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356-930 356-930 is offline
Acceleration Junkie
Join Date: Aug 2007
Location: Laguna Beach, CA
Posts: 263
Originally Posted by copbait73 View Post
356-930: I interpret your reply as there is no issue. If that is true I respectfully disagree and support this with your own statement, "your cylinder pressure and temperature increase.”

Your temperature and pressure may not induce knock or immediate mechanical failure but without knowing what the thermal limit is how do you know this "tune" isn't capable of exceeding the limits in an operating environment other than those established on the dyno? Water-cooled cars tell you - they boil over.
You misinterpret.

You asked a simple question, "What happens to our Porsche’s cooling when we optimize A/F and spark advance with modern electronics tuned on a dyno?" I provided a simple and accurate reply, "Cylinder peak pressure and temperature increase." Optimizing A/F and spark advance to achieve maximum power do not alter Porsche’s cooling scheme, they simply overwhelm it with heat.

Porsche and all good dyno tuners maintain AFR and timing to conservative levels, i.e. less than optimum rich mixture and timing less than optimum to avoid both detonation and overwhelming cooling capacity of the engine’s heat exchanger’s; oil, oil cooling and air cooled heat sinks/fins.

A liquid cooled engine can damage itself long before the cooling liquid vaporizes. Whether air or liquid cooled, detonation will occur under high load if the AFR is lean to a critical ratio and/or timing is too far advanced.

Air is a poor heat extractor compared to a liquid. If one wants to "see" the two cooling mediums at work, heat a finned "air cooled" cylinder to 200F and blow on it with a fan for a minute, monitor its temperature throughout. Heat it again to 200F and drop it in a huge container of fast moving liquid. Monitor its temperature throughout. Liquid wins hands down, probably by a factor of 50. The ability of a liquid to cool is limited by the vapor pressure of the liquid, pressure in the liquid system, and the rate of the liquid container's heat exchanger (radiator) to extract and dissipate heat. As you note, if the ratio of liquid to air extraction is too low for the heat produced, extracted heat cannot be dissipated fast enough and the liquid vaporizes.

Turbos and supercharges are capable of supplying an engine with more air/fuel than it can handle. Perhaps this is the power density to which you refer? Without something (a dyno) to load an engine, monitor it with instrumentation, one cannot readily asses/tune it to safe peak power.

If, as you state, you cannot fix the problem with water, change the fuel to ethanol or methanol/alcohol. And if these fuels are not an alternative, look into water/methanol injection to supplement the intercooler.

The project sounds fun. Keep us posted.
Chris Toy
356-930 Gone

Last edited by 356-930; 08-02-2009 at 06:49 PM..
Old 08-02-2009, 02:54 PM
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