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Sedans Lexus GS Lexus GS 300/GS 430
3068 messages, Last post on Sep 18, 2009 at 6:41 AM
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Replying to: wwest (Aug 30, 2007 7:36 pm)
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Replying to: bdkinnh (Aug 31, 2007 5:27 am) Running regular fuel in a HIGH compression engine designed for premium is a lot like running a TOO LEAN mixture in a low compression engine designed for regular fuel. Timing could be perfect, absolutely optimal, but the lean mixture would still oftentimes result in compression knock. Back in the days of carburation the only option would have been to change the jets in the carb to get a richer mixture. NO MORE...! These days if the engine controlling ECU detects TDC(compression) knock/ping and the ignition is already optimized the ECU will simply enrich the mixture to alleviate the knock/ping. Obviously this will also work with a high compression engine designed for high octane but presently fueled with low octane. So the question becomes.... Will the use of the richer mixture to overcome knock/ping overcome the economic advantage gained by purchasing the cheaper low octane fuel? NO. Provided you are not of the teeny-bopper boy-racer mentality and therefore are often in the WOT parametric realm. Absent a FULL charge, or nearly so, in the cylinders there will be no issue of TDC compression knocking. Which brings us nicely to the subject missed in the link. Knock/ping due to engine lugging. This is when the "back-load" on the piston is so high it cannot travel downward as fast as the flame front is expanding. Obviously any fuel, of any octane level can and will be subject to this and just as obviously ignition timing will play no part in this issue. But. Lower octane fuel (think diesel) contains more energy and therefore burns more "explosively", more rapidly advancing flame front, and therein lies the problem. Most modern day passenger vehicles have automatic transmissions so the controlling ECU executes a downshift if knock/ping is encountered in the parametric "region". With a manual/stick shift the only option, regardless of fuel octane in use, is to enrich the mixture slightly until the driver gets the "message". |
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Why fuel a low compression engine designed to use regular fuel with premium? I would normally NEVER recommend this, but.... Premium fuel has a lower energy level and therefore a slower advancing flamefront once ignited. That will allow a leaner WOT A/F mixture and still not incur compression knocking and lower the probability of incuring knock due to engine lugging. The above is dependent on the engine ECU continually "pushing" the parametric envelope and therefore "learning" of new effective parameters. Again, obviously, absent the "boy-racer" mentality.... |
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Hi all, I am interested in getting a used GS300 or GS400. My budget is $10K-$13K and my research shows that this could get me a GS300 or GS400 from 1998-2000 with 50K-140K miles. My questions are: 1) Any differences in the years 1998, 1999 or 2000 in terms of reliability or features? 2) Is 140K too many miles for a car like this? 3) Would you go GS300 or 400? Thanks in advance
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Replying to: piperjack (Oct 01, 2007 8:40 am)
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Replying to: wwest (Oct 03, 2007 6:29 am)
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Replying to: piperjack (Oct 03, 2007 1:40 pm) |
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Replying to: wbreaux1 (Mar 10, 2007 1:21 am) |
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I am looking to buy a used GS and am looking for input on whether the 300 is adequate. I have test driven a 2007 430 and liked it but was not blown away by it. I found the road noise quite noticeable (I guess that's a function of the 18' wheels) and the power very good but not crazy. I am not looking for a hot rod type car - I like decent power but don't really need a V8 430. Just for ref. I drive a 99 Passat GLX V6 and find it under powered. Looking for input from those who have driven both the 300 and 430. Is there a big difference? Also, what's the reliability of this car? I am sick of all the problems with my VW Passat and can't get rid of it fast enough! Plus the VW dealerships are absolute sleaze bags! |
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