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Regular gas vs Premium in Lt1

 
Old 02-11-2019, 12:58 AM
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scotth48
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Default Regular gas vs Premium in Lt1

Anyone using regular gas in a LT1 stock engine? Will the computer adjust for ghe lower octane?
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Old 02-11-2019, 01:05 AM
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Gunho
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The computers are programmed for premium gas. If your computer is programmable it can be programmed to run on less. Iíve ran midgrade in my 94, and it didnít run as well as premium.
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Old 02-11-2019, 07:37 AM
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mazdaverx7
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I have always ran 93 or 94 octane in my LT1 cars. They've always ran great with no detonation. With the 10.5:1 compression ratio, its best to use premium gas. The L98 will run on 87 and 89 but I have always used premium in my L98 cars as well. Their 9.5:1 compression ratio is a little more tolerable of the lower octane gas.
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Old 02-11-2019, 08:56 AM
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GM claims that the engine control system will adjust for it. Does it do it well? Thatís debatable. As others have stated with the 10:5:1 CR it isnít worth the risk of detonation and the performance loss for what little savings you see. Also try to get fuel from high traffic areas to lessen the risk of poor fuel quality. Its really hard to find but if ethanol free 93 can be had thatís the way to fly. My local station carried this up until a couple of years ago.
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Old 02-11-2019, 09:04 AM
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Barrier
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Try to locate "Top Tier" gasoline as well.
Better Detergent additive package made a difference in my fuel level accuracy along with Techron or another cleaner once in awhile.
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Last edited by Barrier; 02-11-2019 at 09:08 AM.
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Old 02-11-2019, 09:12 AM
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Paul Workman
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The EPA mandated back in the late 1980s that subsequent cars must be able to run on 87 octane. The LT1s fall into that group (as do some [all?] L98s).

With the aid of the knock sensor, the computer will back off timing until knock counts fall under acceptable (programmed) level.

Highway driving @ steddy speeds on level road surface, cylinder head pressures are relatively low and there is little or no affect on gas milage. Only if cylinder head pressure (due to increased accelerator) rises during passing or hill climbing, OR if coolant temps become elevated, does knock counts exceed set norms and timing is reduced until knock counts recede to acceptable level.

However, power is reduced due to retarded ignition timing. And, this is where higher octane comes in: it prevents knock at higher pressure (HEAT). Ignition timing (i.e., performance) is not retarded as much. Power output is better and afforded by higher octain. Performace...is the reason they print, "Use premium fuel only" on the gas fill cap.
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Old 02-11-2019, 09:13 AM
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Brooks94Z07
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Originally Posted by Barrier View Post
Try to locate "Top Tier" gasoline as well.
Better Detergent additive package made a difference in my fuel level accuracy along with Techron or another cleaner once in awhile.
Barrier
My local Costco claims that their "Top Tier" and highlights that they're using a better detergent additive. They actually have a picture of C7 Corvette on the pumps display screen advertising this! So I only go there and fill up with 93...costs less as well. Would never put in anything below 93...LT1s love to run really hot and just love burnin' up that high octane fuel...

Last edited by Brooks94Z07; 02-11-2019 at 09:20 AM.
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Old 02-11-2019, 09:18 AM
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Brooks94Z07
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Actually I just filled up my '94 from bone dry there on Friday. The nozzle kicked at $39.01 and rounded it up to $39.25 for 93

For the amount that I drive the car, that probably will last me a month and a half...
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Old 02-11-2019, 10:11 AM
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skyhawk50
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2 of my C4ís are LT 1ís and Iíve always run 87 in both cars. No issues. Thereís a fuel farm close by and all day long the tankers roll out of there Sunoco, Exxon Mobil and all the unbranded gas tankers. I know they supposedly all have there additives, but according to a driver I know, there is very little difference in the blends. He said that when he hauls Gulf, there is about 5 gallons of additive for 8,000 gal of gas.
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Old 02-11-2019, 11:34 AM
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vader86
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The car can run and you can get to where youre going just fine on 87. The computer will pull out timing when it detects detonation. This will negatively affect gas mileage all of the time and really affects the power output of the engine when you stand on it.

Its not a good thing to do long term but in a pinch you need not worry about it.

The correct way to determine what octane you need to run is plug in a scanner and look at whether it detects knock while you drive, and run the lowest octane that has no knock counts.

Last edited by vader86; 02-11-2019 at 11:35 AM.
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Old 02-11-2019, 12:00 PM
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QCVette
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My LT1's owner's manual states use premium fuel for best performance, but it says it can run mid grade or regular. The area by the gas cap says premium fuel recommended.

My LT4 owner's manual states use premium fuel. The area by the gas cap says premium fuel only ( or something like that).

In practice I have tried regular in my LT1s with mixed results. My '94 ran fine with no apparent difference from premium. My '95 does not like regular at all. It has reduced performance and knocking under load.

My conclusion is that I use premium when available. On my '94 I have used regular for a trip or two when I was planning a long highway trip with small loads while cruising.

You can try a tank and see if you notice a difference especially under load then decide if or when you will try it again.

Good luck.
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Old 02-11-2019, 03:51 PM
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95LT1ZF
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My last three cars have all recommended premium, so that's what I run. Sure, the computer can probably adjust for it, but why give the car more crap to do. I just consider it the price of ownership.
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Old 02-11-2019, 05:30 PM
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GS60th#47
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Do you live in an area that has no Ethyl? Driving it to a 3rd World country?
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Old 02-11-2019, 06:08 PM
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Kevova
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IDK about regulations requiring engines to run on regular 87. Cadillac started building " Premium Required" engines in 90 to boost performance in the fwd models. They also found owners weren't going to use premium. For 2000 engines were redesigned to run on regular. Knock sensor will retard timing to compensate , expect reduced performance and fuel economy. There is no benefit to run premium in engines where it isn't required or recommended. Many years ago when fuel quality sucked premium was recommended because of increased levels detergent.
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Old 02-11-2019, 08:02 PM
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aklim
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Originally Posted by scotth48 View Post
Will the computer adjust for ghe lower octane?
Absolutely. Whether you like what the adjustment does is another issue. If it backs off the timing, you lose power and economy. So what exactly are you trying to achieve?

You want to find out? Run the tank as empty as you can and fill up with 87. Run a scanner and do a few WOT runs. Under similar conditions, repeat the test with 93 and see what the knock counts are. When you have that information, you will be guided as to what next to fill up with. Will you feel knock with 87? Probably not since the ECM will retard timing till it can't anymore and 87 should not put you in that range so the hearing test is probably meaningless.
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Old 02-11-2019, 08:27 PM
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mto
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Probably run OK, but it can cause carbon build up bc not enough additives. I would only use top tier gas that is a premium. https://www.toptiergas.com/retailers/
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Old 02-11-2019, 08:42 PM
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aklim
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Originally Posted by mto View Post
Probably run OK, but it can cause carbon build up bc not enough additives. I would only use top tier gas that is a premium. https://www.toptiergas.com/retailers/
I don't follow. Are you saying that if I got premium gas (93 Octane) it is "Top Tier" but if I use regular gas (87 Octane) it is not "Top Tier"? From what I see, "Top Tier" is a standard and not an octane so I can get 87 Octane from a "Top Tier" station that is also "Top Tier" certified.
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Old 02-11-2019, 08:49 PM
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mto
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I wasnít clear. Any 87 fuel does not have enough additives. 93 does have proper additives.

That said, all 87 fuel is the same. One top tier and another 87 top tier, no difference. With 93, most top tier differ each other by additives and marketing.
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Old 02-11-2019, 08:53 PM
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aklim
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Originally Posted by mto View Post
I wasnít clear. Any 87 fuel does not have enough additives. 93 does have proper additives.

That said, all 87 fuel is the same. One top tier and another 87 top tier, no difference. With 93, most top tier differ each other by additives and marketing.

No. Premium describes a grade of fuel intended for use in performance engines with higher compression ratios, which may be damaged when using lower octane grade fuel. TOP TIERô fuel marketers are required to use TOP TIERô for all for all octane grades of gasoline and diesel sold at their stations. TOP TIERô is a standard in fuel many automakers feel is necessary for acceptable engine cleanliness performance for all vehicles, regardless of octane requirements. All engines will benefit from a higher standard in cleanliness resulting in a vehicle performing as intended: noticeable in longevity, reduced down time, minimized emissions, and higher customer satisfaction.
According to Top Tier, it seems like regardless of what octane, it should have the same additives since it is a standard
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Old 02-12-2019, 01:57 PM
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Paul Workman
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Boy.... There is more (let's say - internet) VOO DOO and ignorant BS myths "experts" regarding octane ratings than just about any topic EXCEPT "What oil should I use?" And, the selected "facts" depend on who is explaining it and how they might benefit if their audience is convinced. The ordinary joe/jane hasn't a prayer of getting at the truth until he/she goes to the objective "well" and endeavors to understand the basis of octane rating, how it is determined, what conditions affect (detonation/pre-ignition), and what happens in the combustion chamber of the gasoline engine under various dynamic (load) conditions.

That said, (speaking primarily of OBD-I C4s in particular) if one really wants to observe how a modern (computer controlled) gasoline engine performance differs between (87 vs. 93+) octane rated fuels, put the car/engine on a dyno. There you can observe for yourself the engine output over a wide range of loads and how the computer (in conjunction with the knock sensors) responds to different octane fuels. There you can witness output performance under light - moderate - and WOT load conditions, and observe the spark advance as dictated by the computer in attempts to satisfy preset knock occurrence limits.

Additives are used to modify octane, yes. But, also long term use success is dependent on the additive package addressing other things, such things as carbon deposits on valves and on cylinder head and piston surfaces - which also affects pre-ignition and performance overall, if not directly related to "octane" (per se').

So, one really needs to get beneath all the layers of hype and repeated myth by "experts" with an agenda to really find the truth of the matter. Only then does one avoid having the wool pulled over their eyes!

Just sayin....
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