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Old 03-15-2011, 06:03 AM   #15
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lllkrob, we agree with your position; our Subaru plainly stated that if 'premium' gas was not available regular could be use but for maximum performance to use the high end stuff.
I really think no turbo, no worries at all.
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Old 03-15-2011, 04:58 PM   #16
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Quote:
Originally Posted by lllkrob View Post
As a powertrain systems engineer for a major automotive manufacturer, I can assure you your engine will perform satisfactorily on 87 octane unleaded regular. You may notice a very slight loss in power and mileage but the engine will not be damaged. Today's vehicle engine management systems will re-map all the operating parameters to account for the loss of octane. The premium fuel " requirement " is so the engine will perform at optimum levels and fuel mileage.
I bow to your expertise sir. I posted my experience from nearly 20 years ago. So what you state is: no engine damage can occur from using regular vs premium gas in recent year engines. This means the owners manual can be ignored, right?
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Old 03-15-2011, 05:35 PM   #17
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Originally Posted by lllkrob View Post
As a powertrain systems engineer for a major automotive manufacturer, I can assure you your engine will perform satisfactorily on 87 octane unleaded regular. You may notice a very slight loss in power and mileage but the engine will not be damaged. Today's vehicle engine management systems will re-map all the operating parameters to account for the loss of octane. The premium fuel " requirement " is so the engine will perform at optimum levels and fuel mileage.
I believe that this means the Knock sensor on your engine will automatically retard your spark to elimanate pre ignition. A retarded spark equals no pre ignition, or pinging, which also causes higher engine temps due to the retarded spark. In a RV this means almost certain death to the engine if allowed to continue. Check with the dealer to see if they will honor your warranty under these conditions.
I could be wrong but am always receptive to being enlightened.
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Old 03-15-2011, 05:51 PM   #18
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A retarded spark equals no pre ignition, or pinging, which also causes higher engine temps due to the retarded spark.
Not necessarily. The reason you retard the spark with a "hotter" (e.g., low octane) fuel is because the combustion process with a hotter fuel proceeds more rapidly. The objective is to wind up with the same peak pressure angle (the crankshaft angle after TDC at which peak firing pressure occurs) as you had with the advanced timing and less volatile fuel. If fuel quality remains constant, retarding timing will result in higher EGTs (exhaust gas temperatures), but that's not necessarily the case as you optimize timing for fuel quality variations.

Knocking or pinging, by the way, is due to detonation which involves multiple flame and pressure fronts colliding (i.e., uncontrolled combustion). Pre-ignition is a different combustion abnormality where ignition takes place before the spark plug fires (typically, due to a hot spot in the combustion chamber) and is silent but even more deadly.

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Old 03-15-2011, 05:53 PM   #19
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So, if the knock sensor retards the timing by 2 degrees, and this takes away pre-ignition (ping), my engine is going to run hot? Not in my expierience. Way back, before electronic controlled ignition timing, and engines that had compression ratios above 8:1 and you could buy real gasoline, it was sometime necessary to retard timing a few degrees to eliminate ping, especially in warmer weather. This did not make the engine run excessivly hot. I agree grossly retarded ignition timing does increase the running temperatures. I believe modern day engines with knock sensors, retard timing just enough to keep ping or knock from occuring when conditions that would cause knocking to occur.

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I agree with Rustys definition of pre-ignition, and pinging.
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Old 03-15-2011, 06:54 PM   #20
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So, if the knock sensor retards the timing by 2 degrees, and this takes away pre-ignition (ping), my engine is going to run hot? Not in my expierience. Way back, before electronic controlled ignition timing, and engines that had compression ratios above 8:1 and you could buy real gasoline, it was sometime necessary to retard timing a few degrees to eliminate ping, especially in warmer weather. This did not make the engine run excessivly hot. I agree grossly retarded ignition timing does increase the running temperatures. I believe modern day engines with knock sensors, retard timing just enough to keep ping or knock from occuring when conditions that would cause knocking to occur.

Dieselclacker


I agree with Rustys definition of pre-ignition, and pinging.
Add me also with agreeing to Rusty's definition.
So it looks like we all agree that retarding the ignition will in fact make the engine run warmer. I never said hot, I said warmer with the accompaning reduction in MPG. I also agree that the on board sensors will retard the ignition timing just enough to eliminate pinging. So then, does the loss of MPG make up for the differance in fuel costs ?
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Old 03-15-2011, 07:21 PM   #21
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Clarification this is an 01 with over 100,000 miles so just a bit past warranty. Evidently the wording from Subaru is premium recommended, for the turbo Subes it is required. The H6 is OBD II so I will see how she likes regular and will check with a Ultra Gauge to see what it does to spark advance. the engine is rated at 212 HP and will run out of speedometer at 120 MPH and keep accelerating.
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Old 03-15-2011, 07:24 PM   #22
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Quick ? here.

Quote:
As a powertrain systems engineer for a major automotive manufacturer, I can assure you your engine will perform satisfactorily on 87 octane unleaded regular. You may notice a very slight loss in power and mileage but the engine will not be damaged. Today's vehicle engine management systems will re-map all the operating parameters to account for the loss of octane. The premium fuel " requirement " is so the engine will perform at optimum levels and fuel mileage.
In my mid-sized Toyota SUV (V-8) normally when not towing, I'll use reg. 87 octane gas. No problems...good gas mileage (17 city / 23 hi-way). while towing I'll upgrade to a mid-level octane gas. It will help me achieve a little better gas mileage while towing my 24' tt. Now my thought. My tow vehicle is 6 years old / 38 k miles, and I just had my oxygen sensor replaced for the 2nd time. Do you think switching back and forth between to grades of gas messes the oxygen sensor up?

I have a 7 year extended warranty, but would hate to think doing this is what is causing the OS to fail..
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Old 03-16-2011, 06:25 AM   #23
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shadow, the wording for our '07 XT was premium recommended also.
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Old 03-16-2011, 10:20 AM   #24
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Our Miata's always required premium. Forgot to tell my wife. Found out only by her mentioning about filling up A COUPLE YEARS LATER. Seems like nothing happened to the engine and it was always smoothe running when I would borrow it.
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Old 03-17-2011, 12:50 PM   #25
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It appears to me that the intent of this thread is to reduce fuel costs. It sounds like with the trade offs there is little if any savings. I have been using a concept for about 4 years that is very simple but admittedly difficult. It requires change between the ears. I use as little pressure on the right foot as possible and still keep a reasonable pace. I have found that an easy start from stop will only cost a few seconds and usually (on local roads) I will be behind the car ahead at the next light. I also maintain some distance behind the car ahead to avoid the fast and slow of a lot of drivers. I have checked shift points on my 91 Pontiac. Easy acceleration: shift to 2nd @20, to 3rd @30 and lock torque convertor @40. Approx. Ĺ throttle, shift to 2nd @35, to 3rd @ 65, thatís where I backed off. I donít drive over 60 anywhere. When I see cars ahead stopped/slowed or a light turn yellow/red I will coast down (not out of gear) and many times I wonít need to brake and or stop. I have seen at least 10% increase in fuel mpg in all my vehicles. Thatís about $.40 per gal. saving. When I got the Pontiac the best I could get was 20/23 mpg. Last summer I made 2 trips to Eastern Wa. (approx. 400mile round trip). I filled before leaving and filled again at the same station when I got back. I got between 30 and 31 on both trips.
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Old 03-17-2011, 01:20 PM   #26
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To get back to the OP's question(s):

We had an Outback (02 or so), with the same engine, and as I recall, I ran midgrade with no problems whatsoever. While the gas cap may say "premium fuel only" or whatever, the fine print in the manual says "at least __ octane." Though I don't recall the # for that Subie, many engines that call for more than regular only ask for 90 or 91 octane, which is a little more than midgrade (usually 89), but less than most premiums. (All #'s assume "sea-level" octane ratings; octanes will be lower for all grades (and your engine's requirements) at altitude.) At that small difference, even if your engine's knock sensor tweaks your timing, you'll likely not notice it, and will do no damage.

On the other hand, do not add kerosene to your gasoline, for any reason. As I recall from my aviation days, a jet engine fueled with gasoline will run, though not optimally, while a reciprocating (gasoline) engine fueled with jet fuel (which is basically kerosene) will stall and drop you at an inopportune time. (Yeah, I know, you're talking about a small amount, but it's not worth the risk to your engine.)
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Old 03-17-2011, 06:49 PM   #27
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I remember during WWII seeing cars driving along at night with sparks coming out of the tail pipe. That was during gasoline rationing and people were trying to use a mixture of Kerosene to extend their gasoline allotment. The sparks were generated from all the soot and carbon that had built up.
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Old 03-25-2011, 11:08 AM   #28
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I've found that on our MB ML320 which says it requires 91 octane, here at 8000ft altitude 87 octane gives me 2-3 mpg better milage. Altitude does make a difference in octane requirement. Pump gas is also lower rated than at sea level with regular being 85 octane.
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