Octane level

putting

With my 1997 ES, that's probably true. I drove 70,000 miles on 87 octane and it never bothered me that I was sacrificing some performance for economy.

But with the 2004 ES, there's a noticeable difference. You'd lose that bet.

Runs smoother (less vibration) and quieter, too.

$2.35/gallon.

Your math is off. Premium is costing you 12.75 cents per mile and regular is costing 12.37 cents per mile. You've got your fractions inverted. :-)

Another way of looking at it is that your paying 8.5% more for premium (2.55 vs. 2.35) and getting 5.3% better mileage (20 vs.19).

So, the net cost of premium is about 3.1% more than regular. Another way of stating it is that premium is costing you $2.42 for the amount of miles that $2.35 worth of regular gets you. All this assumes that your estimate of one additional mpg (20 vs. 19) is accurate. If we had a more accurate measure of the mileage improvement we could refine these figures.

In any event, it appears that much, but not all, of the additional cost of premium of paid for by an increase in mileage.

Oops! Your calculations are correct. IMO, the differences in cost and mileage are little enough that it is still a wash.

If we assume, as you stated above, that premium will yield one additional mile per gallon, then the net additional cost for premium gas is about 0.38 cents per mile. Assuming 10,000 miles a year that's an annual cost of $38.

I agree that it's well worth it for the additional performance, smoothness and quiet that I've noticed with premium gas in my 2004 ES. Not to mention that it's better for the engine to run the fuel it was designed for.

On Tue, 28 Feb 2006 17:43:11 -0500, "David Z" graced this newsgroup with:

I'm curious why your car runs quieter? If it's knocking because of a lower octane level, you need to have the knock sensor looked at.

The ping may still occur at initial throttle and then the knock sensor does it job and retards the timing. More noise may also be created by the engine working harder than it should.

A human mind is very powerful. If you think it's good, it will be no matter what!

On Tue, 28 Feb 2006 23:00:23 -0500, Viperkiller graced this newsgroup with:

..actually, as I understand it. The knock sensor doesn't do this every time the throttle is pressed. Once the knock is sensed, the computer adjusts the timing to retard detonation and it *stays* that way until the engine is turned off.

As far as more noise because the engine is working hard, there isn't THAT much of a torque and/or horsepower difference to make an appreciable difference in rpm, which is the ONLY thing you would hear if the engine was actually working harder.

Personally, I think it's smoke and mirrors. If you *think* you're getting better mpg and hp, you'll convince yourself that the car is performing better. The *only* way to correctly test it is to put it up on a dyno.

I've run as low as 87 octane in my LS430 and the mpg and performance has not been noticeably different than at 91 octane (in routine around town driving). Having said that, , I purchased a $50k car, I'm not about to deliberately try and save a couple of bucks in gas. If I can't afford the higher octane fuel, I shouldn't of bought the car.

No dispute on when the knock sensor works. I merely mentioned that ping normally occurs at initial throttle where the engine gets it's greatest load.

I'm certainly in agreement with you there. I've always contended with others (including in this newsgroup) that people shouldn't buy a Lexus and be cheap on fuel. If they wish to curtail their spending on fuel, they should purchase Toyotas instead.