Thread: dual quads

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The OP asked me a question on PM, but the chintzy PM on this forum allows only 1000 characters, insufficient to answer most any technical question, so I have copied and pasted the dialog onto the OP's original thread.

Originally Posted by hud-49

Hi tech, u suggested 500cfm carbs rather than the 600cfm. would the 500 carbs be better for the air gap intake? an would the 500's have a bit better throttle responce and maybe help the low end torque just a little better than the 600's.I have have another question, i think this motor may have a mild cam in it but is their a way i could find out

Those carb numbers, 1803 and 1804, are what are suggested by Edelbrock and they know a whole lot more about what will work best than you or I do. A 350 Chevy will make the best hp with a 750 CFM carb on a high-rise, dual-plane intake manifold. Two 500's are overkill, but like I said, the secondaries will only open when there is sufficient intake manifold vacuum to operate them. As Mike P suggested, some tuning may be necessary. Jets, step-rods and shooters are available from Edelbrock so that you can dial in your combo. With the proper tuning, throttle response will be outstanding.

You can find out the valve lift and duration by mounting a degree wheel and pointer on the front of the crankshaft and a dial indicator on the valve spring retainer and turning the motor over. First you must determine top dead center of number one cylinder (front cylinder, driver's side).
http://www.crankshaftcoalition.com/w...op_dead_center
You cannot accurately time the motor with a light until you do this. It is also necessary to have TDC located to check cam timing. Once you have TDC, you can mount a dial indicator on the valve spring retainer of the intake and exhaust valves and find the valve lift and cam timing.

If you want to know only the valve lift, view this video beginning at 3:45 minutes. It shows the mounting of a dial indicator on an assembled motor. Never mind the checking springs shown, it works equally as well with the springs and retainers that you now have on your motor. sorry, lost the video, cannot find it.

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