[flash]

higher revs will expand the rings more, leading to better compression - running low revs doesn't allow that as much, reducing compression, increasing fuel wash and deposits, and thereby promoting premature wear



this is not to say that you should run it at high revs all the time, but the periodic 30 minute romp at nearly 6k is good for it (on the presumption that the maintenance is kept up)

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[TheMirror]

Hmmmm.... I'm no engine rebuilder, but that's definitely the first time I've ever heard that not stressing an engine will make it wear out quicker. Care to expand a bit, maybe?



Best,

-Mirror



[quote name='flash' date='Jun 7 2006, 08:34 AM']higher revs will expand the rings more, leading to better compression - running low revs doesn't allow that as much, reducing compression, increasing fuel wash and deposits, and thereby promoting premature wear



[right][post="22459"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[cooz]

there is something sexy/unique/special about both the appearance & performance of a 911.



comparing similar generation 911's (964's & 993's) to 968's...



the flat six has sound, torque, smoothness and free-revvingness that's terrific.

It's light responsive front end and heavy steerable rear end also creates different/unique feeling that can be both challenging & fun.



cooz

aka

norm

95 C2

94 968

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[flash]

it takes heat and pressure to expand the rings - without that, they don't reach full expansion - that means less compression - less compression means less sealing of the fuel from the oil - fuel is a cylinder's worst enemy when it comes to lubrication - unburnt fuel mixing in with the oil will lead to prematurely worn rings



that's why when breaking in an engine, the best thing you can do is lug the motor up a hill in top gear and really put it under a load - that will expand the rings fully - after that, just periodically take it out and romp the crap out of it - high loads are what keep the rings expanded



we all know that the motor runs stronger right after a track day - this is because of the expanded rings - we've also all seen cars that have been sitting and how they smoke when you first fire them up - all the same issue



doing this all the time will of course lead to higher stresses and wear



but, back to the original discussion - we've strayed a bit here

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[TheMirror]

I guess that just doesn't add up for me. I'll have to do some research.



I could see needing high rpms and loads for racing engines, where the heat loads are extreme and the rings are not designed for optimum sealing at lower rpm ranges. Sprint car engines have run gapless rings for a long time be certain of quick and effective cylinder sealing. Not sure if those are still legal though.



http://www.totalseal.com/gaplesss.html



In street engines though, with a vast range of operating temperatures and speeds, I can't see how a manufacturer wouldn't optimize sealing to be when the engine reaches operating temperature....regardless of engine speed. The vast majority of production engines never see the high side of 5000 rpm, even high performance ones. Thus, it seems to me that running the engines in that range (under 5000 or so) should lead to the longest life, not premature wear.



I'm gonna do some reading up on this issue, its interesting!



You're right, back to the original topic. Sorry y'all!

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[flash]

they generally seek a nominal condition in design - the engine will run fine, but if you want maximum power, and longest life, get those puppies to expand to the fullest



keep in mind, when i say "premature" i mean less than maximum



there is a tradeoff though - high revs create more heat and burn valves quicker - so, you get more bottom end, but less top end life - i'll take that trade though



keep in mind too, this is really more of an issue on high compression motors - most mechanics will tell you that you need to get them out there and rev them to keep them alive

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