Quote:
Originally Posted by psalt
The drive for better consumption is documented in the factory literature and prominent in the advertisement of the period. The changes were primarily driven by the requirement that all cars run on unleaded, lower octane fuel. Higher octane unleaded fuel was not available. Once you understand the timeline, the changes in the factory's approach is obvious.
Output is measured at WOT, vacuum advance is irrelevent. Vacuum advance is a device to improve part throttle cruise efficiency. The US 911SC has both vacuum advance and retard. The retard is strickly an emissions device, uses manifold vacuum, and is only really active at idle.
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Not trying to be arguementative, but the vac advance IS relevent as it was for fuel economy during cruise, another hit against increased BSFC solely due to a compression bump. One must comprehend ALL the changes made to the engine. The retard was for the nitrogen oxide @ idle. The bump in comp yields less than 1% to the total HP output....Porsche was engineering an engine that could cruise below 3000 rpm and targeted almost every aspect to achieve this.
Quote:
Originally Posted by psalt
Most SC cold start better and run cooler at idle with it disconnected and the idle speed readjusted.
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This promotes my philosophy, You have no lattitude with this engine unless appropriate fuel is available. Where is the fun in that build?
Too many CIS owners try to put Euro pistons in their cars, get no increase in performance and either break rings or burn pistons. The same with most single plug builds for that matter. Most people try to push compression beyond the reasonable range.
In regards to gestalt1's engine;
This is the few times where a compression bump is fine and recommended! The bump is only about a 1.5 to 2.0% hp increase, but a bit more torque throughout the rev range. If you need new pistons, then go for the increased compression.
Here is what I would do if it was my engine.
9.5/1 comp
You could keep the curve as is but there will be some latitude depending on exhaust, so a little dyno time may yield some hidden ponies.
MOD S cams is you require a regrind.
You will love it!