YOUR RESEARCHRumble after 3k on tach
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Hey all, this is my first 911, a 1999 C4, and love it! It seems there�s a rumble once I get a little over 3k on the tach. The engine seems a little louder and even a slight vibration. Performance doesn�t seem to be affected, in fact that�s when this car gets some *****�..Is this normal?
Resonance flap in the intake plenum opens at 3120rpm, could be what you�re noticing.
Or the variocams r kicking in.....yes its normal. All the performance in these motors is over 4500 rpm so string it out regularly.
If you look in the owners manual, you will see there is a rise in HP and torque ~3100 RPM. I don't let the revs below 4K unless I am stopped. Car much happier to be on the power curve.
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Quotes source post: 19169068
Good post, thanks Joe.... A complicated fluid dynamics and laminar flow, put into simple terms. Thats why bolting on a K&N CAI or using anything other than the oem CAI components hurts power/throttle response/efficiency & torque.
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