428 dual carburetors

[wemooz]

My ERA has a built 428CJ that presently has an original Ford 2 carburetor manifold with two Holley 390 CFM carburetors. I want to change these to 600 CFM units, but am not sure what to get or where to get it. Any help will be appreciated. Bill

[jayscobras]

You might want to try Dearborn Classics.

[ERA Chas]

Bill,
These are 1850, 600's which have been modified. They now flow 654 each.

They are very common and Summit etc sells them. MANY specialty carb tuners and builders sell modified vacuum secondary carbs which will fit and it's easy to spend more money than your application warrants.
Depending on how stout your 428 is, the standard 1850 may be more than enough. A big cam and improved heads changes that.

[saltshaker]

You can get the bj/bk reproduction carbs from Carl's, have Barry make you a set from QuickTime or use a pair of 1850's (600 vac holleys)...all will work. I've tried the mech 450's and switched to the 1850's...hugh difference on my 428....,depends what you want.
Jon

[elmariachi]

On my 427 I am running a rebuilt set of Holley BC/BDs (710 cfm each) with a medium riser intake. Mine are original but I believe Carl's sells them as well.

[wemooz]

Will the 1850's work right out of the box? I suppose that at least I would have to remove the electric choke on the second carb.

[elmariachi]

Read this: Which carbs do I want for 2x4 MR?

[saltshaker]

They should! You might want to change the tops on the vac so they can be tied together so the secondaries open at the same time. I use # 65 jets, #25 squirters and 6.5 pv....and that has worked well. You can also buy one carb without a choke....
Jon

[ERA Chas]

You need to tell us the specs of your 428. If it's a low-rise, hydraulic mild cam, all those specs and cfms are much more then you need.
Yes stock 1850's will be usable but you need to know how to tune them for your application.
Guys can help you better if they know what you have.

[elmariachi]

Regardless of what you run, call these guys and tell them you want the "2x4 Card."

[wemooz]

Thanks for your inputs. My 428CJ is a low riser, has stock heads and has a crane cam peaking at 5500 RPM with hydraulic lifters, so the engine is fairly mild. The intake manifold is an original ford manifold for the FE engine. If more information will help, let me know what it is and I will get it. Bill

[saltshaker]

If money isn't an issue the bk/bj carbs will perform best out of the box....the 600's will also work really good ...I have no hesitation with them at all.
Jon

[ERA Chas]

OK-don't spend a lot of money on trick, modified carbs. 1200 CFM is already too much flow but will run fine if you set them up slightly lean. Watch the plugs and float levels.

[saltshaker]

Bill,why do you want to change the 390's....that's 780cfm which would be just about right....?

[SuperHart]

First, even though you have a 428, your 390 cfm carbs may be quite enough for the street. 390 x 2 =780 cfm which is more than your 428 can possibly use even if 100% efficiency is considered unless you intend to visit 7000 RPM repeatedly. You might get better results to have your present carbs properly jetted and set up by a reputable shop rather than purchase bigger carbs. Even if you decide on bigger carbs, remember that your main carb is still the front one and if I recall correctly the idle circuits and maybe even the jetting may be a little different for the main and secondary carbs. You want to remove the choke assembly from the secondary carb and you MUST install the vacuum pot covers intended for dual quad setups which have a vacuum equalization hose connecting the two secondary pots. http://carlsfordparts.com/parts_imag...VAC%20TOPS.JPG

Lastly, if you are going to use a progressive linkage like the original dual quad medium riser linkage, pay attention to the holes in the throttle linkage plate that you install the trunnions in. The pivot radius on the secondary carb is shorter (closer to the throttle shaft) than that on the primary carb because the secondary carb needs to open quicker than the primary carb. On the original dual carb setups the mounting hole for the trunnion on the secondary carb is closer to the actual pivot point than the trunnion on the primary carb. Take a good look at the trunnion positioning in this photo. http://carlsfordparts.com/parts_imag..._induction.JPG If you use Holley 1850s or any other pair that has not already been set up for dual quad induction you will need to pay special attention to placing the trunnions in the proper position or the secondary carb will not open up 100%.

Anyway, before spending $1000+ on new carbs, find yourself an induction expert and do your homework.

[wemooz]

Chas, do you have your carbs ganged so that both are always in sync and open to the same degree? It seems so from your photo. If so, I can guess that running them a bit lean is in order. But if I use the original type linkage, they will open in sequence and prior to the second carb opening, I would think that the first 600 CFM carb would be about correct. Am I thinking about this correctly? If ganging them is preferable, what are the advantages? Bill

[ERA Chas]

SuperHart's advice is correct-the rear carb must have the linkage bias to come on in staggered relationship to front. For years I ran it with the slotted link opening the rear carb after about 10% of primary.
Then I read a tip here from other members who had better response syncing them 1:1. You have sharp eyes seeing my new link. However this will only work best with a lot of cam and 300+cfm heads.
I advise you set yours up correctly with the bias in the linkage. Your motor won't support much modification. You will have lousy street performance if you don't.
Actually the advice by SuperHart and Saltshaker to have a good shop set up your 390's is very practical and they would have great throttle response on your type of motor. You're not going to find 40HP-you want to maximize low-end torque which is your motor's strong point.