What Octane Grade Fuel for 3800 SC?

I own a 1997 s/c riv and I have always run 87 oct in it from day 1. I get 20-22 mpg in the city and just last weekend took it on a 600 mile trip and got 25.5 mpg on the thruway at 75 mph. By the way my car just turned 238000 and it still runs great.

I think the phrase "runs great" can mean different things for different drivers. I used to own a '70s Dodge with an engine that would knock when it ran, every day for 200k miles. A lot of people would say the car ran great, but what it did was get from point A to B for about 5 years, making that "ping" for much of the time. If you're fueling a supercharged 3800 with 87 octane, everything may seem okay, and it might very well be all right if driven gently (it seems like you baby yours, seeing 20 mpg in the city). You must've been doing something right to get it to last this long, but try pushing the car to do what it was designed to, and things will change. A different driver with more spirited driving style would likely not have gotten as far without problem.

I would describe a SC Riviera running on premium fuel as "performs great". This goes a bit further than merely driving the car without apparent problem, and doing so for a lot of miles (a car can run badly for thousands of miles). It means you know the engine is happy when you put the pedal down. It means anyone can drive the car with confidence, no matter what their style... no need to be careful anymore. Using premium fuel also means the car will perform to factory performance specs without hesitation or failure. A stock SC Rivera should run the 1/4 mile in 15.5 seconds, but it won't do that on 87 octane. I don't know what time it would run; I 'd be afraid to find out.

a lot of mechanics and car "enthusiasts" say the octane doesnt matter, which is true for 80% of the cars today and for most of the daily commuters. most people would never know, or feel, the difference between 87 and 106 octane in their engine. however those of us who have looked at how an engine runs by means of a scanner KNOW the engine runs better, safer, faster, and more efficiently with higher octane. KR is almost never audible, and neither is timing being pulled.

on another note, it takes several tanks of a different fuel to start seeing a difference in econ. the pcm has to adjust to the all of the tables to compensate for the advanced timing.

FWIW i'm sure it is far worse to run 87 in a car that has used 93 for years than it is to run 87 from day 1. i have to use 93, not just b/c i am modded, but b/c i drive "spirited". i might as well just remove a spark plug if i were to put 87 in mine now

In about a week, I'm gonna have Alex registered and road-ready, and I'll be filling her up. I have one notch on the gas meter left, so the tank is almost empty, and getting to the gas station is no problem; there's 4 about 2 miles away in town. Thing is, I'm not too sure what fuel to use.

I mean, I know premium would be the best thing to use, but that stuff is getting expensive, in case you're blind.

Now, here's the deal. She's got 84,909 miles, and for the past 20,000 miles has only taken premium since the last owner was a car nut. I'm not a puritan of performance, but I know what happens if you put regular in, so I'm gonna try to go mid-grade.

Since the tank will be next to empty, I figure that's a good start for weaning a car from premium to mid-grade(93-89). I will not be putting in any regular(87) because of knock problems that may arise and cost me a lot of money inside the engine. I know that using regular in a premium engine will eventually cost more in an engine swap than buying premium all the time, but this isn't a premium engine. It's a basic one that's only gotten premium. The result is a super-clean emmissions test, see the pic below. Cleaner than an '07 Toyota.

Using mid-grade in this engine is a good choice in my opinion, because gas prices are most likely gonna break $4/gal. if our 300,000,000 American citizens don't band together against the companies. Doesn't the buyer control the marketplace and not the seller? Anyway, what's everyone's honest, realistic opinion on this? It's no drag car, she's just a cruiser.





Quick summary:

Engine used to premium
I want to use mid-grade
Tank's almost empty, so no octane mixing problems
Not a racer, just a driving car

Only forseeable effect is that the car will pollute a little more, but if that was a concern of mine I'd've bought a dime-a-dozen Corolla or Civic. Not a beautifully sculpted Riviera. I'll be using Z-Max when it hits 125,000 miles, so it'll still live a long, clean lifetime.

what part of NY car you in central ,southern or northern . then i will tell you also do u live in a big city?

Northern Westchester, NY. First county north of NYC. I hate being that close to the city.

so thats southern. mid grade might work, i asked because were i live right out side the city the high grade stuff is pretty Sh!tty, so i have to go in to the city to run the high grade stuff

Yeah, fuel quality is what it says it is down here, so no watered-down stuff. I expect mid-grade should work because for now it's a town-toter and for college in two years I'm just going to the train station and back for a commute.

No way am I driving MY car into NYC. It'll get smashed up the first time, because I don't like driving aggressively and I get too tense when all the egyptian taxi drivers start to swerve in and out of lanes without signals. Down there, those 8-sided signs are just a suggestion, too.

here's the problem. Running lower octane means you will always be 'bouncing' off of your knock sensor. This is horrible for the engine and you will be replacing head gaskets soon or worse.

What you need is a tuner. That way you could reduce the timing as needed and your performance losses would not be causing engine damage.

The knock sensor works by listening for detonation. When detonation is sensed, timing is reduced double the amount needed to eliminate the detonation. Then it gradually reintroduces timing to see where the detonation starts again. Senses detonation, reduces timing, ....... there is no 'learning'. It just keeps repeating this cycle. Eventually you will regret it. You need to change your timing table if you want to run a lower octane.

Was this engine recommended for running on premium from the factory? And like I said and like you addressed, I'm alright with losing some horsepower as long as it doesn't severely damage the engine. How much will it cost to tune this thing like that?

IDK about the 95's but the series II engines are suposed to have 91 or better octane from the factory.
btw its not bad to mix grades, thats how the stastion gets a middle grade (there are 2 tanks, one of 93 and one of 87, then they mix them in-line to get any number in between.)

as long as you're not going WOT with middle grade (89) you will be ok, but for the small increse in price (what, 10 cents/gal??) isnt it better to run the good stuff?
you probably will not notice a loss in hp, but you may actualy get worse mileage running a lower octane. the pcm could start throwing in more fuel to combat KR resulting in poor mpg.

well, around here it goes 3.25, 3.32, and then jumps to 3.49. If it's not a big jump, I may use premium, but I'll use mid-grade if my wallet seems to be on a diet once I start fronting the gas bills myself.

Oh wait, if it gets more MPG on premium, then it pays for itself in the price difference...well, I guess I'm running with the big boys now!!


Thank god for my Ti-83, here's how I figure that.

If I pay 3.49 a gallon and get 29 miles per gallon(3.49x/29) and pay 3.24 a gallon for mid-grade and get 26 miles per gallon(3.24x/26), I get more miles for my money with premium.

If it's more realistic, and I pay 3.34 for premium at 29 mpg, and then pay 3.24 for mid-grade at 27 mpg, I still get more miles with premium.

use premium. If you're actually cheap enough to consider using mid-grade, at least go for a half and half mix of 93 and 89.

I also seriously doubt that you (and America) should try to "stick it" to the oil companies by using a lesser grade of fuel, which will increase your actual fuel consumption.

Jason wrote:

I also seriously doubt that you (and America) should try to "stick it" to the oil companies by using a lesser grade of fuel, which will increase your actual fuel consumption.

Oh, no, that's not what I'm talking about. I mean that if we could band together and not buy any gasoline for 3 days straight every year, it would demolish the gas companies and force them to lower their artificial prices. It is a buyer's market, not a seller's market, after all. Either that, or absolutely NOONE buys any Exxon/Mobil gasoline or oil for a long period of time. You can buy gas from Shell, Chevron, or anyone else, but when noone buys Mobil they have to lower their prices, and other companies will follow suit. It could work, but it's impossible to get the word out and organize something unless you're on nat'l TV.

Also, thanks for telling me it's supposed to be on premium. I figured a high-feature V6 from the General would be for regular, but I'm wrong here.

The S/C makes premium a requirement.

As to the gas station boycotting, price fixing etc... look deep into your common sense and you know it won't work. You'll just screw over some station owners. Gas prices are controlled by supply, demand and the commodities market (which is where the problem lies).

deekster_caddy wrote:

Gas prices are controlled by supply, demand and the commodities market (which is where the problem lies).

If you believe what the news tells you than yes. It'll work in common sense because it would be all gas stations across the country. What really happens is the gas companies use whatever excuse they can to raise gas prices, from hurricanes to saying that there aren't enough refineries. When they raise gas prices here, the towelheads over in arabia raise the oil prices because the higher gas prices are an opportunity for them to make more off oil. Then the gas companies use that as an excuse, and it's a neverending, artificial cycle. There's plenty of oil, there's plenty of refineries, and there's plenty of gas. There just isn't plenty of money.

Don't get me wrong, I'm no San Fransisco hippie, I'm no vegan, and I hate conspiracies. I did buy a Buick and not a Toyota, right? When one out of many major gas companies makes over $356,000,000,000.00 in PROFITS, I doubt that supply and demand has shit to do with it. They wipe their asses with our benjamins, and I won't stand for it.

IBx1 wrote:

deekster_caddy wrote:

Gas prices are controlled by supply, demand and the commodities market (which is where the problem lies).

If you believe what the news tells you than yes. It'll work in common sense because it would be all gas stations across the country. What really happens is the gas companies use whatever excuse they can to raise gas prices, from hurricanes to saying that there aren't enough refineries. When they raise gas prices here, the towelheads over in arabia raise the oil prices because the higher gas prices are an opportunity for them to make more off oil. Then the gas companies use that as an excuse, and it's a neverending, artificial cycle. There's plenty of oil, there's plenty of refineries, and there's plenty of gas. There just isn't plenty of money.

Don't get me wrong, I'm no San Fransisco hippie, I'm no vegan, and I hate conspiracies. I did buy a Buick and not a Toyota, right? When one out of many major gas companies makes over $356,000,000,000.00 in PROFITS, I doubt that supply and demand has shit to do with it. They wipe their asses with our benjamins, and I won't stand for it.

Then what kind of horse will you be riding?

Your car has one knock sensor compared to the series 2 , two knock sensors. You "should" run premium.

<<<<<<<Also LMAO at the NYC comments

99Rivman wrote:

Then what kind of horse will you be riding?

This kind.

"This" is a link, btw.

Yeah, the thing on my dash says "UNLEADED FUEL ONLY." I figured as much, seeing as this is not a car from 1930 or before. I know now to use premium, and fully understand why I shouldn't use lower octanes than 91. Thanks for your help.

Lots (probably 90%) of cars sold today do not require premium fuel. However, some can benefit from higher octane, mainly those with higher compression ratios and computers that adjust for different gas. The Riviera, with a forced induction engine, is one of the few cars that actually needs premium to run properly.

Hey guys, just curious but is the Grand Prix GTP with the same motor the same way?

Since it's supercharged I'd say that's a safe bet.