I am back! Made it back from LA California with my 77 F250 Ext cab with no problems.

The carb on this truck is the smallest 4bbl I have ever seen. It is TINY ! It is smaller than the 600 CFM Holley on my 390 in my 69 F100. What in Gods name is it? It isn't a Holley carb...must be a Motorcraft? I think it needs to go bye bye...although the motor runs quite good with it on there.

The rule is, if it ain't broke, don't fix it....this certainly isn't broken but MORE is better, right?

 

750cfm vacuum secondary holley............'nuff said..............

 

A guy here at work just suggested that it may be a 500 CFM Holley "economaster" or something like that. Considering it has stock intake and exhaust, should I just leave it alone?

 

is the motor 4bbl?

 

The intake? Yes...

 

If it is the stock Motorcraft, it may look small but it is bigger than your Holley. Just becasue it does not have huge fuel bowls do not make the mistake in assuming it is a small carb. The Spread bore Motorcraft is something like 700 CFM. Hawkrod

 

ill only say it once!!!! i rebuilt the motorcraft on my 460 twice and it in no way compared to the power my holley gave to my engine, all that motorcraft did was blew smoke, literally.......

 

Thank god I never had that problem. Must have been a lemon. Given that several million Ford's, Lincoln's, and Mercury's came with them and they performed as intended I would guess they work well. I know mine do. Hawkrod

 

actually you said nothing relevant to his original question.

Why does it seem that whenever in this forum someone asks a carb question they get someone touting their particualr favorite brand of carb?

there are numbers stamped on the side of the carb that you can compare with the sticky at the top of this forum and find out exactly what cfm your carb is, and if it is indeed a motorcraft, and I doubt that its 700 cfm stock, thats a tad on the high side, a stock 460 only requires about 530 CFM at 4000 RPM.

use the decoder at the top of this forum, or post a picture and find out what youve got first, what was your fuel mileage on your trip?

I wouldnt change until you need to if it runs good.

 

Yes, valid points, and thank you for pointing out my error. After checking the sticky I see that the stock carb was a 715 CFM unit. Slightly larger than I remembered. A 460 would choke on 530 CFM. Even most stock 390's got a 550-600 CFM carb. The smallest stock carb on a 460 was the 68-72 square bore that was 600 CFM. Hawkrod

 

please take note that he wasnt asking a tech question, but rather just spouting off about his experiences and what he noticed about his carburator.....so, all i did was spout off about my carburator and experience with motorcrafts, which by the way hawkrod, i know various people that own and work in carb shops that wouldnt use ANY stock carb(motorcraft,quadrajet) for anything more than a boat anchor on their fishing boats, i know that there are good motorcrafts out there and its all a matter of opinion of what is better.....im not trying to start a stink here, im just opinionated, and having three Fords which all had crappy motorcrafts even after rebuild, i have a bad opinion about motorcrafts....heck i dont even like motorcraft sparkplugs...'nuff said...have a nice day...

 

Displacement * MAX RPM / 3456 = CFM needed at said RPM

460*4000/3456=532.4 CFM needed

Obviously the numbers state that a 460 would not choke on 530 CFM

that is for a stock low compression motor obviously.

no stink started SW OKC, I can handle it

 

That formula is what is known as a "perfect world" formula. The engines are of course rated for more RPM than 4000 so the carb would obviously need to be rated for maximum RPM not 4000 RPM. I'll stick with the Ford engineers recomendations but thanks anyway. Hawkrod

 

Ford's engineers use that formula, as does Holley, edelbrock, and Barry Grant for determining Carb size when purchasing an aftermarket carb, Id say theres quite a bit of Carb knowledge working for those three companies.....

of course the carb would need to be rated for maximum RPM, but who the heck takes a stock 460 past 4 grand, which was the intent when I plugged that number into the formula

The "thanks anyway" comment sorta rubs me the wrong way with its cynicism, like I was offering you something. there will always be people who use the formula and get excellent throttle response and fuel mileage, and there will always be people who want to overcarb, and stumble and hesitate at accelleration, get poor fuel mileage, but sound really cool when they boast to their friends about their 750 holley they slapped onto their 302, give me a break, thats high school teenager stuff.

If its a stock carb, its probably 600 cfm, which I would say is a great size for an aftermarket one on a stock 460, the number on the side of the fuel bowl would be 1.12 The largest motorcraft carb is only 670 CFM it has a 1.19 (I think) on the side of the fuel bowl, and have heard it was ultra rare......so hawkrod, if your gonna go with what Ford engineers say, I guess 600 CFM is the answer.....hmmm funny thing is that its not far off of my estimate using that "perfect world" formula, where I grabbed the 4,000 RPM out of the air as a number most 460's will never see the high side of unless they're built, which is a whole different topic now isnt it......

respectfully......

 

I agree with you but you are still missing my point completely. The STOCK Motorcraft is a 715. The info you are providing about CFM only applies to the 4100 series (those are the ones marked with 1.08, 1.12, and 1.19). The late model trucks came with a 4300D spread bore. I think you need to understand that Ford designed the carb for a 460 and decided upon a 715CFM unit. The earlier 429/460 did use a smaller 600 CFM model 4300 but engineers felt it was undercarbed and made the change around 1973 Keep in mind that this was during teh emissions era and I doubt that engineers would have gone to a bigger carb to reduce emissions! As far as max RPM goes, most people exceed 4000 rpm anytime they pass on a highway and that is a very bad time for an engine to fall flat on its face. I am sorry I "rubbed" you the wrong way but your info is not correct. Go to the Holley website and see what they recomend. It isn't that small. http://www.holley.com/HiOctn/TechSer.../FMCTech3.html Note that Holley recommends a 750 CFM carb for mild applications and good economy on a 450 cubic inch engine. There is a lot more to carb selection than a technical formula. The Holley website even shows the formula but then says it is under specific circumstances and then when you go to teh carb selection they recommend the 750 vacuum secondary. Even the Holley smog legal direct replacement carb is a 750. Hawkrod