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Comments
Fuels developed for aircraft reciprocating (non jet) engines back in the '40s had anti-knock qualities superior to iso-octane, but a ratio (like 115/145) was used to identify those fuels rather than octane numbers. If racing cars are using that type of fuel today, I'm sort of surprised to find out that the fuel isn't referred to the same as the aircraft industry did about 50 years ago.
As I indicated in post 50, I'm really dating myself by discussing this, but to me 100+ octane doesn't sound like correct terminology.
Normally the AOL chain-mail I get is responded to with a threatening note. But this sounds pretty smart. I was wondering about the opinions of anyone here who might know the business of the gasoline industry:
It's time we did something about the price of gasoline in America! We are all sick and tired of high prices when there are literally millions of gallons in storage.
Know what I found out? If there was just ONE day when no one purchased any gasoline, prices would drop drastically.
The so-called oil cartel has decided to slow production by some 2 million barrels per day to drive up the price. I have decided to see how many Americans we can get to NOT BUY ANY GASOLINE on one particular day!
Let's have a GAS OUT!
Do not buy any gasoline on APRIL 30,1999!!!!!
Buy on Thursday before, or Saturday after.
Do not buy any gasoline on
(FRIDAY, APRIL 30, 1999.)
Well? Would this affect prices? How about if they knew this action was coming?
Just how inexpensive do you think gasoline should be? Also, I have no idea why anyone could expect the price at the pump to plummet if it were possible to get everyone to not buy the product for one day. It's a moot point, however, because that will never happen. Maybe you should have posted this suggestion a month ago and recommended April 1 as the day of the GAS OUT.
Just how inexpensive do you think gasoline should be? Also, I have no idea why anyone could expect the price at the pump to plummet if it were possible to get everyone to not buy the product for one day. It's a moot point, however, because that will never happen. Maybe you should have posted that suggestion a month ago and recommended April 1 as the day of the GAS OUT.
Gas *should* cost less than bottled water: Things are cheaper in quantity. When did you last drink 18 gallons of bottled water in a week?
$4 a gallon in Europe and Japan produced small, fast, fuel-injected cars and .50 cents a gallon gas in the US produced the '59 Cadillac. So we get some kind of grotesque nostalgia and shopping malls and they get BMW 528s and the autobahn. I think we've been suckered, personally.
I think we should pay $4 a gallon and use part of the money to take care of us in our old age after breathing the air in LA for 75 years. And besides, then we could buy used Range Rovers for $500.
Sorry to have been condescending in my note on octane ratings. You know this topic well; thanks for the info on SI aircraft fuel.
I have long shared your question regarding the octane numerical scale above 100. The ASTM surely provides an extrapolation procedure but I don't know any details. The "classic" definition does indeed imply, for your 105-octane example, preparation of a lab formulation with -5% n-heptane; quite a challenge.
I've been experimenting with my own car, dropping the octane gradually from the recommended 91 premium, and so far haven't noticed any difference in power or mileage...at least nothing measurable yet. Tomorrow we go to rot-gut 85 octane, and we'll see.
It seems to me that if there's any decrease in performance, this negates the relatively small savings per year between using premium and regular...on a small car this can't amount to much more than $100-150 a year....well, that's a dozen movies with popcorn.
This information would seem to explain your situation up through the early 1990's. However, if you are experiencing this brand-to-brand difference with cars built since ~1992....I, too, would like to learn more.
Returning to 92 octane (Union 76), restored the smoothness...and in a small overhead cam engine that revs high, this is important, so for that reason I'm going to stick with 92 octane and spend the extra $100 a year. It' worth it I think, given this quicky experiment.
A '99 truck pinging on 93 octane? Oh, no, I'm not buying it...something is not right, you need to have a factory rep come in and look at it...excessive pinging will lead to catastrophic damage...that "pinging" you know is your engine's internal parts rattling around and even to a minor extent the cylinder walls flexing (under extreme conditions). A small amount of minor pinging is okay now and then, but a constant noise will only lead to trouble.
But seriously, it's an old nickname and just lent itself easily to Email.
Spokane......I'm even referring to my old 71 Cutlass Supreme (bought in 1985), 1987 Nissan Hardbody V6, 1989 Mazda B2200, and 1995 Dodge Dakota V6. They all seem to have had the same reaction. Needless to say, I don't go to Mobil anymore, but it always puzzled me. It was also most noticeable on the Mazda, which otherwise ran like a Swiss watch. You could feel it shudder at idle. I never considered the System 3...thanks. I know it's another company's slogan, but I have to admit, "your car knows the difference".
Vman, my explanation is certainly lacking if you have the problem in your 95 Dodge Dakota. One point of possible interest is that the 1980's gasoline-chemistry problem was largely related to the distance between the injector nozzle and the intake valve. The shorter this distance, the greater the residue build-up and subsequent operational problems.
Thanks for the sympathy! However, it's not spark "knock," just an occasional spark "ping." The difference may seem like semantics. But surprisingly, my G.M. truck owners manual states that a light ping during acceleration is normal, but a loud sustained knock is not. My dealer confirmed this, and stated it was their opinion that everything was fine on my truck. The engine has two knock sensors, and if they fail the computer gives a trouble code. When the engine senses knock, it retards timing, but not right away. It makes incremental adjustments to the knock retard. Closely related to the 5.3L engine in my truck is the 5.7L LS1 engine in the Corvette, Camaros and Firebirds. Quite a few people on other message boards are reporting "ping" also. But the modification to the coolant thermostat is one that most all of those racer-guys are doing, mostly for the benefit that it increase horsepower, and lowers E.T.'s at the dragstrip. The stock thermostat opens at 195 degrees. That is pretty hot, and the reason for it is the higher temperature burns off emissions. But you only have to go back about 3 years, and they were shipping with 180 degree thermostats. The guys are reporting that they simply run better at the lower temperature, for the reason that it results in a cooler, denser air charge into the intake. The computer richens the air/fuel mixture to match the denser charge, and this lowers the combustion chamber temperature, increasing horsepower, but lowering the tendency to ping. It would be my preference to have the dealer solve this problem for me, but since it is slight, and apparently normal, I don't want to have them tearing into my engine, pulling the heads, head gaskets, intake manifold, exhaust headers to chase a problem minor enough it might get corrected with going to a colder plug or the above thermostat mod. Sometimes the cure is worse than the disease! But we'll see, and I'll keep everyone posted. Thanks!
I am aware of the incremental timing retard/advance but the use of two knock sensors is new to me. Even in "ancient times", with carburetors, ignition points, and no emission controls, we knew that you wanted very slight "ping" when you lugged the engine too much. This hasn't changed. Perhaps this new-design engine, with such added features as dual knock sensors, is designed to be "closer to the edge."
The points regarding temperature as it relates to emission control and intake air charge density are well taken. We really can't argue with results seen in racing. However, because combustion temperature is normally affected far more by air/fuel ratio and timing than by water jacket temperature ...I'm a little surprised. Because coolant temperature is part of the engine control algorithm, I wonder if continuing to operate at 195F, but fooling the sensor circuit to tell the engine control computer you have 180F, would do the trick. Just a thought; this surely would not be practical.
Fooling the sensor circuit is thought provoking indeed. What quite a few of the hot-rodders at http://www.ls1.com have found, is that the closed loop feedback system of mass-air-flow, throttle position, manifold absolute pressure, coolant temperature sensor, and O2 sensor will compensate somewhere else for this trickery, and either re-learn the stock settings, or turn on your SES (service engine soon) light if it can't. To me, modifying the thermostat so that the actual coolant temperature is a few degrees lower offers a little more hope, since there is a fuel/spark curve (called a cell) for every normal temperature range, including 180 degrees where the fuel mixture should be just a little bit richer as would occur during a normal warm-up stage. Having said that, if the computer is so intuitive as to recognize a mis-operating thermostat, I may get an SES light. And some guys at the LS1 site have...but where there is another difference is that the Camaro/Firebird/Corvette has electric, thermostatically controlled cooling fans also, and the turn-on, turn-off points have to me modified also. Whereas on my truck, it's the old fashioned driven from a fan-belt kind. Additionally, some of those guys are going to a 160 thermostat for maximum power. That can be problematic, for the reason that your heater doesn't work very efficiently. But I thank you for your comments and interest. You have motivated me to think about making this change over the weekend, and I will post the result here, although running on premium octane fuel lately, the ping is pretty much absent. So I think you comment about being tuned "to the edge" could be accurate. (But I don't like it that way!)
Here are the before and after temperatures.
Operating Temperature before: 204 F
Operating Temperature after: 191 F
Runs cooler by 13 degrees.
Now my Silverado is the "Coolest!"
Breathes cool, dense air.
Engine feels calm, relaxed and quiet. Improved
response.
Warms up fast.
Heater still works great.
Feels like it gained 15 horsepower, no kidding!
Best part....the modification is free!
Re-used my engine coolant, did not require adds.
I drove it for 56 miles. Mod did not turn on SES
(service engine soon) light. Could not detect any
engine-ping, but I still have premium in the tank.
I hope this mod lets me go back to using regular
grade octane. Looks good so far. Report later about possible effects on fuel mileage! Could get better maybe?
The 191F setting is well within acceptable temp range for most engines (including the GM 5.3L, I presume) so this is encouraging. With this temperature, I'm sure the normal warm-up rate and good heater performance are as you expected. If you had needed to drop to ~170F to get the improvement ...the "second law of thermodynamics" would have been working against you. Too, as you indicated, a conflict with the engine control computer and the accompanying SES alarm would have been much more likely.
Let us know, Quadrunner, what you learn with lower octane at the 191F coolant temperature. Also MPG comparison if you have enough data for it to be meaningful.
Colder plugs have the same physical dimensions with one major exception. The lenth of the ceramic insulation on the center electrode is shorter so heat is conducted away from the center electrode more rapidly. This makes the center electrode run at a cooler temperature. Don't remember what the optimum temp is but 'hot enough to self-clean, but cold enough not to cause detonation' is the rough explanation.
The water temp trick is old hat, and while it probably will do your engine some good on really hot summer days, the rest of the time, especially during the winter months, it'll just waste more fuel.
The theory behind the "added power" when you lower the coolant temp is that the FI computer usually meters fuel on the rich side when the engine is cold, much like the choke on carbed cars. So that was supposed to "enrich" the mixture and give you more power. Except the problem is that enrichment only helps HP at full or near full throttle. At other throttle positions, it might actually hurt HP.
The VW aftermarketeers have been peddling add-on processors that enrich full-throttle mixture through the warm-up fuel injector or regulator. That is a little more sophisticated than others that are no more than some resistors wired in-line with the upper cylinder engine temp sensor to fool the computer into thinking it's never warmed up. None of these gadgets have been proven to improve HP subtantially.
Lower coolant temp. does not automatically mean cooler intake air temp., either. In short, I wouldn't bother. You might actually end up with more carbon deposits on your intake valves because of the constantly "richer" mixture (if that's even true) and tha fact that your engine never warms up enough to burn it off under normal operation.
Knock sensors have been around ever since the mid 80's. It was, if I'm not mistaken , a Bosch invention and so were mostly found on Bosch injection system equipped cars, mostly European. Technically, it is nothing more a ruggedized microphone attached to the engine block and tuned to listen for a particular "signature" of sounds that are characteristic of a knock of ping. Some late model cars with V6 or V8 engines have one on each cylinder bank and will actually retart timing on the individual bank of cylinders.
I don't know every model of car and truck, but I'll go out on a limb and say that if your engine management is Bosch, it'll have at least one KS. Other FI systems are less predictable and are probably more likely to come equipped with one as the MSRP rises.
Quick ways to find out if you engine is KS equipped:
1. read the service manual.
2. call the manuf. tech. service dept.
3. look under the hood and see if you can spot it
4. drive to OKC and I'll see if I can spot it :-)
5. while driving at low speeds, shift to a higher gear and gun the throttle. If you hear loud pinging, you don't got KS. Don't do this too much if you don't have KS, you'll hurt the engine.
LS1 engine has two knock sensors located under the intake manifold, and foam insulated from extraneous noises.
What do you think retarding ignition timing does?
Hint: It lowers the temperature in the combustion chamber, so that the charge does not "pre-ignite" before the spark occurs. Same effect from circulating more coolant with the T-stat mod.
Main thing it does is to give the combustion flame front a little more time to expand and a little more cushion of insulating air between it and the piston crown. This effectively reduces likelyhood of knock, but at the cost of power. Yes, in general, retarding timing reduces power because it reduces the efficiency of the power stroke.
Retarding the ignition timing is the ECU's last ditch effort to protect the engine from meltdown, NOT the way to make more power.
True, lowering engine temperature does help keep the engine froom having to retart the timing, but like anything in life, is best kept in moderation. Lower the temp. too much and you'll open whole 'nother can of worms.
That's because the ignition timing is always advanced relative to TDC on modern cars. Retarding just means it is advanced less, but still BTDC. If an engine at wide open throttle is running 25 degrees BTDC when knock is detected, it may retard the timing to 19 degrees BTDC. Now if the charge detonates itself at 25 degrees BTDC, due to heat and pressure, its condition is 'pre-ignition' since the retarded spark at 19 BTDC followed the explosion. Obviously, retarding the spark cannot prevent the pre-ignition in and of itself, but since running less spark advance reduces the combustion chamber temperature, 1st law of thermodynamics holds that pressure is reduced or volume decreased. And the same holds true when changing the temperature by other methods, like thermostats.
One other point to keep in mind is that the density of a gas varies greatly as it is heated (expands), even if it is heated just a little bit.
The falling late-afternoon temperatures at the race track can lower a racer's quarter mile time by 1/10 second from his early-afternoon times, if the drop in temperature is about 10 degrees F or more. That could mean 15-25 horsepower difference. A good reason why engine dynomometer testing is done best when corrected for temperature and barometric pressure.
Most of what you say about the gasoline Otto cycle heat engine is true, except for the paradox of your statement regarding combustion chamber temperature and power. It is true that less spark advance lowers combustion temperature which , in turn, reduces the likelihood of "pre-ignition". It is not true, however, that this automatically produces more power. The Otto cycle is afterall a heat pump. The more heat is generated at the start of the power stroke, the more pressure (i.e. more enthalpy given the same compression ratio or volume) there is to expand the piston, thus generating more power.
No doubt an overheated engine produces less power because of the ignition retart. The engineers have arrived at an optimum operating temperature for a balance of power and fuel economy. I'm not saying you couldn't arrive at another different balance more to your liking, but without a dyno it's difficult to do it right. "Butt dyno" usually has too many other correction factors built-in to produce accurate results. Factors like owner expectation and operator right foot calibration offset tend to produce false readings. :-)
Seriously, I don't mean to discourage you from experimenting. I've swapped a 180deg. thermostat in my VW GTI before in search of more power. I've since found that unless the cooling capacity of the car is exceeded, the "summer thermostat" is quite unnecessary.
Interesting that Volfy has seen the use of "dummy" temperature signals to the FI computer. More info on the relationship between resistance values and fuel economy/octane requirement/etc. would be very informative.
Recognizing that Quadrunner wants to manage detonation and observe other criteria such as necessary fuel octane, apparent power, and fuel economy; continued trials should be of real interest in this "gasoline grade" topic. Further work with variables such as spark plug type is of interest. Keep us posted, Quadrunner.
You're right that it's probably not a balance between power and fuel economy. On these full-size trucks, though, they sure don't seem like they care too much about fuel economy. Realistically, knowing how engineering projects usually work, I'd say it's probably a balance between power, emissions, fuel economy AND project deadlines. :-)
If you plot HP, emissions, fuel economy all against operating temperature, each will likely be a curve with a single peak. Now it would be nice if all these curves peak at the same temperature, but realistically unlikely. So the game then is to optimize on all three wit perhaps a minimum set on emissions. At least that's how the factory engineers would look at it.
Intake air temperature does NOT correlate well with coolant temperature in a normally aspirated engine. Air is a poor conductor of heat and is unlikely to pick up much heat from the intake tracks. The intake air velocity even at part throttle is great enough that the air going into the cylinders is not much higher than ambient temperature.
Yes, the ambient temperature has a substantial effect on HP. Everybody knows that. Engine temperature's effect is much less pronounced, in the range you were talking about anyways. But I must conceed that if your engine was pinging BEFORE your lowering of the coolant temperature, then lowering it would most likely help reduce the amount of spark timing retart and help HP.
I take it your 1/10 second improvement is consistent. Otherwise, it is well within the normal margin of error.
All said and done, one does whatever make one happy. What others say really shouldn't matter much if you know what you're doing. Even as a skeptic, I still like to hear your results. I'd love to be proven wrong and learn something new.
Topped up tank with 14.019 gallons.
Reset trip-meter after 239.3 miles.
Calculated mpg = 17.1
Problem I have with this, is that I have never achieved better than 17.6 highway mpg, and usually have been getting about 14.5 in-town.
It's possible the fuel filler pump shut off early, but the gauge reads full. And I never try to put in extra fuel once the filler handle shuts off, for the sake of consistency, and also not wanting to spill, or overflow into the charcoal fuel vapor canister, (if they still use those.)
I always wait until near empty before re-fueling, to get a better average tank reading. But economics overwhelmed science when I noticed prices shoot up at the pump. The station across the street was up 0.20/gal, so I topped up early this time rather than lose out.
Still, 17.1 mpg. These miles never left the city. And I was carrying a bigger than usual load for quite a bit.
I wonder if the fuel supply might have changed away from the re-formulated, oxygenated gasolines that we have in the winter months? They are mandated through the end of February, but the vendors will continue selling them until the stocks are used up.
Please stand by while I check my result again after next fuel stop.
Coolant temp down from 204F to 191F, gasoline change from 91 to 87 Octane, no change in spark plug heat range.
Results are near-elimination of pinging, sensation of improved power, and possibly improved fuel MPG.
Next ...further evaluation of fuel MPG.
Is that it, did I miss any process changes or results? Thanks; this is interesting. Please keep us posted.
Don't know about the winter formulations. I do notice the gas mileage on my Tacoma gets worse when the weather gets cold, as much as 3-4 mpg. I didn't think the cold start enrichment would make that much difference, perhaps it does. MPG on my Golf GTI doesn't seem to vary much in cold weather. So maybe it's because Tacoma has an air mass flow sensor and GTI has air volume sensor.
Anyway, you may want to keep these other factors in consideration.
There is actually a complete schematic diagram of the engine in my GM service CD, which i got for free when I got my Grand Prix GTP...
I think (been a while since I browsed the CD), the fuel injection system on my Supercharged V6 is Bosch... But I know for sure that my ABS and Traction Conrol System is Bosch... As is the other W-Body GM cars from 1998 on.. (was Delphi pre98)
Also as a side note, GM had distributorless engines earlier than 86, as my mom's 85 buick century was available with a distributorless 3.8 litre V6.. It said so in the brochure...
Quad, I wonder if your knock sensors could be not sensitive. I suspect my knock sensors trigger an ignition retard (or fuel enrich) in about a second.
My real question is: When towing a trailer that weighs at the max rated GCVW (5,500lbs for my truck), should I run higher octane in this motor to prevent retard and/or enrichment?
At the other extreme, the enthusiasts at http://www.ls1.com have been running high octane, 94, 97, some even using race gas in what appears to be an ongoing struggle to avoid knock-retard. They prefer to let it knock, rather than lose horsepower. And apparently, some knock-retard under certain conditions and rpms is all but un-avoidable even with the race gas. Other measures they are taking include thermostat mods, and recalibrations to the MAF (mass air flow) sensor. According to Steve Cole at TTS Performance Systems, the LS1 for the first time (in a Chevy at least) uses the MAF sensor as the primary "pointer" to the appropriate fuel delivery/spark curve.
But to answer your question, I would have to say while I can't tell you what octane you should run, I can tell you what I would run. If I was towing anywhere near the limit, I would use premium octane fuel. And if my tank was already full with lower octane fuel, I would put in a bottle of Snap Octane Booster. Treats 20 gallons for $1.69 at Pep Boys. The stuff works pretty good, and is said to be compatible with catalytic converters and O2 sensors. But in my case, the thermostat mod has worked the best so far.
You have made several references to thermostat modification. Conventional thermostats are not readily recalibrated as you well know; we normally replace the assembly to achieve a change in the coolant temp.
Does some new engines, such as your LS1 derivative, now use a different type of thermostat that can readily be modified/recalibrated? Thanks.
Fundamentally it is like any other automotive thermostat that uses a wax pellet pushing on a piston/plunger for controlled expansion versus temperature, to open the valve. The difference for the LS1 engine is that the thermostat valve is attached to the inlet housing. Why? I can't say, but when you separate it from the housing, you expose a piston/plunger from the bore it fits into when assembled. This allows you to effectively lengthen the plunger by putting a spacer into the bore. And it stays together because the spring holds it captive.
I find it interesting to note that for many years, all cars had thermostats located to restrict the flow of hot fluid from the engine to the radiator. Now, on many cars, the thermostat is on the "other side" of the radiator and thus restricts flow of COOl fluid from the radiator to the engine. But....perhaps this is something for a new topic.
Eager to hear your next update on fuel-grade/economy/detonation, Quadrunner.
**************************************
Patman
Part of what Mongoose told you is correct. I am the one who told him, but it seems as though something was lost by the time it got to you. The PCM learns spark and it takes it out if there is too much knock. The trick is to understand how and when it does it's thing. If pinging occurs the PCM retards spark until the pinging is gone. Once it's gone it will try to add the spark back in with time. If the pinging continues all the time the PCM learns from this and removes timing, that will not be put back in! When the car is refilled it adds back the learned spark, in this way the PCM assumes the gas was the problem and since there is new fuel let's try again. This process goes on all the time and will remove spark as necessary.
This is why some of you hear pinging that seems to disappear with time, the truth is the PCM learned and reduced the spark. If your add on device causes pinging the PCM will try to learn it to stop the ping! Remeber one thing it does have some limits, once exceeded you will get a SES light!
As far as a release date for the '99 LS1 I don't have a date yet. We are working on the code but it is not complete yet. We can program in house for those of you who can't wait. The '97 and '98 are in production and were are just waiting for them to be completed.
------------------
Steve Cole
Engineering Manager
TTS Power Systems
*******************************************
Can you believe the part about the spark timing being reset by adding fuel? Or that is recognizes when you re-fuel? What would Rube Goldberg have thought?
Seriously, as you know, some engine/transmission computers do now have more than twenty input variables, and further refinements will surely add a few more inputs. But, because the fuel knock characteristic is effectively being monitored constantly, I cannot imagine any sort of "gasoline-batch" sensor on anyone's development agenda.
Now I can understand some kind of "limp home mode". Many FI systems' software have this. If the ECU thinks one or more crutial sensor(s) are bad, it will go into an ultra conservative open-loop mode, which won't damage anything in the worse case scenario but have enough power to, well, limp home.
on his 300M though we have an Amoco gas station nearby. He says that his car performs better on Texaco (87 octane) than Amoco (87 Octane) or Mobil(87 Octane).Do any of you think he is making sense ?