octain level

Originally posted by Mr. Pockets


That's not exactly true. Higher octane gas just requires higher temperature and pressure to ignite spontaneously. It doesn't burn more slowly.

Hmm, i think it might bolth. If it was not slower burning, thus allowing for continuous pressure during the entire combustion stroke, then no power gains would be had at all by changing to premium or a race fuel mixture. I do agree that the spont. ignition issue is a primary use of the fuel, however the HP gains are well known for high octane fuels.

*not contradicting ya, just saying that it also burns longer along with aiding in spont. ingition issues. *

And by all means, if im wrong in the matter do tell me so. I never wish to give out bad info, this is just the info i had been tought.

[Chris]

OK. I am not going to claim to be a god or even a guru on this. I will however state that I have been building race engines for a while, and I have been racing (professionally) an SVX going on 5 years now. I have many experiences and contacts with information about this.

First, 110 octane GASOLINE does not burn any quicker or slower than 87 octane GASOLINE. The earlier stated about its resistance to pre-combustion or spontaneous ignition due to higher combustion chamber pressures are true. FACT: Higher octane fuel is HARDER to ignite and thusly one of the main reasons that hotter spark and or higher energy ignitions systems are required when running a higher octane fuel. GASOLINE at either 87 octane or 100 normally has the same ENERGY released from combustion. In order to change the amount of energy, you must change the fuel. Octane is NOT a measure of fuel energy. Although higher amounts of power can be created with higher octane, its NOT due to the energy of the fuel. Its directly related to the amount of combustion chamber pressure you can apply to the fuel on the compression stroke without the fuel igniting on its own BEFORE the spark plug does at the proper time. The more pressure you can apply in the chamber the higher the yield. An example would be like this: take gun powder and pour it on the ground. Light it off, and it will just burn. Now wrap it up in paper and light, it will pop. Take the same roll of gun power in a paper tube, wrap it tightly with tape, light and it will explode. The properties of the fuel never really changed. By limiting the expansion rate (compression) the fuel went from just a burning rate (releasing mostly heat and flame) to now an explosion. I did not change the “octane” of the fuel nor did the energy of the fuel change. We did chance the characteristics of the yield of power from mostly heat to pressure. Gasoline under higher pressures can yield more of this potential energy. Keep in mind that the “actual” amount of energy in gasoline has not changed. To get this higher amount of energy you must either raise the compression ratio of the pistons (thusly creating a higher combustion pressure) or use a form of forced induction (like turbo or supercharger [will get to NO2 later]). The problem with lower octane fuels in this formula is that when the piston starts to reach its apex and maximum compression, the fuel spontaneously ignites (normally near a hot spot on the surface of the piston) and the flame front starts to burn upwards towards the combustion chamber. Very short moments later; the spark plug will light the air/fuel mixture in the combustion chamber and the flame front will start to burn down (in the proper direction in order to “push” the piston down during the power stroke). Because of the pre-ignition of fuel that started to burn upwards and the properly ignited and timed fuel burning downwards, they meet together with a bang (and or the audible “knock sound”) and a majority of the energy is lost in the collision instead of pushing the piston downwards. This is bad, and the detonation of fuel can cause engine damage. The common misconception is that the use of high-octane fuels yields more power. It related, but not the reason. Ambient air temperature plays a part in this equation as well. Did you know that if the outside air temperature is in the mid-low 30s, our engine will run with maximum optimal ignition timing on 88-89 octane without pre-ignition problems? I will go into this in more detail another time though.

Now to answer some issues with the SVX in pure fact.

Will the SVX engine produce more power with higher octane fuel?
Possibly. There are many variables to consider here. Your trials might vary a bit based on important things like carbon deposits and or build up on the piston surface and ambient air temperature. The computer that operates our engines will continually try to provide for optimal ignition timing. If the computer does not detect problems with the fuel (via input from two knock sensors) the engine will provide us with optimal output power. Without our knowledge, the ECU can detect noise from pre-detonating and try to alleviate this by retarding ignition timing. If this occurs, losses in engine output will take place due to non-optimal ignition timing for the parameters of our engine by design. SO, if you have say 93 octane fuel in your SVX, and the ECU is already following an optimal timing curve (without any detonation in fuel detected), and you added ANYTHING HIGHER than what you already have in it, then NO; there will NOT be any increase in performance or power output. The ONLY way a higher octane fuel will yield more power from the SVX engine would be if the fuel that was in it before was causing the ECU to cripple timing due to detected pre-ignition. On this note, I have found the following for micro-tuners: At my altitude and climate, I have found a two-tenths of a second faster launch in the 60’ time when running 96 octane fuel. I have found NO gains from anything higher than 96 AND the time in the ¼ mile remains about the same as 91 octane fuel.

I hate to sound so scornful and bring depressing news to so many people that want to get all the power they can from their SVX. Trust me, the engine operates at near capacity in stock form. I am NOT saying that more power cannot be achieved. It just cannot be done cheap, nor easy. Now that I have crushed everyone’s dreams, let me remind you that there are still WORLD RECORDS held by Frank Aragoni Jr. in a modified 32 front engine dragster running the ¼ mile in 8 seconds and 150 miles per hour ON AN EG33 ENGINE! Just remember that speed is achieved via horsepower, and horsepower is achieved via money. You can have enough SVX horsepower to squash a Viper…….. if you got the cash!

Excellent post Chris. Thanks for all the much-needed info.

[Chris]

Diesel fuel has much more energy potential than gasoline does.
As does NitroMethane (but I am thinking you all knew that already)

[HighwayUFO]

Leave it up to Professor Chris to spread the word and knowledge of the SVX.

Did I just hear a bell ring, cause I think someone just got schooled.

Keith

Originally posted by civic_slayer
Leave it up to Professor Chris to spread the word and knowledge of the SVX.

Did I just hear a bell ring, cause I think someone just got schooled.

Keith

Heh, exactly
Thanks for the great info! All these years, i have been running of the info my father and his racing buddies spilled apon me. Its good to get the correct info from sombody.

"The more you know!"
Damn CBS, now i feel dirty saying that phraze.

I did not say that 110 octane gave me a huge performance increase. What I meant to portray was that I wanted to minimize the risk of any fuel related problems during my high-speed runs (which this car handles beautifully until 155 when the front end lifts a bit). What I'm wondering is if the octane additive was something quality or something cheap like ethanol, which would burn too hot and possibly dry out the seals, and make my car burn the oil it does.

Okay this might be stupid, but in a lot of tuner mags they show times of cars on race gas and pump. Now I assume that the engine mgmt monitors something to boost hp. Is it just retarding the motor just under knock which would be different on each gas or is it something else.
Did that make sense?
Also how would someone know what their cars "optimum" octane level is?

crash

Just did some quick calculations. 5 gallons of 110 octane will give about 96 octane if then filled with 91 octane. Just for general info.

[svxsubaru1]

Can some one explain how 87 octane burns at the same rate as 110 octane, i really dont understand that.

[PatrickB]

Originally posted by Crash
Okay this might be stupid, but in a lot of tuner mags they show times of cars on race gas and pump. Now I assume that the engine mgmt monitors something to boost hp. Is it just retarding the motor just under knock which would be different on each gas or is it something else.
Did that make sense?
Also how would someone know what their cars "optimum" octane level is?

crash

110 burns slow so you can run more boost or more timing. This is done because the slower burning octane reduces predetonation. Aksi the higher octane it takes more heat for it to combust this also reduces predetonation. Ppl show times for their cars at each level. one is more of what it runs on the street. the race gas is more of a max output.

[NikFu S.]

Originally posted by Chris
Did you know that if the outside air temperature is in the mid-low 30s, our engine will run with maximum optimal ignition timing on 88-89 octane without pre-ignition problems?

Now that I have crushed everyone’s dreams, let me remind you that there are still WORLD RECORDS held by Frank Aragoni Jr. in a modified 32 front engine dragster running the ¼ mile in 8 seconds and 150 miles per hour ON AN EG33 ENGINE! Just remember that speed is achieved via horsepower, and horsepower is achieved via money. You can have enough SVX horsepower to squash a Viper…….. if you got the cash!

You just saved me a buttload of gas money and that was a nifty little racing fact.