Originally Posted by badknuckles
recently purchased a firebird as a (project) with an L03, trying to see if anyone has worked with this engine? i am keeping the 305 not looking to hear you need a 350, the 305 is what i wanted to screw around with. never done one. already got with a local camshaft maker to have a custom cam ground and already in the process for headers. i think i am just looking for head guidance because from what im tracking the heads on this motor suck.
With the exception of heads with valves bigger than 1.94x1.5 everything that bolts to a 350 bolts to or into a 305.
305 heads aren't bad on a 305, they have smaller valves and slightly smaller ports than 350 heads since they don't need as much to feed the 45 fewer cubes. So using 350 heads like the Vortec is in effect like a 350 using aftermarket heads. Problem is the 305 heads run around 55-59 CC chambers where Vortecs run 64-66 CCs so using them cuts compression, but gives bigger ports and valves with a better burning chamber. It'll trade off some bottom end torque for more top end horsepower. Proper recovery would be to replace the factory 305 pistons with aftermarket D dish with less dish volume or flat tops to correct the compression. In the end you need to worry the Dynamic Compression Ratio which is the effect upon the Static Compression Ratio by the point where the cam closes the intake valve. This is essentially adjusting the compression for stroke that is lost up to the point of intake closure. At lower RPMs this is charge lost to reversion which is why long duration cams and/or high ratio rockers tend to kill bottom end torque. Kicking the SCR up to keep the DCR around 8 to 8.5 for the street helps restore the bottom end. These guys have an easy to use calculator http://www.kb-silvolite.com/calc.php
. With the right piston that has a lot of squish/quench and the right head like the Vortec with the spark plug shoved toward the center of the cylinder you can lean pretty hard on the 305's compression because of the smaller bore thus less time for the burn to get across it. With the stock heads and pistons you can't do this without incurring nasty detonation.
Problem with the 305 is that it is as costly to build as a 350 or even 383 and no matter what you do short of nitrous or a blower, you're down 50 and more horses for your buck spent simply because of the smaller displacement and more restricted breathing. The only solution to the breathing because of the tight wall to valve clearance is more timing which emphasizes the need for careful compression control on these engines to compensate for the later intake close needed to make power.