750s and 780s....3310

[ktownkid]

Hello,
It seems the 780 and 750 share a part number. How do you tell them apart???

Didn't have this problem in the 70s.....just walked into the speed shop and bought a 780. Never heard of a Holley 750 then.....

Thank you kindly in advance...
ktownkid

[VintageMusclecar]

The newer (3310-2 on up) 750 cfm 3310 carbs use a straight leg booster which is slightly more restrictive than the earlier down leg booster from the early 3310 (3310 "EH" and 3310-1) carbs. Straight booster = 750, down leg booster = 780.

Eric

[Salvatore]

Arn't the 750's double pumpers?

[VintageMusclecar]

Not the 3310's, they're vacuum secondary. The "conventional" 750 double pumper is a list 4779.

Eric

[ktownkid]

Thank you for clearing that up. One last question, is there a mechanical 780??? I seem to remember one.

Thank you for the reply-
ktownkid

[VintageMusclecar]

I can't think of any mechanical secondary carbs that were rated at 780 cfm. Not saying one doesn't exist, just that I'm not familiar with it.

[Xplantdad]

I'm thinking that if Eric's never heard of it...it probably doesn't exist...

[copo69]

I thought the difference was the 780's have a metering block with changeable jets on the secondary side and the 750's have a metering plate that has no changeable jets. I've got one of each, I'll have to look at the boosters.

[VintageMusclecar]

Greg;

The metering block denotes a 4150 style carb, while a metering plate denotes a 4160 style carb. A 4160 style carb can be converted to 4150 style simply by replacing the secondary metering plate with an appropriate metering block.

Eric