Im enjoying the feedback, this what forums are for,
a range of differnt approaches to a common theem.
any body got 2 cents, thro it on the table…
A “too small” carburetor tends to hide a lot of deficiencies. It’ll be down on power at the top end, but at least it will usually be responsive!
Running one with annular boosters ensures that you get good fuel draw and atomization even when air flow is sluggish. That means you can run a carb that is well-suited to your top end CFM needs (I.E. - a “big carb” that will offer less pressure drop) and still have good performance and economy with low throttle. It’s not crazy to put a 750 on a healthy 351, but if it’s a ho hum Holley or Edelbrock, the bottom end gets pretty soggy! More realistically, for a mild 351, a 600-650 would be better. If it’s an AVS2 or Summit M-series, you could get away with a 750 on a hot 351 and have no problems at all, thanks to the magic of annular boosters.
I’m not sure why you would want to run 4 degrees advance if you have the chosen the correct camshaft?
On the previous combination, was the camshaft phase checked with a degree wheel?
Manufactures tolerances can vary, I once had two camshafts by the same manufacturer, one was 2 degrees advanced, the other was 4 degree retarded. They need to be checked.
When you use a double row, put a straight edge ruler on the gears to make sure they are in line, if they are not, the cam gear will wobble and break off the locating pin on the camshaft. If they do not line up you need to machine up a shim or face the crankshaft gear.
Well said, Yearby. If you’re not checking the timing on valve events you really don’t know what you’re getting most of the time these days anyway.
The mathematical formula for the calculating a 4 barrel carburettor cfm to engine size and rpm is-
4 barrel Carburettor cfm = [(engine cid)x(maximum rpm)] / (3456)
So - (351 x 5000)/3456 = 508 cfm
for a 2 barrel carburettor it is-
508/1.414 = 360 cfm
This is for a daily driver, if for a 351 290hp engine and I was looking for a little more hp, 600 cfm?
It really is a case of ask 100 different people and get a 100 different answers.
If economy was my main concern, I would go the small size carb and take a small hit in total power and them try to regain it with other modifications.
Like use a free wheeling thermo fan or even a windage tray. A windage tray was generally only considered on high rpm engines, but now a day manufactures are using them on their everyday production cars to gain a little economy/power. You will need a hot thermostat for economy.
Smilodon, I have been reading you post you started, you write faster than I can read, have been reading for 2 days, still trying to get through it all, will get to it when I can.
It’s all boring nerdy stuff anyway, Yearby. 
Personally, I agree that the Edelbrock is a great out of the box carburetor, BUT - I hate the “feature” of them that if the car sits for more than a couple days, you have to crank the crap out of it to fill the bowls again to get it to start. Very annoying.
For me personally, that is worse than ease of maintenance. i would not buy another one.
I’ve seen this formula before. I think its garbage. No one in his right mind thinks that 500 CFM is adequate even for a 260 cubic inch engine.
A mild 351 is pretty happy with a 600 CFM Holley with vacuum secondaries. If you have typical modifications like a good intake, cam, headers, and decent cylinder heads then a 750 CFM 0-3310 Holley works very nicely.
If you don’t like quite so much horsepower then there are Edelbrock or Carter carburetors in those sizes that will subtract 10 - 20 horsepower, all other things being equal.
I think again we tend to over carb our engines,
loosing sight of what it is used for in the day to day world.
Thinking a bigger carb is needed because we think we may need the extra power one day ?
Look again at the factory suggestion of a more modest choice of a 470cfm carb OE for this car when it is a 4V .
Some years back i put together a very similar combination with a Holley 500 4b
It worked very well, drove well , tons of torque etc .
I may settle on a 600 holley for no other reason that i have one sitting around already.
Will i have any clearance issues with the OE air cleaner housing .?
A 600 CFM Holley with a banjo fitting fuel inlet fits the stock air filter perfectly and connects right up to the stock fuel line too.
I just put a 500 cfm AVS2 Edelbrock on my cougar, 1968 with a 302 & Edelbrock performer 289 intake + GT40 heads, & it runs great.
Any power losses are most likely to happen at speeds well in excess of your normal speed limits eg 90+ mph.
People tend to put to much cam and carbs on their engines.
Edelbrock only recommends the 500 cfm for a 302. The other nice thing is that low end torque is excellent & you might even pass a gas station once or twice a year.
On my previous 1970 cougar, I ran an older style 600 cfm carb with no issues. Edelbrock also makes a 650 cfm carb in the AVS2 series.
Running a 500 CFM carb on a 351 will give you good throttle response and low end (even with a mediocre carb!), but if you hook up a vacuum meter to your manifold, you’ll probably see a pretty significant pressure drop as you get above 4500 RPMs or so. At WOT, if you’re drawing vacuum, you are giving up horsepower. Just a guesstimate, but I would not be surprised to find out you’re losing around 20 hp to a good 600 cfm carb.
It’s not about top end so much as horsepower, and that would affect you in all three (or four?) gears, whenever the engine’s running with the skinny pedal all the way down.
I’d probably do something between 600-700 cfm if I ever step up to a 351 Cleveland. (Or install that 347 ci stroker kit into my 302 block)
Look that one up on YouTube.