Why sell do we still manufacture 87 octane gas?

Wrong, fuel economy did NOT go up. It went down, rather drastically, as compression was dropped.

Compression ratios dropped because that was the only way to meet new oxides of nitrogen emsssions standards. The fact that the engines could run on lower-grade gas became a benefit in the gas embargo years, but it was not the main goal.

Yes, and no. In 1972, the horsepower rating method was changed from SAE gross to SAE net and that did cause the numbers to fall even when the engine output remained the same, but that is NOT the same thing as "rear wheel horsepower." Not by a long shot. SAE gross power over-estimated the true rear-wheel horsepower (its closer to at-the-crank horsepower with no accessories). SAE net probably underestimated rear wheel power quite a bit, since it required including the maximum parasitic load the engine would ever see (PS pump under full load, AC on, alternator at max output) and IIRC it also threw in assumed losses in the driveline. But again it was NOT measured rear-wheel horespower. The SAE net measurement method has been altered quite a few times since it was introduced, also, so you really can't compare engines across 20 model years based on those ratings.

Displacement doesn't mean anything at all. Its just a design parameter that can be varied, just like compression ratio or whether or not turbocharging is used.

Doing "better" in what way? Certainly not in a) longevity b) torque c) load-pulling capability, or d) economy when its being asked to move the same vehicle.

It was some time ago, maybe 18 years. If they're actually mixing grades at the pump, I wouldn't buy it - just stick with regular or spring for premium. Being mixed at the drop by the driver has been done for a long time (at least a long time ago). Well, I'm showing my age - time for a nap.

Cheers, - Jeff G

I couldn't have said it better myself Doc. A small motor producing a lot of power (relative to its weight) enables the production of a more efficient vehicle. Put another way, the less car you have to carry, for a given amount of payload, the less fuel you're going to burn.

And the guy that said "What about torque?" That only matters if you don't have a transmission, and automobiles do. HP is the single metric describing ability to do work.

So here we are...

12:15pm, restate my assumptions: 1) 91 octane fuel costs (to manufacture) essentially the same price as 87 octane fuel in similar quantities. 2) A high compression motor designed to use high octane fuel will produce more power per unit weight, resulting in increased fuel economy or acceleration (pick one).

Therefore, it is illogical to produce 87 octane fuel and the vehicles that can burn it.

| > The 1st thing that happened in the early 70's with the oil embargo and new | > pollution standards was to reduce engine compression. The 360HP muscle cars | > went down to 200HP with the same engines. But fuel economy went up and | > pollution/emissions went way down. I'm not an expert on the matter, but, why | > would the engine manufacturers do what they did in the early 70's if what you | > state is true? | | Wrong, fuel economy did NOT go up. It went down, rather drastically, as | compression was dropped. | | Compression ratios dropped because that was the only way to meet new | oxides of nitrogen emsssions standards. The fact that the engines could | run on lower-grade gas became a benefit in the gas embargo years, but it | was not the main goal.

That isn't what I remember. My 1967 GTO got at best 8-9 MPG mixed and about

11-12 MPG highway. Early 70's 400ci V8s got high teens highway and low teens mixed.

Oh? Tell me which is more efficient- a 3/4 ton pickup with a "240 HP

4-cylinder" or the same 3/4 ton pickup with a 5.7L v8?

Displacement merely refers to the size of the cylinders (open space.) Big displacement does not necessarily mean a heavy engine. And "big" doesn't necessarily mean 8 liters, either. "Big" in context can refer to building a 2.5L 4 cylinder instead of trying to over-work a 1.6L engine in the same weight vehicle.

But if you have a wide, flat torque band over which the engine is efficient, you don't need the weight and complexity of a 5 or 6 speed transmission. And an engine with sufficient torque to cruise in top gear (70 MPH at 1800 RPM, for example) without downshifting for every slight hill is FAR more efficient than a mosquito motor that has to downshift constantly to maintain speed.

Which is false...

Which is not necessarily true, as the example engines I've shown have proven. With good engineering design, octane demand can be decreased while compression ratio is increased. Compare the Cadillac Northstar to its predecessor the 4.9. Compare the Chrysler 3.5L v6 to its predecessor the 3.3L v6. Compare the 5.7L Hemi to its predecessor the 5.9L v8. All 3 have higher compression and similar octane requirements.

Strike 3, you're outta here.

With the same gear ratios in the rear end? Were the weights comparable? Did the cam grind stay the same? Did you have radial tires on that '67 GTO? I seriously doubt it! That's another thing that happened- cars that used to get 3.9, 3.55 and 3.23 gear ratios in the axle started being shipped with 2.9 and 2.76 ratios, cars started getting lighter, cam grinds got less radical, and tires got less rolling resistance. And often, mileage still went down or held about the same.

They mix mid grade at the pump around here.

Steve Triangle Pump Service

Two words: Torque Convertor.

Doc

That would be the former. Efficiency being defined as job finished/ fuel consumed.

If you can get the same power out of the smaller displacement motor then for all intents and purposes, you have a more fuel effiecient (if shorter lived) solution.

Driving around with all that extra capacity wastes fuel. The key to power in light weight motors is revs, look at F1 engines. Point taken, shifting can be inconvenient, but both my vehcles are manual. I recently did an experiment where I plotted instantanious HP (delivered) against time of my daily commute and realized that most of the time the motor is just puttering along at 15-20% of peak HP. Only during hard accelleration do I even get near it's rating.

We'll have to agree to disagree on this one because neither of us have access to the real information and never will.

The anecdodal information your provided are just examples of how these GM products have been able to raise the compression on "similar" octane. That doesn't mean they couldn't have done even better with a higher minimum octane requiement. They've just done better sticking with the old low octane fuel paradigm (which is commendable in its own right).

No YOU'RE outta here!

Two morewords: inefficient, inadequate.

But the overloaded engine will generally consume MORE fuel than the normally loaded one, will take more time to accomplish the task, and will have a shorter service life.

Why more efficient? If you run a 2 Liter motor at 4000 RPM and a 4 liter motor at 2000 RPM at equivalent volumetric efficiency and producing the same power, then you're burning no more fuel and air with the 4-liter engine. And in fact you'll be burning less when other losses are thrown in.

1) Nothing I mentioned is anecdotal- you can look it up and go lay hands upon the engines if you so desire. 2) I only mentioned 1 GM engine 3) Higher octane is wasteful of resources when the exact same gains can be made through better engineering.

Yep, I've proved my point.

You talking about the torque convertor or yourself?

Doc

You ever seen a torque convertor that didn't convert a lot of energy to heat when it was in a high torque-multiplication mode?

I'm not getting hot yet, I must be pretty efficient ;-p

Only your wife can tell us that:

Don't lie to us now!

LOL

Refinish King

PS

You didn't walk into that one, you took a bus into that one!

It still is up here in Canuckistan. You can get up to 94 octane which can have up to 10% methanol.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs

It was Citgo in Texas

I work for a big pipeline company. We handle 96 different products coming out of Houston refineries going up the East coast. The only grades of gasoline are regular and premium. Some sub-categories are BP Amoco water white, branded regular, and store brand regular. No mid-grades. The terminal operator who loads the trucks makes the mid-grade by mixing. Sometimes we foul up a batch cut and put some regular in to the premium tank (BIG tank) and the whole tank gets downgraded to regular, but its 95% premium. This does not happen often, every couple months or so.