What Octane Grade Fuel for 3800 SC?

Hometown Hero wrote:

See heres my thing, I am swapping to a series III and I really could care less about the health of my Series I. So why should I spend an extra $ at the pumps when I can put it towards the series III?

Series III SC? As in L32?

Hometown Hero wrote:

See heres my thing, I am swapping to a series III and I really could care less about the health of my Series I. So why should I spend an extra $ at the pumps when I can put it towards the series III?

Because let's say you come up to a snag in the plans to drop the motor in, and you've been abusing your SI to the point that it doesn't last until you can actually do the swap and have it running. Oops.

There's a major difference between Premium fuel being recommended and required. For the supercharged Rivieras, it's required. And trust me, an extra $2-3 per bone-dry-to-beyond-full tank is nothing compared to buying a new motor(which you plan on doing) or not having a car to drive until you get the new motor(your case).


Also, octane boosters usually don't do much, so don't invest full confidence in them.

Yes L32, I can get a fresh drop in crate through my Brother at the GM dealer for cost +5% a few modifications and some TLC and everything should be ballin. I was gunna go to an L67 combo with a beefed up 4t65E but they are getting more difficult to get through the dealer and are an inferrior engine compared to the L32.

I'd say it comes down to where you want to spend your money. Many people will ask me why I bother owning two cars that feed on 94 octane all the time, and I usually respond that you have to "choose your expenses." In my case, Ive chosen the expense of building the series one engine, paying for my wife's series 2 build, and proper gassing for both.

In your case, if you are set on investing in swapping to a series 3, then it might make sense to run on the 87.

As much as many of us here would cringe at the idea, it would be a ballpark guess to say that 80% of the 8th gen rivs ever driven would probably have passed most their lives on 87.

In your situation it would come down to the mileage of your engine, your driving tendencies, and how long you estimate it will be before you can afford the time/money for the series 3 swap.
If you're looking at 2 years or so for the swap, the engine is "elderly", and you drive it like its stolen... well, it would make sense to go with premium.

Its a 95 Riviera not a Bentley relax guys, its only gasoline.

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Never seen anything like this in my life..

and to the OP E85 works well. If you are able to tune for it AND get bigger injectors

Hometown Hero wrote:

I normally just run 87 with a Lucas booster to bring me up to around 90 same basic priciple. 1-2 octane points are not going to decide whether or not your engine blows, and if so you probably had a problem long before that happens anywayz. Just figure out which is cheaper premium or running reg with a booster, or even try both and see which you prefer.

So what are you paying for a bottle of Lucas octane booster? Adding 1 bottle per tank of gas has to cost more than paying 25 cents more per gallon?

I've read some test results that showed 1 bottle of Lucas added to 10 gal of 93 raised it to 96.6. So 1 bottle per an 18 gal fill would add around 2 full points. But what's a bottle cost? I've never used an octane booster myself.

I see around $9 on Amazon, or by the case it's around 5.50. By the case, if you add 1 bottle per tankful of gas, it would at least be close in price compared to buying a higher octane fuel.

I'm a partsman I get a bottle for like 2 bucks cost. I think its substantially cheaper on that size of tank don't you?

Well sure, if you only pay $2. The rest of us wouldn't be so lucky.

If that's true, I'll have to see what I pay for that stuff. I wouldn't mind turning my 93 into 95 in the summer time. That's a hell of a discount though. $2 from about $10. Where do you work man?

Hometown Hero wrote:

Its a 95 Riviera not a Bentley relax guys, its only gasoline.

Bentley owners generally don't know all that much about cars except that they like expensive stuff. Here on the Riviera Performance forum, we have a different attitude.

To me, it all depends how long you want your motor to last. If you never go WOT and don't mind the loss of performance and early head gasket failure and potential for chipped pistons or worse, then by all means go cheap on your fuel. Since you are planning to replace your motor anyway, I concede your point. If you want your motor to perform and last, run the required octane.

If you get it on promotions that happen usually twice a year you can get it through drop ship in large quantities for dirt cheap. So I pay that basically all year cuz we get so much in at once. Same goes with alot of other products we stock from Lucas oils. I work at a B 2 B in town here. Good perks with cheap parts and that helps a great deal considering I am running 3 vehicles and an additional 2 project vehicles.

Not argueing with you guys here just so you know... I agree 100% that higher octane is better. However it depends on the scenario is all I am saying, and my position atm with 2 other projects on the go cheaper is better, I can reach my goals faster @ 31 years old I gotta get er dun fast or I'll be 60 by the time I can drive them all.

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I am swapping to a series III and I really could care less about the health of my Series I.

Just to clarify what I've been reading, Hometown Hero is running 87 with the intention of shortening the life of his engine, so that he can upgrade to a better one.

This is understandable, I just wanted to make sure everyone reading this thread caught that part. 87 octane in supercharged engine = shortened engine life and lesser power output. Running 87, your engine will not produce published HP numbers, and your car will not perform to factory specs.

You can never be too rich, too thin, or have too many octane...

Question for all of you. Id take the time to read this whole thread but, I have a busy weekend and I can get a better opinion faster just from asking. I just recently put in Regular Unleaded 87 this last tank of gas. Normally, I put in Unleaded Plus 89. My car tends to run better with the 89 I think mostly cause it runs hotter, less water and such. Is 87 going to be better for me? I have not yet figured out the gas mileage for this recent tank of gas, and im hoping my plugs wont have the white residue on them from running hot like they always are when I run the 89.

Contrary to how it may seem, 89 actually doesnt burn "hotter" than 87. It is designed to not combust as easily therefor reducing detonation.
The white deposits on the plugs is likely coolant burning off. you can try a colder plug to make certain they are not too hot, but chances are the deposits are coolant.
What motor is in the riv you have? is it the N/A 3800? if so then you are probably safe running the 87.

yeah it comes with the N/A 3800. Ever since I got the car I was told by the dealer that the original owner never ran anything but 89 in it. So I continued that. I have put in 87 once or twice before and it caused my valves to tap. Especially under any load. So I stuck with 89. I doubt it is antifreeze. If it was I would be losing antifreeze slowly. And the level hasnt changed since I got the car. The engine does run hot though. Recently, I have added some Water Wetter to the antifreeze to lower the engine temp. It went from running 197 min and 205 max after being on for a while to 186 min and 195 max. So it did help lower the temp a bit, but the plugs still have white residue. I have thought about getting colder plugs, but I am not sure what they would be exactly. Everytime I ask the guys at Autozone they just show me what they have. Not much help there. Now I do run my engine hard. High RPMs a lot. Just from running back and forth to philly on the turnpike. Im sure that has a lot to do with it.

That's not valve-tap, that's "pinging"/spark-knock/detonation from the lower octane fuel, and the hot spark plugs...

200 degrees is the normal temp for these engines.

White plugs with no fluid leaks means too hot a range. Generally speaking, to lower the heat range of your plugs, just drop the last digit of the part number by 1, like from a 605 to a 604... But any competent part store ( or spark plug website ) can guide you as to heat ranges.

Personally I would run 89 in your car, especially the way you drive it

sooo..ive run 93 in my car for about 2.5 years straight...noticed for a while i got AWFULLLL gas mileage...switched to 87 when my dad filled my tank up with it...got about 4mpg's better. about 12 mpgs better on the highway...again..with 87....i tried putting in 93 the other day...in 5 gallons...i got 63 miles. yes...93...im talkin crusing at 55 mph for 30miles no accel. with 87 im getting aruond 25 mpg at these conditions. WEIIIRDDDDD...also..no knock. the only thing i noticed difference is the power with 93 is much better...

xxsupergman25xx wrote:

sooo..ive run 93 in my car for about 2.5 years straight...noticed for a while i got AWFULLLL gas mileage...switched to 87 when my dad filled my tank up with it...got about 4mpg's better. about 12 mpgs better on the highway...again..with 87....i tried putting in 93 the other day...in 5 gallons...i got 63 miles. yes...93...im talkin crusing at 55 mph for 30miles no accel. with 87 im getting aruond 25 mpg at these conditions. WEIIIRDDDDD...also..no knock. the only thing i noticed difference is the power with 93 is much better...

You would need to make your tests long term over similar driving styles to see if there is any real difference.

How DO you know there is no knock? You don't hear it? That's because the knock sensor is doing it's job, reducing timing... You should never have audible knock if you have a knock sensor, and to my knowledge there is no real time scanner for the OBD-1/1.5 systems, so I don't think you can monitor your KR... so how are you measuring knock?

xxsupergman25xx wrote:

sooo..ive run 93 in my car for about 2.5 years straight...noticed for a while i got AWFULLLL gas mileage...switched to 87 when my dad filled my tank up with it...got about 4mpg's better. about 12 mpgs better on the highway...again..with 87....i tried putting in 93 the other day...in 5 gallons...i got 63 miles. yes...93...im talkin crusing at 55 mph for 30miles no accel. with 87 im getting aruond 25 mpg at these conditions. WEIIIRDDDDD...also..no knock. the only thing i noticed difference is the power with 93 is much better...

That just makes no sense if the system is working... The knock sensor allows more spark advance with more octane, which is why you have more power. By the same token, when you're cruising, that extra timing should give you better mileage.
I get 27 MPG every time I do a highway trip on this lame-ass 91 "premium"...

My guess is your driving style changes when you put in the 87. You're probably a lot gentler on the throttle, being mindful that it could knock, and it's not going to give you the power like 93 does. You may not even realize it. Then, putting 93 in, you can enjoy the power again - that takes extra gas.

Although Mark is technically right about the advanced timing giving the best fuel economy, I've taken trips using 89 over flat ground; it gave me the exact same HWY economy as 93 (I did this with a scanner to monitor knock). As long as you don't hit a big hill or use heavy throttle, the timing doesn't change, no knock, and economy is good. You must monitor and drive carefully to do this. But as soon as you let you let down your guard, things can get ugly fast. Imo, you can get the same economy with lower octane, but never better.

deekster_caddy wrote:

Personally I would run 89 in your car, especially the way you drive it

Well I think I will go back after a while, but I'm going to run 87 for a bit just to test out the gas mileage. If it doesnt get much better, then Ill think about switching back. These days, I would rather have the economy and save the hot roddin for when I drive my girlfriend's Galant, but I love to show off in my Rivi at times too. And to do that more effectively, i need a bit more power and in turn higher octane. I will check out a Lower heat range plug. Kinda sucks though cause the current plugs i've only had a few months.