What Octane Grade Fuel for 3800 SC?

Abaddon wrote:

Hometown Hero wrote:

WOOHOO! Found 94 octane 20 minutes from town. This lousy place only goes as high as 91.

LOL you guys are funny. EVERY gas station here has 93 as their premium. Sunoco, BP, and Valero all have 94 here. That's all the Riv gets!

And since when does a little EcoTec G5 get premium? I used to work at a Pontiac dealer and I never remember that.....

The 2.4 and 2.0 S/C motors both ask for premium its the 2.2 that didn't.

Remember, there's a difference between asking for premium and requiring it. A lot engines recommend premium so the PCM can advance timing for more power, but they will run fin on regular. Our supercharged engines say "preimum only". Regular octane is not an option.

AA wrote:

Remember, there's a difference between asking for premium and requiring it. A lot engines recommend premium so the PCM can advance timing for more power, but they will run fin on regular. Our supercharged engines say "preimum only". Regular octane is not an option.

Yes. But, most of the time, using or buying Premium fuel when the car doesn't call for it is a waste of money, and has no positive or negative effects on driveability. I wish I had a scanner. I have a Tech News Letter (from GM) in my top drawer that I keep just for when the "I run Premium in my car" arguement arises. It's good info for unknowing customers. I'll see if I can take a good pic of it....

True, a car that neither recommends nor requires premium will not benefit from the higher octane. I was pointing out there are lots of cars that can use both premium and regular with different results, because their timing adjustable. These cars say "premium recommended".

However, the fuel companies have been playing a trick in the past few years. They have begun to add engine cleaning detergents to only the premium gas, and not to the regular and plus blends. They give the premium a special name(Shell V-Power for example), and claim it gives power to any engine. And technically it might, if the engine is dirty, because the engine cleaning benefits could restore power, even if the engine can't use the octane. It's brilliant marketing, imo. A bit deceptive, but technically not wrong. They do in fact explain how their premium gas will add power to your car.

Yeah, that article talks about the detergents and stuff too. I'll figure out a way to get it on here.....it's good info. I may just have to type it all in....

Just as a point of interest... my '05 Yukon recommends regular, and gets 4-5 degrees of KR all over the place. Runs fine on 89 with occasionally 1-2 degrees of KR but mostly 0. I've seen this on many many cars that "recommend" regular. So just because the book says it, doesn't mean it's the right fuel to run either!!!

That is interesting. It would also indicate a little knock isn't that bad. I've always found 2º to be within reason. Imagine how many engines are rolling around, knocking away, because people don't use the recommended fuel, or - as you've pointed out - it can even happen if they use the 'correct' octane!

deekster_caddy wrote:

Just as a point of interest... my '05 Yukon recommends regular, and gets 4-5 degrees of KR all over the place. Runs fine on 89 with occasionally 1-2 degrees of KR but mostly 0. I've seen this on many many cars that "recommend" regular. So just because the book says it, doesn't mean it's the right fuel to run either!!!

So what you're saying is, General Motors produced an engine that A.) has not been thoroughly tested on all fuels, and B.) They would release an engine like that and not recall it....

Cmon. What is it with you ppl and KR. 5* of KR ain't sh@t. It isn't going to hurt your engine. The PCM and engine management is simply doing it's job....and putting in premium fuel because that number goes down a hair is a waste of money. Don't get me wrong, it's your money, so have at it. My point is this, most engines nowadays run at about 13* advanced at idle, and get as high as 40* advanced at WOT. If you have 5* of KR, big deal. That just means that at WOT the management system has to cut that 40* back to 35*. It's not going to hurt a thing. As many of you know, the weather has a drastic effect on KR. "They" are designing these engines to be sold, and run efficiently all over the country. "They've" severely tested these engines, with all fuels, and the determination is that unless otherwise specified, regular fuel is it.
Now, if your KR gets out of hand, and the management system can't keep up, or detects a potential problem, a KS code will be set, not to mention it would be an audible knock.

I forgot to bring that article home dammit.....

Regarding some previous posts on the cleaning agents used in fuels...When I lived in San Antonio there were Chevron stations on almost every corner and they added Techron to their fuel. I thought it was all a bunch of hype but found out otherwise from the chief engineer at the Research and Development company I worked for in Texas and it just so happened that they were contracted by Chevron some years prior to do a lot of the continuous testing on Techron.
The conclusion that the independent lab came to was that the product did indeed work and work well. So I filled up at Chevron from then on. Chevron added it to every grade of fuel, not just the premium grades.
Since moving back to New England I haven't come across any Chevron stations otherwise I'd be using it to keep the Injectors and combustion chambers clean for free.
Here you have to buy the product as an additive if you want it.

Abaddon wrote:

Now, if your KR gets out of hand, and the management system can't keep up, or detects a potential problem, a KS code will be set, not to mention it would be an audible knock.

That's a very important point: The electronics hearing a knock is a lot different than hearing a knock with your own ears... The knock-sensors hear a lot better than we do, and the computer can adjust the spark a lot faster and more accurately than we can.

Whenever I've set up a conventional ignition, besides playing with vacuum & centrifugal advance curves, I always ended up setting the base timing where I'd occasionally get pinging under heavy load - that way I knew I was getting all the potential from the fuel, but I never lost a piston. I'd never worry about detonation on a computerized engine if I can't hear it myself.

Abaddon wrote:

deekster_caddy wrote:

Just as a point of interest... my '05 Yukon recommends regular, and gets 4-5 degrees of KR all over the place. Runs fine on 89 with occasionally 1-2 degrees of KR but mostly 0. I've seen this on many many cars that "recommend" regular. So just because the book says it, doesn't mean it's the right fuel to run either!!!

So what you're saying is, General Motors produced an engine that A.) has not been thoroughly tested on all fuels, and B.) They would release an engine like that and not recall it....

Cmon. What is it with you ppl and KR. 5* of KR ain't sh@t. It isn't going to hurt your engine. The PCM and engine management is simply doing it's job....and putting in premium fuel because that number goes down a hair is a waste of money. Don't get me wrong, it's your money, so have at it. My point is this, most engines nowadays run at about 13* advanced at idle, and get as high as 40* advanced at WOT. If you have 5* of KR, big deal. That just means that at WOT the management system has to cut that 40* back to 35*. It's not going to hurt a thing. As many of you know, the weather has a drastic effect on KR. "They" are designing these engines to be sold, and run efficiently all over the country. "They've" severely tested these engines, with all fuels, and the determination is that unless otherwise specified, regular fuel is it.
Now, if your KR gets out of hand, and the management system can't keep up, or detects a potential problem, a KS code will be set, not to mention it would be an audible knock.

I forgot to bring that article home dammit.....

The electronics absolutely hear knock long before the human ear. But running against the knock sensor will still cost you a head gasket after years of continued KR. The sensors hear detonation, reduce timing, then return timing to see if the detonation is still there. In my opinion this is still detonation. I've replaced and heard about more head gaskets blown out that people who run higher octanes don't have to replace. Why is that, if 5* is no big deal? BTW 5* is just from gentle driving - stepping on the gas results in 7* or 9* at times. You are telling me that over time there isn't some damage being done? I don't buy it. I understand the knock retard system is just doing it's job, and doing it properly, but I still think it's wrong to advise people that 87 octane is safe to use long term when you have a ton of KR as a result. Or in the case of the Series II L67 they advise 91 octane minimum and I know of many GTPs and Rivs that have KR with 91 that gets less with 93.

From the performance standpoint, if you are racing (or towing), the knock retard programming is to take away twice as much timing as what is thought to be required to reduce that noise level of KR. Then reintroduce the timing slowly. The performance effects are real. Measured HP differences based on timing changes alone. I know it's only a few HP per degree (I forget the exact number) but when you are racing or hauling, it actually matters.

You're right. But, in the Riv's case, GM states that 91 octane is the minimum grade for safe engine operation. Even on the newer cars that say regular gas, you are going to get KR at some point. Now, regarding your Yukon. It's a 2005, so I'll assume you have somewhere between 80k -100k on it? It could have carbon deposits in the heads, the plug gap could be worn, the intake/TB could be dirty, the injectors may be flowing less than normal, Air filter may be flowing less, etc etc. There is a million things that could be causing your KR (the 10*). I'm just saying that GM wouldn't warranty engines 100k miles on 87 octane if it was going to hurt it. Yes, in some cases, KR is bad, but in all the forums on the internet, a fear has been put into everyone, which is ridiculous. There is a very BIG line between normal KR and bad KR. If you feel up to it one day, take your scanner to a dealership and test drive a brand new car while monitoring KR. You'd be amazed at what you find.......

Abaddon wrote:

You're right. But, in the Riv's case, GM states that 91 octane is the minimum grade for safe engine operation. Even on the newer cars that say regular gas, you are going to get KR at some point. Now, regarding your Yukon. It's a 2005, so I'll assume you have somewhere between 80k -100k on it? It could have carbon deposits in the heads, the plug gap could be worn, the intake/TB could be dirty, the injectors may be flowing less than normal, Air filter may be flowing less, etc etc. There is a million things that could be causing your KR (the 10*). I'm just saying that GM wouldn't warranty engines 100k miles on 87 octane if it was going to hurt it. Yes, in some cases, KR is bad, but in all the forums on the internet, a fear has been put into everyone, which is ridiculous. There is a very BIG line between normal KR and bad KR. If you feel up to it one day, take your scanner to a dealership and test drive a brand new car while monitoring KR. You'd be amazed at what you find.......

I agree with all this. For your average sedan, 5* is no big deal. But for anyone interested in performance and longevity 5* is too much.

Yes, my Yuk has 110K on it. I did a full tuneup at 100K (when I bought it), plugs, wires, filters etc. It has an occasional 'spit' at idle, much the way my Riv used to until I changed it's injectors with some cleaned/flowed ones. It's my DD though, so I can't take the downtime to send the injectors out for cleaning... I haven't tried too hard to locate a set yet but at some point I'm going to make that investment. Also planning for a top engine cleaner treatment soon to make sure the intake is clean and break up some of that carbon. For now, though, I hardly ever see KR when I use 89 octane, so I'll just keep at that until I get the rest taken care of, then see how it goes. Even though it's not mine anymore, my Riv is still in the family and has 150K on it now, still running fantastic on 93.

deekster_caddy wrote:

I agree with all this. For your average sedan, 5* is no big deal. But for anyone interested in performance and longevity 5* is too much.

Wasn't trying to argue. I'm just trying to clarify GM's logic. Ultimately, 0* KR is the goal of all cars. But there is a "safe" window that is there. All this talk about timing advance, but we all forget that too much retard causes knock also. As long as the car is operating within that "window", all is good.

And I agree, 91 octane in the Riv sux (modified Riv anyway). 93 or bust!

Also keep in mind that the PCM is adaptive. Is you drive your car "normally" every day, and then at one point introduce something like a trailer, your KR is going to increase. If you drove with that trailer every day, your KR levels would eventually go down, as the PCM will adapt, and not advance the timing as much.....

So the moral of the story is don't tow large trailers with your Riv, you'll get more KR and/or have to register as a locomotive.

Abaddon wrote:

Also keep in mind that the PCM is adaptive. As you drive your car  "normally" every day, and then at one point introduce something like a trailer, your KR is going to increase. If you drove with that trailer every day, your KR levels would eventually go down, as the PCM will adapt, and not advance the timing as much.....

And of course, a truck has a much greater possibility for changes in load weight/trailer use...

I knew that the fuel trim is adaptive, but the timing is too (besides a worst-case limp-home  mode)?

Eldo wrote:

I knew that the fuel trim is adaptive, but the timing is too (besides a worst-case limp-home mode)?

Technically no, the timing isn't adaptive....I didn't mean it that way. What I meant was the Fuel Trims (LT for the most part). If you've ever seen the Fuel tables, it's nothing but a giant graph, with cells labeled by number. You can see which cell the FT's are using on the scan tool, which is usually listed with the FT numbers. This giant "graph" is always changing, based on temperature, barometric pressure, engine load, throttle position, etc. The PCM uses these cells to "remember" how much fuel to add/subtract under certain conditions. As you know, if you drive the car in the same state, under the same conditions, day after day, the PCM learns your driving habits. Now, I refer again, to the trailer, or possibly that 400lb aunt you have to drive to IHOP Now you've introduced something the vehicle isn't familiar with....now you'll have some spotty KR, until the PCM can "adapt" the fuel tables and re-arrange the cells accordingly.

This is why every time I do a driveability-related repair, or an engine upgrade, I reset the FT's, so the PCM will learn the "new" stuff faster, instead of having to back pedal, then relearn. Ford even tells you to do this every time a repair is done. Ford has a little bit different logic than GM, and they're programming is a lil different....along with the PCM, they use something called KAM (Keep Alive Memory) to control FT's. This must be reset after every driveability repair, otherwise the SES light may come on even after the new part has been installed, or the problem has been fixed; the KAM tables have the "bad" part learned. Installing a new part will fix the problem, but the KAM takes too long to adapt, which is the reason for the reset, it learns faster.

If I babbled , I apologize....just woke up, on the couch

Thanks Scott, that's what I thought.

It's funny what you mentioned about KAM... Every time I've looked at my LT fuel trim, it seemed to start at zero and change more often than I'd expect from "long term", as though it was starting over with each ignition cycle.

can we put 87 in to daily drive, I commute 40 miles a day

bmcd9179 wrote:

can we put 87 in to daily drive, I commute 40 miles a day

No.Not recommended at All! I'm pretty sure I blew a head gasket thinking I could save a few bucks despite the members warning.Live & Learn.

I always use super.

Just use premium. Do the math. Say $3.30 a gallon for 87 octane times 17 gallons is $56.10. Now, $3.70 for 93 octane times 17 is $62.90. For $6.70 you get better mileage and better performance.

Figure 16 mpg for 87 octane on day to day driving (city and highway) is 272 miles per tank (I usually fill up with 17 gallons). 18 mpg for 93 octane is 306 miles per tank. It pays for itself. Even if you only gained 1 mpg, that still puts you at 289 miles per tank. Figure 17-34 more miles per tank with 93.

*figures based on what I average, mileage may vary for different drivers.

98riv wrote:

Were you at Casey's?

No, it's a family owned station out in the countryside.

robotennis61 wrote:

bmcd9179 wrote:

can we put 87 in to daily drive, I commute 40 miles a day

No.Not recommended at All!   I'm pretty sure I blew a head gasket thinking I could save a few bucks despite the members warning.Live & Learn.

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  

Jack the R wrote:

98riv wrote:

Were you at Casey's?

No, it's a family owned station out in the countryside.

robotennis61 wrote:

bmcd9179 wrote:

can we put 87 in to daily drive, I commute 40 miles a day

No.Not recommended at All!   I'm pretty sure I blew a head gasket thinking I could save a few bucks despite the members warning.Live & Learn.

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  

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.

matt270avian wrote:

Just use premium. Do the math. Say $3.30 a gallon for 87 octane times 17 gallons is $56.10. Now, $3.70 for 93 octane times 17 is $62.90. For $6.70 you get better mileage and better performance.

Figure 16 mpg for 87 octane on day to day driving (city and highway) is 272 miles per tank (I usually fill up with 17 gallons). 18 mpg for 93 octane is 306 miles per tank. It pays for itself. Even if you only gained 1 mpg, that still puts you at 289 miles per tank. Figure 17-34 more miles per tank with 93.

*figures based on what I average, mileage may vary for different drivers.

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......


Jack, just go grab yourself a bottle of Lucas Octane Booster and dump it in there. No sense in sucking out the tank.