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On 19 Nov 2004 at 17:13, Toby Erkson wrote: > Jim Adney wrote: > >I think I've heard this both ways. It's certainly true that engines a long time > >ago were expected to wear quite a bit at first, but my impression lately is > >that finishing techniques in modern engine machining has greatly reduced this. > Still gotta break-in with conventional before using synthetic unless the > engine builder states otherwise. Porsches and Corvettes come stock with > synthetic oil (as do a few others), turbo'd or not. Does this mean that Porsches & Corvettes are broken in at the factory and then switched to synthetic before shipping, or are they just better machined and don't need that much of a breaking? > >>I recorded an averaged 5hp GAIN by switching my engine and tranny oil to > >>synthetic in my VW Jetta (NOTE: The Mk.III trannys come stock > >>w/synthetic but I refreshed it during my testing). > >Maybe the synthetics have an advantage in film strength, which allows them to > >be used in lighter viscosities. Did you test different oils with the same > >viscosities? > Conventional was 10w-30, synthetic was 15w-50. Technically speaking, > the conventional would be thinner than the synthetic at temp. (For > those that don't know, read up on oils at this web site: > http://www.chris-longhurst.com/carbibles/index.html?menu.html&engineoil_bible.html That's a nicely done site, but I'm not sure how much of it we can trust. I'm pretty sure I found some pretty blatant mistakes, but most of it seems pretty good, and carefully done. > >How did you measure your HP increase? What do you mean by "average" when you > >just have a single sample? > Used by G-Tech accelerometer for testing, strictly adhering to the > instructions and I never said it was just one sample ;-) Yeah, sorry. I was just thinking about the one car, but later I realized that you could have done multiple tests on that one car. > 5 runs with fresh conventional oil (changed at house, drove to testing > road, about 15 minutes away). Dropped the best and worst runs and > averaged the remaining three. Drove home. Changed oil to synthetic, > drove to test road, 5 more runs. Dropped best and worse runs, > averaged the remaining three. Warm day, temp. consistent (and likely > humidity but I didn't test for that) and gas tank refilled to equal > first run (1/2 tank, actually a little bit more in volume then the > first run). Most of this sounds fine. I'd want to know more about the G-Tech just to know how sensitive it is to interpretation. Does it record a digitized record of the run so that you're not left to choose a max meter position? If so, one thing that might be wrong about this would be the fact that the test was not "Blind." Not being blind makes any test more likely to turn out the way the tester wants it to. Another might be the fact that this car was rather new to you, and the synthetic runs were done after you had some practice. Most people will show some improvement with practice at things like this, especially if they get to look at the results each time. How do you get from acceleration to HP? > >How many miles were on your Jetta when you did your testing? I'm asking because > >you would expect some increase just from whatever breakin occurred in a new > >engine. > I bought it used with over 45K miles on the odometer. It had 47.5K > miles on the odometer when I did the testing. Sounds just fine. ;-) -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~