Well the main determining factor here is budget. So which of these two would be best..

Using my holley 600, or finding and buying/rebuilding a factory non feedback carb?

The 600 needs rebuilt, no biggie. I'm looking at about 40$ for my rebuild kit, shipped. If i go this route, i'll need a new intake manifold.
Offenhauser 6019DP - Offenhauser Dual Port Intake Manifolds - Overview - SummitRacing.com
That's an offyh DP intake manifold, I'm looking at about 270$ shipped. So using my holley would cost right in the ballpark of 300-320$

If i wanted to go the route of a factory non feedback carb, where do i even start looking for one? and what would i be able to get one for? If i knew what year truck, i would need to pick one up from i can just order one through a local parts store (autuzone) but it will cost around 250$.

Correct me if im wrong here, but using that offyh intake manifold would probably open up some power and fuel economy with this straight 6, but that 600cfm would slaughter the fuel economy benefits gained from that intake manifold.

 

Actually, not necessarily.

If you stay in the primaries and keep your foot off of the floor, you can net some good gas mileage with the 600 CFM Holley. Another member on here, AbandonedBronco, kept screwing with the 390CFM Holley trying to get gas mileage and power out of it. He got gas mileage like a 351 did with that 390, but when he put that 600 CFM on, he got all of his power back and his mileage went up to around 17 mpg. A lot of these 300's, even stock, didn't do much better than 16 or 17, even with a proper tuneup. Talk to other people who have just the right combination and they're seeing up to 22 or 23 mpg!

I myself wanted to know if there was a way to put the 1 bbl carter on the Offenhauser C manifold. I haven't had any luck yet. Searching 4 bbl to 1bbl adapter on the net doesn't do much for you.

Put a set of headers or EFI exhaust manifolds on the truck with that Offenhauser intake and 600 CFM Holley, and you're truck will really wake up. Don't forget though, if you ditch the old exhaust manifold, you'll need a heating plate on the bottom of the intake.

 

If money is the determining factor you should just find a Carter YF from a mid-70s Ford on eBay or at a local yard and rebuild it.

A 4-bbl won't necessarily kill mileage, but if you're anything like me it does because you're enjoying the added power and rpms. Upgrading the intake and exhaust makes a huge difference in performance.

 

Or a new 600 cfm edelbrock carb....same as a carter afb/avs.....carter may still even seel them

 

Hell yeah, and yes i will appreciate the added power.

I wouldn't be going as far out of my way to fix this trucks problems if i didn't plan on keeping it for along time. So with that being said, offy intake and the cold blooded holley it is!

Next question, anybody know where i could possibly find a used offy intake for a 300 straight 6? It would be awesome if i didn't have to shell out 275$ for that intake.

Also, i havn't checked yet, but there is a possibility my carb is a 650, not a 600. I had about 10-15 holleys a year ago and slowley sold them all off, i ment to keep that 600 for a SBC 327 build, but we rebuilt the stock Qjet instead, and i might have sold the 600 by accident thinking it was the 650. Would this make a big difference?

 

This wouldn't be very difficult. You'd just need two adapters stacked on each other. A 4bbl to 2bbl adapter, and then a 1bbl to 2bbl adapter turned upside down.

 

Check fleaBAY (ebay) for an offenhauser. They usually pop up from time to time and there are probably a couple on there now.

If I remember correctly, a 650 Holley has bigger primaries than a 600. This means you'll have less air velocity coming through the carburetor to atomize the fuel and help it run correctly. You should be able to check the numbers on the carburetor to see what it is. As far as using the 650 on the 300, you shouldn't have any trouble, but it might not run as good as it would with a 600 because of the larger primaries (that is, if I remember correctly).

 

If you have the Holley 600, rebuild it and run it!

But don't run the 600 on a Offy DP. Go with a Offy C-series.

Watch Ebay for a used Offy C-series or a Clifford intake. You might be able to save a few dollars on a used one. But I've also seen the used ones sell for almost as much as a new intake! If you go with a used one make sure it doesn't have any stripped threads, cracks or broken mounting ears ( Or poorly done repairs ) .

 

Makes perfect sense, I've rebuilt plenty of holleys, it all else fails i'll tinker it till it does what i want. I did check ebay there's one on there running 125$ right now, with 25 bids. So I'll likely just be buying a new one.


Just a wild thought, but has anybody ever stuck a Qjet on a ford? Didn't ford use qjets early on? I've got a few of those laying around, the smallest being a 750CFM. Qjets had HUGE secondaries and tiny primaries which make them great for street rods, and maybe situations like this.

 

F-250 restorer just got done putting a QJ on his and has a writeup on it. He said it drives great.


Fordman75, why do you advise against a 600cfm on a DP? That's what I have on my '81.

 

I don't like the DP with any carb period. Why buy an intake that has a built in restriction in the intake ports & plenum? The 300 has large enough cylinders to where there is no need to restrict the intake port ( to increase port velocity, vacuum signal, etc. ) . The 240/300 cylinder head does a good enough job of this already!! I really don't understand it when guys will do a bunch of head work, bigger valves, bowl work, etc. to increase flow and then run the DP intake.

It's one thing to run one if you already have one laying around or you get one for dirt cheap. But to go out and buy a new DP intake I just don't get.

I've ran both intakes on the same engine and noticed enough of a difference, in the old seat of the pants dyno, to swear off the DP's for good.

 

I'm all for using the QJ. I love mine...better power and mpg than the Edelbrock 500. The tiny primaries give great throttle response, and the secondaries kick butt. You just have to buy an adapter on ebay and port it a bit. Use the 750 cfm one from a sbc. You may need tighten the spring for the secondary air flaps, but you'll know. It is a variable cfm carb. That's the beauty of using one. You may also need block your idle bypass air holes to get it to idle down a bit, but that is simple. Ck my thread with a search. You'll also need to cut off the chevy throttle ball, and buy the kit made by holley to so you can hook up to it.



The round holes in the primary bores are idle bypass air. I had to plug mine to get the idle down. The pros recommend tapping the holes and installing a set key, but heck, I used a bit of an aluminum rod and epoxy.





I also took the oem throttle cable bracket from the j/y and modded it to fit my cable. I think I paid $2.00 for the bracket.

I really got to say I love the swap. Oh, and be real careful to check how the carb bolts to adapter. I had an issue with a major v. leak. Good luck.

 

Awesome! I don't need to block idle bypass, i'm positive i have a model that doesn't have it. BUT i installed it the lazy way (small holes in the primary/ or secondary flaps) I'll just swap the flaps with a parts carbs. I love my Qjets, you should see the 850CFM i have for a olds 403 build i'm doing.

 

I'm starting to love the QJ too. There is mega support in the aftermarket, and they're everywhere in the j/y. Once you get them dialed in, then forget 'em.

My carb is a Cal. emissions carb, so I'm sure yours may not have the idle bypass holes. K

 

Some baseplates have the places marked for idle bypass air but they never got drilled. I've got allot of qjets sitting in two boxes in my garage, after i rebuilt my first one i decided to hitup the junkyards around here and horde as many as i could lol.

I scored big on one in particular though, slashed vent tube Qjet from an oldsmobile 455, 850 CFM. Phenomenal carb, it's what I'm using for my 403 build.