I always hear people with high HP cars complain about the octane in the gas where the live not being high enough. Does higher Octane make your car run better?

Rumor is there is a place around me that sells 93. Should I get my gas there?

 

Compression = power. Higher compression = higher power. Higher compression also = higher chance of preignition in low octane fuels.

You don't have high compression, so you don't really need high octane gas. However! If you raise your initial timing(to make more horsepower instead of torque) enough that your engine knocks(preignition knock), then you can use higher octane gas to prevent it.

 

93 octane a rumor in buffalo? Don't they have it at every pump? They do out here in eastern NY... I use 93 in my 305 TPI. I also have the timing advanced about 12 degs.. But from what I have read, (after I advanced it) the only effective way to advance the timing is through PROM programing. I'd love to get into that, just don't have the free time.

 

93 octane isn't unusual, Sunoco has it "Super" 93. However they also sell "Ultra" 94 octane. I tried it, not much difference, however my car isn't running top, gotta fix wires, coil and sheeet.

Yeah me too, I want to get into PROM burning, I got the time, I just don't know where to start, books?

BTW, my brother's friend, owns a gas station, and he has a license to carry and sell RACING gas, pretty hot eh? I'm so lucky

 

higher octane doesn't make more power ,but running higher octane allows you to have and engine that doesn't knock, you can run more timing, more compression. actually the more octane you have the harder it is to light, you want the lowest octane your engine will run on

 

EDE , is right the lower octane you can run WITHOUT knock the better.

nick

 

its kind of a double edge sword...

"I want power" it comes at a price... in a stock vehicle use the manufactures recommended octane... If you bump the timing on a cmp controlled vehicle sometimes you can get away with using s higher octane... the spark timing is controled by the ecm.. to truely get the ultimate spark timing you must tunr the fuel and spark tables in the ecm prom...

zroc

 

As mentioned by Ede (and others), you should run the lowest octane that your engine will run without detonating. Some of the newer cars can actually detect the "knock resistance" of the gas and make appropriate timing changes to take advantage of the higher octane (or retard the ignition if lower octane).

The SD 7730 (used in 90-92 TPI) cars actually have such a routine in their "logic", but I can tell you that it does not work properly. The moment it detects any detonation above a certain magnitude, it will pull 4* of timing out UNTIL you turn off your engine and reset it. I did a lot of playing with this routine and found the best thing to do was to "disable it" and then tune my eprom to the grade of gas I was willing to run.

Right now, I have my eprom set to the point where I NEED to run 94 Octane and there is a definite performance increase (but my eprom was never optimized for a lower grade of gas). But I am now looking at backing it off a bit to determine the BEST peformance I can get with 89. If the difference is only .1 or .2 seconds, (which I suspect) I will probably "detune" my engine since I only am in WOT about 1% of the time I am driving (primarily when passing other cars). 99% of the time I am cruising on the highway at part throttle and the price difference between 89 and 94 is noticeable (in my wallet).

 

At 9.5:1 should I be using 91+ octane?

 

with a new 305(the '87), I run 87( ) perfectly. I guess I have carbon buildup in the convertible('88) b/c the 89(octain) runs better in that. I hate runnign higher octain gas....mo money down the tubes.

 

Thanks for all the replies guys!~


Cleared it up

 

Hot Rod did a test of everything from 87 octane to 100 octane leaded. They found that the octane increase was minimal in the pump gasses, but with the race gasses it made a tone more power. I think they added 106 octane boost to race gas and made some wicked hp numbers.

 

with 6 degrees of base timing. I get audible knock only if I bog while letting the clutch out from a dead stop. I think I'm gonna bump it up to 8 or 10 and try refining my driving technique, but playing with the PROM would be so much more fun. Advancing base timing definitely did pull out a bunch of off idle torque, but it cured a whole host of power loss problems I had through out the rpm range. As for racing gas, the pump next door to where I work sells 103 octane gas, but it's a good $1 more than 93 octane stuff.

 

I've been experimenting a little with octane lately. On my 350 TPI with 9.3:1 compression, 87 octane knocks a little more (measured via the ECM knock sensor) than 89, but 91 (the highest here) didn't make much of a difference. And the only time it retarded the timing due to knock was when it bogs a little before kicking down from 4th to 3rd gear. Using 89 octane cured that. The average knock count went from 40 to 7 over a 5 mile trip and was never audible.

My VW Bug requires 97 octane with 9.5:1 compression (stock is 6.9:1), due to the way higher combustion temperatures it has. It has audible detonation that I just plain can't get rid of without mixing my own fuel.

 

If you can keep you're foot out of it (keyword: if ), higher octane gas is just a waste of money. I actually noticed an increase in gas mileage a few times when i filled it up with 87 with no problems.

 

Higher the octane the less carbon build up you will get. Higher octane gases run cleaner. If this was already said then sorry.

 

up by me theres a race gas station that sells 110 octane! $$$
but i use 89 and sometimes 93

 

Gotta raise the flag

 

If you're gonna call then atleast correct me!! edited because of unneeded comment.

 

I await you documented, scientific proof No4NJunk.

Octane rating is a fuel's ability to resist auto-ignition. Just because a fuel has a higher octane rating doesn't necessarily mean that it will burn cleaner.

Example, add Tetra-ethal lead, that will increase octane, but should not affect the cleanness of combustion. And lead flying out the exhaust is not clean.

Now adding ethanol to a fuel to raise might clean up the fuel. Since ethanol contains oxygen, there is the possibility that there will be more complete combustion. But if your car has an oxygen sensor, it will pick up this extra oxygen in the system and add more fuel to compensate. More fuel makes a richer mixture and produces more pollutants.

If you don't know something, dig a little finding facts, and formulate an opinion. Just because you believe something doesn't make it factual.

And if I'm wrong, then so be it. Won't be the first time, won't be the last.

 

I dont know too much about the whole gas thing.....all i know is that in my camaro and my buick they both run better or at least seem to with the 93 octane......(maybe its all the illusion of power

 

It will make a difference if you run 10.1 compression. Stock shouldn't effect you if youre running a decent type of fuel. Not Citgo!

 

Its about time a73! How long did it take you to research that?? No...I don't have scientific proof just yet (trust me I'm going to look into it!) but I do have the experience of rebuilding. Every engine I have owned (or my family has owned) that has run higher octane gases (104 octane racing gas..well because we have 4 drag cars) have had cleaner combustion chambers, valves, and exhuast system believe it or not (this is compared of course to engines run with 93 and 89). While I don't yet have proof of why this is so I can and will get it. As for 93 octane I'm not sure if it has the same effect but I will also find this out as well.

 

For one higher octane gas wont run cleaner if it came from arco because they have a tendency to get water in it during transport. For two if the combustion process that happens to the fuel cant support the ignition of it (i.e. 102 octane in a 9:1 motor it wont completely ignite the fuel because the flash rate is too high resulting in a rich or raw fuel condition in the cylinders and exhaust) you could advance the timing to ignite the fuel and start the combustion process sooner in the cylinder so it is complete after the comp stroke. But the duration of the firing time is not long enough to just put 102 in your car and go to the track. But 93 is possible with a small timing advance, nothing significant.

 

audiman-for 1 the 104 didn't come from arco (I can't remember the name but I'll find out). two is that all the cars we run have 11.5 or better compression ratio.

 

Someone want to do a poll on how much everyone's paying for their gas?

This is one of the better discussions I've ever read, I've learned a lot about why that extra .20 a gallon probably isn't helping me any (didn't think it was)..

I heard in a round about way that you shouldn't fill up at a station that has recently been replenished by a tanker... never got the reason but there was one. Could be ... anyone ever heard this?

James

 

11.5:1 can definitely take advantage of 93 octane then. I am payin 1.09 a gallon in Kent,WA.

 

I heared that too. They said it stirs up all the dirt and crap from the bottoms of the tanks. But I also heard that the pumps have real good filters on them so it really isnt much of a problem. This is just what I heard dont know how true it is but it seems to make some sense.

 

Gee, I'm so sorry that I did not respond sooner, Know4NJunk, I don't spend my life on the computer like you evidently do.

That was knowledge off the top of my head.

To your observation, a drag car running race gas will have less build up on the valves, combustion chambers, piston tops, etc, because of 90% WOT conditions. A street car sees WOT 10% of the time. It would be easier for deposits to build up in an engine that is idling/part throttle cruise.

Race gas is more consistently blended. I believe that there are not as many additives in race gas as there are in pump gas.

I see what your are meaning by burning cleaner (not leaving deposits). But you totally said it wrong.


Know4NJunk, you may want to remove the two extra feet per spark plug wire you proudly display in you signature. They look like they are about to wrap around the steering shaft. And you will pick up some time in the 1/8 mile if you'd ditch that 8"x1" air filter. Heck, even the factory air cleaner will flow more than that setup.

 

Got me!! Ever since I've had my car in the shop I've been on this damn computer. I'm addicted.

Trying to flame huh!!?? Well I bought the accel superstock wires for my car but they are so long and I'm not sure why. I can never find short wires. Maybe some suggestions. As for the air cleaner, its because the intake manifold is a high rise (or higher than stock anyway) so thats the only filter that would fit underneath the hood. I want to get a cowl hood soon. Proudly!!?? Maybe! I have worked hard for what I've got and being a college student I can only do so much for my car. Sorry It doesn't look like a show car. I didn't mean to hurt your eyes


This is very true. I guess it depends on your driving conditions and habits.

 

Fair enough No4NJunk, I truely want to make this world a better place to live in. Sorry 'bout the jabs!!!!

For plug wires, I always get the custom length ones. Sorry, it a Mopar but it shows what I mean. It is the only way to make it look clean.



As for the air filter, won't an offset base work like



Moroso also has an offset, but not nearly as much.

 

The wires I have are the accel superstock made for my year car. But I don't understand why there so long. Where can I get costum length wires?? As for the air cleaner you mean offset as in the bottom of the filter sits lower than the base right?? I saw one somewhere at advanced. I'll see if that works and then get a moroso if I can.

 

You can buy 8mm accel super stocks in a "universal" kit.. they're unterminated and you cut them to your desired length, strip the insulation around the core (depending on core, this is the hard part), crimp on a terminal, and slide on a boot.. and they'll all be happily as custom as it gets.. tis how I got accel wires on my 2.8l v6.

 

I have bad experience with those, they caught on fire on my 81' lowrider. I tossed em and bought MSD wires they hold up much better. They also come in a cut to fit set.

 

Just a stab at this one but could be when the tank is empty there is a greater risk of condensation forming, fill it up and the water has to go somewhere, probably straight to the bottom where the pickup for the pump is.
Back when I used to fly it was something that was part of the preflight inspection. Small drain on the bottom of the wing (cessna, no jumbo jets here ) to check for any condensation in the fuel. Nothing worse that sucking water at 5000ft, no where to pull over , just........:lala: :lala: :lala: :lala:

 

Any octane of fuel has the same amount of stored energy, so if you think higher octane in itself adds power, you are only fooling yourself. The ideal octane to use is the one that doesnt create any knock in your engine from pre-ignition, that way the speed of burning is just right and all of the fuel gets burned by the time the exhaust valve opens. Using higher octane, which will resist burning more than lower octane, will just send unburned fuel out the tailpipe unless you change something like the timing. Some newer cars have different timing curves for different octane fuels, dont know how the heck it figures it out though.

Also, if you think higher octane in itself makes an engine run cleaner, again, you are only fooling yourself. The pump gas grades have totally different chemical compositions due to additives, the higher octane fuels have more cleaners and such in them than the lower grade fuels do.

 

Here's an informative post about Octane for all that's interested. Sure it's gearly mainly toward VWs, but it covers the history behind octane research, compression ratio, cylinder head temperatures, oxygenated fuels, etc.... It helped me figure out why my VW ran like garbage between October and March (oxygenated fuel season here.)

http://www.geocities.com/MotorCity/L...0/octane1.html