Why our cars need 87 octane gas

[bu-bye]

Ok,

Higher octane DOES NOT mean better fuel. The different octane fuels sold today are made for different engines not better performance or cleaner burning. Gas companies sell gas with names like "Premium" to get you to buy the high priced gas. After all the gas that costs more must be better right....NO!

Different octane fuels are sold for engines with different compression and timing. My dads 2000 Jag must have the premium gas because of the high compression of the engine. 91 octane fuel is more resistant to burning from engine heat and compression then 87. The reason for this is because you don't want a high compression engine igniting the 87 fuel due to compression before the piston has reached the top. If the explosion happens before the piston reaches the top it’s forcing the piston back down while all the other pistons are forcing it up via the crankshaft. Needless to say this causes loss in power, MPG, and can even damage your engine if not corrected. Using high octane gas in a low compression engine (like ours) also cause loss of power, MPG and can cause you to fail a smog test. See, the high octane burns slower so it takes longer for all the fuel to burn. You want that fuel to burn FAST before the exhaust valve lets out the trapped gasses. You don't want unburned fuel leaving your engine. That’s what clogs O2 sensors and CAT's.

If you really want to use high octane fuel you need to change your timing. If you are getting a knocking sound and the way you fix it is higher octane then you might want to look into why your engine is knocking in the first place when using the right fuel.

Don't be a marketing target for the gas companies. They are all laughing at the world because people don't know any better.

[saved1]

That is so true. You gave a very good explanation on octane.

[therock]

yeah you said it pretty plan and simple thats why most race cars i mean high performance race cars use higher octane my dads race car has 13:1 compression and he has to run 103 octane

[94TeaL]

I'll have to run 93 octane due to my car's compression going from 9:0:1 to 10:1.

[vegeta5486]

So true and well said. I just wish my friends would believe me when I tell them that. I tell them all the time that their cars don't need it but they tell me I don't know anything.... yet I'm the one who tells them whats wrong with their cars when they break down and help them fix them. Yes I'm totally clueless... Damn ricers.

[Ian]

Originally posted by 94TeaL:
I'll have to run 93 octane due to my car's compression going from 9:0:1 to 10:1.

you dont even really need 93 for that. we just completely redid the engine on my buddies 393 stroker for his mustang and its 11.2:1, and he can run 94 (sunoco only).

10:1 you could probably get away with 89, but hey, 93 cant hurt!

[BLLDOGG]

very good explination.

[95Batmobile]

My car runs terrible with 87 octane [img]smile.gif[/img]
91 pwns j00

[img]tongue.gif[/img]

Oh and you forgot that they filter out more stuff in 91 than in 87 and some cars that run on 87 actually run on those things that are not filtered out... something along those lines. Was in an issue of Hot Rod [img]smile.gif[/img]

[camaroincal]

Well sorry to say that you are pretty much wrong. First of all, the 9.4 compression ratio of our 3.8's is not low at all. Also, in my Chilton's manual it even says that engines with a compression ratio of 9.0 or higher should use a premium fuel. Also, alot of it depends on your driving style, if you use your Camaro for commuting and hardly ever bring the revs up..87 will be fine. But if you are like me and probably most F-body owners, you like to get on the gas quite a bit, and that's when using 91 octane helps in performance. Also, after being on this message board for quite some time, the majority of us 3.8ers get better gas mileage and our cars run better on premium.

Now of course our cars are no powerhouses, so using 87 or 91 octane, either way you won't tell much of a difference, but still..saying that using 91 instead of 87 will clog your cat and casue worse gas mileage just isn't really true. Infact, someone on this board who knows a ton about our cars and undertands how the pcm works..said that the car will adapt to the higher octane and give it some timing all on its own.

[bu-bye]

This post was a gernal post about octane. Every situation is different. My post above applies to most 3.8 owners with little or no mods. Take it as you will.

[SD6]

Also the timing can come into play. If you retard the timing some, you can run lower octanes. Or if you advance the timing, you can run higher octanes and see gains. Most new high compression engines that require high octane can retard the timing if it senses it's running lower octane and gets pinging. Or if it's running it's usual high octane and still gets ping, it'll retard the timing to compensate. Of course when this is done, performance and usually fuel economy will go down hill.

[silvachris1]

Well. I will have to dissagree with you on some points. My car (Y87 Auto) is relatively stock (FRA, K&N, 3" cat, no air baffles, no MAF screen), and I used to run 93 all the time. Here's my story...
I ran 93 in my car all the time. ALLLLL the time. Never had any problems. I ran 10.04-10.18 (1/8 mile track) on average. But gas prices went up and I decided to go cheap. I started buying 87 cause everybody told me that I was just wasting money. Well, I returned to the track and ran 10.37 all night. About 3 months went by, and I started getting noise from my exhaust. Then it got bad, the cat completely died, cracked up inside, and melted my O2 sensor. So now I've got everything fixed (O2 sim, and 3" catco cat) and running 87 octane still. The car still seems to run a little sluggish, but I ran 10.003 and 10.05 on my last trip back. I will try Thursday on 93 and see if my times get any better. I only average 1-2 mpg(city) better on 93 though.
I still think that the 93 is better (at least) for my engine, but everybody is different.
Either way, I can't bring myself to pay 2.13 for premium (take that Californians heh heh heh).

[camaroincal]

haha you would be lucky to find the cheapest non english speaking gas station selling 87 for that price. lol

[slow]

from a thread i quoted from jerryw on another forum.

"There are basically four things that control an engines likelyness to knock; Fuel octane (meaning its ability to resist autoignition), combustion chamber design, cylinder pressure and air temp. "

too many variables to state "you need 93, ect" but with tuning for max performance your going to want the highest octane you can find.

stock V6 motors, don't have agressive timing tables, as they are designed to run on 87

Ryan

[speedy-v6-camaro]

87 is actually better for power if your engine isn't knocking. It has more energy to burn than the 93 does.