document.write('<div id="pan_container"><div id="pan_header"><div id="pan_stationAsksImage"></div><div class="pan_pad"><div id="pan_tq"><div id="pan_content_title">Premium versus Regular</div><div id="pan_content_question">What do you think? <br/>  <br/> Is premium a ploy designed to add to Big Oil coffers? Or, do you think it\'s a "must" for all high-compression engines, no matter what we said? <br/>  <br/> Want to chime in with a second opinion on something else we said? (It wouldn\'t be the first time. But you probably already know that.) <br/>  <br/> Tell us what you think -- and thanks for joining the discussion! <br/>  <br/> Tom and Ray</div><a id="pan_replyImage" href=\'http://action.publicbroadcasting.net/cartalk/posts/list/214813.page\' style="display:block;"></a></div></div></div><div id="pan_messages"><div id="pan_commentsTitle"></div><div class="pan_messageContainer"><div  class="pan_messageStats"><div class="pan_pad"><span>Re: Premium versus Regular</span> Added: 06/28/2009 12:49:35 PM</div></div><div class="pan_messageBody"><div class="pan_pad">My independent Mercedes mechanic (highly experienced and knowledgeable) says that running regular when premium is required can ruin the catalytic converters, which are about $800 to replace.  Nobody loves Big Oil, but careful that you don\'t cut off your nose to spite your face.</div></div></div><div class="pan_messageContainer"><div  class="pan_messageStats"><div class="pan_pad"><span>Re: Premium versus Regular</span> Added: 05/24/2009 12:33:41 PM</div></div><div class="pan_messageBody"><div class="pan_pad">PS to my above post: <br/>  <br/> I think Tom and Ray have ignored the possibility of the more complete burning of the fuel when premium is used - especially in the every day road car with lower compression and operated at lower rpm normally. It\'s necessary in higher compression engines, but in my slug 87 Samurai it did provide more power at all rpm\'s. <br/>  <br/> Premium achieved using ethanol does have less energy per gallon, but burn efficiency can\'t be ignored. I don\'t pretend to have the answer in all situations, but understanding the constraints (like the ECU adjusting slowly, etc) means you can run your own more accurate experiment. I recommend keeping track of miles and gallons over at least 10 tankfuls and averaging all of it before deciding. There\'s too much error in a calculation based on a single tank or even two.  It might be best to buy all that gas from the same station, too.</div></div></div><div class="pan_messageContainer"><div  class="pan_messageStats"><div class="pan_pad"><span>Re: Premium versus Regular</span> Added: 05/24/2009 12:08:46 PM</div></div><div class="pan_messageBody"><div class="pan_pad">The discussion seems to ignore the relation of ignition timing to fuel octane ("regular" is lower octane than "premium"). Higher octane gas burns slower than lower octane and therefore requires the spark earlier in the cycle. <br/>  <br/> If you switch from regular to premium, the spark must be advanced to match. If your car has computerized ignition timing (ECU) and vibration ("knock") sensors, then the software will SLOWLY seek more advanced settings after you switch to premium. The first few tankfulls may actually get worse mileage, but eventually the correct timing will be achieved and then you can tell if premium gives better performance or mileage. <br/>  <br/> The timing software algorithm behaves like the blind man warming his hands by a stove every morning. Then someone moves the stove further away (switch to premium and the "knock" moves further advanced in the timing spectrum). The blind man finds much less heat, but CAUTIOUSLY moves forward seeking the heat. Eventually he finds a satisfactory place and is happy again. <br/>  <br/> On the other hand, if the stove is moved closer, then the next morning he burns his hands and RAPIDLY moves away. That\'s what happens in the software if you switch from premium to regular, causing immediately more vibration (maybe even knocking/pinging) and the software quickly retards the timing. <br/>  <br/> I switched to premium on my old (\'87) Suzuki Samurai with manual timing adjust. Because I set the timing myself (normal tuneups when running regular and re-adjusted to a more advanced setting just as I switched to premium) I didn\'t have to worry about how long it took for the correct timing to be achieved. <br/>  <br/> My results were both better mileage (enough to pay for the difference in price) and much smoother operation, especially at lower rpm where I achieve best mileage (this thing has the aerodynamics of a brick).  <br/>  <br/> By the way, if you want to switch to premium to test it, and you have computerized timing with knock sensors, you can adjust he timing more quickly by disconnecting the ground lead from your battery for an hour or so to erase the computers memory regarding ignition timing. Unfortunately, this technique also may erase your radio\'s settings and you should check your manual to refresh your memory about the security alarm if you have it normally turned off. It may come on when you reconnect the battery. <br/> </div></div></div></div></div>');