My New Car

[bishop]

Ty for the info about octane, I always thought that higher octane mean more hydro carbons since have more hydrocarbons does make your engine more knock resistant.

Cars only monitor the AFR during idle and light throttle, during hard acceleration it disreguards any information from the oxygen sensor, also most cars use narrowband oxygen sensors and not the better wideband oxygen sensors.

Knock sensors are a good tool, but you want to avoid knock as much as possible. By looking at AFRs you have a very good predictor of when knock might occur and can compensate before your engine detonates.

Also knock sensing is hit or miss, every engine has a different knock and noise profile, detecting knock is not an exact science. Most tuners/modders perfer to use a stethiscope(sp?) type of device and detect knock with their ears than use a electronic based detection system. But anyone who is serious about performance has a wideband reader.

 

[Why Not?]

Ty for the info about octane, I always thought that higher octane mean more hydro carbons since have more hydrocarbons does make your engine more knock resistant.

Gasoline is a mixture of hydrocarbons of varying complexity. Octane is the hydrocarbon with 8 carbon molecules in a chain (octo = 8, so octane) and is one common component of gasoline along with heptane and others. Short carbon chains like methane and propane are gases at room temperature so gasoline has mostly 7 or 8-carbon molecules or longer. These fuels can remain as liquids or gases at room temp.

Pure octane (the chemical) is arbitrarily defined to have an octane rating of 100. The octane rating of any gasoline mixture is measured in a ratio to a theoretical pure 100% octane fuel. So a fuel with a 91 octane rating has 91% of the knock resistance of a pure octane fuel. Therefore you are right that fuels of different octane rating will have different amounts of the different hydrocarbons in them.

Octane (the fuel) is one of the shorter chains and has a very high octane rating though. So I think that a higher octane fuel whould actually have fewer carbon-hydrogen bonds than a lower octane fuel. I am not certain about this last bit though. I believe that this is also why high octane fuel is more expensive as it has more of the lighter or higher distillates in it.

 

[slowpoke]

Octane boosting fuel additive??

I've never tried this but I've heard it is a good remedy. Buy regular gas and increase the octane by adding this stuff.

http://www.lubeoilsales.com/products/fueladditives.htm

Improves the performance of all two-cycle and four-cycle gasoline-fueled engines. Just one treatment significantly increases engine response and power. AMSOIL Octane Boost reduces engine knock, improves ignition, helps fuel burn cleaner and inhibits corrosion. Recommended for all high performance off-road and racing applications. Increases octane number by up to 7 points

 

[goodtime]

Been driving all week on premium and it makes a huge difference in performance.
I think I'll stick with it

Will keep away the knock & pings in the long run. I know few Mazda owner wish they read the manual.

 

[zekestone]

If it's a Turbo (like a Mazdaspeed 3, 6 or CX7), then premium all the way.

If not, regular will likely cause no harm.

The octane rating is basically how slow the gas will burn. The higher the number, the slower it'll ignite. Turbos run much hotter because you're recirculating exhaust gasses. Therefore you get pre-ignition and knocking on low octane because the fuel ignites before it's supposed to due to the heat.

The key is whether Mazda says x octane is "recommended" or x octane is "required"

Hey guys, my new car says premium gasoline only.
This to me sounds like some kind of carmaker/oil company conspiracy and so far I've only put in regular gas.
Butwill this harm the vehicle??????

Also, can Mazda void the warranty if they find out I havent been putting in premium??? And how would they know, can they test for it????

 

[zekestone]

However, if you intend to tow especially during the summer, he suggested premium. He also recommended to avoid Petro Canada and Shell gas as they have higher sulphur content which may over time impact the turbo (just after the warranty runs out ;-) ). I recall a couple of years ago certain GM cars had problems with their fuel level sensors due to the sulphur in the gas.

Regulations have changed and now all fuel sold, including diesel, must be low sulfur.

 

[l69norm]

....Turbos run much hotter because you're recirculating exhaust gasses. ..

Turbo and superchargers also run a lot hotter because you are compressing air (Charles law= http://en.wikipedia.org/wiki/Charles's_Law ). This is why intercoolers are used to reduce the temperature and safely allow more boost pressure.