Octane revelation

[bu-bye]

Lots of smart guys in here. Yes there is more to octane then the price. Haz-mat said it all. Those three things tell you what Oct to use and yes for older cars Chas was on the money. I don't buy that 93 oct is any better then 87 oct, its just different for a reason. Its like saying basketball shoes are better then running shoes. It all depends on what you are using them for. sure you can use either but one fits just right ;) .

[ July 03, 2003: Message edited by: bu-bye ]</p>

[camaroincal]

Ok I find it VERY interesting that out manual's state that 87 is ok. BUT in the Chilton Manual it says if you have a higher than a 9.0/1 rating you should use premium. Also I saw it mentioned that you can get 93 octane at the station? Here in Cali I'm pretty sure the highest you can get is 91. I get the feeling a lot of the tuneup info in our manual is incorrect so that our cars need to be serviced more as was said earlier in a previous post.

[camaroincal]

Here's another question...My car has about 83,500 on the clock and I'm wondering what the compression is now approxiamately? The car has been well maintained the past 10k miles and hopefully before that as I bought her used. It runs like a champ. As engines get older the compression rises right? So then for sure I should probably use premium as the compression is now proabably over 9.4/1?

[camaroincal]

Ok, I need to stop hitting "add reply" before I finish thinking. Does racing fuel (i.e. the 100+ octane stuff) increase performance or is it bad on our engines? Has anyone experimented at the track. How much of a difference were there in the 1/4 times? Thanks

[merlinsrealm]

<blockquote>quote:</font><hr>Originally posted by camaroincal:
Ok, I need to stop hitting "add reply" before I finish thinking. Does racing fuel (i.e. the 100+ octane stuff) increase performance or is it bad on our engines? Has anyone experimented at the track. How much of a difference were there in the 1/4 times? Thanks<hr></blockquote>


It will perform for a limited time but If you dont have the compression ratio to help burn the Cam2 fuel all you will do is foul the plugs....

Eric

[malice10985]

<blockquote>quote:</font><hr>Originally posted by CamaroKing:
If you use higher octane than the motor was designed for, you may not be burning all of the fuel off, as the engine can't use it that fast. This would actually hamper performance. I know the 4 cylinder motors actually get unburned fuel build-up over time if an unnecessary grade of octane is used. I'd stick with what the car was designed for, and save some cash.<hr></blockquote>

I wonder if we are sending unburned fuel into our exhaust with 91up octane. Does anyone have an exhaust gas temp gauge to stick into a header or manifold for a while?

If the gauge is considerably hotter with premium fuel, then it is doing our engines no good. If 87 and 91 produce the same average egt reading, then premium does have a benfit. I would try it out and tell you but I have no money for an egt right now.

Second, compression ratio is not importand when dealing with octane, but rather absolute cylinder pressure. There are streetable 91 octane engines with 12:1 comp runniing around. The secret is the cam. They have a huge valve overlap to keep the cylinder pressure down. My engnines cylinder pressure is 210psi in each hole. I am guessing that maybe above 240psi you need to have premium. That would be a good question for a car mag like HOTROD or CARCRAFT.

You guys should read mags like that, I know they make fun of our little engines, but they do a better job than me explaining concepts like this one.

[Darknight]

Malice, is that average cylinder pressure or peak cylinder pressure? With performance tuned cars, the ignition is typically advanced, and there is a significant amount of unhealthy, unuseable pressure on the bearings and wristpins at top dead center. Higher octanes minimize that stress by distributing the force of combustion more evenly throughout the stroke. It's really a matter of geometry. The piston must be on the way down, therefore moving the rod with leverage, before it can produce useable power. The longer the stroke, the more the engine can benefit from smooth power release.

4 cylinder engines that rev high don't have enough time to wait on the slower burn of the higher octanes, which is a big part of why they don't have good torque, besides the fact that they're missing two cylinders.

Simply put, higher octanes better utilize engine geometry to create higher torque at any given rpm of our 6 cylinder engines, thus translating into more horsepower as well. Besides that, they simply have a higher energy density because their hydrocarbon chains and aromatic rings are bigger.

As far as carbon buildup...my engine is virtually spotless inside. My plugs never foul, or even have an unhealthy coloration. I credit that mostly to taking long drives rather than short ones, as well as changing the oil on time, using Sea Foam, and not being afraid to open up the throttle. It really cleans out the carbon.

DK

[ July 03, 2003: Message edited by: Darknight ]</p>

[camaroincal]

Damn Darknight you really know your $hi+ man. You use premium right? ;)

[Darknight]

Without question. Only 93 goes in my baby.

DK

[RancidCamaro]

Well now I'll admit that when I came into this thread i was convinced that 87 octane would be fine for the engine, and that using a higher octane was a waste of my money. Anything I should watch out for going from 87 octane to 91?

And just what is Techron that Chevron has?

[zlexiss]

Well, higher octane doesn't necessarily have a higher energy density - usually MTBE or ethanol are used to boost the octane, and they have less btu/gal than the base gasoline stock.

Techron is Chevron's detergent package. Like some (but not all) petro companies, they add more of it to the premium octane blend than to the base and midrange. I can pull the webpage on this if needed, saw it doing my injector cleaner research.

I used to have a nice list (from click and clack or somewhere) on all the petro companies and if they used same, different amounts, or different packages in their gas grades. Anyone ever seen this (and can post a link or a scan?)

-Jeff

[Darknight]

I prefer gasolines that use standard aromatic "ringed" compounds and hydrocarbon chains
of known lengths to create a desired octane equivalence. Adding oxygen to the fuel is a deceptive way of bumping up the octane rating while not delivering comparable performance improvement for the money. When people buy the high test gasoline, they expect better performance.

By the traditional means of raising octane, the larger hydrocarbon molecules make for both increased octane ratings and more energy density, and power. It's kinda double the benefit.

DK

[javifp]

I only run 93 on mine I would not even think on going cheap on my ride, it's my BABY, and my peace of mind.

[zlexiss]

Darknight: yes, very true. But how do know which places use which method, especially with the base blend sharing going on in many cities?

[Darknight]

That, unfortunately, is the tricky part. No one can know all the ingredients in every brand of gasoline they use, especially when on a trip, when you might be forced to use an unfamiliar brand. I personally watch out for anything that clearly labels ethanol as an ingredient, especially the "Contains up to 10% ethanol" signs. I run like cheap makeup on a two cent whore if I see it.

DK

[ July 05, 2003: Message edited by: Darknight ]</p>