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Old 06-04-2005, 06:03 PM   #1
abq focus
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Focus Needs Higher Octane At High Elevation?

The owners manual states you must run at least 87 octane in the Focus even at higher elevations like our 5300 feet above sea level here in Albuquerque.

Our problem is the state of New Mexico rates it fuel "One" full octane grade lower than the "Flat-landers do. Our regular is 86 octane so I must by the middle grade which is 88 octane in order to comply with the Ford requirement of 87 octane.

Now I read this from a thread below and it sounds like the cars computers are suppose to compensate and lean out the mixture so that the higher octain is not need here at high altitudes.

http://chemistry.about.com/gi/dynami...com/octane.htm

I know when I flew my Cessna that I would lose aprox one inch of manifold pressure for each 1000 feet in elevation which means that I would never see my max horsepower or rpm because the egine just could now pump enough air into the cylinders up here. I would expect the car engine is the same. That would mean that I would only be seeing aprox 97.5 horsepower max out of the ZX3 engine if I ran it at full power (130 hp x .75 (max hp at alt) = 97.5 hp.

If I am not going to get close to max horsepower here at high altitudes, why does Ford insist that we run 87 octane. Have they given the Focus a dumber computer that cannot compensate for the altitude?

Terry


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Old 06-04-2005, 09:24 PM   #2
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I'm sure the computer does compensate for altitude. The knock sensor might hear a ruckus going on and cause the computer to retard the timing until it quiets. Of course, that would impact your performance. Also, the MAF sensor plays a big role.

Why don't you try a tank of the highest octane gas you can get, and see if there is any difference.

At any rate, I don't think you're losing as much HP as you think. How would you get over a 10,000 ft mountain pass? Get out and push? With the trucks, we figure about 2% per 1000 ft., but in reality, it's hardly noticeable. What you maybe don't realize is that all foci are as slow as yours, even at sea level.
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Old 06-04-2005, 10:37 PM   #3
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I live in Alamogordo, NM and I did notice a bit more punch in my engine when I went back home to Alabama for two weeks. The altitude does have some effect on performance, but I honestly don't think higher octane gas is going to help much.
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Old 06-04-2005, 10:54 PM   #4
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I have an SVT and let me tell you, this altitude is killer on the engine. The computer cannot compensate for the altitude because the air is thinner up here. No computer can make the air thicker (denser) so you lose the related hp associated with the thinner air. Less air means less gas which means less ignition which means less power. I hear FI can compensate because it can compress the air that you loose but unfortunately, we don't have a turbo or supercharger. Good news, better gas mileage because you use less fuel/air. Here's a link to an altitude calculator you can use to see how much power you lose. It has a few other neat calcs too. Check it out:

http://www.wallaceracing.com/Calculators.htm
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Old 06-05-2005, 01:06 AM   #5
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Running the 130 bhp through the calculator shows a net loss of 20.67 hp because of the altitude. Factor in the "density altitude" (pressure altitude corrected for temperature) and the 5300 elevation of ABQ can now be 8,000 feet plus on a 90 degree day. Now the Focus losses a little over 30 hp when the temp gets hot as it does out here.

Some years ago I had a Chevy Cavalier with what ever the 4 cylinder engine the factory put in. I took a trip to the flat lands (Dallas) and I thought the car had a V-8 because I had so much extra pep even with the air temp in the high 90s. That was because the air was more dense at lower altitude. I seem to remember that the lowest octane fuel was 87 and it was called regular.

Here in the ABQ area, we have to run that reformulated fuel in the winter to control the smog. That fuel has less BTU (burns with less energy) and thus causes the mileage to drop 1-2 mpg. Instead of messing with the quality of the fuel, we need to insure the engines are burning it more efficiently.

While stationed at Luke AFB in Phoenix AZ, in order to get non-resident license for my New 1977 F-150 4X4, I had to get it smog inspected. The truck with less than 5,000 miles on it barely passed the first year I was there. The second year it failed big time and I had to try and get it tuned up to pass the test. If you failed to meet the specs the second time and could prove you spent at least $50 to correct the problem, AZ would give you a waiver to get your plates. The third year I took the truck back home to Ft Wayne IN and had some performance parts put on the truck. They were an Eddlebrock aluminum manifold, a Holley 4 barrel, and a Morroso racing air filter. I already had headers on the truck and guess what. That 351M motor now ran like a 428 Cobra Jet.

Playing on the sand dunes in upper Michigan, I now could go places at almost an idle compared to having to rev up the motor when it was in stock factory form. The hill east of ABQ and Clines Corner is a long winding grade that gets you up over 7,000 before you reach the top. Before the truck was modified, I would go over the top of the hill in 2nd or 3 gear (manual tranny). After the mod, I could stay in 4th and even accelerate going up the hill. Finally, when I took the truck in for the annual smog test in Phoenix, the tech had to run the test several times because my emissions coming out were almost non registering on his machine. He asked to pop the hood and when he saw the new goodies he asked if I paid to have it done and I said no. I told him my cousin did it in his driveway. Seems it was against the law to pay someone to remove the smog equipment back then. I was getting better mileage and a lot more horsepower after the mod and was putting out a whole lot less pollution. All I did was to let the engine which is just an "Air Pump" breath and work more efficiently. We did not have fancy computers and fuel injection and yet we seemed to have the best of both worlds. (Performance and clean burning engines) Why can't Detroit and Japan do this today instead of making the vehicles so complicated that you need a computer science degree just to diagnose you need to fill the windshield fluid bottle?

Stop messing with the fuel octane and just let the motors breath.

Terry

PS: Thanks for the performance links.
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Old 06-05-2005, 01:07 PM   #6
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"why does Ford insist that we run 87 octane."

K.I.S.S.

I suppose they could say something like "if you are at elevations above x,xxx feet you can use gasoline with an octane 1 less than we recommend, as long as you do not plan on driving to a lower altitude while that fuel is in the tank. Pleas ensure that you use all of the lower octane gasoline before traveling to a lower altitude."

Or they could just say "Use 87 Octane."

They chose the latter.

Considering the variation in octane needs of engines due to manufacturing tolerances, variation in octane formulations of gasoline, and carbon build-up over time, I doubt a one octane difference will have any impact at all, particularly on a low mileage engine.
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Old 06-05-2005, 02:42 PM   #7
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octane won't give you hp. It allows you to do things to the engine to increase hp without detonation. By being at high altitude, your effectivly taking away performance, so higher octane could actually make it worse.
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Old 06-05-2005, 09:09 PM   #8
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"so higher octane could actually make it worse."

Exactly how could higher octane make it worse? I would be interest in the mechansim that would explain how a higher resistance to pre-ignition would have any possible negative effect on performance.
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Old 06-05-2005, 09:42 PM   #9
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Yeah, with higher octane the computer wouldn't have to retard the spark as far and you would think you'd get better performance.

By the way, the 2% loss per 1000 ft is indeed with a turbo, a little detail I forgot about.
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Old 06-05-2005, 09:55 PM   #10
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"By the way, the 2% loss per 1000 ft is indeed with a turbo, a little detail I forgot about."

Yes, a turbo is a great way to compensate for altitude, which is why they are good for aircraft.
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