91 vs 93 octane fuel - Page 3

Gen6cyl · 05-19-2022, 10:58 AM

I think auto's have to be able to run on 87 to be sold in US.

arpad_m · 05-19-2022, 11:57 AM

Quote:

Originally Posted by Gen6cyl

I think auto's have to be able to run on 87 to be sold in US.

Is that a federal requirement? If that exists, I sure didn't know about it.

Gen6cyl · 05-19-2022, 12:58 PM

I read that Mazda had a 15to 1 compression engine.The article said it could not be sold in us because 87 would blow it up.

David Gordon · 05-20-2022, 02:50 PM

I saw a video on a turbo motor where the difference in boosted motors making a bigger differnce. Like 30-40 hp

overdriv · 05-24-2022, 08:55 AM

Well to update this thread I'm home now and Camaro ran fine. Covered 6085 miles and averaged 25miles per gallon.
No problems what so ever.
But, when returning home through the mountains on I70, we ran into snow and rain with temp down to 26deg. I wonder if that is enough to ruin the runflats?

ctrlz · 05-24-2022, 09:25 AM

Quote:

Originally Posted by overdriv

temp down to 26deg. I wonder if that is enough to ruin the runflats?

I suppose you could look for cracks.

As far as 87 octane i don't think there is any regulation. Manufacturers accommodate this because they know there may be situations where 1) higher grade fuel is not available, and 2) some customers may be forced to buy cheaper grades if fuel prices spike.

James6speed · 10-12-2023, 12:31 PM

Revisting this. After I have ran without issue for 10k miles and no knocking on Shell 89 octane, I decided to change to 93 Shell. I have noticed no difference at all in power.. I am switching back to 89 at this point. The internet keyboard pounders we're wrong as I suspected. The computer does automatically draw back with DFI to adjust for the octane and the power difference seems to be negligable. I daily this car, so an extra $20 bucks in my pocket for nothing is good enough for me.

CalgaryZL1 · 10-12-2023, 01:24 PM

Quote:

Originally Posted by James6speed

Revisting this. After I have ran without issue for 10k miles and no knocking on Shell 89 octane, I decided to change to 93 Shell. I have noticed no difference at all in power.. I am switching back to 89 at this point. The internet keyboard pounders we're wrong as I suspected. The computer does automatically draw back with DFI to adjust for the octane and the power difference seems to be negligable. I daily this car, so an extra $20 bucks in my pocket for nothing is good enough for me.

I commented on your other post, if you notice no discernable difference then 89 is a good choice to save money. here in Canada we have a up to 10% ethanol blend law so I choose the highest grade gas I can find at 94, but my car is also not a daily driver.

RobZL1 · 10-12-2023, 08:21 PM

Quote:

Originally Posted by James6speed

Revisting this. After I have ran without issue for 10k miles and no knocking on Shell 89 octane, I decided to change to 93 Shell. I have noticed no difference at all in power.. I am switching back to 89 at this point. The internet keyboard pounders we're wrong as I suspected. The computer does automatically draw back with DFI to adjust for the octane and the power difference seems to be negligable. I daily this car, so an extra $20 bucks in my pocket for nothing is good enough for me.

How many tanks of 93 did you run after running 89 for 10k miles? And what is DFI?

2SS Capt · 10-12-2023, 08:49 PM

Quote:

Originally Posted by RobZL1

How many tanks of 93 did you run after running 89 for 10k miles? And what is DFI?

I'm guessing "DFI" is "Direct Fuel Injection"... Meaning "Direct Injection" which our motors are...

RobZL1 · 10-12-2023, 11:19 PM

I guess. I'm not sure what draw back means in this context. Anyway, I would assume no power difference was felt because it takes longer for the knock learn factor to rise than fall, if he only ran one tank perhaps.

It's been proven again and again on dynos that you'll see power gains from 93 over 89. Not sure why we think the keyboard pounders are wrong. Some of them run shops and tune hundreds of these cars.

dfwcowboy · 10-13-2023, 04:19 AM

It’s worth discussing how the engine is designed. I’m not familiar with the exact design of the LT1 and LT4, but generally how it works for modern high compression engines is the engine has a knock sensor and when it detects detonation caused by too low octane for the compression ratio, the ECU retards timing to correct for that situation which will be something less than optimal. The net result is lower horsepower. No question about it. The amount might be debatable, but the effect is not. So when someone says, I ran lower octane without knocking, this should be obvious because the engine is designed to compensate. What will be much less obvious is the loss in horsepower. Published horsepower ratings are determined under standard atmospheric conditions at a given RPM. So if you aren’t running your engine at red line, you probably won’t notice any difference, and even in that situation it will be hard to objectively tell the difference without timing something like 0-60, quarter mile, etc. Another objective method would be to measure manifold pressure and RPM which directly relates to HP for a given engine. Putting the car on a dyno, would be another method.

Another aspect is the ECU learns how to adjust timing to prevent knocking. It makes sense the effect will be near immediate if knocking is detected and much less immediate going the other way. I have no idea how much higher octane fuel it takes to return to optimum, but my guess is it’s going to be more than one or two tanks full.

WhiteMale · 10-13-2023, 06:57 AM

Too the LT1 and 4 run on the knock sensors as in they're very sensitive.

Gen6cyl · 10-13-2023, 11:22 AM

Another aspect is the ECU learns how to adjust timing to prevent knocking. It makes sense the effect will be near immediate if knocking is detected and much less immediate going the other way. I have no idea how much higher octane fuel it takes to return to optimum, but my guess is it’s going to be more than one or two tanks full.[/QUOTE]

That makes sense if the ecu has detected knock it will stay conservative and the longer it goes with out knock the more it will advance timing. I have read where tuners say it takes at least a thousand miles to fully adjust to higher octane. I used 87 for the first ,18 k miles on my v6. Since then been using only 93 , now at 57 k miles. It runs better, smoother , has to be better for the engine. If I never ran it hard 87 we probably be ok.

05-20-2022, 02:50 PM	#32
David Gordon Drives: 2018 Grandsport Corvette Join Date: Apr 2022 Location: Granbury Posts: 270	I saw a video on a turbo motor where the difference in boosted motors making a bigger differnce. Like 30-40 hp __________________ 2022 Orange ZL1 4/07/22 7-01-22 Past 2018 Gransport 2018 GT Premium 2009 ZO6 2008 Z-51 Vette 2001 Stroked/ blown C-5 2001 SS 1998 SS vert. Garage 2020 Range Rover V-8 2021 Ford F-150 Platinum Powerboost

10-12-2023, 11:19 PM	#39
RobZL1 fo'shizZL1 Drives: 2017 ZL1 Join Date: Aug 2017 Location: ATL Posts: 1,281	I guess. I'm not sure what draw back means in this context. Anyway, I would assume no power difference was felt because it takes longer for the knock learn factor to rise than fall, if he only ran one tank perhaps. It's been proven again and again on dynos that you'll see power gains from 93 over 89. Not sure why we think the keyboard pounders are wrong. Some of them run shops and tune hundreds of these cars. __________________ 2017 ZL1 M6 Black \| Maggie 2650 // 103TB // Big Gulp Past Rides- 2014 ZL1 M6 Red Hot \| Tons of mods 2004 CTS-V M6 Silver \| Many mods 1995 Corvette M6 Torch Red \| A few more mods 1992 Camaro M5 White \| A few mods

10-13-2023, 11:22 AM	#42
Gen6cyl Drives: Chevy Camaro 2021 ,rs, v6, manual Join Date: Feb 2022 Location: Georgia Posts: 868	Another aspect is the ECU learns how to adjust timing to prevent knocking. It makes sense the effect will be near immediate if knocking is detected and much less immediate going the other way. I have no idea how much higher octane fuel it takes to return to optimum, but my guess is it’s going to be more than one or two tanks full.[/QUOTE] That makes sense if the ecu has detected knock it will stay conservative and the longer it goes with out knock the more it will advance timing. I have read where tuners say it takes at least a thousand miles to fully adjust to higher octane. I used 87 for the first ,18 k miles on my v6. Since then been using only 93 , now at 57 k miles. It runs better, smoother , has to be better for the engine. If I never ran it hard 87 we probably be ok. __________________ B6 dampers, x pipe, mbrp axel back

05-19-2022, 10:58 AM	#29
Gen6cyl Drives: Chevy Camaro 2021 ,rs, v6, manual Join Date: Feb 2022 Location: Georgia Posts: 868	I think auto's have to be able to run on 87 to be sold in US.

05-19-2022, 12:58 PM	#31
Gen6cyl Drives: Chevy Camaro 2021 ,rs, v6, manual Join Date: Feb 2022 Location: Georgia Posts: 868	I read that Mazda had a 15to 1 compression engine.The article said it could not be sold in us because 87 would blow it up.

05-24-2022, 08:55 AM	#33
overdriv Drives: 1969 Chevelle SS 2019 2SS Camaro Join Date: Jul 2018 Location: IL Posts: 246 View My Garage	Well to update this thread I'm home now and Camaro ran fine. Covered 6085 miles and averaged 25miles per gallon. No problems what so ever. But, when returning home through the mountains on I70, we ran into snow and rain with temp down to 26deg. I wonder if that is enough to ruin the runflats?

10-12-2023, 12:31 PM	#35
James6speed Drives: '23 LT1 conv, '07 911 Turbo Join Date: Jun 2018 Location: Lexington, KY Posts: 44 View My Garage	Revisting this. After I have ran without issue for 10k miles and no knocking on Shell 89 octane, I decided to change to 93 Shell. I have noticed no difference at all in power.. I am switching back to 89 at this point. The internet keyboard pounders we're wrong as I suspected. The computer does automatically draw back with DFI to adjust for the octane and the power difference seems to be negligable. I daily this car, so an extra $20 bucks in my pocket for nothing is good enough for me.

10-13-2023, 04:19 AM	#40
dfwcowboy Drives: 2024 ZL1 M6, 1969 Cessna Skylane Join Date: Jun 2018 Location: Dallas Posts: 368	It’s worth discussing how the engine is designed. I’m not familiar with the exact design of the LT1 and LT4, but generally how it works for modern high compression engines is the engine has a knock sensor and when it detects detonation caused by too low octane for the compression ratio, the ECU retards timing to correct for that situation which will be something less than optimal. The net result is lower horsepower. No question about it. The amount might be debatable, but the effect is not. So when someone says, I ran lower octane without knocking, this should be obvious because the engine is designed to compensate. What will be much less obvious is the loss in horsepower. Published horsepower ratings are determined under standard atmospheric conditions at a given RPM. So if you aren’t running your engine at red line, you probably won’t notice any difference, and even in that situation it will be hard to objectively tell the difference without timing something like 0-60, quarter mile, etc. Another objective method would be to measure manifold pressure and RPM which directly relates to HP for a given engine. Putting the car on a dyno, would be another method. Another aspect is the ECU learns how to adjust timing to prevent knocking. It makes sense the effect will be near immediate if knocking is detected and much less immediate going the other way. I have no idea how much higher octane fuel it takes to return to optimum, but my guess is it’s going to be more than one or two tanks full.

10-13-2023, 06:57 AM	#41
WhiteMale Drives: 23 ZL1 A10 Rapid Blue Join Date: Aug 2020 Location: MO Posts: 1,982	Too the LT1 and 4 run on the knock sensors as in they're very sensitive.

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