Sunoco Racing Fuel
Team Owner
Joined: Jul 2004
Posts: 28,420
Likes: 3,273
From: Hartford WI
Forgetting ethanol or not, simply a higher octane could benefit a Stingray I think. Several posts above mention the ecu pulling timing to prevent detonation. OK great no detonation, but how about power loss from less timing?
Think about how we drive these cars generally in an rpm range that back in the day would have been considered 'lugging' the engine.
What happens when you're driving around in 6th at 1500 and need to go up a hill. Put your foot down, or the cruise does it for you, think maybe it knocks a bit and the ecu pulls timing?
I am old enough to have messed around w/ cars w/ distributers and no ecus. Spent plenty of time trying a little extra timing to see if I could get more power and used 1500-2500 rpm full accel to see if I got any knocking.
So basically, if I could get a gas identical to my normal 91 that had all the same qualities but was also higher octane, I'd love to try it.
Think about how we drive these cars generally in an rpm range that back in the day would have been considered 'lugging' the engine.
What happens when you're driving around in 6th at 1500 and need to go up a hill. Put your foot down, or the cruise does it for you, think maybe it knocks a bit and the ecu pulls timing?
I am old enough to have messed around w/ cars w/ distributers and no ecus. Spent plenty of time trying a little extra timing to see if I could get more power and used 1500-2500 rpm full accel to see if I got any knocking.
So basically, if I could get a gas identical to my normal 91 that had all the same qualities but was also higher octane, I'd love to try it.
Why do we care about "back in the day" when the day to care about is today? Many things have changed so much, comparing what was and what is might not be that easy.
If you think it is happening, scan it and you will know.
How would you know if there was knocking unless it was severe enough to be heard over the engine noise? Without a dyno, how would you know if you got more power or not? Also, without the ECM, isn't the timing a little more linear as opposed to today?
Even if you do, how will you advance the timing to test it out? If it isn't knocking already, how would more octane help unless you do adjust the ECM to advance timing more than it currently is?
Drifting
Joined: Dec 2019
Posts: 1,810
Likes: 615
From: Blacksburg Va
A scan of the ECM should provide the answer as to whether it is having detonation or not.
Why do we care about "back in the day" when the day to care about is today? Many things have changed so much, comparing what was and what is might not be that easy.
If you think it is happening, scan it and you will know.
How would you know if there was knocking unless it was severe enough to be heard over the engine noise? Without a dyno, how would you know if you got more power or not? Also, without the ECM, isn't the timing a little more linear as opposed to today?
Even if you do, how will you advance the timing to test it out? If it isn't knocking already, how would more octane help unless you do adjust the ECM to advance timing more than it currently is?
Why do we care about "back in the day" when the day to care about is today? Many things have changed so much, comparing what was and what is might not be that easy.
If you think it is happening, scan it and you will know.
How would you know if there was knocking unless it was severe enough to be heard over the engine noise? Without a dyno, how would you know if you got more power or not? Also, without the ECM, isn't the timing a little more linear as opposed to today?
Even if you do, how will you advance the timing to test it out? If it isn't knocking already, how would more octane help unless you do adjust the ECM to advance timing more than it currently is?
Team Owner
Joined: Jul 2004
Posts: 28,420
Likes: 3,273
From: Hartford WI
The reason I mention 'back in the day' is because we could easily change ignition timing and listen for a result. All engines will knock if there is too much timing for the conditions. Modern engines w/ modern ecus retard the timing so quickly and accurately that the initial trace knock never gets loud enough that we can hear it. For me it is a given that modern ecus 'pull timing' depending on conditions.
I imagine there is a data point that could be watched on a scan tool to see when it happens.
I don't care enough to bother because there really isn't much I could do about it anyway.
But, as I said, if I could buy a tank of gas identical to what I usually buy but w/ a higher octane rating, I would enjoy trying it to see if I feel any difference.
I imagine there is a data point that could be watched on a scan tool to see when it happens.
I don't care enough to bother because there really isn't much I could do about it anyway.
But, as I said, if I could buy a tank of gas identical to what I usually buy but w/ a higher octane rating, I would enjoy trying it to see if I feel any difference.
I'm sure there is in every scan tool to detect knock. If I could in my 91 C4, I am sure you can in any modern car.
I don't follow. You should be able to tune it up or down in one of the tuning programs. I haven't wanted to get into it but I am not a commercial guy and want to learn to tune more than my own car so probably not worth it for me to learn by booking some dyno time to see what happens when you do something.
Unless it is more than a couple HP difference, I don't think any of us have that sensitive a butt to be able to feel it.
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
I seem to remember hearing at an NCM Bash the GM guys said C7s are not tuned for higher octane 100+, so it would be total waste of money. With a tune it would be different case.
Race Director
Joined: Mar 2001
Posts: 19,941
Likes: 6,743
From: Bonneville Salt Flats
I'm sure you've been told, by now, to use as close to the GM recommended as possible. Higher octane does nothing, but waste your money. Even racing engines use a specified octane depending on the build, not necessarily the highest available at any given venue (like Bonneville where I raced for 3--decades). All the best. 
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Melting Slicks
Joined: Jun 2001
Posts: 2,264
Likes: 546
I have done this. Under ideal conditions, ambient temp at 59 degrees, OIl, Water, transmission temps less than 190 degrees. With 91 octane (highest octane in South Dakota) It pulled timing. Car runs strong, Just what I have seen.
Team Owner
Joined: Jul 2004
Posts: 28,420
Likes: 3,273
From: Hartford WI
I would try a few gallons of racing fuel and see if it reduces knock.
Burning Brakes
Joined: Jan 2019
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From: Louisiana
Team Owner
Joined: Jul 2004
Posts: 28,420
Likes: 3,273
From: Hartford WI
Burning Brakes
Joined: Jan 2019
Posts: 954
Likes: 376
From: Louisiana
That's not a good plan for a car that sits a lot (storage), since you'll increase the amount of water in the tank. Reducing fuel quality and increasing the ability for it to corrode what it interacts with. Ethanol reacts with the air volume in the tank. Less air = less exchange.
Same principle for liquor. The lower the bottle gets, the more alcohol end up losing to the air inside the bottle.
Race Director
Joined: Jul 2018
Posts: 10,537
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From: San Antonio, TX/Mahopac, NY
2024 Corvette of the Year Finalist - Modified
2024 Corvette of the Year Finalist - Unmodified
2023 C7 of the Year Winner - Modified
A couple of points to add:
- Don’t store your C7 corvette with a completely full tank. 1/4 tank is fine. Gasoline is a solvent and there are some adhesives in the fuel system components you don’t want immersed in gas for long periods of time without the risk of a costly failure.
- Using high octane fuel in an engine designed for regular not only wastes money it can negatively impact performance and gas mileage. Higher compression engines create more combustible fuel charges and tend to run more aggressive timing which promote hot spots. The higher octane is more resistant to premature detonation which is not an issue as a high compression engine makes up for the lost power potential through the increased efficiency of higher compression. Your engine is designed for 93 octane and will not perform as well on 100 or 110, plus see #3 below. By the way, 94 octane is a rounding error when it comes to fuel and will not hurt your C7 engine, so spend away if it makes you feel better or your butt dyno tells you it is better.
- NEVER run leaded fuel in a stock C7, NEVER.
Last edited by Factoid; Feb 20, 2024 at 02:38 PM. Reason: I originally said 3/4 tank but meant to say 1/4 tank
Burning Brakes
Joined: Jan 2019
Posts: 954
Likes: 376
From: Louisiana
A couple of points to add:
- Don’t store your C7 corvette with a completely full tank. 3/4 tank is fine. Gasoline is a solvent and there are some adhesives in the fuel system components you don’t want immersed in gas for long periods of time without the risk of a costly failure.
- Using high octane fuel in an engine designed for regular not only wastes money it can negatively impact performance and gas mileage. Higher compression engines create more combustible fuel charges and tend to run more aggressive timing which promote hot spots. The higher octane is more resistant to premature detonation which is not an issue as a high compression engine makes up for the lost power potential through the increased efficiency of higher compression. Your engine is designed for 93 octane and will not perform as well on 100 or 110, plus see #3 below. By the way, 94 octane is a rounding error when it comes to fuel and will not hurt your C7 engine, so spend away if it makes you feel better or your butt dyno tells you it is better.
- NEVER run leaded fuel in a stock C7, NEVER.
2. Can you cite your source for this statement or clarify it? "The higher octane is more resistant to premature detonation which is not an issue as a high compression engine makes up for the lost power potential through the increased efficiency of higher compression."
Race Director
Joined: Jul 2018
Posts: 10,537
Likes: 8,284
From: San Antonio, TX/Mahopac, NY
2024 Corvette of the Year Finalist - Modified
2024 Corvette of the Year Finalist - Unmodified
2023 C7 of the Year Winner - Modified
1. Why would 3/4 of a tank protect you where a full tank would not? List the specific component that will be damaged while submerged that is being spared. Why is it a good trade off to increase the water content of the fuel by storing with 3/4 of a tank? Water can cause oxidation.
2. Can you cite your source for this statement or clarify it? "The higher octane is more resistant to premature detonation which is not an issue as a high compression engine makes up for the lost power potential through the increased efficiency of higher compression."
2. Can you cite your source for this statement or clarify it? "The higher octane is more resistant to premature detonation which is not an issue as a high compression engine makes up for the lost power potential through the increased efficiency of higher compression."
1. In addition to that is what GM recommends, watch this video
2. I’ll save you some time, read the third paragraph in the Introduction and if you are still interested spend some time on the entire article. By the way, I was told this tidbit by a chemical engineer I worked with at GE in the 1980’s and he had the math to prove it! This article is enough for me: https://www.sciencedirect.com/scienc...59431104002042
Oh and I fixed my typo, I meant 1/4 tank.
Burning Brakes
Joined: Jan 2019
Posts: 954
Likes: 376
From: Louisiana
Oh ye of little faith!
1. In addition to that is what GM recommends, watch this video https://youtu.be/cvfPCGGSUMA?si=F45h-BM3I1n4LxoA. As anyone who has had fuel sender, pump, or tank issues will tell you these are very expensive to resolve. The moisture in the fuel tank bs is ancient and not true for modern fuel systems.
2. I’ll save you some time, read the third paragraph in the Introduction and if you are still interested spend some time on the entire article. By the way, I was told this tidbit by a chemical engineer I worked with at GE in the 1980’s and he had the math to prove it! This article is enough for me: https://www.sciencedirect.com/scienc...59431104002042
Oh and I fixed my typo, I meant 1/4 tank.
1. In addition to that is what GM recommends, watch this video https://youtu.be/cvfPCGGSUMA?si=F45h-BM3I1n4LxoA. As anyone who has had fuel sender, pump, or tank issues will tell you these are very expensive to resolve. The moisture in the fuel tank bs is ancient and not true for modern fuel systems.
2. I’ll save you some time, read the third paragraph in the Introduction and if you are still interested spend some time on the entire article. By the way, I was told this tidbit by a chemical engineer I worked with at GE in the 1980’s and he had the math to prove it! This article is enough for me: https://www.sciencedirect.com/scienc...59431104002042
Oh and I fixed my typo, I meant 1/4 tank.
2. Regarding: https://www.sciencedirect.com/scienc...59431104002042 I don't see anything here that explains how higher compression is a solution to lower running a lower octane fuel. Your source is conflating octane with flame-speed, but that's not correct. Flame speed changes based on the type of fuel, AFR and compression-ratio of the engine.
https://www.wikidoc.org/index.php/Octane_rating
http://www.faqs.org/faqs/autos/gasol...section-1.html
We adjust timing (and AFR) to optimize output while staying out of knock, but increasing octane given same fuel type doesn't require adjusting timing to adapt to a new flame-speed. Ethanol and Gasoline have different flame-speeds, but octane cannot tell you the flame-speed.
https://www.researchgate.net/figure/...fig5_270760982
Excerpt from training manual:
If octane informed flame-speed that would be a lot easier for tuning.
Last edited by CPB; Feb 20, 2024 at 04:00 PM.
Team Owner
Joined: Jul 2004
Posts: 28,420
Likes: 3,273
From: Hartford WI
Fine for a daily.
That's not a good plan for a car that sits a lot (storage), since you'll increase the amount of water in the tank. Reducing fuel quality and increasing the ability for it to corrode what it interacts with. Ethanol reacts with the air volume in the tank. Less air = less exchange.
Same principle for liquor. The lower the bottle gets, the more alcohol end up losing to the air inside the bottle.
That's not a good plan for a car that sits a lot (storage), since you'll increase the amount of water in the tank. Reducing fuel quality and increasing the ability for it to corrode what it interacts with. Ethanol reacts with the air volume in the tank. Less air = less exchange.
Same principle for liquor. The lower the bottle gets, the more alcohol end up losing to the air inside the bottle.
Team Owner
Joined: Jul 2004
Posts: 28,420
Likes: 3,273
From: Hartford WI
I'm sure it will if there was a lot of moving air but isn't there only so much moisture in air and once the cap is closed, where is the fresh air coming from with moisture? Now if you are talking about your boat at the Marina, I agree. If we go with a 20 gallon tank, whether it is 5 gallons full or 15, how much more water will you get that is going to be significant? If I get a gallon of water after it sits for 4 months, I'd be crapping my pants but if it is 3 drops more, probably not. So my question is, how much more water will you be able to get with the cap on tight and the fuel system not exposed to fresh air?