S/C3800 Hi Octane myth?

[1tinindian]

Without this turning into a flame war, I just have to say, that the 1997 SSEi we used to own (sold at 170,000), only ever saw 87 Octane on a very regular basis from 2001 through 2010.
At no time did we ever have a fuel related problem with this car and the engine ran awesome up to the day we sold it.

So it makes me wonder, why all the talk about needing to run high octane fuel in these engines?

Yes, I know it says so inside the fuel filler door, but my first hand experience might have been more common than you might think.
Granted, my wife put the bulk of the miles on this car, and she is not a "hot-rodder", so that in itself may explain a lot to our longevity with this car.
I have talked to other owners in my area and fellow mechanics, and we just haven't seen a problem with engine damage due to the 87 octane.

Has there been documented proof that internal engine damage was the direct result of using 87 octane in one of these motors?

Obviously, if someone is trying to run max boost ALL the time and only running 87, then I can see the problem.
But if the car is just logging highway miles, year after year, where is the problem?

Or has this just been something that has taken on a life of its own on this forum, and it's just accepted practice to recommend high octane, no matter what.

So, like a said, please don't go off on me for asking this, as I have owned this car and know what worked in it, I just don't understand all the hype, (my word).

Thanks for keeping it civil.

Leon

[crash93ssei]

That's an honest question that many people don't understand so don't feel bad for the inquiry.

Octane rating is the resistance to the fuel igniting, the higher the octane the more resistance it has to ignition. Generally you want a higher octane fuel in an engine with a higher compression ratio because the heat caused by compression can often self ignite a lower octane fuel.

Now, the L36 engine actually has a higher compression ratio then the L67, but when under boost the L67 has much higher cylinder pressure then the L36 which creates the need for the higher octane fuel so it doesn't self ignite causing knock.

Can you safely run regular in your L67? The short answer is yes, but it isn't really that simple. Staying out of boost you would never run into any issues, however even just a little bit of boost will throw you into the danger zone. When knock occurs (ping, detonation etc.) It can actually damage the engine, taking chunks out of pistons and just generally destroying the engine. We have seen this here and it is documented and known on other forums as well regardless of make, model, or country of origin.

Premium fuel only runs about $3 more per fill up so really that extra bit of insurance against damage really is worth it. There really is a reason the engine requires premium and that is because it is near impossible to stay out of the boost 100% of the time and even one time under boost using regular can damage the engine. Sure it may go years without damage, but doing so any time might be the last time.

Long story short is that premium is required for a reason, you will at some point most likely use some boost and if the tank has low octane fuel in it the engine is absolutely on borrowed time.

[Zeik75]

IMO you won't stay out of boost even on highway cruising. My cruise control can put about 4 psi from time to time. I personally won't risk putting anything less than 91 in because what if i need to punch it to avoid an accident or merge with traffic and such?

[1tinindian]

Thanks, I have always understood the differences between the L67 and L36 and what boost does to the CR in the engine under load.

I guess one of the reasons I even bring this up, is that I have read on the forum MANY times where people will go to such great lengths to NOT burn 87 in a L67, including draining the tank, if it was found to have 87 in it.
My feeling is that is overkill and really not need.

If I'm not wrong, these engines also have knock sensors that will pull the timing back in the event that the engine does enter a detonation period during acceleration, reducing or eliminating damage to the pistons.

But like I said, our car was 100% stock, and driven easily for 99% of it's operational life with us.

Leon

[crash93ssei]

IMO you won't stay out of boost even on highway cruising. My cruise control can put about 4 psi from time to time. I personally won't risk putting anything less than 91 in because what if i need to punch it to avoid an accident or merge with traffic and such?

^^^This exactly.


All it really takes is one time for an engine to knock and cause damage. That doesn't mean that it is a guarantee for damage, but that means it is a possibility. As for the knock sensors, sure they are there to sense knock and pull timing in the event that it occurs, but the problem is that for the knock sensor to detect knock, the detonation has already occurred and damage could already happen by that time.

Personally, I would never go to such lengths as to drop or drain a tank to avoid running lower octane, but I certainly would run it very easy and make sure I stay out of the boost then refill with premium.

[Trinity]

I pumped in some 87 by mistake one time and my Aero kept flashing KR at me just driving in town. I pulled into Oreilly and grabbed some boost. I was seeing up to 6 just driving in town not getting on it.

[DaMaroon]

I'd be surprised if the retarded timing didn't cost some MPG so you weren't saving as much money as you thought. You paid extra for a car with a supercharger that basically didn't get used and you tried to save money by using cheaper gas that might destroy it. I fail to see any logic in this.

http://www.google.com/search?hl=en&site ... e&tbm=isch

[haro1225]

When people ask me why I put premium in my car I tell them about this.
http://m.gmforum.com/showthread.php?t=263718&page=5

[1tinindian]

I'd be surprised if the retarded timing didn't cost some MPG so you weren't saving as much money as you thought. You paid extra for a car with a supercharger that basically didn't get used and you tried to save money by using cheaper gas that might destroy it. I fail to see any logic in this.

http://www.google.com/search?hl=en&site ... e&tbm=isch

I never once, said anything about saving money, and you have no idea what I paid for that car, so I fail to see your logic.
And in my area, it's common knowledge that the L67 never did get the MPGs that the L36 could get .
I'm only stating that we put a lot of miles on this car with no problem using 87 and thought it was unusual that people on this forum are so dead set on using premium fuel.

All any one here, so far, has said is that they "fear" possible damage, and not wanting to take the "chance" that something "might" happen using 87.
I'm just here to say, in our experience, that we had "no fear", we "took the chance", and got along just fine by not using premium.
Not saying it was the right OR wrong thing to do, just simply saying we never had a problem.

Leon

[Jfridge92]

This isn't documenting physical damage, but here is my $.02.

Dad has a Park Ave Ultra supercharged that he likes to run 87 in. I kept telling him to run premium because knock could damage the engine, and he likes to drive hard. He's very stubborn, so to test this, I hooked up my scan gauge to his car to monitor KR while we were driving.

On 87, I saw over 9* of knock registered. we filled up with 93 and repeated, and the most knock I saw was 1-3* around the shifts, which is normal. If that isn't proof enough for me personally, I don't know what is. I don't want to get a call from him saying he grenaded a piston through the block, so he runs 93 now after seeing those results. I am in GA, so it's a lot hotter around here and we have increased chances for knock in the heat, but that's just what I saw during the test. And yes he did try to floor it on 87.

[gweg_b]

Well, I would think that GM spent a lot of time and research to determine the best possible octane for their engines. The owner's manual says to use premium, so I do.

Could it run 87? It seems your '97 did just that. However, with my luck, I wouldn't want to take that chance. 87 octane + boost + Greg's luck = BOOM!!

Now, I found the previous owner of my Bonneville ran 87 all the time, and now I have constant knock that will not go away, even with a PCM tune and 93 octane. Was that a result of the previous owner? Hard to say, but my guess, since I've replaced almost everything on the top end of the engine (has to be internal at this point).

Heck, I won't even run 87 in the G8 - I've noticed more MPG and throttle response by using 89 or higher in it.

I think, for me at least, I will stick with premium (have to anyway since I'm making more boost over stock), but I am intrigued on where this conversation might go (assumming it doesn't turn into anything nasty).

[00Beast]

When people ask me why I put premium in my car I tell them about this.
http://m.some other club.com/showthread.php?t=263718&page=5

http://tinyurl.com/n7enh6e

That's the link in a usable format.

Yes the car does have knock sensors to react to knock occurring. It also has low-octane tables to keep timing lower when it senses lower octane fuel, both from the AFR and knock. However, these are both reactions to something that has already occurred, and with it, damage can also occur.

Obviously the question posed isn't "Is this safe", because you did it for 12 years. Would I recommend it to anyone else who drives a supercharged car? Not a chance. Like said before, GM put a lot more time and money into this than any of us did, and they made their recommendation for a reason. While you were lucky, mostly because your wife didn't drive the car hard in all likelihood, others haven't been so lucky, and for us to go against a factory recommendation like that, knowing that doing just that has caused issues for others would be foolish on the part of any forum member. People are free to do as they like, at their own risk. We're here to recommend folks do the best things for their cars, and for the supercharged ones, that includes running 91+ Octane Premium Fuel. YMMV.

[MattStrike]

All the 'possible' damage that could happen really depends on the quality control of the parts in the motor. No two pistons will be alike, some will be weaker. It's just the normal variation you get from mass produced parts. Short of a destructive test, I would have no way of knowing where my parts fall in that range. So I have no way of knowing how long the pistons will last under varius amounts of knock. It might only take once, it might last a few months, who knows? But that's the point, running with zero knock is safe and you can't damage a piston. Premium fuel gives less knock, usually zero knock, on the factory setup (other mechanical issues aside). So you can run 87 and eventually you will crack or chip a piston by doing so under boost. Or you can run premium and know it can't happen. Sure, the key is that you have no knock not if it's safe to run 87 octane, but are you always scanning?

Also KR is pulling timing and losing performance and MPG and the cost at the pump does not offset the cost per mile. What kind of fuel mileage were you getting on 87?

[1tinindian]

When people ask me why I put premium in my car I tell them about this.
http://m.some other club.com/showthread.php?t=263718&page=5

http://tinyurl.com/n7enh6e

That's the link in a usable format.

Yes the car does have knock sensors to react to knock occurring. It also has low-octane tables to keep timing lower when it senses lower octane fuel, both from the AFR and knock. However, these are both reactions to something that has already occurred, and with it, damage can also occur.

Obviously the question posed isn't "Is this safe", because you did it for 12 years. Would I recommend it to anyone else who drives a supercharged car? Not a chance. Like said before, GM put a lot more time and money into this than any of us did, and they made their recommendation for a reason. While you were lucky, mostly because your wife didn't drive the car hard in all likelihood, others haven't been so lucky, and for us to go against a factory recommendation like that, knowing that doing just that has caused issues for others would be foolish on the part of any forum member. People are free to do as they like, at their own risk. We're here to recommend folks do the best things for their cars, and for the supercharged ones, that includes running 91+ Octane Premium Fuel. YMMV.

That is a fair statement and much appreciated, as I see your point of view..

What this topic reminds me of, is the time back in 2001 while spending a lot of time on Third Gen. org with my 1983 T/A.
I swapped a 320HP 350 into it backed by the stock T-5 trans and I was bombarded by forum member telling me it was NEVER going to last behind that engine, and the stories of doom and destruction at every turn.

Well, that car is still running just fine, never having had a wrench put to it since the day I finished the swap.

The point of that story was to show that I have been through this forum stuff in the past, and have experienced the direct opposite of what was being recommended , not to make it sound like anyone here in wrong, far from it, but I guess I see the advice given, not just here, but on any forum, is to warn against future problems assuming that the car will be having a lot of hard driving done to it. And it is always best to prepare for failures if you plan on using anything to the extreme.

My dad used to say that anyone can break something on a car, no matter what you drive, it all boils down to the amount of abuse the part can tolerate before failing.
I have never blown an engine up and I have to attribute that to the care I have given to my cars.
I have fun with them, but I'm not constantly beating the living *shoot* out of them every time I crawl behind the wheel either.

But, as a mechanic, I have seen the *dang* stuff break for no apparent reason too!

And to answer the MPG question on our old 97 SSEi, it was getting 24-26 mpgs on the highway.

Leon

[repinS]

I'd be willing to bet you could see high 20's or even 30mpg or more on premium

Back when I had my 95 SSEi it was 26-27 on a bad day, 32 on a good one.

[crash93ssei]

Agree on the MPG. Even with 250,000 miles on the 03 SSEi we can hit 27 - 28 MPG fully loaded running 75-80 MPH. I tried running regular in it years ago and found that I not only got more power but also a couple more MPGs.

Like I said, if an L67 never sees any boost then it would last forever, however that is near impossible without removing the supercharger belt..... that's a whole different subject though that we won't get into

Bottom line is that boost pressure creates a much higher cylinder pressure creating high temperatures that will cause knock if premium is not used.

[2003 SSEi]

heres the deal. Should the L67 have Prem....well sure, its a boosted application.....

HOWEVER, there is a high octane table, and a low octane table in the PCM. If the car is seeing excessive knock then the car will use the low octane table for the timing.

also the 04+ Supercharged Grand Prix Owners manual States:

"If your vehicle has the 3800 Supercharged V6 engine (VIN Code 4), use premium unleaded gasoline with a posted octane of 91 or higher for best performance. You may also use middle grade or regular unleaded gasoline rated at 87 octane or higher, but your vehicle's acceleration may be slightly reduced. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it is bad enough, it can damage your engine"

[Jrs3800]

Pat just to have it in here...

The engine has a compression ratio of 8.5 : 1 , with the M90 its roughly 11 or 12 : 1 with full boost correct?

[MattStrike]

When did they start utilizing a second timing table? '00+? '04+?

I was also seeing 28-31mpg before I got a cam & pulley & headers. Now it's about 26-27.

[Jrs3800]

Way before that Matt... I think my 95's original PCM even had Low Octane and High Octane spark advance tables..

The PCM's did get faster and smarter over time.. Not sure if smarter is really the right word tho...lol