Currently I'm running a Holley 650cfm double pumper dual feed mechanicle secondary carb on my 300. The motor is bored over .030 over with a .265 cam, cliffard intake, a header, with a stock head.

Is anybody running there rig with a bigger carb?

How about the dual carb set up?

 

I'd be surprised if you find someone here with a carb bigger than that. How does it do? Any idea what your gas mileage is like? I run a 500 CFM Edelbrock on mine and would be hesitant to go above that. With a 30-over bore, you're only adding just under 5 cubic inches. I've been surprised before, though.

 

The guys who really beef these engines up bore them .050 over. That allows them to run 390 high performance flat top pistons, ARP bolts everywhere, lol.

I'm surprised Clifford has missed that trick, but, then again, there just isn't a market for it.

I notice the dual set up Clifford sells is for 2v carbs.

 

Got you all beat: 750CFM Quadrajet. Though I doubt those vacuum secondaries ever open much. :-)

 

I ran a holley 670 truck avenger very briefly. After I took the feedback carburetor off a 1985 300 and put on a clifford and EFI manifolds I put that 670 truck avenger on to drive the truck where I needed it. Then once I got there I put on a propane system instead. So it was only 10 miles total I drove it with that big carb. But it drove great, didn't feel overcarbed at all. Pulled great ride from idle, just like a big six should.

 

Holley 4160/1848-1 465cfm.

 

Why? and why run as big as you are? Have you checked your exhaust saturation/temp... the only time you might use that much fuel is well over 6000 rpms. I have seen it at the dragstrip... it is very impressive. SOunds like a 2 stroke. Keep in mind unless you have some seriouse machining done your head wont even flow enough for that many cfm carb to benifit... It will hurt you. especially when it is hot and humid

 

I will be running an Autolite 4100, 480 cfm. And I should be firing up the engine for the first time on Thursday, I hope, if we get all the wiring done in time.

 

Well the gas milige with the Holley 650cfm is pretty bad, probally around 5-7mpg I'm guessing. But I have my motor in a 1986 Ford Bronco with 36.5'' super swamper TSL's, so I could care less about mpg. I'm all about more power and perfomrance!!

The carb runs great with my setup, but I know how to tune a carburator which has alot to do with how the motor runs with no burps or hesitations and idealing around 550 rpm. Thats why I can't wait to get a head thats not cracked so I can modify it with bigger valves, port and polish it, and all that good stuff.

I know for a fact that the motor is burning the extra fuel that the Holley 650cfm is putting out. The plugs are never wet, but a nice golden almost redish tint to em. But yes when I do get in a nasty mud hole I'll have the motor reving around 5500rpm's till I get out or just having fun running through the gears!

 

BigBlue88 probably has the optimal large carb arrangement. The Qjet with the small primaries makes for good, economical driveability for street and highway driving plus the potential with the big secondaries to feed the engine all it can use and have some change left over. I have a Qjet off a 77 Pontiac...a good year for Qjets...that I want to have rebuilt in the not too distant future.

 

Won't that be the 3rd carb you're tried on that guy? What size are the primaries on that Qjet?

 

1 3/8". The secondaries are real toilet flushers...2 1/4". I am carburetor poor. Four Holley and two Qjets. I could probably get rid of some of them or obtain five more 300 powered vehicles just to use up the carbs?