High Octane/Low Octane

[knightbr]

I have seen a couple of posts about how high octane gas does not make a difference if your car is not built for high octane.

I personally have noticed a difference on my 00 rolla, it has a bit more pep to it. So my question is does anyone have any links to sites that confirm/deny the benefits?

[Chris Corolla S]

The octane related thread in the hardcore forum says it all.
It's not something that needs to be confirmed or denied, how octane works in fuel is a fact.
There is two reasons you might feel a gain.
1) It's totally psychological
2) Your car needs a tune up.

Higher Octane does one thing, it prevents spark knock.
The 1zz-fe has 10:1 compression, which is high, but the cylinder head is specially designed to combat spark knock so that it runs perfect with 87 octane. You would not get any more power from higher octane. If the engine was re-designed to have even higher compression and produce more power, you would need higher octane.

[knightbr]

Cool thanks.

[RedAE102]

Many cars can have a very slight (usually not very detectable) improvement in response from premium fuel, as long as the car is capabale of that sort of ignition timing advance. This is only in partial throttle (closed loop mode) situations. Under full throttle (open loop mode), there won't be any sort of gain, because it tends not to read some of the sensor info under these conditions.

Now, putting regular 87 in a car made for a minimum of 91, there is usually a very noticeable difference, and you wouldn't even want to do this in a car without knock sensors. My '96 LS400 is plastered with PREMIUM UNLEADED FUEL ONLY, and I've been running regular old 87 octane petrol in it (hard to justify $2.50 per gallon for premium) for a few months now without a hint of knock from the thing. There has been an appreciable loss of power under load, but not enough that I'd consider putting premium in it. Gas mileage hasn't suffered at all either.

[Chris Corolla S]

"Many cars can have a very slight (usually not very detectable) improvement in response from premium fuel, as long as the car is capabale of that sort of ignition timing advance"

1) in 98-00 Corollas The 1zz-fe has no VVT-i

2) If it did have vvt-i like mine, and the vvt-i is programmed to make max power at maximum advance or whatever with 87 octane, how is it going to advance the timing further just because you put 89 or 91 octane in it?
It seems like you are saying that peak HP is unaffected but you would somehow gain more mid-range power? I don't see how this can happen.

[Hatch]

My Corolla XRS says to use premium and i have used everything regular - mid - premium with regular it is very sluggish and gets HORRIBLE gas mileage and with the premium it ends up costing me less because of the additional mpg and improved performance.

Jeff

[Rolla97]

if it does not need Premium, dont use it. Premium is needed in F/I or Hi compression engines to prevent detonation, simple as that.

[RedAE102]

Originally posted by Chris Corolla S
"Many cars can have a very slight (usually not very detectable) improvement in response from premium fuel, as long as the car is capabale of that sort of ignition timing advance"

1) in 98-00 Corollas The 1zz-fe has no VVT-i

2) If it did have vvt-i like mine, and the vvt-i is programmed to make max power at maximum advance or whatever with 87 octane, how is it going to advance the timing further just because you put 89 or 91 octane in it?
It seems like you are saying that peak HP is unaffected but you would somehow gain more mid-range power? I don't see how this can happen.

Well, first of all, I said IGNITION timing advance, NOT camshaft timing. Second, '00 Corollas had VVT-i. All cars have some sort of ignition timing advance. Before computer-controlled electronic ignition, cars relied on two types of timing advance, with most cars employing both: centrifugal advance and vacuum advance. I won't get into the nitty-gritty on this... Anyway, most cars, even those with knock sensors, rely on preprogrammed ignition maps under full throttle, and ignore sensor input until there is a problem. This is called open-loop operation. Under most other conditions, e.g. partial throttle, it runs under closed loop operation, in which all sensors are input. Basically, the ECU does not try for optimum spark advance under full throttle, but it can still cut it back if needed, while it's constantly adjusting under partial throttle.