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Old 05-06-2008, 01:14 PM   #41
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Higher octane fuel has less total energy than lower octane fuel. It is not a "better" product,..
Agreed.

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with a set of engine parameters it will produce less HP and lower gas mileage.
Sort of. If those 'engine parameters' dictate high grade only, you need to use high grade. If it is designed for low grade, then yes, high grade will give lower mpg.

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What it [high grade fuel] IS good at is lowering the tendency to detonate prematurely in an engine with higher compression ratios and/or higher heat in the combustion cylinder. That stability is gained through a loss of total energy during combustion.

Some engines will adjust the engine timing to reduce detonation if its detected, so you can use lower octane fuels. The retarded engine timing also reduces mileage and any detonation or knock (which may be undetectable to the ear) can damage pistons and valves.
Exactly - and this is why some say that in a car designed to take a range of fuels (many of today's vehicles), high grade may improve mpg - because it can adjust the timing for better efficiency.

My guess is that if you drive conservatively anyhow, you will rarely hit those times when the engine needs to retard the timing to avoid knock (normally only under hard acceleration). So I also guess that high grade won't help conservative drivers get better mpg, but it may be possible.


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Its highly advised that you use the fuel octane the manufacturer recommends. This is also a really bad place to try and save some money.
Yes, don't try a lower grade unless your manual says it is OK, like I said.

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Seems theres some misinformation on octane being thrown around.
Where was the misinformation on octane? I missed it.

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Old 05-06-2008, 01:16 PM   #42
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My smile-age is way up though, and i consider the chip to have been one of the best things done for the car. Performance is much improved at all RPM ranges.
Do these still meet EPA regulations for emissions?


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Old 05-06-2008, 01:18 PM   #43
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It's not worth an extra 5 MPG to significantly increase my chances of plowing into the back of an 18-wheeler. I don't care how much gas costs.
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Old 05-06-2008, 01:27 PM   #44
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Is the maximum PSI printed on the tires themselves an unsafe pressure? Would that PSI cause uneven wear on the tires, does anyone know?

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No, the max is okay.
Leonidas, are you certain that is good information?

The way I look at it - the tire is one component; the car, it's weight, suspension, etc, are others that make up a system. I don't think it is correct to take one specification of a component, and assume it is good for the whole system.

Car suspensions are designed with the PSI that is on the sticker. Going beyond that range may not damage the tire, but it could adversely affect handling of the car, and make it less safe. I wouldn't do it unless the manufacturer said it was OK, and I personally think you should tell any passengers that they are in a car that has been modified past it's design limits. Maybe they'd rather walk.

My tires are rated for 170mph - but I doubt my brakes are! And the cylinder head bolts are probably rated to take 200 ft-lbs - but that is *not* the correct torque spec for the cylinder head. I think you are making potentially dangerous assumptions.


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Old 05-06-2008, 02:03 PM   #45
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Overpressure is probably safer than underpressure. I don't have any statistical evidence, but it seems to me I've never suffered overpressure problems. Most of my tire failures in the past have happenned when I hadn't checked the tire pressure in a long time; I'm guessing the tire had too little pressure so the rim scissored it going over a bump.

A larger contact patch will also increase the amount of road debris (e.g. nails) collected by the tire. Also a large floppy contact patch has a tendency to work debris into the tires, whereas a small taut contact patch has a tendency to push debris away.

The right amount of pressure is the amount that causes even tire wear... the environmental and monetary costs of replacing tires early are not worth any gas savings that might accrue from hyperinflation. I measure my tread depth (center and sides) every time I get an oil change with a $2 gauge, so I know that my 42psi gives more even wear than the 33psi manufacturer recommended pressure.
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Old 05-06-2008, 02:07 PM   #46
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The right amount of pressure is the amount that causes even tire wear... the environmental and monetary costs of replacing tires early are not worth any gas savings that might accrue from hyperinflation. I measure my tread depth (center and sides) every time I get an oil change with a $2 gauge, so I know that my 42psi gives more even wear than the 33psi manufacturer recommended pressure.
The manufacturer of the vehicle may be making recommendations based on the smoothest ride, not necessarily what's necessary for the rest of the vehicle to perform as it should.
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Old 05-06-2008, 02:33 PM   #47
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Originally Posted by ERD50 View Post
Do these still meet EPA regulations for emissions?


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Some chips do, some don't. As i understand it going through the testing is very spendy, so while some aftermarket chipped cars may post better scores for emissions than stock chips they may not have undergone testing for all states. Superior power, tractability, emissions numbers, and fuel economy is achieved with better fuel maps, the chip taking readings of all the different sensors that give inputs for adjusting timing and fuel pulses more frequently, and tightening up the tolerances on timing for instance. BMW-wise I think Conforti is 50 state legal, Dinan is legal in California, DaSylva is not legal in California. I run DaSylva cause it has better dyno performance throughout the rpm range. California residents who happen to have left a DaSylva chip in their E30 have passed smog tests with super numbers. Good enough for me -
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Old 05-06-2008, 03:16 PM   #48
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But you have to be going 180mph to draft off a car.
I personally just go to the truck stops and chain my vehicle to the semi's rear axle while the trucker isnt looking.....if you use a long enough chain, you have plenty of breaking distance....
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Old 05-06-2008, 03:23 PM   #49
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Leonidas, are you certain that is good information?
Multiquote is not working for me today, so you'll have to go back to the first page of the thread to see my original post where I said overinflation was not a good idea due to handling, safety and wear issues.

I am certain that inflation up to maximum PSI is okay for tire wear, but that you have to fill them cold and be aware of temperature changes from environmental factors to avoid overinflation.

You are correct that almost everybody should run their tires at the recommended PSI (look in the owner's manual). Personally, I tune my tire pressure by adjusting it by a few PSI at a time until I find the spot where ride and handling feel right. It's usually very close to what the recommended PSI is. A couple of pounds of pressure difference can make a vehicle feel and act very differently.

However, when I was w*rking I usually kept my tires at, or very close to max PSI. It significantly improved handling, but I felt every little bump in the road. It also tended to track along with grooved pavement (not a good thing to have happen in curves at 140). But we ran V or Z rated tires and I also had lot of training and experience in how far I could push the car at different speeds and with that much inflation in the tires.

I have blown whole tires stores full of sidewalls over the years, but those all were because I got overly aggressive in a turn and my apex point was a curb that I kissed a tad too hard. The only negatives that I ever worried about were that tires with high inflation can break free from the pavement if you push them hard enough, and (I believe but can't prove) that they tended to hydroplane easier. The first wasn't too big of a problem because you had to be really aggressive in shifting weight around to make them break free - like a J-turn - and there were times when I needed to do some of things I could do when I aggressively shifted the car around and made the tires break free - like a J-turn. The hydroplaning thing scared the crap out of me though, and if it was raining I usually dropped the pressure down a couple of PSI at a time until I felt comfortable pushing the car a little.

I see your points and agree, although I think that anyone on this forum who is looking to boost gas mileage while talking about "imagining an egg on the accelerator pedal" is very unlikely to get themselves into trouble by riding on fully inflated tires. And if they are, then they probably aren't paying attention to anything I say about tire inflation - or saving gas.
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Old 05-06-2008, 03:55 PM   #50
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[quote=cute fuzzy bunny;653748]
Some engines will adjust the engine timing to reduce detonation if its detected, so you can use lower octane fuels. The retarded engine timing also reduces mileage and any detonation or knock (which may be undetectable to the ear) can damage pistons and valves.
quote]

Yes... I have a car that 'requires' 92 octane... but it says you can get by with 87... but reading up on the results, it retards the timing and whatever else it does and the HP is lower and also the MPGs are lower...

And my thought.... if you paid a bundle for a car that NEEDS high octane then why cheap out and buy low octane fuel Decided upfront what grade gas you want and buy a car that uses it...
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Old 05-06-2008, 04:01 PM   #51
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Believe it or not, that was a deciding criteria for a car I bought. I had it down to two that I liked about equally and couldnt make up my mind. One took regular, one took premium.

So I bought the one that took regular.
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Old 05-06-2008, 04:48 PM   #52
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re - ERD50 earlier post...

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Originally Posted by Leonidas View Post
so you'll have to go back to the first page of the thread to see my original post where I said overinflation was not a good idea due to handling, safety and wear issues.
Sorry, you're right - I missed it as we were on page 2 already.

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Old 05-06-2008, 06:33 PM   #53
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I've agreed with the consensus here on most things, but I noticed one person mentioned the cost of wearing out my clutch. If someone could expand on that, my thought was when I have a downhill on the freeway I can push it in and ride for the 1-2 minutes at 800 rpm instead of 3000+ and save gas that way, and it would not be that many more gear shifts a day. Would that really shorten the lifespan of the clutch?
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Old 05-06-2008, 06:51 PM   #54
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I've agreed with the consensus here on most things, but I noticed one person mentioned the cost of wearing out my clutch. If someone could expand on that, my thought was when I have a downhill on the freeway I can push it in and ride for the 1-2 minutes at 800 rpm instead of 3000+ and save gas that way, and it would not be that many more gear shifts a day. Would that really shorten the lifespan of the clutch?
I doubt it. But it could shorten your lifespan, as freewheeling down a hill get can hairy. Also, on a steep hill you likely would have to ride your brakes to stay anywhere near the speed limit. In any case, you are not saving much gas, as the engine is running on a closed throttle anyway.

In WW2 gasoline was rationed, and people frequently did stunts like this. Overall a bad idea IMO. Also, a real PITA to other drivers.

Ha
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Old 05-06-2008, 07:08 PM   #55
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Re drafting behind a semi on the highway--wouldn't that hurt the semi's MPG to be pulling you along? I could see some sudden stops on the truckdriver's part to deal with that problem....
No, because you are in the air the semi already cleared. (which is a super simple explanation)
The only important thing is whether the (beer drinking, speed-taking, hairy-knuckled, pot-bellied, shaver-challenged) trucker thinks you are hurting his gas mileage.
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Old 05-06-2008, 07:17 PM   #56
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Hypermiling is crazy. Millionaires trdading a marginally increased gas mileage for an increased risk of death is not smart.

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Old 05-06-2008, 07:25 PM   #57
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Go Dale Go!
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Old 05-06-2008, 07:35 PM   #58
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Was he drafting when he bought it?

ha
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Old 05-06-2008, 07:40 PM   #59
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Dale Jarett? Nah just a UPS commercial. Hes retiring this year. He hasnt bought it yet. The whole drafting thing reminds me of Nascar something fierce...
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Old 05-06-2008, 08:10 PM   #60
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I've agreed with the consensus here on most things, but I noticed one person mentioned the cost of wearing out my clutch. If someone could expand on that, my thought was when I have a downhill on the freeway I can push it in and ride for the 1-2 minutes at 800 rpm instead of 3000+ and save gas that way, and it would not be that many more gear shifts a day. Would that really shorten the lifespan of the clutch?
I'd say that in your neighborhood there's about a 1/365 chance of hydroplaning every year during the annual 90-minute rainstorm.

Overinflated tires-- bad tread wear patterns. There's also no forgiveness if you hit a bad pothole or scrape a curb or hit a patch of standing water. But as Leo says, right up to the upper limit of the tire is fine.

If you're going downhill with your foot pushing the clutch in, that's considered more wear than if you put it in neutral and take your foot off the clutch. It has to do with which parts stay spinning when the clutch is pushed in. But many manufacturers have changed their clutch designs in the last decade, so I'm gonna have to defer to a Volvo expert on that one. Hmm... strange... Andy doesn't seem to have acquired a Volvo board yet.

During my working days when I bicycled home from Ford Island, the causeway runs northeast-- right into the $%&ing tradewinds. It used to take me nine minutes of max effort to cross the 1.5 miles of road before I could turn Ewa-bound. However if I could happen to pull right behind one of the departing trolleys from the USS MISSOURI Memorial (with just a foot from my front tire to their rear bumper) then I could draft the causeway in under three minutes with very little effort. I got good enough that if I backed more than two feet away from the rear bumper, I could feel the back of the slipstream's turbulence start to tug. (Luckily the passengers never thought of throwing things or spitting over the back bumper. They'd just smile & shaka.) So to get the max advantage from a truck draft you'd have to be within three feet. They drivers wouldd probably never see you in their mirrors, so they'd never feel you slide under after they hit the brakes.

I think your best results would come from driving 55 MPH. Of course every other car on I-15 would ram you from behind, but you'd get great gas mileage from their pushes...
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