How much Spark Advance

[majicwrench]

Okie,
You arecorrect, you should run the lowest octane available without it pinging. Using higher octane fuel than the engine needs not only costs more, it will REDUCE your gas milage.
Pope,
You are correct, use what the manufacturer recommends. But let's be clear, octane will not "change the timing of your engine", if your timing is set at 10deg, it will always be set at 10deg regardless of octane. But I think I know what you were trying to get at, so excuse me for being picky.

[mdrburchette]

Compression ratio has a lot to do with what octane gas to use also. It wouldn't hurt to check the mileage of your car with tankfuls of the different octanes to see which gives better fuel economy and performance. I know that my '99 Pontiac uses more fuel and doesn't have the power it should with a higher octane gas. Timing and fuel delivery is programmed to use 87 octane. But, my 72 Fiat likes 93 and every so often, I treat it to 110 octane and bump the timing up a bit when I'm autocrossing it. I don't notice a difference in economy but I do like that smell!

[pope]

Majic,
If your car is timed to 92 octane and you start using 87, the engines timing has changed, it is incorrect timing. Wether you pull out the timing light and correct the timing is another story.

[racydave]

The octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark-ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design.

The octane number of a fuel is measured in a test engine, and is defined by comparison with the mixture of iso-octane and normal heptane which would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of iso-octane in that mixture is the octane number of the fuel. For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. [1] Because some fuels are more knock-resistant than iso-octane, the definition has been extended to allow for octane numbers higher than 100.

Ok, so I can cut and paste, a low compression engine will have its detionation at the same time with 87 octane or higher. A high compression eng will knock on 87 and the timing would need to be retarded to compensate with a loss of performance.

[majicwrench]

Pope,
With all due respect, the timing does not change when you change octane rating. How could it? Does the distributor move?? It will still be at 10deg (if that is where it was) no matter what type of gas, water, whisky, whatever you put into the tank.
Looking forward to hearing how the timing changes...
Keith

[pope]

Keith,
Its not a big deal. I know your being very literal.
Is it your assumption that once you set the timing on the Spider, you would not have to change it, no matter what gas you used? Fiat assumes that you are timing the car at 10° BTDC using 92 octane (on later model Spiders).

You put whiskey in your car?

[So Cal Mark]

I put the whiskey in me, 87 oct in the car and set the timing at 10-15, make sure it's getting lots of fuel and life is good

[mdrburchette]

Pope, you know the timing does not physically change when you use a different octane...just the need of the engine changes.
Keith, I learned a long time ago that it's easier to agree with Pope. His timing is set differntly than ours.

[Tappy]

I've been reading this interesting post :

first of all the wiskey will get you the knocking sound !
I was wondering about the differences on the fuel octane ratings
because in europe we have 95 and 98 octane @ the pump but those seems to be the same as your 91 and 93 octane ratings
now i wonder witch one they mean you need to use in the manual , the american octane or the european octane ?

I use always octane 98 in the spider from total fina they have a formula called exellium , its high octane fuel with additives

"IT makes your engine last longer " harhar (sarcasm)

[baltobernie]

As Racydave implies, octane rating is not a measurement of the energy potential in the gasoline.

Tappy, you guys measure differently than we do, but its a moot point anyway, since gasoline formulation has changed so much since these cars were built.

One of our club guys is in the gasoline measurement business, and he could give you the specifics, but the bottom line is that unmodified Spiders should use 89 in most parts of the USA, according to him.

[pope]

Mark, please pass me the bottle when your done.

Saw the new Bond film yesterday morning...did not care for it. Lots of action but weak storyline compared to Casino Royale, and a poor villian. Dissapointed! There is a Alfa Romeo in the opening chase scene.

[So Cal Mark]

was the Alfa being chased? and did it outrun the other guys?

[pope]

It was chasing Bond...needless to say, it is not around anymore. The driver was seriously hurt in filming. It is a Alfa 159.

[MIGHTY 8]

It was chasing Bond...needless to say, it is not around anymore. The driver was seriously hurt in filming. It is a Alfa 159.

Wow! Great thread by the way.

It seems to me, that the driver could of been more then "seriously hurt", judging by the precariousness of the Alfa in that picture!

[dartme]

I don't know who is right or wrong but last time i give my '70 spider 87 octane I found her KNOCKED OUT on the front lawn(naked)