Hey, does anybody know where i can get an intake manifold for a 4.9 that a four barrel carb can hook up to? Mine is for a 1 barrel carb and its limiting me a little bit. But im not sure, can i put a 2 barrel carb on that manifold?

 

Offenhauser makes 2 types of 4bbl intakes, the dual plane and the open. The dual plane is more for a street engine, where the open is more for even more performance with high rpms. Clifford makes 2 and 4bbl intakes but they are more expensive than offenhauser. Jegs, summit, and ebay all have the offenhausers. Personally im going with offenhauser dual plane with my 300 build and the EFI exhaust manifolds that i've already picked up. The offenhauser goes for $199 brand new. Cliffords are $289 brand new. Fred

 

If i go with that offenhauser intake, what would be a good carb to couple with it?

 

You can put a 2bbl on your stock intake. Cliffords makes an adapter plate to install a 2300 series Holley 2 bbl ( basically the same carb as the 2 bbl used on most Ford V8s) on your 300. I got mine for 60 bucks.

 

if you go with a 4bbl carb, on the holley side, probably no bigger than a 450cfm, from what i've seen, and i've seen guys talk about up to a 500 on the edelbrock side....take yer pick....myself personally, i'm gonna run a holley 390 4bbl on an offy dual plane intake with EFI exhaust manifolds...

MontanaFord

 

I know this thread is a little dated, but I can't resist! I'm really excited about it! I've been drooling over Clifford's website and dreaming of pulling my boat over the mountain without difficulty for YEARS!! I've finally done it, and ordered Clifford's intake and header setup. I'm going to put an Edelbrock model 1403 500 CFM 4 barrel w/vacuum secondaries on the intake, and have an X pipe put on my dual outlet header with a couple flowmaster mufflers. OOOOOO, baby, this old truck deserves it! I can't wait to pull the boat out of the water with that monster! 6=8, baby!

 

500 cfm may be pushing it just a bit, my research has come to tell me that 400 is a good maximum for cfm. Unless you do some other mods to your engine as well....
just my 2 cents...

 

Yes, I am a little concerned that 500 will be too much. I did call the professional techs at Summit Racing and asked them about it. They said that it would not be too much for that motor, and if I had any trouble, I could jet it down. Besides, I don't think it'll actually dump 500 cfm of fuel until the vacuum secondaries open. If that happens, then the motor will be turning enough to burn it! That'll be my boost to get over the hill pulling a boat. Thanks for the input!

 

I think unless its a thunder series AVS, Edels have mechanical secondaries.

I have read many places that 500 cfm is not too much carb for a 300, its not too much for a 302, we have a 500 cfm edel on a 302, and the throttle response and off idle acceleration are incredible.

Have plans for another one on Brother in laws inline six, and another on our 292 Y block, remember its all about displacement, not number of cylinders.

what is the summit part number for that Offy intake on Summit guys, I didnt know summit had it.

 

The edelbrock afb utilizes a weighted air door to smooth the transition into the secondaries. The biggest problem with this setup is tuning the air door. The only way to tune the air door is to add or remove weight from the counterweights. It is the counter weights that control the rate of opening, smaller engines will pull the door open slower than larger engines. I think the 500 cfm carb would be a little large, but not untunable, some throttle response will be lost, but will really come alive at the top end.

 

I don't know that Summit has the Offenhauser intake. The part number I have for the Offenhauser intake on the 300-6 is OFY6019DP, but that's straight from the guy I called. I was looking at that intake at one point. I decided to go for the Clifford setup because they engineered their intake and headers to work together, so I know there won't be any conflicts in bolting them on. I know that the Clifford intake won't work with a stock exhaust manifold, so I had concerns about the Offy intake in that respect. I wish Offenhauser had a website so I could eyeball what they have to offer for the I-6. At any rate, I appreciate the input on the Edelbrock 500. I was under the impression that it had a vacuum secondary, and that setting the timing for the secondary would be as easy as changing the spring as you would with a Holley. I haven't ordered the carb yet, so I will do more research on a Holley 390 vs Edelbrock 500. Just as a note: I called the Summit guys about whether or not the Edelbrock 500 would be too much carb for the 300, I didn't ask them about the manifold.

 

I agree that when considering the size of the carb, one should look at displacement. But the formula that I have seen on this forum and others uses the max rpm for that particular engine also. (We all know that a 300 does not rev anywhere near as fast as a 302) The logic for me is that the carb produces a certain max volume measured in cubic feet per minute and the displacement of the engine times its max rpm produces a certain volume. These numbers need to be about the same. Not having the actual formula at my fingertips, this is the closest I can come to an explaination. Most people I know say to get the 390 cfm holley for these inline sixes. Otherwise throttle response and mileage are reduced. John

 

Summit part number for the intake is OFY-6019DP.

Dave.

 

I have the 390 Holley, and I am well satisfied with it. It has smaller primaries and runs well for all normal use on those alone. Unless you substantially increase the rev range of the 300 six, and most do not, you do not need more carburetor than this. Additional cfm's is capacity you'll never rev high enough to use.

I think the cfm formula is as follows. Sounds simplistic, but it works:

(Engine displacement (Cubic inches) X RPM)/3456

(309 X 4300)/3456 = 384 cfm

My 309 cubic inch rebuilt six would have to rev past 4300 rpm to exceed the capabilities of the 390 Holley-in theory. In actual practice, you'll never rev a 300 to that level-not with any power, anyway, unless you do some engine mods.

Using the same calculations, a 500 cfm carb would get you to 5500 rpm. Best to tune the carb for the rev range it is used in, and in a work truck that would most likely be 3000 rpm and below. I've overcarbed vehicles before with an overoptimistic guess at where the engine would make power, and poor fuel economy and no bottom end/mediocre midrange performance changed my mind about carb size on low revving motors pretty quick.

The 390 Holley was literally a bolt on. No adjustments needed, seemed set up nearly perfectly right from the box. I admit to liking the tunable metering rod design in the Edelbrock better, as I'm an old Carter carburetor fan, but the Holley was drop it on and go.

 

'Good to see someone doing their homework! You should be as pleased as I am with selecting a carb - based on reality, not myth (bigger is better).

Not to rain on your parade, but the above equation is usually modified by a VE ( volumetric efficiency) value. From one Holley book - with essentially the same equation - the final cfm's must be reduced by the VE ( volumetric efficiency) of the engine . Stock VE = ~.75, High performance VE = ~.85.

The VE # is used in decimal form as a multipier. Take the stock VE of 75%, and multiply the 384cfm X .75, for a realistic flow capacity of ~ 288 cfm. At 90% VE, (384 X .90), you're still under 350cfm @ 4300 rpm.

Bottom line - the 390 is a very good choise for MOST 300's.