What Octane Grade Fuel for 3800 SC?

Or, drive like a little old lady until you can fill with premium again. Odds are way against doing any damage if you can keep yourself from smashing the gas pedal. Premium is absolutely ideal, but careful driving will get you by until you can get to the right station.

cool thanks guys!

Abaddon wrote:

Our S/C cars need Premium to prevent spark knock, not for MPG's. The only reason you get less MPG's when you use 87 is because the ECM retards timing and dumps more fuel to alleviate KR. MPG is certainly not the reason to use premium......

I think cost savings will make more people listen to put in 93. However, you are correct with what you say.

Abaddon wrote:

yourself a bottle of Lucas Octane Booster and dump it in there. No sense in sucking out the tank.

Looked at the comments for Lucas Octane Booster on Amazon and a Harley owner also had a problem with only being able to get regular in the country.  Sounds like this could be more of a general trend than a fluke situation I came across?  


Hmm Torco Accelerator looks good too, and not much more expensive by the ounce.

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That's not good - I thought I'd read on here that the computer would detect the octane and adjust for it? So I guess I've got to drive an extra seven miles to get gas now, and siphon the 87 octane out of my tank

It's not good, but it's not the end of the world. Just put it in 3rd and go slow. The PCM does pull timing when you use 87, but it's not a "Premium Recommended" car, it's a "Premium Only" car. When the Cadi NorthStar engine overheated, the PCM would deactivate 4 cylinders to keep it cooler. This didn't mean you could keep driving it that way forever, but it would certainly get you home. Similar idea here.

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Our S/C cars need Premium to prevent spark knock, not for MPG's. The only reason you get less MPG's when you use 87 is because the ECM retards timing and dumps more fuel to alleviate KR. MPG is certainly not the reason to use premium......

Agree, no real MPG difference between the two. Using 87 is cheaper, just not better.

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You should be fine with the 87 octane if you don't get into the boost at all. Even if you do get into the boost a little, the knock sensors "should" pick up the extra knock and adjust accordingly. I wouldn't run it all the time, but one time shouldn't hurt anything on a close to stock car if you drive carefully.

These engines are so strong, you could probably do this hundreds of times without issue. Some Riv owners undoubtedly use 87 no problem. It doesn't mean it's a good idea. A car that makes it from point A to B is a different thing altogether from a well-oiled machine that achieves OEM performance specs.

If you're driving a Riviera because you like a supercharged engine, use premium.

If you're driving a Riviera and don't know if it has a supercharger, use 87.

AA wrote:

Agree, no real MPG difference between the two. Using 87 is cheaper, just not better.

I did notice a slight increase with premium. When my dad drove the car daily before I had my license, he filled it with 87. When I started driving I started filling it up with 93 and noticed a very slight (1-2 mpg) increase like I said in my above post.

I'm not saying you guys are wrong from the performance aspect (you're actually completely right), I'm just posting my real world results which may vary between owners. Sorry for any confusion.

I've been using 87 the last few times and it feels like its running rough. Kinda lagging when I hit the gas. I'm just glad I managed to pass emissions. I did have the p0107 code that comes back once in a while stored

Jack the R wrote:

Hmm Torco Accelerator looks good too, and not much more expensive by the ounce.

I'm not a fan of Torco. I would rather pour in a gallon of toluene or xylene from the paint aisle. Use the ingredients that are already in your fuel! Torco's primary ingredient is MMT which is what leaves the orange deposits behind.

MMT has an interesting history. Using it once in a while won't kill you but it's got a lot of restrictions on it's use and it will leave deposits in your cat. http://en.wikipedia.org/wiki/Methylcyclopentadienyl_manganese_tricarbonyl

Toluene and Xylene are existing components in your gas and you don't risk anything by adding them. They are usually right in the paint aisle at any hardware/home improvement store.

The manual calls for no less than 91. Why you would want to put 87 in just to save a few bucks every fillup is beyond me. the effects of detonation can be more costly in the long run.

I'm starting to feel guilty for being cheap and getting 87 in the rivi. I'm going to BP and fill her up with premium right now.

No joke dude. 87 will lead to detonation issues and pinging! Premium car, premium gas haha

Super-fuel.... only.

chitown_riv98 wrote:

I'm starting to feel guilty for being cheap and getting 87 in the rivi. I'm going to BP and fill her up with premium right now.

You wont feel cheap when you have to drop $350 to $550 to have the heads milled and refurbished.Not to mention gaskets and labor.You'll feel like a big spender then!  

( I speaking from experiencing )

Or u can just cut the wires splice resistor on knock sensor and run full timing all times beat her hard!!!

flyineagle96 wrote:

Or u can just cut the wires splice resistor on knock sensor and run full timing all times beat her hard!!!

  

flyineagle96 wrote:

Or u can just cut the wires splice resistor on knock sensor and run full timing all times beat her hard!!!

   

It felt better after I drove it around for a couple of hours on the premium. I dunno if it's my imagination. I'm due for a good tune up soon. Its starting to warm up over here finally

chitown_riv98 wrote:

It felt better after I drove it around for a couple of hours on the premium.  I dunno if it's my imagination.       I'm due for a good tune up soon. Its starting to warm up over here finally

It's not your imagination. Your Fuel Trims are so screwed up from running 87, it's going to take awhile for them to get back to normal on Premium. There's a reason it says "Unleaded Premium Only".

It's probably been using the very low performance "Bad Fuel Spark" table instead of the normal "Good Fuel Spark" table. It's what the system reverts to when it has excessive amounts of knock due to low octane fuel. It's not safe to run 87 all the time because there is a lot of detonation/knock, and the system is constantly trying to revert back to the 'gfs' table, seeing that there is too much knock and going back to the 'bfs' table. Which means you are constantly causing unnecessary detonation, which will result in replacing heads and gaskets after a few years, or worst case scenario (and this has happened somewhat often):


(if the pic doesn't work just google image search "L67 chipped piston" there are plenty of examples for you)

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I did notice a slight increase with premium. When my dad drove the car daily before I had my license, he filled it with 87. When I started driving I started filling it up with 93 and noticed a very slight (1-2 mpg) increase like I said in my above post.

Understood, but there are more variables in your test than octane rating. The driver and the route can make more difference than the car alone, let alone fuel. For example, I can drive for a week on premium and see 19 avg MPG. The next week I can drive on different roads with the same gas and see 17 MPG. The week after that I can fill up with 87 and drive to Grandma's house and see 22 MPG. I haven't tried using 87, but a 1-2 MPG difference is within the normal variance for a Riviera from week to week using the same fuel, especially with a driver change.

Yep, conditions are a huge factor. When I'm fighting a headwind I lose a good 4-5 mpg, regardless of vehicle. Last weekend on a 500 mile round trip in our '11 Acadia, only did 17.5 first leg into a wind. Ugh... About 23 mpg on return trip with tailwind.

Interesting info guys. I'm usually consistent on using the premium but gas has been killer lately. I remember when premium was $1.19/gallon. I used to drive a 91 sedan deville with a 4.9L and it was also premium only. $30 would fill er up back in 2000

Ahhh, those were the good ol' days !

Think about this. I'm 21, started driving when I was 16. Gas consistently now costs in excessess of twice as much as it did when I first started driving just 6 years ago....blehhh.

deekster_caddy wrote:

Jack the R wrote:

Hmm Torco Accelerator looks good too, and not much more expensive by the ounce.

I'm not a fan of Torco. I would rather pour in a gallon of toluene or xylene from the paint aisle. Use the ingredients that are already in your fuel! Torco's primary ingredient is MMT which is what leaves the orange deposits behind.

MMT has an interesting history. Using it once in a while won't kill you but it's got a lot of restrictions on it's use and it will leave deposits in your cat. http://en.wikipedia.org/wiki/Methylcyclopentadienyl_manganese_tricarbonyl

Toluene and Xylene are existing components in your gas and you don't risk anything by adding them. They are usually right in the paint aisle at any hardware/home improvement store.

Here's a comment on Lucas Octane Booster from Amazon.com -

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Sven Svensson (Montana, US) - See all my reviews
This review is from: Lucas 10026 Octane Boost. 15 oz. (Misc.)
This product uses MMT (Methylcyclopentadienyl Manganese Tricarbonyl) to raise the octane, which is bad news for any car with a catalytic converter. During combustion, the manganese is liberated from the compound. This manganese vapor is then deposited on your spark plugs and in the fine mesh structure of your catalytic converter. The deposits in the catalytic converter can significantly obstruct exhaust flow and impede the ability of the cat to do its job wrt NOx emissions.

It appears to use MMT too?