Ideal Dual-Carb FE setup for a street 390/FE?

[Woodz428]

Typically, you get a bog, not a surge when the secondaries open too soon. If it surges,as in picks up some acceleration, then it is probably pretty close. The bog is a drop in power, because the engine isn't ready for that much opening. I don't even think it is an issue much with double pumpers if the pumps are adjusted correctly, mostly with vacuum secondaries. Having said that, I was actually wondering if he meant when the primaries on the secondary carb opened? They have a progressive linkage. It is also pretty important to put a balance line between the 2 secondary vacuum tops. There are special tops available, they keep the secondaries on both carbs operating together. Without the balance line it's possible to have the secondaries open on the primary carbs, then drop closed again when the secondary carb primaries open and the vacuum signal drops. Under mild throttle conditions this can create a less than linear acceleration and weird carb actions.

[Ibr8k4vetts]

I believe the 427 came with 550 bj-bk carbs

[69boss429]

Originally Posted by Ibr8k4vetts

I believe the 427 came with 550 bj-bk carbs

I bought a set of those from Carl's Ford Parts,he said they were 715 CFM each.

[Woodz428]

I believe 550 cfm sounds right for the 2-4 set up. The 715 was used in a single 4 bbl. application, including the early Shelby GT350. If they are the correct carbs they aren't 715s. You can pull the list# off the airhorn to find out for sure. I think (2) 715 carbs are a little much on any street engine...even a Boss 9. I also believe that the 715 only came with the cathedral bowls and won't even fit a 2-4 set up without a bowl change.

[69boss429]

Originally Posted by Woodz428

I believe 550 cfm sounds right for the 2-4 set up. The 715 was used in a single 4 bbl. application, including the early Shelby GT350. If they are the correct carbs they aren't 715s. You can pull the list# off the airhorn to find out for sure. I think (2) 715 carbs are a little much on any street engine...even a Boss 9. I also believe that the 715 only came with the cathedral bowls and won't even fit a 2-4 set up without a bowl change.

I tried to find the numbers on the Holley site with no luck,
Carbs are: C5af 9510 BD List 3800,and, C5af 9510 BC List 3301
I'll look up the invoice from Carl,but he told me on the phone when I ordered them they were 715's
Whatever they are they work well,and the throttle bore's look to big for 550 or 600's. I have a 715 wit center hung float bowls ,I'll check the throttle bores on it for comparision

[Woodz428]

According to the NV SAAC site, those were used on some S/C and later 3000 series cars. They are 710 according to their site, so 715 is almost the same. The secondary is a 3300, you may have read the stamping incorrectly, they can be a little crude at times. Learned something new, now I can back to sleep :-)
Just a note regarding the throttle bores, if you are referring to the butterfly openings...they aren't what determines the CFM, it's the body venturi. More than one CFM carb uses the same baseplate, when examining look down the venturis to compare size.

[69boss429]

Originally Posted by Woodz428

According to the NV SAAC site, those were used on some S/C and later 3000 series cars. They are 710 according to their site, so 715 is almost the same. The secondary is a 3300, you may have read the stamping incorrectly, they can be a little crude at times. Learned something new, now I can back to sleep :-)
Just a note regarding the throttle bores, if you are referring to the butterfly openings...they aren't what determines the CFM, it's the body venturi. More than one CFM carb uses the same baseplate, when examining look down the venturis to compare size.

Old eyes maybe don't see those little numbers as well,but since these are the rerelease Holleys they may have gotten it wrong.I'll look again.
And,they work very well,does not seem to be overcarbed and throttle response is awesome.
I made only 2 jet changes to get them dialed in,and didn't touch the vaccum secondary spring
P.S. Carls has more than one dual 4 bbl setup avail for big or small block use