johnyIROC

Hi I have a Holley 780 4150 VS with annular boosters, milled choke horn and a few other tricks.

I am now running a 5 speed, so I really want to go to a DP so the secondaries don't flop shut between shifts.

I'm wondering what all needs to be changed to convert a VS carb to ad DP. Specifically is the main body the same?

I think I will need to change:

-Throttle plate with linkage
-Secondary fuel bowl
-Secondary pump cover
-Secondary pump diaphram
-Possibly secondary metering block/plate

Has anyone ever done this before? Is it possible? If I can do it without changing the main body I will..... I have a 650 DP for parts, but I may have just sold it.

Here's a pic of the 780VS as it is now:

Stekman

I think its in the linkages. Not sure...

On a side note, doesnt the dizzy get ported vacuum? Looks like you have it on full time. Just a thought.

five7kid

iTrader: (14)

It's not possible to convert. You need a different main body. To put it simply, go buy a DP carb.

Manifold vacuum is fine as long as you tune accordingly (for instance, the Proform main body isn't drilled for ported, so there isn't any other choice).

five7kid

iTrader: (14)

Oh, a 650 DP will work as the basis for the Proform main body 750 conversion. That's what I used.

RB83L69

AFAIK it is not possible to convert a 3310 to manual secondaries. There are different passages in the main body.... like the ones for the secondary pump discharge for example.

So, here's how to convert a 3310 to man sec, in 2 easy steps:

• Sell 3310
• Buy a DP

Personally if I was going to buy a carb, I'd buy a Demon. I've never had one but have had other Barry Grant stuff over the years. I'd suspect that it's a better made piece than a Holley in every way.

scottland

ditto. My speed demon runs great, i can't even compare it to the carter that was on there.

darbleinad

hahah...thats bad news for me, cause i wanna buy that 650 DP.



hey...Jay, I think Dave has a 750 DP around, maybe a i could get that and perhaps we can trade?

johnyIROC

That would be excellent... we'll figure something out man.

F-BIRD'88

Get a rev limiter and hold your foot to the floor during the shift. no need to mess with the carb.

johnyIROC

I'm going to run the 780VS for this summer... and get the engine dialed in... but for next summer I definitely want a DP so I know they are open when my foot is down.

F-BIRD'88

You could rig up a Micro switch like the ones used for WOT activation control of a Nitrous system, to light a lamp to tell you when the secondaries are wide open. As long as the switch lever is fairly light to activate should work pretty good.

bet you'll find the secondaries are pretty responsive to throttle transitions during a shift.

five7kid

iTrader: (14)

Using the "standard" CFM formula and assuming 100% VE, you'll have to spin (what I'm assuming is) a 355 to 7600 RPMs to use all 780 CFM.

With a VS, it isn't going to fully open until it's "needed". The difficult part is balancing the VS opening so it thinks it "needs" more earlier against an initial bog. The DP resolves that issue.

There's some interesting links on this thread https://www.thirdgen.org/techbb2/sho...hreadid=250137 . The 2nd car in the video is running a 780 VS on a 428 w/Jerico 4-speed. The secondaries probably stay open for him.