ok i have a completely stock 460 from 78 f350 camper special. the intake is edelbrock performer rpm. and i have two possible carbs to use. i just dont know what cfm is best suited for this thing. help.

 

just putting a reply to my own to put back at top of posts haha

 

https://www.ford-trucks.com/article/...arburator.html

 

750 would not to big.
I run a 500 carter on my 300I.

 

Unfortunately, charts and ratio calculators are a little on the bogus side. Identical spec engines, can use different carbs, and each one will react differently.
For example:
the exact same 460 in a truck with an automatic, stock converter, that tows a 5th wheel, stock 31" tires and 3.55 gears might be best suited with a carb in the 600 CFM range.
Now, take the same engine, and put it on a truck that weighs less, has a 4 speed, some decent gears, and spends most of its time in the mud at a silly rpm. Well this truck might gain benifits from a carb in the 750 plus CFM range. Same engines, different applications, and each one will have different carbs.
Now we have to also consider, which type of carb you will use. Holley, Eddy, Demon? Even at equally advertised CFM, each performs differently, and each has an advantage.
Other variables would be whether or not the secondaries are vacuum operated or manual, and your ability to tune.
Many will stay with small carbs because they lack the ability to tune a carb. Its really that simple. Some will argue that larger carbs lack throttle response, and this too is kind of a wives tale.
The key here is air speed, or velocity, and booster signal.
I run a Demon, 750 manual secondary, carb on a fairly stock 460, with an automatic trans. 2500 rpm stall, (flashes to 3200), 4.56 gears, 39.5" tires, and this thing screams.
Nails the rev limiter at 6600 in a flash, idles like a stock engine, and fires up dead cold with no choke. Revs like a 12:1 289, and has throttle response like you cant imagine.

I truly believe that if one can keep air speed up, and bosster signal reasonable through the venturi, that you cant run a carb that is too large.

Give the ngine what it wants, and dont limit power potential because some chart tells you to run a conservative carb.

Dont get me wron, it is easy to run a large carb and have poor performance, but this is usually not because the carb is too large, it is because the carb is not tuned.

Worlds largest mistake with carbs, is that too many tuners, open the throttle blades, too far and idle on the main circuit, and not on the idle circuit. This is why larger carbs idle so rich and burn eyes, blah, blah. Easy to blame the carb for being too large, but the truth is that the air moves past the booster too slow, and the air / fuel ratio is messed up. The fix, is to install a smaller carb, and this seems to fix the problem, but is this the real fix? Not really. The only reason this appears to be a fix is that the smaller venturi naturally increases the air speed, and the signal is stronger, making the mixture slightly better.
The larger carb is still capable of providing the same low end performance, but e as tuners have to be capable of dialing them in.

Case in point:

current throttle bodies for fuel injected engines have CFM ratings far above the 600 CFM range, and they run reliably.
Matter of fact, some are capable od exceeding 1000 CFM. Still they are used on small engines. They run fine because the ari / fuel ratio is adequate.

The same is true for a carb...........

Do some research on Demon carbs. In my opinion, the hottest ticket out there. They require some reasonable tuning, but have the best performance of any carb on the market.

 

75F350 - excellent writeup. One of the best explanations I've seen.

 

Wow. Thank you sir. Actually thought I was gonna recieve some heavy criticism, for this view.
Pretty sure I still will, but thank you for the positive comment.

 

ya i didnt make it too my third year tuning and electrical. so i know little about them. but i have a pretty much brand new edelbrock 750 i bought years ago and never used. and i also have a used edebrock 600. the 750 has a little hesetation at lower speed when i step on it but i think its lack of air. so everything you saying makes sense to me. i have to plug a hole below the choke pulloff and set idle mixtures again. will that help with the hesitation? i really dont want to run open air cleaner it will get wet with what i do.
[IMG]file:///C:/Documents%20and%20Settings/Craig%20Christ/My%20Documents/My%20Pictures/vlcsnap-105647.png[/IMG]
i dont know how to put pictures in.oh no i suck again.

 

A hesitation is actually a combo od things, but the first thing is the simple accelerator pump. Too short of a shot, and the engine will bog or hesitate. Interestingly enough, too large of a shot, and the same symptoms are present.
Two things to consider:
the duration of the shot, and the volume.
What happens is that the throttle blades open so quickly, that air speed cant move past the booster fast enough to draw enough fuel to compensate for the huge vacuum leak. Thats what a carb is really, a controlled vacuum leak. To operate effieciently, it has to provide some fuel so the engine stays happy.
Anyway, when air in a large amount is introduced, more fuel has to be present. Since the air speed immediately drops off, fuel cant be drawn through the booster, so it has to be artificially introduced. This is the accelerater pumps job. Squirt fuel dirrectly into the carb to compensate for the carbs inability to mix the fuel, and the transition can be seemless. Mess this mixture up, and this engine will struggle, and will labor to reach rpm. Some are so bad that they do not actually recover, and the thing takes a ton of time to rev.
Remember, too much squirt, and too little squirt can act identical.
I go to extremes when I tune. This way I see which direction I need to go.
This really becomes a trial and error type of thing.
The Eddy carb seems to be the easiest to calibrate, and is very forgiving.
If all else seems to be fine with that carb, then work out the little stumble bug, and you will have a good running engine.
Be sure to have your timing set right before you adjust the carb. Believe it or not, a degree or two can change the hesitation too.
Yup, another variable. Fun stuff though.......

 

timing is bang on 12deg at 650 rpm. full advance at 2000rpm is 43 degrees now from what i have learned that because of the lobes on a 460 cam. you should ty to keep full combined vac at about 30-35. mechanical is giving me about 10 deg at 2000rpm and vac advance is 20ish. any of this making sense? i dont know how to change accelerator pump or anything about it. so my idle mixture should help a bit then at the lowest of the rpm range?

 

im thinking too much of a shot if it is accelerater pump. the 600 has no hesitation. how much difference is there in the accelerator pump from 600 to 750?

 

ok i think i was just looking at accelerator pump linkage and there is 3 different holes in it that i can move linkage down. the 750 is on the top hole and the 650 is in the middle hole. am i looking at the right thing? do you know the edelbrocks well?

 

I'm running the same intake on my stock 460 SCS. I had a Holly 600 on for a while and it ran well. I have my timing set to about 12 also. I am now running a 670 Street Avenger, and it runs even better. Pretty decent throttle responce for such a giant Wag.

 

I have the 600 and the 750 Edelbrock. I read all the junk about the 750 being too big as well. I have a slightly modified 460. The heads have been reworked with Manley oversize S/S racing valves and a port and polish job. Otherwise the engine is pretty stock except for bolt on items.

That engine was like turning on the lights when I put the 750 on. The 600 has been in the box ever since. But to answer your question my accelerator pump rod is in the center hole. It seems to work best there. The engine fires so fast that you can hardly get the starter engaged before it fires. It is so quick firing up that I even get comments from people that hear it start. I would never go back to the 600

 

I run a 770 on mine performer rpm and small voodoo cam