do i really need premium gas for my new car?

[strawjack]

gents- its all the same shit coming out of the ground...doesn't matter what button you push...there's only one hose!

[Patches]

If you live in the mountains and have a normally-aspirated engine (i.e. non-turbo) you can get away just fine with 87 octane. The air is thinner at altitude, at 7000 peak cylinder pressures are 25% lower than sea evel so knock isn't a problem. If you live at sea level I'd buy the 91.

My car requires 91, I run 87 all the time and never knock, so why waste the $$$? I just have to remember to switch back if I do down to the flats to visit friends.

[JTrue]

Not even $3, really, assuming that you'd otherwise use the mid-grade gas rather than regular.

I believe that Subaru's ECU attempts to adjust for lower octane gas by reducing available power (I don't know of a modern turbo that doesn't), but isn't that what you spent the extra money to get?

Probably just a knock sensor, when the sensor senses detonation it retards the timing which in turn lowers power output by a bit.

[Steven S. Dallas]

You're on the original turbos? If so that's sick.

Yeah, I thought those old Saab turbos uniformly blew up at 100K. Sweet ride, Frank.

[ljm]

Speaking of older Saabs, I'll share my story.

I bought a single owner '85 900 Turbo a few years ago for my girlfriend at the time. The guy absolutely babied the car. 185k, hell of a good looking car, a lot of the SPG stylings. Only drawback, it was an automatic. It's gone now, but that pic of the dash brings back good memories of that car.

[iceman]

Honest to god I didn't even know 900 turbo automatics existed. huh.

[FrankZappa]

Honest to god I didn't even know 900 turbo automatics existed. huh.

Especially back in '85. Wonder what it does if you get on it & just when the boost overload goes to cut out... the tranny does a shift

[ljm]

Honest to god I didn't even know 900 turbo automatics existed. huh.

yeah, I'd imagine they're pretty rare... I can't fathom why the guy bought an automatic. he was a pilot, seemed like the type that would have loved the manual. he loved that car... hid a decent bottle of wine in the back seat for us when we bought it.

[AltaPowderDaze]

i've been running 93 octane per manufacturers instructions and my car does fine in the flat lands. when i come to utah and get stuck using 91 octane, my car constantly gets spark knock at high rpm's. i've been considering using hotter burning plugs but short of using an additive is there really anything else to try? i am beginning to wonder about the octane ratings like strawjack suggests.

[f2f]

my golf, bought in canada, has a minimum octane rating of 87, which means i need to put premium (88) here in the us. it's 10 cents more per gallon, but it has raised my mileage by a considerable amount, especially when you count in that the car is being driven at 7000ft above sea level constantly (i'm at 7400 or thereabouts). i've gotten cleaner engine, lower noise, better performance out of the whole deal. that, and i now know which gas stations spike their "premium"

for me it is worth it.

[FrankZappa]

i've been running 93 octane per manufacturers instructions and my car does fine in the flat lands. when i come to utah and get stuck using 91 octane, my car constantly gets spark knock at high rpm's. i've been considering using hotter burning plugs but short of using an additive is there really anything else to try? i am beginning to wonder about the octane ratings like strawjack suggests.

Fill up at the airport.

[Evmo]

yeah, I'd imagine they're pretty rare... I can't fathom why the guy bought an automatic. he was a pilot, seemed like the type that would have loved the manual. he loved that car... hid a decent bottle of wine in the back seat for us when we bought it.

Those autos were 3 speeds... amazing. I had an 89 SPG 5sp... such a great f'ing car. Blew the tranny @ 235k, didnt have the funds to input new tranny + new clutch (also in need). Still have the rims in case anyone wants some vintage SPG wheels (3-spoke)... toight!

[f2f]

If you live in the mountains and have a normally-aspirated engine (i.e. non-turbo) you can get away just fine with 87 octane. The air is thinner at altitude, at 7000 peak cylinder pressures are 25% lower than sea evel so knock isn't a problem. If you live at sea level I'd buy the 91.

My car requires 91, I run 87 all the time and never knock, so why waste the $$$? I just have to remember to switch back if I do down to the flats to visit friends.

hmm, frankly, i kept thinking that at higher altitude i'd need a faster-combusting fuel because the oxygen is so low.

back to grade 10 physics textbooks for me!

[FrankZappa]

Those autos were 3 speeds... amazing. I had an 89 SPG 5sp... such a great f'ing car. Blew the tranny @ 235k, didnt have the funds to input new tranny + new clutch (also in need). Still have the rims in case anyone wants some vintage SPG wheels (3-spoke)... toight!

You should have called me - I'd have taken it off your hands. Thats an easy enough fix.
Maybe someday I'll take the rims (how much) - savin' for ski tix now. + need to check the bolt pattern '85 to '89.

[lemon boy]

i've been running 93 octane per manufacturers instructions and my car does fine in the flat lands. when i come to utah and get stuck using 91 octane, my car constantly gets spark knock at high rpm's. i've been considering using hotter burning plugs but short of using an additive is there really anything else to try? i am beginning to wonder about the octane ratings like strawjack suggests.

Check the car for instructions on high altitude operation. Cars operating at higher altitudes should run a little timing advance (usually ~2*s). I dunno if newer cars do this automatically though.

[1000-oaks]

If youre driving around town regularly, chances are you arent loading your engine enough to create a scenario where it will detonate and wont make any difference. Also depending on how each engine manufacturer programs their ECU, it could retard fuel as well as spark to compensate for detonation and the possibility exists for lower fuel consumption.

Actually I have two Toyotas that ping only at very light throttle - such as slowly accellerating or climbing a slight hill. At heavier throttle I presume the ECU increases the fuel to air ratio and the pinging goes away.

[routter]

Start here:
(http://www.howstuffworks.com/question90.htm)

What does octane mean?


If you've read How Car Engines Work (http://auto.howstuffworks.com/engine.htm), you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1. (See How Car Engines Work for details.)

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.


Most articles on octane claim that the major problem is pre-ignition (igniting before the spark plug fires, as the above article from HowStuffWorks mentions) when in fact pre-ignition is responsible for only a minority of the bad ignition events in an engine running on too-low octane. the article in SCC said a majority of the bad iginition events occur after the spark plug fires. There are supposedly two types of post-spark events, but this article (http://www.superchargersonline.com/content.asp?ID=104) mentions only one, detonation:


What is detonation / knock?

Under normal conditions, the combusting air and fuel mixture inside the combustion chamber ignites in a controlled manner. The mixture is ignited by the spark, normally in the center of the cylinder, and a flame front moves from the spark towards the outside of the cylinder in a controlled burn. Detonation occurs when air and fuel that is ahead of the flame front ignites before the flame front arrives because it becomes overheated. Under these conditions, the combustion becomes uncontrolled and sporadic and often produces a pinging noise, or a "knock" noise when the conditions become worse.

So far, detonation sounds cool... why is it bad?

Detonation is definitely not cool. Detonation causes sudden pressure changes in the cylinder, and extreme temperature spikes that can be very damaging on engine pistons, rings, rods, gaskets, bearings, and even the cylinder heads. Even the best engine components cannot withstand severe detonation for more than a few seconds at a time. More severe detonation obviously leads to more severe forms of engine damage. If there is enough heat and pressure in the combustion chamber, detonation can begin to occur before the spark plug even fires, which would normally initiate the combustion. Under these circumstances, known as "pre-ignition", the piston may be travelling up towards a wave of compressed, exploding gas. These are the worst kinds of detonation conditions, and can bend con-rods and destroy pistons.