Specs on AC,AD carbs

[Drew Pojedinec]

Look at the BD linkage too

[jcarlson]

Just an update from Saturday's race.
I jetted the carbs per Drew's specs (70 jets) and put a long yellow spring in each secondary. BTW, those spring colors are poorly marked by Holley. In any event,  on Friday night I looked at the weather report and saw 30's-40's predicted for Saturday morning.  Kinda worried about being too lean, I succumbed to internal pressure and re-jetted to 72's....racing vintage 427's can make one do funny things! Set the timing to 40 degrees total.
1st pass: 6.99 at 118
2nd pass: 7.01 at 117 (leaky needle and seat in one of the secondaries, replaced it with a new one)
3rd pass eliminations: 6.992 at 118 (6.99 dial, but red bulb)
A best ever 60ft of 1.51.....very happy! I can actually feel the difference off the line.

These carbs work great. Now I can look at the 6.99 dial on my window all winter long! Been aiming for the 6's for 20 years.

Thanks Drew!

[jcarlson]

Uh thats not right. 98 mph not 118

[Drew Pojedinec]

For reference, with the same size venturi and throttle plates a bc/bd carb runs:
68 jets, .028 pvcr (very small)

The main difference is with those boosters. That is why you can get away with 70/72 and no power valve.
As always, jet based on results, the data is just a good starting point. Happy to hear it all worked out.

Also of note, do not compare 1850 VS spring with these.
These have a larger booster, larger venturi, but they also have a VS amplifier tube to assist in opening the secondaries. So totally different ballgame.

Good luck

[jcarlson]

Thanks Drew, I have a set of BD carbs also, so that's good info.
Interesting about the spring, I hadn't thought much about that with the different booster. I'll try different springs next year and see what happens. For some reason, I cannot find a set of "plain" springs. I'm sure I have a set, but who knows where. At what rpm would you expect them to be open fully, if ever?

[Drew Pojedinec]

Depends on a million factors. Anything I give is a “best guess”
Easiest way to test is using too light of a spring so it flops open, and going stiffer until you cannot feel them opening.

I am a fan of removing the checkball, drilling/tapping the VS lower casting at the face, where it meets the main body. Insert a set screw with drilled hole for use as a restriction. Slightly too light of a spring and a drilled restriction is my preferred method if possible. Start with a .045 hole and work up until you get what you want.
Bench testing with an air gun will give you somewhat of a feel for the opening characteristics, but again, needs to be tested on the vehicle.