Yea its true...but eh its worth it. It's waaaaay 2 hott now a days! I'll deal with the extra $$$

 

so if the car says run premium only does that mean it has a higher compression?

 

hmmm good question but turbo vehicles for the most part have lower compression then non-turbo vehicles and we need to use premium fuel only. My car clearly states premium fuel only in two places on the car that I am so far aware of.

Could be some performance based vehicles such as the 350z more then likely states premium fuel only. But I can't necessarily say that.

But it seems more performance based cars its always recommended to run synthetic oil just like your told to run premium fuel only.

I'll let someone who has more knowledge on that answer your question in full.

 

but even my 92 prelude si non vtech says premium only in 2 place as well

 

[quote=WhiteFwdsm;4385334]Just a quick note .. the octane of the gas will not change your airfuel ratio.quote]


Sorry, David is wrong. Ive laid this out 100 times on here, ill do it again.

Octane is a measure of a fuels resistance to detonation, as measured by the MOTOR octane number (increasing the compression till detonation is reached) or RESEARCH octane number (advandcing timing until detonation)

Higher octane fuel usually have a richer a/f ratio due to a lighter specific gravity. (in gasoline)

The additives put in to increase octane, mbte and the like, decrease burn rate and have less energy that the gas. This slows burn rate and make the fuel more detonation resistant. It also means 93 has less btu/lb than 87.

87 also has a higher latent heat vaporization rate, which means it ignites quicker due to increased off-gassing.
If a car can run without detonating on 87, it will be more efficient in every aspect besides thermal efficiency. This is the reason we can start a Top Fueler on 87, not 93.

Putting 100 in you street car is worthless unless you have the compression, timing, or boost to require it. And that bring you to tuning.

The more timing, the more pumping losses=less efficieny

Boost is a measure of restriction. With the right cam ive seen 15 less indicated lbs of boost and 70 more hp. That get into proper dynamic compression for the fuel and cylinder design.

Compression ratio is a chapter in itself, just know in a street-ish car, I can make more power with 93 octane at 10:1 than with 110 octane at 12:1.

If I missed something lemme know, until then I will no longer bore you with this nonsense

 

Just to try to define detonation:

When the flame kernel expands, the radiant heat combined with the compression heaating/pressure, cause a deisel like compression ignition of the fuel at the opposite part of the cylinder. This again recreates the problem, and what you have is a explosion instead of a burn. On a pressure graph youll see 300 times the peak pressure.

Preignition is just the hot metal in a cylinder causing a kernel to intiate before the spark, than the spary ignites, and can cause colliding flame fronts, either causing detonation, or just a lack of power.

 

This thread pretty much has been covered...octane has a bunch of times as well. Run only the minimum required octane else you'll be wasting money.

At a stop light, when it turns green, turn off the A/C until you're at about 30-40 or so, then turn it back on. I have to do this anyways as my car is pathetic and slow even with the A/C off and I can feel a huge loss in power from the extra load.

As far as 93 oct. having less BTUs than 87, I didnt think that was true...I thought all levels of street octane had the same levels of BTUs

 

Unless its oxygenated fuel, all higher octane gas = less btu

 

You will save gas if you turn on your a/c at speeds above 60mph. Anything lower than that will kill your mpg with the a/c on. Mythbusters told me so!

 

[quote=dragula;4385962]Basically, a street car, that is relatively stock, CAN benefit from a higher octance rating with adjusting the timing, but only to a certain extent.
Correct?