Mixing gas ok ?

Let me guess...manual boost controller!

CompUser wrote:(clip) ECU responds only post-knock event, so damage could already have been done; (clip) ^^^^^^^^^^^^^ Preignition knock will damage the pistons severely if it is allowed to persist, but it takes time. Since the ECU retards the spark immediately on detection of the "ping," there should be no damage. In a properly timed engine, this should happen only some combination of heavy load, high temperature and lugging. Regardless of what the octane rating of the fuel is, there will not be preignition if these conditions do not exist, so the ignition does no6t retard, and engine efficiency does not suffer.

If your driving is mostly cruising on the highway, or toodling around town at fairly light throttle, the full octane of the fuel is not being used and I don't see why you couldn't blend down to save money. If you drive a lot in the mountains, pull a trailer, or like to accelerate fast, cutting the fuel octane will hurt performance.

I was just courious. I'll stick to the 93, just gonna drive it easier to increase my milage. I'd rather be safe then sorry. My milage is crap, but i do drive it hard and sit in alot of stop and go traffic.

You best hope it's detonation/knock/ping, NOT preignition. They ain't the same animal. And, the "time" it takes for preignition to put a hole in your piston can be as short as single event.

It responds as "immediately" as it can, it's all after the fact.

Totally correct, and where I live, I can't always find 91 octane, only

89 or 93, so if I have a half tank of 93 in my car (and think to remember!) I'll top off the tank with 89 to get a blend of 91. But I won't run my car with anything less than 91 octane for engine reasons as well as the fact that I have noticed slightly better gas mileage with the higher octane.

Remember the water injectors installed as aftermarket devices on motor homes and gasoline powered trucks back in carburetor days?

The injectors mixed a small amount of water into the fuel to prevent preignition. It didn't take long to destroy an engine with preignition.

Barry

I have had great results with "Sea Foam" 1/3rd in the brake booster vacuum line and 2/3rds in the gas tank. TG

Damn, you americans get crap petrol. Here in Aus we get 98 octane... No wonder I get better economy and acceleration than you. but 83 octane? Shit. You must have a lot of engines blowing themselves up due to serious knock problems... even my Toyota would refuse to run on that.

-- mark

98 Starlet Life 1.3 MY02 Forester 2.5XS

I think you guys go by the 'research' method.(hydrocarbon densities or something). We use that number averaged to a 'motor' numbe acheived by actually using a grade in an engine in a lab and measuring the output somehow. Our pumps even list it as RON+M/2 . A pure RON is 'theoretical' and seems inflated. But I suspect you also get a different owner's manual with appropriate fuel recomendations for your region.

What makes our gas 'crap' is ethanol and/or methyl tertiary butyl ether.

Carl

1 Lucky Texan

Mark H wrote:

Yeah, ethanol got the big FO over here not too long back. Part of the reason I switched to 98 for my Starlet... Forester's always been run on it. Bigger outlay, but worth it IMO. Never had the Forester so much as hint at pinging, engine running as smoothly as the day it was bought.... 52,000KM on the clock now.

Starlet picks up a bit of extra power and fuel economy on 98 over say 95 or

91 octane. I reckon an extra 50-100km/tankful is well worth the outlay.

-mark

Hi,

My understanding is many trucking companies have been doing exactly that for at least a dozen years! Stand on the brakes a bit hard cuz some idiot cut the driver off, go a mile over the speed limit, take a catnap after lunch and let the engine idle, then get called into the office for a "chat" kinda stuff drove some of my driver-clients nuts!

Rick

Hi,

I actually think it goes further back... I remember reading car rags in the late '60's-early '70s that mentioned the US being listed as an "inferior" fuel grade country by some German mfrs long before we spiked our "punch" with ethanol or MTBE!

Rick

Hi,

I'd spring for the minimum grade called for in your owners' manual. If the price differential between the lower and right grades of gas for the engine's gonna break somebody, it's probably time they trade their WRX for an econobox...

Rick

Sounds reasonable. Oz fuels I use have the same RON whether 10% ethanol or "straight" petrol - with whatever other additives the hand-on-heart ethanol free brigade have instead! AFAIK 92RON unleaded works out about 93.5 equivalent in real life ping/knock resistance. Still won't use it in stationary engines or fibreglass tank bikes though. No problems in 4 different cars or my old Suzuki 1100 over the last four years except for an inital sacrificial fuel filter. Blending 83/93 still only gives you 88 on 50:50 though. I'd stick with premium for any sort of high stress running - incl. stop/start. Cheers

Here's my experience from Wednesday. Think about it and then you decide. We drove my son's STi from LA to Phoenix to have it dyno-tuned at a particular shop. It had had some mods done to it and needed a reflash as well. We bought some gas in Blyth CA at a Union 76 station. It was labeled 91 octane. On the dyno, the car would barely make 250 hp and it was very sensitive to ping. Given the circumstances, we were advised to refuel with 5 gal of Sunoco 100 octane and up to 9 gal of 91 octane. We did and the car now made

275 hp and the detonation problem was gone. On the way back to LA we filled up at a Chevron station using their 91 octane. We've had no ping or rough running since that refill. So, does the gas matter.....damn straight it does. That crap we bough in Blyth was anything but 91 octane. The WRX and the STi require premium gas...no exceptions. We have to pay $2.60 a gallon for it out here in the People's Republik of Kalipornia. So, buck up me boy and buy the good stuff. The alternative is some pretty heavy negative cash flow after you screw up some pistons and valves.

You got a tank of bad gas. Taht's all. Water, contamination who knows? Try good gas at 87 or 89 at let us know.

From my experience if you get gas from outside the state of California, your engine will run much better. I fill up in Nevada when I am up there and it makes a big difference in how the engine performs.

I think this was black market gas. This was a small station right off the highway and I suspect they ran it on a very thin margin. I should have known better than to buy gas there. In Valencia where we live, I buy Shell, Chevron or Exon and have had no trouble to date. The turbo at 17 lbs boost is really cramming the air in that dinky little 4 banger. Add some heat and if the octane isn't really 91 or better you get detonation.

It doesn't need to be that complicated. If the pump fills the tank slowly the storage tanks are generally nearly empty and putting out some sludge.

Also, several years ago Chevron let out an incorrect blend of gas in my area and *all* the cars that got it wouldn't run and had to get their tanks pumped. It was a fluke.

-John