Octane Question

[KinLM]

Hi. My car has a compression ratio of 10.5:1. I was wondering if this level of compression calls for any type of step up in petrol I put in as far as the octane is concerned. The manual says that it will run on regular but I've read around online and seen that any car with a compression over 10:1 will generally have a slight benefit from running a higher octane.

I was wondering if anybody on here has any suggestions. So far I've been running the lowest octane but my car is very high mileage and I was wondering if running a higher octane could have any effect on extending the life of my engine. I don't have the money for repairs or a new car.

Thanks in advance,

KinLM.

 

[mustangGT90210]

If it is made to run on regular, run it on regular. Waste of money to bump up octane if its not built to handle it. More than just compression goes into determining what octane fuel a car needs.

It sounds like your car is a bit older, so it doesn't sound like it has the computer capability to sense what octane is being run and then retard or bump timing to get a complete burn

 

[KinLM]

If it is made to run on regular, run it on regular. Waste of money to bump up octane if its not built to handle it. More than just compression goes into determining what octane fuel a car needs.

It sounds like your car is a bit older, so it doesn't sound like it has the computer capability to sense what octane is being run and then retard or bump timing to get a complete burn

It's from 1997. Not that old.

 

[mustangGT90210]

Being that vintage, just keep to 87 octane. Unless you have some high end car, its not going to have the technology to run as well on higher octane. Higher octane is harder to ignite, which is why cars that run it have advanced timing compared to those designed for 87.

What do you drive?

 

[SRV2LOW4ME]

You can run on a lower octane if it says it can in the manual. It will say in the manual or somewhere else (under the gas cap lid for example) if the car requires a higher octane.

My car requires 91+, but will retard the timing if it detects a lower octane fuel. With the lower horsepower/performance the engine produces with the timing change, its not generally preferred, but there are people out there that have put 200k+ miles on their cars running only 87 octane with no major problems. (or so they say)

 

[Dragonwhisky]

I've got a '97 Suzuki Bandit 1200 and have never put anything less than 91 octane in the tank, as advised by the owner's manual. Admittedly, it's a motorcycle, not a car. It'll run on lower octane fuels but IIRC the manual states to use them only if that's all that's available and it may be necessary to use an octane booster additive. I'll have a look at the manual when I get home to be sure.

At any rate, if you can track down the owner's manual for the car/motor in question, do what it advises.

Most passenger 6 and 8 cyclinder cars run lower compression than 4 cylinder, but can still suffer what used to be called "pre-detonation" with lower octane fuels. Way back in the day, before computers were doing the fuel mapping, going to a higher octane fuel would sometimes help with this. At least IIRC. That was 20 or more years ago and I may misremember... It happens to us old folk like that.