I hear people claiming to get "better performance" and "it's better for the car" using higher octane. Stumbled upon the episode of Engine Masters where they tested 87, 91, 110, 116 and E85 on an LS3. Bottom line was that it didn't matter what you ran as the differences were minute. I realize octane is more related to pinging and doesn't do anything to increase power.

I have a '22 and have been running 93 octane since day

In any case, it's an interesting episode if you haven't already seen it.

 

Not true. When I had a 91 ZR1 it came with a owners kit that had dyno sheet differences between 91 and 93 octane. From what I recall it was around 18-19hp on the LT5. Put 87 in your C8 and see what happens!

 

It does matter to a certain point. When I data logged my stock LS3, I had knock retard using 91 octane CA premium fuel. Unfortunately, 91 octane is the highest octane for CA and many other states. I added a specific amount of Boostine to bring the octane to 93-94 octane and K.R. went away. Did I need 96 or 98 octane? NO.

Dyno testing in a controlled environment is not the same as real world driving. On the LS3, when engine coolant temps and intake air temps reach 213*F/ 86*F respectively, the ECU will start to pull timing. As those temperature increase so does the reduction of timing. Add the lower octane rating and the knock sensors will activate sooner causing the ECU to gradually go into the lower timing table reducing HP. Increase engine load or drive on an incline and the engine will be affected by the octane rating. Keep in mind, as the ECU retards timing the combustion chamber temperature increases and the A/F ratio starts to lean out. Now you have the perfect storm with an engine that is not very happy. GM engineers designed the ECU to protect the engine using the recommended octane rating. Lower than recommended octane puts the engine in a narrower safety threshold, increasing the chance of engine damage.

 

Octane isn't going to make a difference in performance UNTIL there's enough heat and/or load on the engine to trigger the knock sensors on low octane fuel and change the ECU to a low octane map. Then there will be reduced HP and MPG under load. Whether you'd notice that in around town driving is doubtful, but it's there.

 

Go Dyno your car stock on 87 & 93 report back here..... Not going to be the same.

 

To some degree you are comparing the stone age (LS3) to modern technology (LT2). While they are similar in some ways they are worlds apart in most areas.

The LTx engines are higher compression ration, use direct injection and have a way more powerful ECU than the LSx series engines. While octane doesnt typically "increase" power, it actually does keep you from losing power along with keeping damage to the engine from happening. Run 87 octane enough under the right environmental circumstances and push the C8 hard and you will see detonation and knock, if it happens enough you can exceed what the ECU is able to control and can eventually cause damage to the pistons, valves and combustion chamber.

So with that, just run the gas the vehicle is certified for, the savings from running a lower grade are not worth the chance of damage to the engine.

 

Yeah, I'm always going to run recommended fuel, I just thought the show was interesting is all.

 

It depends what the motor is built for. If its a low compression motor econobox then 93 is useless for performance.

 

Run the lowest octane possible that does not allow detonation. So much false information regarding octane levels out there. At 5K feet elevation my C8 gets 91 and is perfectly fine.

Sam

 

I prefer using the highest octane that prevents knock retard. It is best to have a wider safety threshold for varying driving conditions.

 

You are at 5K elevation. 91 is perfectly acceptable at that altitude.

 

And the computer is adjusting for the lower octane, hence your car is not making full power.

 

Best thing to do is just log the car on your pump gas. If you're getting timing retard you can tell how much the stock timing profile will benefit from higher octane and pretty much exactly how much. I have cars that retard 6 degrees on shell 93 and they can benefit from up to about 97 octane. I have cars that retard nothing on 93 and low and behold if i put in a pale of ms109 it does absolutely nothing.

 

Wrong. At my elevation it is making full power at 91 Octane.

Sam

 

All Natural Asperated internal combustion engines loose 3% of HP for every 1000ft above sea level at standard conditions. On a hot day it would loose more, cool day loose less. Density Altitude (DA) will be the corrected altitude. So if you are at 5000ft DA above sea level you will be 15% less HP regardless of what octane you use. Now you can claim this is Full Power for 5000ft and you would be right.
What ever the octane and DA, just have fun and enjoy the ride!!!!

 

Can you post a data log at wot in hot weather? With 91 I'm seeing power falling,( mph and et, 5000-6000 DA) my mvp pro won't log my C8. Hope to get logging soon.

 

That is a false statement.

 

Believe what you want.

Sam

 

He is meaning full power for the octane not compared to sea level. Hes just saying he's not knocking on 91 so theres no additional power to be had for him at higher octane which is true. Of course hes making less power at altitude than we can make at sea level.

 

octane does great to slow and even out the burn and flame front. But if the engine doesn't need it the octane can work against you in the wallet and performance.

Interesting he mentioned the lt5, with a dished piston and 4 valve head, it's very detonation resistant, but at the higher octane the computer can advance the timing and get a bit more power

I run 12.5 cr on pump gas on my old LPE LT5, and it ran the same times on 93 octane as it did on 103 race gas. Logging in the computer showed no detonation on the 93 so the higher octane just burned $$ and didn't improve times

On the turbo buick, I could raise the boost and make more cyl pressure and gain a couple of tenths at the track.