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copbait73 copbait73 is offline
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Join Date: Nov 2003
Location: Chesterfield IN
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Originally Posted by copbait73 View Post
You can use twin plugging to increase your safety margin against knock or you can take a power increase up to the same margin with increased boost. That is how you get increased power. At the the risk of repetition, twin plugging allows the equivalent HP increase as 1 point C.R. increase before onset of knock. This is not about timing.

In the N.A. 911 forums this benefit is readily understood and accepted.
If we were talking about non turbo 911s would you dispute a 3.0L 11:1 C.R. (made possible by twin plugging) makes more power than one at 10:1 C.R.? Turbocharging does not change the impact of fixed and equivalent C.R. (fixed plus boost) on power output.


This is another very interesting chart coming directly from Porsche engineering SAE technical paper, Hans Mezger, Aug 7, 1978.

Interesting, the presentation is discussing geometric compression ratio (fixed C.R.) in terms of.....hold on to your hats power junkies...not throttle response, not boost response, not ultimate power production......FUEL ECONOMY.

Posted fuel consumption values are set at low power production (20-30HP ? for a 930 on the interstate). They wanted to maximize engine efficiency at low throttle angles, off boost. High fixed compression delivers this.
Old 03-07-2008, 10:22 AM
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