I just installed a new cam in my '70 Stage 1. It is bone stock other than this modification,timing chain and valve springs. The cam is a Poston GS113. It has 490 lift and 284 intake duration and 304 on the exhaust. What do I need to do with the carb to supply fuel for this combo? It is the stock Quadrajet. I just don't want to lean it out too much. Thanks guys. Headed for the Nats on Wed -Steve:3gears:
Some tips from Doeg Roe's book... (heavily paraphrased) Measure the Vaccuum on the intake and swap the power piston accordingly, light spring for 10-12" I think. Also port the secondary pulloff to make sure it engages in about 1 second. If you're on the gas more, think about a fuel filter swapout to give the carb a little more buffer for when you nail it. Here's a good article on the subject as well: Damon's articles & summary
My suspicion is that there will be more involved than a power piston spring. It is likely that the carb will be too lean at idle and low speeds. Do not assume that, but expect that. If so, it will require the enlargement of the idle and off-idle tubes in the bow. This is tedious, but will pay off big over the infernal Holey carb, spelling intended. The Q-jet is very reilable, tuning is somewhat difficult, but will stay tuned once there. The Qjet is misunderstood, not junk. Roe's book has been well written, and is easy to understand. Try this combo before going anywhere in the tuning section. You might be surprised. The lower vacuum anticipated MAY affect tuning. Assume nothing. Ray
