FAUEE

I don't think it's fair to say we would be at the coolest and lowest rpm possible. I think a lot of people use 87 as their fill up and just drive normally, so they get on the gas and all the other stuff then fill up and wonder about their fuel economy. While I agree cruising on a flat road with plenty of cool air you'e unlikely to knock, I wouldn't agree that' the typical situation for these cars, and that people wouldn't notice any knock on regular.

I feel.like people like that would have been better off to buy an old man buick like a reatta.

Tom400CFI

This thread was about driving across country, then it turned into a cost debate relative to octane. If you're driving across country, the conditions that I described are most likely, detonation is highly unlikely and the the claim that it will cost you more money to run a lower octane is ridiculous. (It's ridiculous, what ever the "reason"). If you're fooling around and getting on the gas...well then you probably don't GAF about fuel economy and so you're not to likely to observe a difference in consumption under those conditions either. SO...the claim that it will cost more money to run lower octane is pretty empty.

I'm not advocating that the op runs lower octane...I mainly wanted someone to cite where they read that "the knock sensors will just tell the computer to run richer"...and now we have a little debate about octane vs cost...and "how engines work".

Drew95

So let me make sure I get this right:

You bought this car from a FRIEND of yours who never let it see rain, and you're asking if you can put cheap shitty gas in it?

Did you ask your buddy what HE wants his baby to eat?

Jesus Christ.

California people....

EVERY.
TIME.

64Scout

Why do you assume the OP is in California? Maybe he is in Louisiana?

PatternDayTrader

I run regular in my 95 car without any meaningful spark knock. My car says premium is recommended, and if I ran it hard then I would certainly use premium.
For some reason I was under the impression the l98 cars were more sensitive to fuel octane. I don't know if that's true or not, but if the owners manual says required, then I would use it, but if it says recommended, try a tank full of each and then decide.

cdm747

The 88 owners manual states "Your engine is designed to operate on premium grade unleaded fuel. However, with the electronic spark control system, you may use either middle or regular grade unleaded fuel at slightly reduced acceleration performance."

1stVetteFinally

It's not his friend's baby anymore.

I personally haven't driven an L98 Vette, but the two LT1 Vettes I have owned/own do run on 87, and I feel it every time I give the car gas. It's not what I would call a "minor" loss of performance. I only run premium because of that. If someone is good with the loss of performance, they shouldn't be driving a Vette IMHO.

Renfield

You had a point, then went three lines too far there stud. When you lump a group of people together like that, it's called bigotry. My Dad's C7 resides in So. Cal. (where I grew up), and I assure you we both only uses premium Tier 1 gasoline in our Corvettes.

Also I imagine that Christians, celebrating their highest holiday about now, would take exception to your reference to their savior. WTF has any of that got to do with Corvettes Joisey Boy?

Up your nose with a rubber hose.

hcbph

Getting back to the original question/issue: what octane to use on a L98?
I would start with what the manual says, after that I'd look at the CR on the engine (assuming there isn't some exotic cam etc in it).
IIRC my 86 L98 has a 9.5 CR, that's good for 87 octane fuel. You start getting into the 10-10.5 CR then IMO you had better be looking at 89 octane. Anything beyond that and you'd better be looking at as high an octane as you can find, including octane boosters.
You notice I didn't mention blowers or turbos, water or meth injection. I'm so out of date on those subject, anything I might say is likely out of date and no longer accurate.

You need as much octane as your engine requires to run properly. If it's been modified, all bets are off on requirements.

Remember also you want a clean burn. If there's too much suppression on the burn it will potentially carbon up the engine.

ddahlgren

The car needs a certain amount of power to run at a certain speed probably around 30 to 35 hp. to go 70 mph. HP is a function of torque and rpm. The torque comes from cylinder pressure. You get cylinder pressure from burning the least amount of fuel within the chemical constraints of the fuel at the hottest temperatures.

Higher cylinder pressures need less throttle opening to generate the same pressure and torque.

Retarding the timing burns the fuel later in the cycle and more heat is lost to the exhaust and cooling systems.

This requires a larger throttle opening to maintain the same cylinder pressures and torque.

This results in a greater airflow through the engine and a greater amount of fuel to maintain a mixture within the fuel burning constraints of the fuel.

There are ways to lean burn gasoline but retarding timing is not the way. The lean burn works with the idea the larger throttle opening will reduce pumping losses. Retarding timing and burning low octane fuel is not one of the ways.

Tom400CFI

Yes, I'm well aware of how an engine works. Are you? I especially enjoy this line:
"Higher cylinder pressures need less throttle opening to generate the same pressure and torque."

You mean "Higher compression..."?



Please explain why/how we're retarding timing, as we cruise on the highway? :

This is getting dumb with the hair splitting anyway. I've ran enough GM products, enough highway miles and hand calc'ed enough tanks of gas to know that in service, it don't make one whit of difference to fuel economy, which grade you select. Selecting high octane gas to "save money" is folly.



.

PatternDayTrader

Octane and energy content are two different things.

JrRifleCoach

Just another Yankee blow hard.

Go throw your rocks in a Mustang forum.....

Cool Runnings

Lower octane burns slower.

aklim

You mean actually use a scanner to see what is going on instead of guessing what is happening by what you feel? Sounds insane. What next? Not using tea leaves to read the future?

ddahlgren

If it burned slower you would not need to take timing out to prevent knock.

ddahlgren

Noticed you lived out west in the land of flat earth. At least from Salt lake city to Wendover as the only run I have made through there several times to race at Bonneville. In New England we have large changes in elevation complete with multiple escape roads for trucks if brakes are failing going down them. It is not just one but can be one after another. At the end of the day none of this conversation really matters t save 20 or 30 bucks to go cross country. it costs more than that to stay in a decent room vs. a flea bag dump normally rented by the hour.
I like mine the best when it gets 3 1/2 to 4 mpg LOL

JrRifleCoach

Ship it. Breaking down with a C4 is not going to be fun if you're not familiar with the car.

Interestingly the 89 L98 is a 9.5:1 engine. And the 90 is a 10.25:1.
This I did not know..... mid grade to premium is just fine.
You wont hurt it with reg for your journey.

But if you plan to have some go-pedal fun, load it with the good stuff and turn on your radar detector.

aklim

Good point

Probably not.

Who wouldn't? I'd be stomping on it every chance I can when I see the straight road clear of cops. Doesn't matter if it is a sedan or a high performance car.

JrRifleCoach

My daughter questioned this "folly" on one of our monthly trips to LA. So we had a full tank of premium, zeroed out the MPG and trip meters. We avg'd 32 for a 350 mile run. For the return trip we burned regular and avg'd 29 for the same number of miles on the same roads. After the calculator was turned off she was convinced that either fuel will net approximately the same costs.

350 / 32 = 10.93 gallons @ $3.49 or $38.17
350 / 29 = 12.06 gallons @ $3.29 or $39.70

How about that.....








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