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Old 07-07-2011, 09:09 AM
 
14,780 posts, read 35,982,514 times
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Quote:
Originally Posted by Drover View Post
It's also worth noting that in order for a car's computer to dial back the timing and/or enrich the fuel mixture to prevent knocking, it has to have detected it in the first place -- in other words, knocking has already taken place and the computer is compensating to ensure it doesn't keep happening. But, it's already happened.

If your car calls for premium, use it.
Very good point. Knock has to happen in order for it be detected and compensated for. You are causing damage everytime it happens.
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Old 07-07-2011, 02:23 PM
 
Location: Santa Monica, CA
1,626 posts, read 3,272,553 times
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Wrong, the engine computer is taking readings hundreds or thousands of times a second. You don't need to worry about damaging a modern engine with 87 octane gas.

My BMW 330 had over 100k miles when I sold it and it saw nothing but 87 octane.
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Old 07-07-2011, 03:28 PM
 
8,402 posts, read 20,336,309 times
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Quote:
Originally Posted by whiteboyslo View Post
As long as the knock sensor can pull enough timing to compensate, you'll be fine. However, if it can't, you'll be exposed to the wonderful world of pre-detonation, burnt valves, and all the other fun stuff that comes along with running crap gas in a higher-compression engine. Unless you're already completely familiar with the basics of an internal combustion engine, gasoline octane, and how the two correlate, I would suggest reading up on it. Not only will you come to understand why putting lower octane fuel in a car that requires it is bad, you'll also learn why putting higher octane in a car that doesn't require it makes no sense, either.

I'd agree that spending that kind of money on a vehicle seems rather pointless if you have no intention of following through on the basics. And aren't you the one who started a thread on whether a warranty on an Acura is worth it? Put it this way: if you ever have problems with the car related to the damages associated by running lower octane, you won't have any leg to stand on when they deny the warranty claim.

Mike
This is my understanding from anything I'd consider to be a reliable source.

I had to run regular in my GTO for a week during Katrina's aftermath, and the power was down quite a bit. The engine didn't feel "right"; like I was pulling a trailer.

Lower MPG also come about due to the driver pushing on that go pedal harder to compensate for the loss of power.


EDIT-I found this forum entry while looking for info on the subject:
May 01, 2006 (1:49 pm)

I emailed BMW and asked them if it was ok to use 87 octane, they responded with the following reply:

Thank you for contacting BMW of North America, LLC regarding fuel for a new BMW 3 Series. We are happy to address your query.

BMW recommends premium gasoline with a minimum octane rating of 91 AKI. Our BMW engines are equipped with knock sensors and will adapt automatically to different octane ratings, provided the minimum octane requirement (87 AKI) is met. Fuels with higher octane ratings will provide
enhanced performance with lower fuel consumption; however, fuels with lower octane ratings will have the opposite effect.

I have had the car for two month now and have never used premium fuel. I get 30 mpg on the highway and i have been averaging 25.5 mpg overall.

I have plenty of performance, this car screams! Best car I have ever owned (325xi)!


The guy bought a performance car, and never even tried to see what the recommended fuel would do for performance and economy. I don't understand that mentality. That is simply pathetic. He should have just bought a 318 and saved the difference.

Last edited by vmaxnc; 07-07-2011 at 03:37 PM..
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Old 07-07-2011, 04:23 PM
 
Location: Maryland Heights, MO
3,293 posts, read 6,998,627 times
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Yeh, VW/Audi require premium, especially in their turbo motors. A kid trusted his dad who said "it doesn't need premium, that's just what it says in the book" he then took his GTi and added a full tank of regular to it....within a day or two he had holes in two of his pistons from the detonation. You might get away from it on a naturally aspirated vehicle, but i'd be very leery of it if you had a power adder of any type.

Wouldn't really call a 325xi a performance car. It's a nice sports sedan though. Had he really been interested in performance, than he'd have been looking for a 328xi, 330xi, or a 335 Depending of course on what year bimmer he was looking at
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Old 07-07-2011, 10:59 PM
 
Location: Santa Monica, CA
1,626 posts, read 3,272,553 times
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Quote:
Originally Posted by flynavyj View Post
Wouldn't really call a 325xi a performance car.
Not to mention the 318 wasn't being sold by BMW in The States in 2006.

BTW, it's doubtful you'd do damage to a late model turbocharged engine with regular fuel. But forced induction engines are one of the few engines that really take advantage of premium fuel. Here's some interesting reading for those of you convinced premium makes any difference in performance.

Regular or Premium? - Feature - Auto Reviews - Car and Driver
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Old 07-07-2011, 11:30 PM
 
Location: Chicago
38,690 posts, read 89,169,700 times
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Quote:
Originally Posted by Dunbar42 View Post
Here's some interesting reading for those of you convinced premium makes any difference in performance.

Regular or Premium? - Feature - Auto Reviews - Car and Driver
Uhm... neglecting the fact that this article is 10 years old, best I can tell it supports the proposition that premium makes a difference in performance. The relevant portion:
"The results were more dramatic with the test cars that require premium fuel. The turbocharged Saab's sophisticated Trionic engine-control system dialed the power back 9.8 percent on regular gas, and performance dropped 10.1 percent at the track. Burning regular in our BMW M3 diminished track performance by 6.6 percent . . ."

Furthermore, the article doesn't even attempt to answer the question about the effect on fuel economy, which is really the bigger issue for the OP.
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Old 07-08-2011, 12:16 AM
 
15,924 posts, read 17,411,425 times
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As an owner of a 2005 Acura I'll tell ya right now the car gets worse gas mileage and performance suffers.

I tried one tank of the medium priced gas, will never do it again.
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Old 07-08-2011, 05:11 AM
 
Location: Earth
4,227 posts, read 21,091,729 times
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Quote:
Originally Posted by Drover View Post
It's also worth noting that in order for a car's computer to dial back the timing and/or enrich the fuel mixture to prevent knocking, it has to have detected it in the first place -- in other words, knocking has already taken place and the computer is compensating to ensure it doesn't keep happening. But, it's already happened.

If your car calls for premium, use it.
Excellent post, as well as NJGoats post.

In short, detonation in an engine is bad...bad...bad.

Detonation is basically a sudden spike in cylinder pressure. That alone can and will cause blown head gaskets. It also causes the rods to hammer on the crank and bearings. The pistons also take a beating. In short you can actually blow an engine due to too much detonation. That's blown as in "shiny metal parts being ejected from under the hood".

And as posted the knock sensor is really nothing more than a microphone that "hears" what it thinks to be knock, and then translates that to the ECM to pull timing. However once the knock sensor picks up knock, if it really even is knock (they can pick up "false knock" too), it's already happening, as posted.

So one must ask himself is it really worth saving $3-$4 a tank to fill up with 87 as opposed to premium?
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Old 07-08-2011, 06:00 AM
 
Location: Suffolk County, NY
874 posts, read 2,489,694 times
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Quote:
Originally Posted by Drover View Post
It's also worth noting that in order for a car's computer to dial back the timing and/or enrich the fuel mixture to prevent knocking, it has to have detected it in the first place -- in other words, knocking has already taken place and the computer is compensating to ensure it doesn't keep happening. But, it's already happened.

If your car calls for premium, use it.
I also agree with this being an excellent post. The 2009 Acura TL has a 11.2:1 compression ratio. That is high compression and although the sensors will try to compensate for you using lower octane fuel, you are bound to get detonation at some point using lower octane fuel and not high octane fuel.

I would also think that there is a good chance your vehicle is still under warranty since it is a 2009 and I am pretty sure you would not want any engine damage caused by pre-detonation due to low octane fuel to occur, take it to a dealer and have them tell you that they are not honoring the warranty since they can tell you have been using lower octane fuel than that which the vehicle calls for.

Pre-detonation is a condition in which the fuel in a cylinder detonates before the piston reaches TDC (top dead center). This means that the piston is still moving upwards when the fuel detonates. This puts a tremendous amount of stress on the piston, piston rods and crankshaft. I have seen this condition ruin pistons, valves, piston rings and in extreme cases, even bent piston rods and cracked engine blocks. This condition can also cause the piston to rattle back and forth in the cylinder which can eventually cause the cylinder to become slightly out of round. The tolerances of the piston rings to the cylinder walls are very precise and being slightly out of round can cause a gap between the cylinder wall and the piston rings which will cause a loss of compression in the cylinder. An engine needs compression to run.

Although the computer will adjust the timing to try and overcome this condition, it can only compensate so much. As the post I quoted above states, some pre-detonation will occur before the vehicle does adjust the timing. Saving a few dollars at the pump is not worth the chance and cost of premature engine failure.
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Old 07-08-2011, 06:56 AM
 
3,673 posts, read 4,931,180 times
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Quote:
Originally Posted by Drover View Post
Uhm... neglecting the fact that this article is 10 years old, best I can tell it supports the proposition that premium makes a difference in performance. The relevant portion:
"The results were more dramatic with the test cars that require premium fuel. The turbocharged Saab's sophisticated Trionic engine-control system dialed the power back 9.8 percent on regular gas, and performance dropped 10.1 percent at the track. Burning regular in our BMW M3 diminished track performance by 6.6 percent . . ."
Furthermore, the article doesn't even attempt to answer the question about the effect on fuel economy, which is really the bigger issue for the OP.
actually no. it's not. What i meant was that i don't mind losing performance (a few HP), but if i lose enough MPG, then it might not make sense. (ie. if i lose more in MPG than what i'm saving by putting regular, then what's the point?)
I care mostly about 'hurting' the car's engine.....i'd like to avoid that.....but i'm not going to blindly accept what the 'manual' says. some folks here brought up some points that make it more logical to put in Premium though.
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