4412 VS 7448 Holleys

[wsa111]

I, thought this would be better addresed as a new post.
I am finishing up testing on the two holley carbs 7448-350 CFM, 4412-500 CFM. These carbs are tested on a modified log manifold.
In the future i plan to do a dyno test or drag strip times comparing these carbs. The 350 carb is easier to get a decent idle & the driveability is more responsive at slower speeds than the 500. The seat of the pants goes to the 500 cfm carb for max power. The 350 is much more responsive in low rpm situations.
I know the brothers CZLN6 & hot6tfalcon, are in the process of testing both carbs. I think the brutal winter in idaho & the dakota's have delayed their testing. I think i have fine tuned the carbs as far as power valves.jets & accerator pumps so when the weather breaks we can get some concrete results. Dennis & David feel free to give me a shout. William

 

[ASMART]

Thanks for keeping up to date. This is the kind of infowe are all interested in. Keep up the good work!

 

[mcmillal]

Hi William,

I have been playing a lot with various carb setups. You probably remember the 1/4 mile results I posted after each change. The last time I ran with the Holley 7448. Great setup. I have since installed stronger valve springs and a Holley 4412. I didn't make it to the track with my latest configuration, but the way it drove around the street, before I stored it for the winter, was awesome and a lot of fun. I am looking forward to returning to the track to measure the improvements. The initial indicators, g-tech and seat of the pants fun, are looking good. I was concerned that I would lose some bottom end with the bigger carb, but did not. It was actually stronger all around, and the top end is way better. I was surprised especially because I am running this carb with an adapter on a small log head (1967). The only thing that did not improve was my gas mileage, but hey, we don't do all these things worrying about gas mileage do we?

...............Alex

 

[CZLN6]

Howdy William:

Thanks for sharing. You're right about the winters! That's why I'm in the rainy, but warmer, sunny southland right now. Dennis is holed up and waiting out the character-building North Dakota winter.

My #4412 is on the work bench with a new kit in it, waiting for warner weather, dry streets, and a new u-joint.

I am at 5,000 ft elevation so I'm fairly certian that I'll need a leaner setting than yours. But then, I'm testing on a 250 engine in my Roo. Time will tell. Could I ask you to post your current setting on your 500?

Thanks again.

Adios, David

 

[wsa111]

David, first get 6-7 # of fuel pressure, second set the float level so the level is right at the lower threads of the fuel level plug, third put in #70 main jets, fourth put in the blue accerator pump cam in the #2 screw hole. fifth with the throttle wide open there should .015 clearance between the accerator pump lever & the adjustable screw on the end of the link, this can be adjusted with a 3/8 box & open end wrench. You have to take a pair of pliers to fully open the accerator pump lever & measure & adjust the proper clearance if you go back to the 30cc pump housing which is not necessary. Last but not least try the 8.5 or the 7.5 power valve, but i am using a 2 stage power valve to cover the lean hole in the part throttle position. The holley # is 125-210 which starts to open @ 9.0 hg & fully open @ 2.5 hg.
You have a 250 head so you may have to go to a #71 main jet???
I have modified the blue accerator pump cam & rounded the sharp corner at the opening ramp to have the same contour as the top corner of the orange cam. I will do a post on this later.The blue cam has the extra lift to richen up the mixture as needed, but without the 50cc pump cam. Remember you can still leave the 50cc pump on the carb but you just are not using the cam that comes with the 4412 carb. if you still need more pump put the stock 50cc cam back on and try it.
I am running a .0295 accerator discharge nozzle, it is a drilled out .028 & works fine, you could try a .031 cause of the size of your engine.
This will give you a bolt on setup darn close to what you need.
I am running the 264 FSPP cam with a 112 lobe center & 1.65 full roller rocker arms.My exhaust is the 6601 hooker headers with a 38" 1 1/2 primary pipe to a 2 1/2 collector then to a 2" pipe out of each collector then through a X pipe to dual flowmaster hushpower II mufflers.
The air cleaner is a 14" x 3" with a recessed base & i have plenty of hood clearance on my 67 mustang.
When the local drag strips open around here, i will do some further testing.
Hope this helps .William

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