Unleaded in a car that`s specd for premium.

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• High octane gasoline burns slower than low octane gasoline. The slow burn prevents engine knock when cylinder pressures are high.
I thought high octane gasoline resists pre-ignition better than low octane, not that it burns slower once ignited.
 
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"Burn slower" always meant that the flame front would move more slowly to me. Igniting later wouldn't be burning slower, just burning later.
 
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Originally Posted By: aquariuscsm
*It is normal for an engine to ping a little at full throttle* ^^This. That`s what happens to me,whether it`s premium unleaded or regular unleaded. Just light pinging,no knocking whatsoever.
This is more advice that is HIGHLY platform specific. Many modern cars have the top ring positioned very high up on the piston for emissions reasons. This combined with cast pistons can create a weak spot and it is VERY susceptible to ping damage. I have personally disassembled many engines with severe damage caused by preignition. Most notable was a 78 Pontiac 400 with every single top piston ring in at least 6 pieces and a broken main bearing web in the block! This motor still ran! Just note that some engines are designed to run at the edge of allowable timing and thus can ping a bit under certain conditions. For others it can mean rapid death.
 

aquariuscsm

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I knew a guy who had a 94 TT Z32 (was actually the service manager at the Nissan dealership) and always used regular unleaded,never used premium. Last time I saw him he had a little over 350,000 miles on it!
 
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Originally Posted By: aquariuscsm
My Z is specd for "Premium Unleaded Fuel Only". Last week I accidentally put regular unleaded in it (yeah,I had my head in the clouds!). What`s weird,my car seemed to run smoother and had harder pull and smoother upper rpm acceleration. Seemed to get better gas mileage too. Is premium gas a sales scam? NOTE-I get occasional "pinging" when I shift really hard and put my foot in it,BUT,that happens whether I use premium or regular unleaded. Is this pinging being caused by the ethanol being put into gas nowadays? I also read that using regular unleaded in a car that`s specd for premium won`t hurt a thing (Cartalk.com). What`s everyone`s take on this?
aquariuscsm, My Impala SS is also speced for premium as well. I was told regular can be used but expect different performance habits. Why not just use midgrade instead of regular? Either case your on board computer will make changes on your behalf. Durango
 
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I actually have 350Z finding I was getting hugely inconsistent performance. My hypothesis is premium fuel sits way too long from the very low demand and is getting contaminated with water or oxidizing. I'm an engine designer and at the point where I'm going to buy an octane meter. Ridicules. I've consulted with oil and mining companies and they use a product called fuelflux, and the company is called lubriflux. I apparently aligns fuel molecules and one of the characteristics is increase in natural octane. I bought some from their site and my 350z runs like its angry now. If your engine is designed to run with octane, take advantage of it. Otherwise your building heat and wearing things out fsater.
 
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OK, we have a got somebody who just registered here and touting a product "which aligns fuel molecules". You should know the rest!
 
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Originally Posted By: aquariuscsm
My Z is specd for "Premium Unleaded Fuel Only". Last week I accidentally put regular unleaded in it (yeah,I had my head in the clouds!). What`s weird,my car seemed to run smoother and had harder pull and smoother upper rpm acceleration. Seemed to get better gas mileage too. Is premium gas a sales scam? NOTE-I get occasional "pinging" when I shift really hard and put my foot in it,BUT,that happens whether I use premium or regular unleaded. Is this pinging being caused by the ethanol being put into gas nowadays? I also read that using regular unleaded in a car that`s specd for premium won`t hurt a thing (Cartalk.com). What`s everyone`s take on this?
Don't worry. I've been using mid grade (89) in my BMW for over two years . No problem and no difference in performance that I can tell.
 
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I stopped at the Farley S rest stop on the AC expressway for a full fill up. It's a Sunoco there. When I asked for "Ultra" 93, the gas attendant did a double take and asked again if I wanted Ultra. She said she had not heard anyone ask for anything but regular. I'm not sure how long she had been working, but even if she had just started, it makes me wonder how long premium sits underground.
 
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Originally Posted By: gathermewool
Originally Posted By: SteveSRT8
But back on topic, most folks do not even understand octane. Slower burning/harder to ignite fuel is not always the best fuel. I used to retune vehicles a lot in the 80's to run well on regular, and many times a bit of fuel enrichment was all they needed. Most times we ADDED timing. Talking about tuning across differing platforms can confuse folks, as even the same cars can require slightly different tweaks to run sharp.
Absolutely, but we're not talking about tuning here. We're talking about stock blocks that either recommend or require higher octane fuel. While tuning, both fueling and timing (and valve control and wastegate duty cycle, and etc) need to be adjusted. The first thing most do in turbo Subie tunes is mess with the fueling - stock likes to keep AFR near or just less than stoich even after the onset of boost. Aftermarket or pro-tunes dump it down to ~11-12 quickly and keep it there. Tip-in enrichment is important, too, to combat exactly what the OP seems to be experiencing. Add a little more fuel and maybe take away some timing and no more pinging. Outside of tuning for fuel, a fuel suited to your stock requirements, even if only recommended, is what should (not shall) be done (I.e., running 93 octane in an engine that recommends 91 octane is a waste of money if 91 is recommended; however, 93 is just fine if 91 is required, and the stock tune is known to be aggressive - my STI, for example.) In the end, use what's required or recommended. You're doing yourself ZERO favors by using a lower-than-recommended octane. Unless you've got an old iron block, like the OP, or a motor known for taking abuse and low octane without spinning a bearing or damaging pistons, then run the required octane. Even if you drive gently and mostly highway, where the higher octane may provide no benefit, the first time you get on it, which we all do, damage may occur. It's as simple as that.
^ This. Everything else is falsehoods grin
 
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And like I said, no mfr would spec a higher and more expensive octane for no reason. They would always prefer [for a bunch of reasons] to spec the lowest octane. But they don't. Why? Because the extra octane is needed. Maybe sometimes for certain conditions, but it IS needed.
 
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Yeah, I certainly wouldn't drive a turbo'ed car on regular gas an expect to get anything but alot of timing pulled along with boost to compensate...and therefore less performance. Theoretically you can but if you're doing that why the [censored] did you buy a turbo sportscar in the first place?
 
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