Premium or regular?
Race Director
Joined: Oct 2012
Posts: 17,334
Likes: 6,509
From: Melbourne, FL
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.
I feel.like people like that would have been better off to buy an old man buick like a reatta.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
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'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".
Racer
Joined: May 2013
Posts: 278
Likes: 7
From: Long Valley NJ
I'm buying a 1990 C4 convertible (with the L98 engine) from a childhood pal who bought it new and has kept it in showroom condition all these years (for example, it's never been rained on). I'm deciding now whether to ship or drive it from its New York home to my primary residence in LA, and while my friend says he's always used premium gas I've read some threads asserting that regular is just fine. Is it?
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.
Race Director
Joined: Oct 2008
Posts: 17,982
Likes: 1,074
From: Lansing MI
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.
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.
Burning Brakes
Joined: Jan 2017
Posts: 961
Likes: 237
From: Diamondhead Mississippi
St. Jude Donor '17-'18-'19-'20-'21-'22
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."
Pro
Joined: Sep 2014
Posts: 588
Likes: 35
From: Smithfield VA
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.
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.
Last edited by 1stVetteFinally; Mar 31, 2018 at 08:25 AM.
Drifting
Joined: Oct 2015
Posts: 1,674
Likes: 191
From: Shit Creek, USA
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.
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Safety Car
Joined: Aug 2013
Posts: 4,427
Likes: 604
From: Minneapolis Mn
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.
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.
Last edited by hcbph; Mar 31, 2018 at 09:14 AM.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Right....I know how engines work, and I also know that YOU already know that. You might want to review your own understanding of how the engine works, though.
When we're driving in such a manner as to be concerned w/fuel economy, (driving across country) cylinder pressure isn't typically a big problem w/regard to detonation; we're running with a very small throttle opening...aren't we? Yes we are.
We're also running with some EGR. We're also running on the lowest end of the acceptable temp range (down against the stat). Under these conditions, detonation isn't typically a big problem, regardless of octane. So how are we going to get detonation, retarded timing, and lowered efficiency? We aren't very likely to.
In addition to all that...how do you explain this;
"The knock sensors will just tell the computer to run richer" (?)
B/c ^That was what I was REALLY interested in hearing about.
When we're driving in such a manner as to be concerned w/fuel economy, (driving across country) cylinder pressure isn't typically a big problem w/regard to detonation; we're running with a very small throttle opening...aren't we? Yes we are.
We're also running with some EGR. We're also running on the lowest end of the acceptable temp range (down against the stat). Under these conditions, detonation isn't typically a big problem, regardless of octane. So how are we going to get detonation, retarded timing, and lowered efficiency? We aren't very likely to. In addition to all that...how do you explain this;
"The knock sensors will just tell the computer to run richer" (?)
B/c ^That was what I was REALLY interested in hearing about.
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.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
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.
.
"Higher cylinder pressures need less throttle opening to generate the same pressure and torque."
You mean "Higher compression..."?
: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.
.
Last edited by Tom400CFI; Mar 31, 2018 at 09:45 AM.
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
Just another Yankee blow hard.
Go throw your rocks in a Mustang forum.....
Last edited by JrRifleCoach; Mar 31, 2018 at 01:31 PM.
Melting Slicks
Joined: Jan 2017
Posts: 2,099
Likes: 47
From: Minneapolis MN
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.
.
"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.
.
Lower octane burns slower.
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
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.
.
"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.
.
I like mine the best when it gets 3 1/2 to 4 mpg LOL
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
I'm buying a 1990 C4 convertible (with the L98 engine) from a childhood pal who bought it new and has kept it in showroom condition all these years (for example, it's never been rained on). I'm deciding now whether to ship or drive it from its New York home to my primary residence in LA, and while my friend says he's always used premium gas I've read some threads asserting that regular is just fine. Is it?
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.
Team Owner
Joined: Jul 2004
Posts: 28,432
Likes: 3,285
From: Hartford WI
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.
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.
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.
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
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..
350 / 32 = 10.93 gallons @ $3.49 or $38.17
350 / 29 = 12.06 gallons @ $3.29 or $39.70
How about that.....
.
Last edited by JrRifleCoach; Apr 1, 2018 at 12:53 PM.