Has anyone installed a vacuum secondary Holley on a 350? I'm wondering what jets/secondary spring I should start with for tuning purposes. I would be very interested in those of you who have similar setups. I am currently running a cam with 214/224 duration at 480/480 lift with iron heads and a Holley dual plane street dominator intake. What psi should I start with? Is there some sort of resource out there that could help me size jets/secondary spring according to cam size? thanks

 

Way more than the cam will decide the correct jets to use. Carb tuning isn't an exact science. Trial and error to find the perfect jets. Same goes for the secondary springs. For example, a deeper gear ratio can take advantage of a lighter spring in the secondaries and maybe a fatter set of jets. Not all thirdgens weigh the same--that makes a difference. The list goes on and on. Trial and error... For a baseline, use what is in the carb already.

 

As far as psi keep it at 8. Holley's will handle 9psi but that's pushing it. Keep in mind Holleys come shipped "rich" After you install it take a 15 or 20min hwy run-a nice smooth ride so the carb can flow freely and not load up, come back and pull a couple plugs. If thery're black drop down jet size (rule of thumb is drop or raise 2 numbers ex. have 70, now drop down to 68 or go up to 72 if plugs are white, same for back jets always raise or lower both together.) As for secondary spring-save yourself some time and get the adjustable secondary kit-uses screw to adjust secondaries instead of replacing springs costs like $29.99. After you get jets close, then fiddle with secondaries-start bringing them in sooner until you get a bog, then back it out a little

 

Try your new holley 3310 "as is" the way it comes
from holley. It will be real close to optimium the way it comes.
Stock calibration should be #72 pri jetting, 6.5/10.5 pri power valve, #21 secondary metering plate (equivelent to a #76 sec jet.)
Experimentation with different jets will find the optimum
tune but it will be close to stock. Within about 4 jet sizes.
I run mine with #70 primary jets and replaced the #21 sec metering plate with a metering block and use #80 secondary
jets. The primary side power valve should be a 6.5 to 10.5 in HG
and will be fine for your application.
If you find you need to jet your carb much differently than this
you should suspect some kind of poor airflow into the carb
or poor fuel delivery. (4 jet sizes either way).