Discussion in 'Motor Sports' started by bigmoguls, Jan 23, 2012.
As the title says.
Higher compression ratio needs higher octane to prevent detonation
You might be able to get away with it for a while...but one day the fuel/air mixture will ignite to early because the lower octane level and your engine will go kaput!
you'll notice poorer fuel economy and poorer performance. Highly unlikely to see the engine self destruct, there's enough safe guards in place to help prevent detonation.
Higher grade fuels also sometimes have additional additives to help keep the system clean... but you also never want to run higher octane then your car is designed for. Higher octane fuels have less energy, and will also cause driveability problems.
I can't speak for the Audi, but I have an 07 Acura TL Type S. I have never put regular in. I have read that if you use regular, the computer will adjust for less octane, then you'll get less power and worse gas mileage. So some, maybe most, of what you save at pump will get chewed up on road. If you do put regular in, be sure you are not putting your foot hard into the gas pedal, that will ask for trouble, worst case being what AwPhuch showed above.
here's one decent discussion I just found on the web, has some good points on both sides of the debate:
You are just making it harder on your engine than it needs to be.
With the more modern engines and computer controls, the electronics will adjust timing etc to make the engine run. Your economy will suffer, and as mentioned above, at some point you will start getting detonation and/or fouling.... eventually, it COULD do some damage to the engine.
I had a '03 VW Jetta with the turbo 1.8 and while it called for Premium, I ran nothing but regular unleaded through it 100% of the time. No problems, but mileage did suffer.
If your car is turbo, higher octane is a necessity for it to run without detonating. Of course, if you stay out of boost, youll be fine
Electronic timing will adjust...but it cannot adjust far enough out to prevent damage if it did prematurely detonate..that sound that sounds like marbles rattling around is detonation or knocking..just a little bit more fuel and kaput!
There is not less energy in higher octane fuel..the octane rating is the ability of the fuel to withstand higher compression ratios w/o pre-detonating
I've noticed a fifference in my bike. Been on 89 for a month, and I'm switching back to 91 when I get gas next. Bike ran good for a week or so, but now it seems alittle sluggish. Need to clean my air filter and do an oil change too. I know you didn't ask about bikes, but I do notice a difference in the octane.
I highly reccomend k&n air filters, and amzoil for you speedy guys.
it will run like crap, its only a few dollars difference. dont be a cheap ass haha.
higher octane ratings have lower Btu, that is a fact. Higher octane ratings also have a slower burn, which is why you can increase compression ratio.
researched...agreed (there is a caveat to your theory though)
Simply put: Read the owner's manual. Most newer cars can run lower octane and will pull timing to reduce the chances that detonation will occur. In boosted cars (forced induction), I wouldn't run anything other than the highest octane I can find at a station. If your vehicle can run lower octane, you'll see a penalty in economy. Try it and find out if you can live with it.
Also, keep in mind that altitude changes octane requirements, which is why you'll find 91 octane in CO, and 93 in TX.
Follow the owner's manual. My A4 is premium only. Some cars are 'premium only' and some are 'premium recommended.'
Agreed, you will get a few different problems. Knock and pre-det (same thing for the most part). All newer cars have knock sensors, when they see that the car is knocking, it will in turn, tune for that. It retards timing, adavances fuel as much as it can and it gets you out of knock. You end up lossing fuel economy and your ECU (typically) "learns" this problem and no longer allows for you to get into that knock range, by pre tuning. Doing so can have negative effects if you go back to the fuel you should be using. The ECU takes longer to relearn new fuel trims because the new fuel isn't causing issues. The best way to fix that is by resetting your ECU. Disconnect the battery and press the brake pedal for 30seconds to bleed the caps charge. Reconnect the battery and you are now back into "learning" mode.
Thanks for all the replies. I think we'll stay away from "Premium Required" autos. Don't want to pay the "premium".
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