Recalls & Engine Knock Info

[snoman]

You need to understand that the higher the compression ratio of a engine (for higher power and better MPG from increased thermal efficeincy) the octane requirement increase. For your dealer to "fix" this he needs to detune your engines octane requirement by programing in a more retarded spark curve which leads to less HP and reduced MPG. There is no free lunch here!!! If your engine knocks from low octane you can complain about it and try to get the dealer to detune engine or buy better fuel. A lot of factors effect octane requirements including air tempature, altitude, humidity and vehical load and gear as well which can change requirements a point or too as well by the amount of combustion pressure require to motivate vehical. If you want to use 87 reliably, get a old 70's or early 80's beater with low compression. If you want a new modern truck for 30,000 or 40,000 bucks, pay the extra 5% or less and get better fuel for it. The irony is that it may actually be cheaper to drive on better fuel due to increased performance and MPG as well.

[toneman]

snoman--I understand completely where you're coming from; my point is that if your truck has engine knock issues when running on 87 octane even though the owners manual clearly states that it can and/or is supposed to run fine on 87, then one of the following two things must be true--either the manufacturer is lying, or there's something wrong with your engine. Pumping higher octane gas to fix/quiet engine knock does not eliminate either of these two possible truths...I mean, wouldn't you ask the dealer why an engine should knock when running on 87 octane if the friggin' manual explicitly states that it should be able to run fine on 87? Or do you just assume that everything that is stated in the owners manual is incorrect?:kidding:

[Sseug]

I used to work at a chevrolet/oldsmobile dealership and chevrolet did this about two years ago and we took the defective bags and blew them up in the back lot, they went about twenty feet in the air. It was pretty cool.

[snoman]

Originally posted by toneman
snoman--I understand completely where you're coming from; my point is that if your truck has engine knock issues when running on 87 octane even though the owners manual clearly states that it can and/or is supposed to run fine on 87, then one of the following two things must be true--either the manufacturer is lying, or there's something wrong with your engine. Pumping higher octane gas to fix/quiet engine knock does not eliminate either of these two possible truths...I mean, wouldn't you ask the dealer why an engine should knock when running on 87 octane if the friggin' manual explicitly states that it should be able to run fine on 87? Or do you just assume that everything that is stated in the owners manual is incorrect?:kidding:

And just how badly do you think it would kill sales if they stated you must use 89 or better huh??? Unless your really have your head in the sand, when you have a modern high compression engine, you need more octane for it to run correctly and you are remind of that fact every time you fill up and see that there is atleast 2 other grades. If there was not need for it, it would not be sold. Poeple as a hole are too cheap to spend a extra 5 or 10 cents for better gas even though they will shell out over 30 grand for a truck and then complain it runs poorly on the cheapest gas there is.

[Stroker 1500]

Snoman- what do you consider a modern high compression engine?? To me 9.3-9.5ish compression isn't all that high. Most the engines that require high octane are around 10:1, like most of the sport cars

[snoman]

Originally posted by rcfast
Snoman- what do you consider a modern high compression engine?? To me 9.3-9.5ish compression isn't all that high. Most the engines that require high octane are around 10:1, like most of the sport cars

I consider the engine with TBI or Vortec "modern" and from 73 till 86 carb'ed ones not as they had 8.5 to one or less as a rule. 9.3, 9.5 is plus territory for sure. 87 octane was born for a few reasons. One was when they took lead out it lower octane of fuel and auto manufactures chopped ratios for it and the lower compression also helped reduce NOx emissions (Nitrous Oxides) by lowering peak combustion temps. As cats improved anlong with engine cotrols they started to raise compression back up to improve thermal efficency of engines (power and MPG) and increase octane requirements of engines. 87 is a vestage of old times and should not really be used in modern engines, especailly in hot weather

[toneman]

snoman--instead of knocking me (no pun intended), why don't you argue your case against all those manufacturers who state in the owners manual (gee, I think I emphasized this point a gazillion times) that 87 octane gas can be safely used. I mean, with the manner in which you are replying to my posts/comments...it almost seems like you're insinuating that I'm the one who's misinforming the masses about why 87 octane shouldn't be used in modern engines. Well guess what? I never said that 87 shouldn't/can't be used in modern engines; what I said (or meant to say) was that, if the owners manual stated that 87 can be safely used, then the manufacturer must either be right or doesn't have a clue as to what octane is really required.

The owners manual for my '03 Yukon XL says I can use 87 octane; your posts seem to imply that this is not correct, yet it seems that you find it easier to criticize me for not using higher octane in my truck rather than lay blame for this "misinformation" where it should really go to--namely, the manufacturer.

You keep pushing the "higher octane is better" mantra--if I didn't know any better, I'd almost say that you're doing so 'cuz you must have some vested interest in the oil companies.:kidding:

Oh yeah--I've been running 87 in my YXL--with its "modern" engine--for almost 2 years...and I'm not getting any knocking/pinging at all, even during the hot summer months here in Sacramento where the daytime temps regularly reach 90 deg. F or higher.

An extra 5 to 10 cents? I dunno about where you live, but here in CA, it's at least a 10 cent difference between 87 and 89, and another 10 cents between 89 and 91...so between 87 and 91 you're looking at a 20 cent--if not more--difference. 5 cents? I've yet to see any gas station here in CA with a 5 cent difference between octane grades...maybe where you live in OH, but not over here...

[snoman]

You kinda miss the point here. The only reason it says 87 "can" be used it marketing. If owners manual said 89 or better must be used, it would hurt sales. Hey, I did not make the rules but as you raise compression, you must raise octane or performance will suffer plain and simple. The auto makers use knock sensor to retard timing to try to minimize the knock with low quality fuel but it hurts performance and MPG too. Also, you have to remember that I come form a time when regualr was called 94 (about 90 with todays ratings) and premium was 100 or better and you bought cars fully expecting to use premium though some tight wads would try to burn regular in than and let the knock away. I do not have a proble with using better gas so regardless of what manual says I will use the fuel it really needs baised on how it performs. Most of todays drivers are not to bright anyway as they will blow a tire and sue tire maker when they are too stupid to check tire pressures themselves and low pressure is the number one cause of failures anyway.

[Steveo_supremo]

I consider the engine with TBI or Vortec "modern" and from 73 till 86 carb'ed ones not as they had 8.5 to one or less as a rule. 9.3, 9.5 is plus territory for sure.

A TBI 350 is 8.3:1.

[snoman]

Originally posted by Steveo_supremo
A TBI 350 is 8.3:1.

Check again, my factory service manual on a 89 burb states 9.3 for vehicals under 8600 GVW and 8.6 for ones over that.

[toneman]

snoman--please don't get me wrong; I hear ya when it comes to using higher octane fuel to take advantage of modified tuning tables or reduction/elimination of knocking/pinging, or if it required for ideal/optimum operation. However...there have been studies (I can't recall the exact source, but trust me on this) where the use of 89 or 91 octane gas in a perfectly-running unmodified car tuned to run on 87 octane--even those with "modern" engines with "high" compression ratios (there seems to be a difference of opinion here as to what value a compression ratio is considered "high") did not show any significant noticeable improvement in fuel economy or performance. Heck, I'm willing to bet that if I put 91 octane in my all-stock YXL, I won't see any noticeable improvement in fuel economy nor will I gain more than a tenth of a second--if at all--in the quarter-mile. And since I'm not getting any knocking or pinging to begin with (other than the CSK that happens every once in a while during cold startups), using higher octane in my truck won't change a thing in the knock/ping departgment.

So...why should I be using 89 or 91 octane instead of 87 in my stock YXL if the above is true?

[toneman]

Originally posted by snoman
...The auto makers use knock sensor to retard timing to try to minimize the knock with low quality fuel but it hurts performance and MPG too...

"Low quality" fuel and 87 octane fuel aren't necessarily one and the same; you may not have explicitly stated this but the above comment, taken in context with your other posts, clearly implies that the two are indeed the same. As such, it can almost be considered a non sequitur...87 octane fuel may very well hurt performance and/or fuel economy, but it should not be generalized as "low quality".

Plus...if you believe that those of us who pump 87 octane gas in our $30K-$40K trucks instead of 89+ octane are doing so because we are being cheap--remember this quote?

Poeple as a hole are too cheap to spend a extra 5 or 10 cents for better gas even though they will shell out over 30 grand for a truck and then complain it runs poorly on the cheapest gas there is.

--you are grossly mistaken, and I'm sure others would take offense to such a statement. Again, my truck runs fine on 87 octane; am I being cheap for doing so, in light of this observation?

As far as "modern" engines go...how "modern" can the Vortec/TBI be? If you consider the fact that GM is still pushing their two-valves per cylinder pushrod engine on the majority of their vehicle lineup--like practically all FSCs--then I guess the foreign manufacturers are light-years ahead of GM, what with their 4 (and even 5) valve, single or dual overhead cam engines. Heck, IIRC even Ford now offers multi-valve (more than two) overhead cam engines on quite a few of their vehicles...like the current F-series truck and Mustang GT, to name a couple.

[snoman]

Originally posted by toneman
"Low quality" fuel and 87 octane fuel aren't necessarily one and the same; you may not have explicitly stated this but the above comment, taken in context with your other posts, clearly implies that the two are indeed the same. As such, it can almost be considered a non sequitur...87 octane fuel may very well hurt performance and/or fuel economy, but it should not be generalized as "low quality".

Plus...if you believe that those of us who pump 87 octane gas in our $30K-$40K trucks instead of 89+ octane are doing so because we are being cheap--remember this quote?

--you are grossly mistaken, and I'm sure others would take offense to such a statement. Again, my truck runs fine on 87 octane; am I being cheap for doing so, in light of this observation?

As far as "modern" engines go...how "modern" can the Vortec/TBI be? If you consider the fact that GM is still pushing their two-valves per cylinder pushrod engine on the majority of their vehicle lineup--like practically all FSCs--then I guess the foreign manufacturers are light-years ahead of GM, what with their 4 (and even 5) valve, single or dual overhead cam engines. Heck, IIRC even Ford now offers multi-valve (more than two) overhead cam engines on quite a few of their vehicles...like the current F-series truck and Mustang GT, to name a couple.

And Ill bet you have never run it on plus or better for a extended period of time to really find out either. You can blindfold me with 3 of my cars and fill then up and I will tell quickly if it has 87 in it. Especailly my burb. It never liked 87 from day one and that was 170k ago.

I stand by what I said that people tend to buy the cheapest gas they can find!

[toneman]

Originally posted by snoman
I stand by what I said that people tend to buy the cheapest gas they can find!

In that case, one can fairly conclude that nothing but expensive gas goes into your vehicles...:kidding:

You say that the reason the owners manual for our FSCs says to use 87 is due to marketing--is that pure speculation on your part, or do you have official documentation from GM to back it up?

[firestorm]

To me, this whole octane debate is simple... burn the lowest octane fuel you can that does not result in knocking. There is absolutely no other reason to spend money on higher octane... no increase in performance (unless knocking is robbing power), no added cleaning abilities... nothing.

However, I've never known of a vehicle, which was rated to run on 87, that wouldn't without problems; that is, unless there was something wrong. There could be manufacturing flaws that introduce hot spots that could make it nearly impossible to fix without major work, otherwise, if the problems are fixed, it should run on 87.

Again, if it does run fine, there's no point in wasting your money. I certainly don't.

[snoman]

Originally posted by firestorm
To me, this whole octane debate is simple... burn the lowest octane fuel you can that does not result in knocking. There is absolutely no other reason to spend money on higher octane... no increase in performance (unless knocking is robbing power), no added cleaning abilities... nothing.

However, I've never known of a vehicle, which was rated to run on 87, that wouldn't without problems; that is, unless there was something wrong. There could be manufacturing flaws that introduce hot spots that could make it nearly impossible to fix without major work, otherwise, if the problems are fixed, it should run on 87.

Again, if it does run fine, there's no point in wasting your money. I certainly don't.

And this was pretty cut and dried 30 years ago when computers did not adjust timing while listening for knocks. Today It is not always a obvious (except is some cases) unless you run a few tanks throw vehical and let ECM tune spark timing to a higher octane fuel. Toady when it knocks or "pings' it is because it is so bad that the ECM cannot retard timing enough to "cure" it.

If ya want to clean carbon from an engine follow the old farmers method..

Start and bring engine to operating tempture.

Get about a gallon of tap water


Bring block in park to approx 3000 rpm.

While you are at 3000 rpm "slowly" pour water into the carb or in our cases the throttle assembly


At no time do you want the water to stall the motor so stay in the throttle and feather the engine to over come the addition of water..

As you do this make sure the exhaust is not pointing at another auto or something you care about because the carbon is gonna shoot out of the tail pipe..in a liquid form as black water..

[snoopyspaz]

New to the board here...

With my experience in engines knocking, being my last couple of cars were honda's, my honda del sol (civic chasis) was a high revin' high compresion motor and with different grades of fuel you will notice increase/decrease in power with the various grades. My wife drives a Honda crv and the same thing, this motor has an 8.xx:1 ratio and even with a low ratio, you feel the difference of lower octane fuels as compared to higher ones. My '03 silverado ss says in the book 91 is the lowest grade i can have and since have only used 91. With all my vehicles and the little bit of experiences with motors, I would say there is a huge difference in octane levels to what the performance will be. The manufacturer says 87 will work, and it's true, to a degree, but remember that it isn't going to last as long as say a motor that is fed 91 octane. Have to remember there are exceptions to the rule and I'm not saying that if you have a vehicle that is running on 87 octane and runs great to go out and spend more money, whatever works for you more power to you, just saying that in my experience the higher octane fuels make a difference.

My fatehr-in-law explaned that the higher octane fuels burn "cooler" allowing for a cooler chamber and allowing to disapate the heat better. With heat you create friction and wear the parts faster over time. So in theory, you will have a longer life motor fed higher octane gas. As we all know theory's aren't fact and you have to factor in maintenance and other factors as well. In the long run, a higher octane fuel will help but this is just my opinion and my experiences. Hope that helps some a little.

Peter

[ricair]

I just bought a 2001 silverado 1500 z71, and I don't hear any ticking or knocking. May be the hammer is about to drop, it has 75k on it and runs strong. THere is a slight roughness while in gear and stopped, and I feel a slight hesetation when I accelerate off the stop light (only when I floor it). The dealer replaced the master airflow senser (the "service engine soon" light came on even before I got it home!!!!) any Ideas what is causing this. May be I need premium unleaded in it. I just sold my 92 silverado, and it got sig. better millage with premium unleaded...

[markz71]

03 chevy z71 5.3 csk, ticking .at 7,ooo miles dealer says its normal ,bunch of bs