct compairison is difficult. The older chemistry was rated the same as today's pump gas.

[oab_au]

Originally Posted by kwren

There was different octanes in fuel before there were any "cats"

People on the USAF that stole airplane gas would burn the valves on their car because the burn speed was too slow.

Yes Keith, there has been octane changes since we moved from using Kerosene.

Well don't know about the USAF. but the burn speed is fairly constant for most of the hydrocarbons, at the same temp/pressure, regardless of the octane rating.
If the burn speed was slower, we would have to change the spark advance, with different octanes. We only have to change it to suit the compression pressure/detonation point.

Harvey.