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beepbeep beepbeep is offline
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Join Date: Jun 2001
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Originally Posted by copbait73 View Post

Thanks, but no fair jumping to a solution. We need to understand and measure.

Have you seen or discussed CHT limits?

According to what I have read regarding alloy used in heads: heads shouldn't be subjected to more than 225 deg. C or they get soft. So that is probably a never-exceed limit. Chances are you would get into knock before that depending on ignition timing, CR etc.

But I don't think thermal management for small capacity aircooled 911 engines is radically different from stuff you have to do on big capacity engines. Bore is somewhat smaller but overall engine dimensions are the same. It wouldn't surprise me if smaller capacity engines are actually easier to call as there is more material in the heads compared to bigger ones.

So if your engine is not knock-limited (which means you can play back-forward with timing for given boost), I wouldn't let the heads go past 200 deg. C. (Un)fortunately, hotter heads mean higher probability of knock so I believe you have greater chance for running into knock than melting the heads.

As there are so many factors to take into equation here (boost, CR, twin plugs, IAT, octane, ignition timing) I would venture and say that overdriven fan is probably the easiest way of solving temperature problems if such exist. It introduces some other challenges itself (belt shredding due to generator inertia, failed generators etc.)
Thank you for your time,
Old 08-03-2009, 03:57 AM
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