Holley 4780

[Mpcoluv]

Guys,
Any downside to the Holley 4780? I know it has differential primary and secondary bores.
I have run across an older one (1974 date code) that looks nearly mint condition.
Since it's 1974, can I assume it already has the lowered idle?
Its cheap enough that I may buy it to play with.

[RFSPHPbb]

that's a known good carb. one of the all-time favorites in NASCAR and other forms of racing. If you lose interest please let me know, I'd be interested.

[Mpcoluv]

It was too clean to pass up so I bought it.
Is is interesting how long the 4780 carb has been around and there are not many tuning threads on the web about it.

[gntkllr]

4780 is a 3310 (1-3/8" primary & 1-7/16" secondary venturi, and 1-11/16" throttle bores) that's a double pumper. Calibrated like a good old school 3310, they should be golden performers... #72 PMJ + 0.063" PVCR, #84 SMJ, 0.031" PIFR if stock/mild, few thou bigger the grumpier the camshaft is... 0.040" SIFR up high under cup plugs or ~0.035" down low... combined with 0.028" SIAB's, and the usual starting point for most if modified to be adjustable, 0.070" PIAB's... the ones I've seen had 0.025" primary and secondary MAB's...

[Mpcoluv]

Sounds like it was designed by the guys who did the OEM calibrations for Ford and Chevy.
When I have the spare time, I’ll pull the bowls and make sure everything is stock. The stock calibration looks like a good starting point.
When did Holley start changing things for the worse? By the 80s?

[jmarkaudio]

When all the original engineers that had to deal with OEM carbs either quit, retired or died...

[Mpcoluv]

I’m finally going to try this carb out. Took it apart and it looks minty fresh. Changed the primary jets from 75 to 72. Left the rear at 80.
It looks like someone drilled or replaced the primary butterflies. I’m tempted to change them back to non drilled setup. I think my cam too small to need the holes.

[Mpcoluv]

BTW, I’m sure this does not need to be a stickey
Post. Not sure how I did that.