68 Mustang 390 with Dual Quads

Anyone have any experience with Dual quads on a 68 390? My buddy just bought a 68 fastback with a factory 390. Someone put a dual carb intake from a 63 Galaxy 427 on it, and it runs a little rich! It could be as simple as buying new carbs or rebuilding the ones that are on there. He claims they are 450cfm's, and they look like factory Holleys to me (only seen pictures).
My first guess, is that a 68 390 may not have the cam to support dual quads. The car has a 4 speed, so I think if it were mine, I would put in a bigger cam, and check the head casting numbers, maybe even pull one of the heads to see which pistons it has, so I knew the compression ratio. The seller said the heads had been replaced, but don't know the casting numbers yet.

Any thoughts?
Tom


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The CFM to RPM calculation suggests that much carb could handle a 390 at 100% volumetric efficiency up to 8000 RPM.

Sounds like too much carb, but if you like the look you could tune to it as best you can.

You are right about the look! I think that is the only reason it was setup this way, but it does look pretty cool! Here are some pics! You don't think a bigger cam would help to "swallow" up these carbs?

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I lied, one more without the air cleaner

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What kind of linkage set up do you have??? Do all eight barrels open at once or does it open up on a progressive setup?

the air filter cover has the corvette crossed flags , was it monstered on there from a chevy or is it a chev 427??just wondering

mikeweyman that emblem on the air cleaner is a Ford 427 emblem, that is the way they looked. That is a Ford FE, I don't think Chevy 427's had distributor in the front of the block.

On the top front rt. side on the choke housing are the part nos for the carb (top ones are the part #).
They are vacuum secondaries from the pic. so their not 450's.
I would advise a good tuneup and a better air cleaner that allows more air flow, like K&N.
Here is Hollys part # site.
http://www.holley.com/HiOctn/ProdLine/PartList.html

site with free downloadable manual and troubleshooters guide.
http://www.holley.com/HiOctn/TechSe...fo/FMCTech.html
Please let us know what you find.
LOL

__________________
Luv the smell of NITRO in the morning.

I would do two things.
go down in jet size two sizes in your primaries on both carbs. See how that does.
The second thing would be to go to slightly stiffer springs in the vacuum secondary linkage on both carbs.
As for camshaft, it all depends on what model 390 is in the mustang. If that is the 335 HP job, it has the same cam as the 428's had with dual quads, and its a pretty warm cam.
The reason for putting slightly stiffer springs on the secondaries is to delay the rpm at which they start to open. Fact is you dont need all that carburetion, and it is more than your engine can handle. The trick with the secondaries is a somewhat cure for that. If that has factory linkage on it, the linkage between the front and rear carbs should be progressive, with the rear carb being the base or primary carburetor.

I had a 61 Ford that came from the factory with a 390 with 3 dueces. It was rated at 401 hp at 6000 rpm.
I had to do that with my outboard carbs. They were vacuum operated as well.

Been running FE's since the late 60's and have run both 3-2s and dual quads on several cars and have a 2-4 set-up that's going on the Cobra. By the way Max, if you had vacuum end carbs on your 406 they were either Mopar or Chevy carbs because all the Ford trips were progressive just like the 2-4s. Your problem sounds alot like one I chased on a 428CJ I had a set of trips on.I chased the usual problems (power valves),which seemed to fix it . But it would only last a day or two. I've rune several of these so knew something was up. This was in the 90's and I hadn't taken in to consideration the age. After a bunch of flogging I started looking at AGE related things and found that over the years the bowls/metering blocks had been on and off so many times that the mounting surface on the carb face (where the metering block attaches) had been sprung (warped), I stripped them to the bodies and filed the surfaces flat and they worked great afterward. I've since found the problem on other Holleys that have some age on them. What was happening is the surface that seals the power valve chamber was not getting good compression, after the carbs warmed up and it was driven as soon as you let off the gas it would cause the seal to be sucked through and the power valve would always stay open. That of course causes gas to run into the engine and making it rich,smelly and a real gas hog. I'd check that first.The stock carbs are rated at 652 CFM each for a total of 1304 CFM. That's a lot,but if set up right work fine. I ran a 2-4 setup on my first car in 1969 and loved it, it was a stock 1960 T-bird. I have put a couple of 600s on the Cobra to make it a little more tractable,but that is still more CFM than I'll ever need, that's why progressive linkage is nice.

Great pics. The look and vibe is worth the extra trouble. Just looking at those pics I felt like I was back on my old street -- where two neighbors had drag cars and the old guy had a built 390 in his otherwise sleeper 63 Tbird.

Learn something new every day. I do know that the 3 duece manifold on my 390 was a 61 390 unit. As far as the carbs went, thats an intire possibility that they had been changed. Although you know Ford did some strange things back then.
That 390 was rated from the factory at 401 hp, wich cracks me up as the 406 with the same setup was only rated at 405. Ya think there was some underrating on those engines?
Im thinking it was entirely possible that Ford did put both progressive linkage and vacuum operated 3 duece set ups on those engines, at least on the 61's when they first came out with that intake.

The 3 dueces on my 390 were mounted backwards, which I always thought was interesting, as they were in all the pictures I ever saw of the Ford 3 duece setups. I guess it was for the clearance on the distributor.