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Old 08-31-2007, 06:49 AM   #31
DSMer
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Quote:
Originally Posted by windsonian
my point is that you're paying $30k per year to believe everything your teachers tell you. you're not learning to learn things for yourself.

you do not, and will never know it all ... and your school probably doesn't make you better than the rest of us with formal training.

No I'm paying $30k a year to receive a piece of paper that will make me more qualified. Its a science. Its must be learned, understood, and applied. It has nothing to with what my "professors" tell me to believe. More to do with what IS fact and what is NOT.

No one knows everything. I don't care.

I don't need a school to make me better than you. My self proclamation that I am better than YOU makes me better. Who is this "us"? I don't recall myself talking to anyone other than YOU.
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Old 08-31-2007, 12:18 PM   #32
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30k a year?? damn...how much do courses cost on average over in the US?
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Old 08-31-2007, 04:52 PM   #33
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Quote:
Originally Posted by DSMer

If you require MORE fuel to produce a proper combustion on a higher octane gas, how will leaning out the mixture better your fuel economy if you're inevitably going to need MORE fuel than is normally necessary?

You ASSume that the car knows what a proper combustion is on the higher octane gas. This assumption implies that the car knows how much power it is making, more importantly a proper combustion on premium, and that the car understands premium when it was set for regular. That is the whole issue. The car DOESN'T know the difference. The only way it can know is through its sensors. I was merely pointing out that since burning premium fuel results in higher emissions that MAYBE the O2 sensor would pickup on that, read it as "rich", then compensate by leaning it out. YES you will make less power this way, NO you won't consume more gasoline. Got it? Thanks for schooling me like I'm a freshman with your overly priced education at the fine University of Illinois. I will take my University of California Davis education and be quite content with keeping my mind open to new possibilities and ideas. Maybe that way one of us can actually LEARN something???

I could go on amazon.com or the registrar site and simply find all the engineering books offered in every subject at Davis and post them all here. That doesn't change a damn thing. Until you put in english a quote that EXPLICITLY says what you are trying to say from a reputable source, preferably a couple, then it doesn't make it any more true. You can have your hypothesis, I have mine. The only difference is that I can admit that there is a decent chance that I am WRONG.
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Old 08-31-2007, 11:30 PM   #34
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Quote:
Originally Posted by DSMer
My self proclamation that I am better than YOU makes me better.
As long as you believe that. It won't take any skin off my sniffer.

Quote:
Originally Posted by DSMer
Who is this "us"? I don't recall myself talking to anyone other than YOU.
If you read my quote, I was talking about those of "us" who have had formal training. I'm not the only one (as rudypoochris points out above), so why would I claim to be?

And Chris, you seem pretty dead on to me. The control system is not smart, no matter how much we'd like it to be. It takes its inputs (ie sensor values), and will interpret the same set of parameters exactly the same way each time, regardless of what set of circumstances led to that state.
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Old 09-01-2007, 05:01 AM   #35
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Hello there. I am confused. Why does running PULP result in higher fuel consumption, reduced power and lower performance?

I would be very interested to see the published independent data that two members have referred to as bible in their comments. There should be no excuse not to provide this data as the one gentleman who stated 4 points of supposed fact and the other engineering student both seem fairly emphatic it is correct and accessible. I don't understand the reluctance of the student in providing the proof unless he is being deliberately awkward.

Am I correct in assuming the '05 Elantra is fitted with a knock sensor for closed loop control of ignition timing? What are the published calorific values of standard gas and PULP gas in the USA? Do Hyundai admit to selling a car that loses power, performance and economy with PULP?

Enquiring minds need to know.
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Old 09-01-2007, 10:13 AM   #36
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Quote:
Originally Posted by rudypoochris
You ASSume that the car knows what a proper combustion is on the higher octane gas. This assumption implies that the car knows how much power it is making, more importantly a proper combustion on premium, and that the car understands premium when it was set for regular. That is the whole issue. The car DOESN'T know the difference. The only way it can know is through its sensors. I was merely pointing out that since burning premium fuel results in higher emissions that MAYBE the O2 sensor would pickup on that, read it as "rich", then compensate by leaning it out. YES you will make less power this way, NO you won't consume more gasoline. Got it? Thanks for schooling me like I'm a freshman with your overly priced education at the fine University of Illinois. I will take my University of California Davis education and be quite content with keeping my mind open to new possibilities and ideas. Maybe that way one of us can actually LEARN something???

You've still failed to answer my simple question. Until you CAN answer that I'll hold your opinion in the "everyone has an asshole" box with the rest. I would like for you to explain the simple solution of.

1.) Combustion ratio does not change. It will always be the same optimal ratio regardless to what octane you have in the car.

2.)Doesn't matter if the car knows how much power it is making. You will give the car more throttle if it is not making the proper power to propel you to a given speed.

Again to my simple question.

If your are making less than normal power per combustion stroke. How will this save you fuel if you are inevitably going to need more fuel to make a normally powerful stroke?
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Old 09-01-2007, 10:21 AM   #37
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Quote:
Originally Posted by windsonian
As long as you believe that. It won't take any skin off my sniffer.


If you read my quote, I was talking about those of "us" who have had formal training. I'm not the only one (as rudypoochris points out above), so why would I claim to be?

And Chris, you seem pretty dead on to me. The control system is not smart, no matter how much we'd like it to be. It takes its inputs (ie sensor values), and will interpret the same set of parameters exactly the same way each time, regardless of what set of circumstances led to that state.

Who is this us? Can you account for anyone else's formal training other than your own? Do you have everyone else's credentials? Thats exactly what I thought. YOU are alone in YOUR own opinions.

Real MEN stand behind their own thoughts and morals. They don't need the backing of other people to support their own theories and beliefs. You're too old and "formally trained" to be a p*ssy. Stand for yourself and stop relying on other people to back you.
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Old 09-01-2007, 03:49 PM   #38
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How is it then, that I get better gas milage than it's EPA rating? I read in some places on the internet that premium does have other ingrediants than gas that improve fuel economy. My car improved 4-6 miles per gallon when I switched to premium. My wifes PT cruiser only gained 2 miles per gallon. One time I only paid 13 more cents for Shell premium. Is it true that some companies ad ethanol or toluene to thier gas? Octane ratings in the US are a measure of anti-knocking.

I read that compression ratio increases when carbon builds up. How do I clean carbon out? With Lucas or Gumout? If my transmission has been replaced with a new or rebuilt transmission, would I still have the carbon build up?
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Old 09-01-2007, 08:25 PM   #39
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Quote:
Originally Posted by tbaxleyjr
It does not change the stoichiometric air-fuel ratio of approx 14.8:1 nor does it change the higher heating value of the fuel ranging between 18,000 and 20,000 btu/lbm fuel depending on actual fuel blend. If one were to sort out the major components of the fuel and did the combustion equations one would find little or no difference in pollutants or other things detected/measured by the O2 sensor.

Higher octane fuel does have a lower energy content than lower octane gasoline. Higher octane fuels allow for a higher combustion ratio inside of a given engine. Packing more fuel and air into less space will produce a stronger and hotter combustion, which is more efficient. When these fuels are introduce to an engine with a lower compression ratio there would indeed be a lower overall power output because they contain a lower energy content. The lower compression of these cars tuned for regular are not able to optimize the benefits higher octane fuels and overcome the lower power due to the lower energy output of higher octane fuels.

Ethanol has a lower energy rating than regular gasoline. And ethanol is often used to increase the octane rating of premium gasoline. I don't know the exact blend of all gasoline(because it varies so widely) but there is a definitely an overall energy difference between regular and premium gas. But....

Will it be enough to dramatically effect your fuel economy?
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Old 09-02-2007, 01:48 AM   #40
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Quote:
Originally Posted by DSMer
Who is this us? Can you account for anyone else's formal training other than your own? Do you have everyone else's credentials? Thats exactly what I thought. YOU are alone in YOUR own opinions.

Real MEN stand behind their own thoughts and morals. They don't need the backing of other people to support their own theories and beliefs. You're too old and "formally trained" to be a p*ssy. Stand for yourself and stop relying on other people to back you.
huh??
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Old 09-02-2007, 02:34 AM   #41
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Quote:
Originally Posted by DSMer
1.) Combustion ratio does not change. It will always be the same optimal ratio regardless to what octane you have in the car.

By combustion ratio do you mean the air to fuel ratio? If so I realize that the AFR is largely set by the O2 sensor. If there is more C8H18 in the gasoline it stands to reason there will be a greater amount of emissions in the exhaust gas. IF the O2 sensor picked up on increased emissions from premium the O2 sensor MIGHT send a rich code to the ECU which in turn MIGHT lean it out. That is what I was getting at pages ago. I don't think it is necessarily possible, but it could be. I am not saying that is what the computer does, I was simply saying that is one situation in where it COULD be possible that the ECU would lean the mixture out which would inturn reduce consumption.

Quote:
Originally Posted by DSMer
2.)Doesn't matter if the car knows how much power it is making. You will give the car more throttle if it is not making the proper power to propel you to a given speed.

Actually it does matter... which is one of the reasons why 400hp cars typically get much worse fuel economy than 70hp cars.

Quote:
Originally Posted by DSMer
If your are making less than normal power per combustion stroke. How will this save you fuel if you are inevitably going to need more fuel to make a normally powerful stroke?

You simply don't NEED all the power the engine can provide. Yes you are making less, but you don't necessarily need more. At cruising speed a vehicle only uses a fraction of its total potential power. This means that the throttle body will be very much closed. A closed throttle body is a large restriction which results in increased fuel consumption. The very fact that we cruise at say 2000 instead of 6000 is testiment to the fact that making less power results in better fuel economy.

As far as higher octane fuel having less power potential than lower octane fuel, that largely depends on the rest of the mixture. Yes if all things are the same a higher octane fuel has less potential, NO not all things are the same. Refineries DO often mix their premium blends to carry more energy than their regular blends.

Look guys. I am not flat out saying that he will get better economy by running premium in a regular car. That would be dumb. I never made ANY indications that I believed this to be true. I simply pointed out a hypothetical scenario in which it COULD work. Just thinking out of the box. Take it for what you will. Was just an idea, after all it could be right. I don't see any way that I could prove my side or anyone else could prove their short of actually running multiple regular gasoline motors on engine dynos at various speeds running premium with a stock ECU setup. I don't think I will find anywhere in any college text that would support or disprove my concept. I am talking about changes int he ECU strategy and how that results in economy gains or losses, not necessarily how the combustion itself occurs. Thus I find it kind of hard to find support in texts that limit themselves to thermodynamics. I DO admit though, now and long ago in this thread, that he would still probably end up paying more since premium is another 20 to 30 cents a gallon.
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Old 09-03-2007, 03:18 AM   #42
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I'm confused at your apparent about face on this issue Tbaxleyjr. Early the subject you whole heartedly endorsed the comments made by VWHobo and haven't corrected DSMer in his incorrect ascertions. You asked members to produce discounting proofs, but did not equally ask for proofs for the originating statements which is traditionally required by engineers to support theorems.

Supporting documentation is difficult to acquire, because the data is generally company sensitive. In the absence of fact, the auto industry thrives on tenuous comments which gain credibility by adoption, eventually moving from folklore to blind acceptance.


Comments like these are just not true:

Quote:
Originally Posted by DSMer
You're thinking that because higher octane fuels burn slower(not burning all of the fuel)

They are predicated on a myth and unlikely to be found in the course books offered up as supporting. Unless you change the molecular structure of the gasolene with additives it will burn at the same rate as the gasolene from the same drum without additives. If high octane fuels made the burn slower they would not be used on high performance engines which typically must release energy faster than a moderate redline street car running regular unleaded. The exposed surface area of the molecules to oxygen gives rise to the volume of burn, but the rate of molecular burn remains the same.

The octane additive is included in the fuel to inhibit detonation. It helps to break the fuel into a homogenious burn pattern rather than one or two almighty explosions followed by a trivial afterburn. It allows for a controlled ignition and if tuned correctly a more complete burn. Even well tuned engines don't achieve complete burn, so there is scope for improvement.


The blanket argument that a fuel injected car tuned for 87 will be adversely affected by higher octane fuels is highly questionable. Anecdotal evidence by everyday consumers alone suggests there are noticeable benefits, not withstanding the evidence amased by technicians intimately involved in engine tuning, this is no slight on service mechanics, but the correct testing apparatus is not something typically found in a repair business workshop. Driver attitude is an influencing factor, but can equally be helpful and detrimenetal to fuel economy. Car makers are quite open in suggesting poorer fuel economy and possible rough idling, but they rarely suggest loss of power, when using very high ethanol content pump fuel.

If the engine has been designed and constructed to run most efficiently on 87 there may not be any improvement in performance and if oxygenated additives are used,a loss of economy. For instance the Elantra engine is designed for 95 RON fuel. If the quoted 87 AKI meets the RON specification then there there may not be any tangible improvements to be had, but in this instance it doesn't appear to. Heating values for gasolene vary, but in many parts of the world the potential energy of premium pump fuel is at least equal if not higher than standard pump fuel.

At the outset the type of fuel to be used is a factor in the engine geometry and construction. If the engine was to rely soley on the spread of flame speed of gasolene in air it would never complete anything approaching complete burn or desirable rpm, so the mythical argument about gasolene burn rate differences becomes minor in the overall scheme of things anyway. The metalic octane fuels like lead enhanced didn't rely on the metal combusting, it was primarily there to inhibit detonation associated with high compression ratios, secondary benefits to valve seats were a bonus.

Knowing the regular pump grade fuel knock index and the availability of premium fuels allows the designer and calibration engineer the opportunity to construct an efficient combustion chamber which propogates and accelerates multiple flame fronts rather than one that results in a big bang at the instance of ignition. Automatic detuning of the engine for regular grade pump fuel after development means there is always scope for improved performance using higher octane fuel. The program and tables in the engine controller should account for this by adapting via the various sensor inputs, perhaps some controllers are not so bright as others.

The reliance of AFR figures is also no longer as credible as it once was. With direct injection and fuel stratification now being employed the ratios are substantially less, yet power output is commendable.

Last edited by BestPractice : 09-03-2007 at 03:25 AM.
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Old 06-03-2009, 05:21 PM   #43
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Clarification

Ok, there seems to be a definate need for some clarification in this thread.

1) Octane Rating.
Alot of shit seems to revolve around this, probably due to it being called 'premium'
Truth: Petrol is made up of hydrocarbons (usually with 4 to 12 carbon atoms) derived from petroleum. Originally thatís all it was. A fraction skimmed off petroleum during refining that was usually just burnt off. People were more after the heavier oils and heavier fuels like kerosene for lanterns.
It wasnít really till the invention of the petrol engine that anyone used it for much.
And it really wasnít till the world wars when engineers were trying to develop high performance plane engines that people started to give a hoot about octane ratings.
Truth: Octane rating is a measure of how the ANTI KNOCK properties of a particular fuel blend compare to a mixture of pure octane and Heptane, (C8H18 and C7H16) ONLY. Burn rate, energy content, detergent whatever content are not governed by octane rating at all.
An example is fuel with an octane rating of 98 displays the same resistance to detonation in a test engine to a mixture of 98% octane to 2% heptane by volume.
Yes you can have fuels with octane ratings above 100. This is because Octane is not the highest detonation resistant compound there is around For example ethanol, often used a racing fuel (thatís right, its actually good!) has an octane rating of about 130.
I must apologise, I do not know how octane ratings above 100% are calculated, I just know it can.
What I do know is the different octane ratings can be achieved with many different additives and blends, some of which increase energy content a bit some donít. Anyway same end result, High octane fuel isnít really much different to standard fuel.

2) Fuel energy content.
The energy content in different grades of petrol does not differ too much and if it does its just due to things like where the oil came from, who distilled and how exactly they did, whether it had more heavy hydrocarbons in it whatever. It probably only differs by about +-0.5MJ/kg or something. Petrol is usually about 44 to 45 MJ/kg.
High octane fuels DO NOT give you extra mileage in the same engine.
To prove this, diesel engines. 5 to 6 litres per 100km say. A similar sized petrol car would probably get 8 to 9 litres 100 km. thatís a 50% to 60% increase in mileage. Diesel has between 45 and 46 MJ/kg. only 1 MJ/kg increase. 2% more energy. Think about it.
This leads onto the next point, well second next point (does that work?), Compression Ratio.

4) Thermal efficiency.
Simply a ratio between the rate chemical energy is supplied to the engine (in the fuel) compared to the rate of mechanical energy (work, crankshaft spinning) is recovered from the engine.
High thermal efficiency, more power more miles less petrol. Happy driver.

3) Compression ratio.
Compression ratio is a simple ratio between the volume in the cylinder and combustion chamber when the piston is high at TDC over the volume when the piston is low at BDC. So itís the difference between the big volume when the piston is down low and the little bit thatís left when the piston rises to the top.
This value is often critical to the thermal efficiency of an engine, so high compression ratio, generally, high thermal efficiency, more power more miles less petrol. Happy driver.
As to why, the explanation lies within thermodynamics which is not really the topic of this post, so we will just accept that it does for now (explaining it could take a while).
So why donít all engines have massive compression ratios?
Well we all know the piston compresses the petrol air mix on the compression stroke, and we know the higher the compression ratio the greater the change in volume. Lots of gas, tiny space. As the pressure of a gas rises so does the temperature. Things like fuel catch fire at high temperatures, called DETONATION or KNOCKING and this is what limits the compression ratio in petrol engines.
Detonation is when the air fuel mix ignites before the spark fires. This is bad because the spark is precisely timed to ignite the fuel slightly before the piston Ďrocksí over top dead center so that when this happens the fuel has just finished combusting. The pressure (and also the temperature) in the cylinder is at its maximum here and begins to pres the piston down. As this happens the pressure and temperatures relieve while the piston is pushed down. Energy is passed to the piston in the form of mechanical motion.
If the fuel burns to early two things happen. First, the peak pressure is reached while the piston is still rising. This puts massive strain on your bearings and totally destroys any efficiency the engine had. Second the temperature peak is reached at the same point, and this does not relieve very much until the piston starts moving down again. This means heat has more time and conducts into your piston and head more. Again wrecking performance and possibly your piston. Aluminium alloys melt.

So we want a performance engine. Among other things like high RPMs, good head flow and nice bearings (turbos and superchargers are another kettle of fish when talking compression ratios) were going to try and push the compression ratio up, to get more thermal efficiency and by that more power.
This is why we have high octane fuel, for these engines. The additives to make high octane fuel, mentioned above, cost money so average cars designed for soccer mums and grandmas have an engine that can use cheaper, lower octane fuel. It makes pure economic sense. They can easily make the choice to part with a few kilowatts and a small efficiency loss if they can save 15c per litre at the pump. Truth is most of us can.

Now, before we go any further, TO CLARIFY: You may notice I just spoke of an increase in mileage and in the same sentence octane fuel ratings. Critical difference, the difference is the ENGINE not the FUEL.
Engines with high compression ratios are more efficient. They require high octane fuel however. Engineers would rather use the lowest octane.
Lower performance engines with lower compression ratios can run on lower octane fuel. They can also run on high octane fuel. This really (because of the reasons mentioned previously) doesnít effect them at all. It wonít stuff your cat, it wont lower your performance, it will make absolutely no difference. It will just hit your hip pocket. Thatís why itís a false economy to put it in a 2001 Hyundai Elantra.

4) Rev ranges, Torque vs power and shit.
Ok first things first. Power. Usually measured in watts it is the rate that energy flows through something or is Ďusedí. Yep the word rate is in there, that means it has a relationship with time.
Torque. A turning or twisting force. Measured in newton meters. This is what actually moves your car along.
RPM. Revolutions per minute. A common measurement for rotational speed. Speed is a rate. Has a relationship with time.
In these forums, mostly performance ones and usually when comparing jap 4s with (often slower) V8s you hear Ďwell your 4 banger has more power but the V8 will smoke you with its torqueí. Two words, often used together as one word, bullshit.

Lets go back to power, specifically, shaft power, which is what comes out of an engine. It is the product (two things times each other) of torque and shaft speed (in radians per second, another form of shaft speed). The formula literally looks like this:
P = T x ω ( P power, T torque, ω shaft speed)
This means both torque and high redline are a way towards high power.
POWER IS WHAT MAKES A CAR FAST

Now I did say before torque is what moves your car along, so im going to mention something else.

Gearbox. Wonderfull invention, gears are fun to change.
We all know its what is in the middle of your drive train, the group of components that transfer the energy from your crankshaft your wheels. We also all know its what matches the speed of the engine to that of the wheels. So it changes speeds.
It also changes torque!!
Your energy going through your wheels follows the same relationship as your engine, as far as torque and power are concerned. So our good old formula P = T x ω still applies.
So two cars. Both making 5kw, both going 60km/hr, one the engine is going at 900rpm, the other at 2500rpm.
Road speed is the same, wheels are the same size so they are spinning at the same speed, powers the same, TORQUE AT THE WHEELS is also the same!!
This is why torque does not mean shit when you are talking fast cars because an appropriate gearbox changes it to match the load on the wheels. Arenít they great?
In the example above the slow reving engine will be producing a higher torque reading but the high reving engine is making up for that with its shaft speed.

The two cars would be different to drive. The slow engine will be nice cruizy and lazy, the fast engine will feel highly strung and it will feel like you are driving it harder. Its subjective though.
Did I mention F1 cars? 2.5l or something, 20,000rpm redline, next to no torque, would smash the fark out of a 5l V8 with maybe 1 and a half times the torque rating?

Its cool, you can like your V8s, just donít say it will smash an evo or something with1 and a half times the power and 2 thirds the weight. Like wise, a worked V8 with massive torque and more power but lower redline might smash a jap car whatever.
Donít start an argument about this please, its been done before.

Anyway, one price you can pay with high revving small motors is a loss of efficiency. Because everything is moving faster, pistons going up and down faster etc there is more friction in relation to the power produced. So there it goes, your efficiency can just fly away.

Anyway, fark im getting vague

Ciao

PS heaps of books on this stuff read em if interested

PSS this is not written well enough to be used as an assignment, go copy Wikipedia
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Old 06-03-2009, 05:26 PM   #44
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Oh and a side note, there is heaps of shit you can do in engine design (if your an engine designer for toyota) to inhibit detonation and allow high compression ratios.

Things like swirl velocities, squish (basically a way of creating swirl) and sheer engine speed can help an engine achieve a high comp ratio with low octane fuel.
Have a look at motorbikes.
GPX250. 11.5:1, standard 91 fuel. Engine designed in the 80s when allot of cars were around 9, 9.5
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Old 06-03-2009, 05:43 PM   #45
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Oh yeah, rudypoochris, thermal efficiencys and mechanical efficiencys are the main factors that determine your mileage in a car and alot of factors influence these figures.
Just saying more power means less milage is too simplistic and just plain wrong in this case.
Perhaps they havent taught you this stuff in your engineering course yet
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