CIS Intake Runners on ‘83 911SC

[porschedude996]

I’m exploring options for increasing power output on my slightly modified 3.0. I understand that the ID of my intake runners are smaller than early SC’s. I also understand that the ports in the heads are smaller at least at the immediate inlet face to match the runner diameter. What, if any could be gained by changing out the runners and blending the ports to match?

Currently I have a freshly rebuilt 3,0, bumped CR to 9.8:1, 964 grind on the cam, and a Andrew Cologne Digital ECU. Everything else is stock. It is a US 49 State Car.

[AndrewCologne]

Hi Keith,
Since you're running cams with 964 profiles, you'll need to drive at higher revs to really feel their benefit. Higher revs pull in more air in the same amount of time, so you'd benefit from larger ports and intake runners.
But … besides machining the heads and installing new intake runners, you'd also need to switch to an airbox that supports the larger runners.

If I were you, I’d rather focus on the ignition timing. Much more potential there.