Hey there, Ray.
Just curious, why are you replacing the Q-Jet? Does it run poorly, or does your engine have any performance mods? Is the truck stock, and used for daily transportation? Do you already have the Edelbrock carb? The only reason I am asking, is to help myself understand the situation, and maybe help save you some money, or maybe spare you some disappointment. I'm sure you are a lot younger than I, and I wish I would have asked more questions in my younger years. Better yet, I wish we'd had Automotiveforums.com!!
If you haven't yet purchased the carb, go to
http://www.edelbrock.com/automotive/index.html and click on Carburetors. Then check out the Q-Jet/Spreadbore section.
Before you go there, here is what I do know: Most Q-Jets flow a whopping 795 CFM. Smallest were 750, and Edelbrock also makes an 850 (too big for a 305). The 650 Edelbrock is a square bore, which means you will not only have to buy an adapter to your Spreadbore manifold, (plus top & bottom gaskets), but you will lose 145CFM, the mixture distribution will be off-kilter due to the adapter, you will need a throttle-linkage adapter, you may need a trans kick-down linkage adapter, and you will have to re-route your fuel line. This all adds up to Time, Money, and Work! The Q-Jets from Edelbrock are brand-new, but they are also stock/identical to the factory Q-Jet. They bolt right onto a 305 ci Chevy Truck, with all fuel line, throttle linkage, and kick-down parts you'll need. Fast & easy! But, what you will gain is essentially equivalent to a precisely rebuilt GM Q-Jet. Why not rebuild yours? They are pretty simple animals, really. And if yours runs fine, you will gain nothing, except for the beauty of a brand new carb, which will be hiding under your air cleaner. A 650 Square bore will give you more torque, and a bit more punch when leaving the stoplight, but it will "run out of breath" at a lower RPM, and give less top-end power than a Q-Jet. I use Holley's on my drag race cars, but a fellow racer runs 10-flat quarter mile times in a Nova with a GM Q-Jet!! They can be made to really perform. And at cruising speeds, they get better mileage than a square-bore. If your Q-Jet needs replacing, the Edelbrock Q-Jet is a good choice, but note on their website that you can buy Factory Rebuilt units, same exact carb, for a lot less than brand new. And they look & run just as good. Feel free to e-mail me if you have any more questions! If you are planning to make your truck a "runner", the plan should include headers, a square-bore performance carb, and eventually a matching Performer RPM intake manifold, and then later on a 350!!
Best wishes, and you are starting out the right way, by asking questions! -Dan.
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