Thread: Lets talk cams
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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
BSKI,

Note that Totle did not just add cams. He also seems to have relived the ports.

Increasing ports from 32mm to 35mm increases cross section and potential by 20%.


I belive stock 930's seem to be very "port restricted."

I think I calculated once that before the intake valves are opened to 50% of stock lift, the area under the valve seats are equal to the area of the intake ports.

SC cams with increase intake duration from a stock 209 to 229 deg's. This keeps them open about 10% longer but the increase is more near TDC or TBC, not when the piston is moving at its peak speed during the intake stroke.

Being CIS complicates things as the small ports helps with air fuel mixing in aid of better low rpm pre boost ignition.

I suspect if one did two builds, one with SC cams and stock ports and one with larger ports and stock cams, the ported motor with stock cams will show a better improvement in TQ and boost response.

Never seen anyone do this. It is easer to just add cams.

Combine the longer duration cam with a less restrictive ports should maximize breathing potential as much at 30% or so for the best performance bang.

That dose not mean you can not make big power through the stock ports. I know one SC cam'd 930 motor that made 425 CIS whp with them.

SC cam, ports, a K27-7200, with optimized ignition and AFR's is a great combo for response and mid range HP.

I actually detuned my car back to this combination from C2 cams w a big K29 as I preferred the kick I got from it and it fit my driving style in town better.

Just what I belive so far.
Old 09-23-2010, 09:50 PM
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