On my 1972 250 I want to build it as a hotrod motor. I want to put a header, twin exhaust, cam, and have the motor bored with about 12:1 pistion. About what size carb do I need
I think you are going to need to use three 1-bbl carbs. You can find that setup on this forum... http://fordsix.com/forum/index.php
i have an edelbrock 600 carb you can trade for a holley 650 a 650 would be the best place to start.. but if you are running a true 12.0:1 compression.. maybe a 750?? not sure
I probaly want get to build that motor for awhile. Right now I am going to put a header and exhaust. I am probaly just going to put a basic 2v on it right now. Later on I would like to buy pistons, and a good head.
A motorcraft 2 barrel for a 302 (a little under 300 cfm) will do you fine for now. After you get you`r cam and all that good stuff you`ll be wanting a 500 - 600 cfm carb . Have fun
this is the best head...seen a falcon with one and it was awesome had 300Hp http://classicinlines.com/products.asp?cat=31
The head is the lowest performance part of the 250-6. Start there. You are much better off with a good head than with compression, headers, cam, carb, etc. Have the head work done (I recommend Sissel) and size the cam, intake, and carb to that. The stock bottom end will make good power if the induction system is properly sized.
are you wanting to run 12:1 compression? in your signature you said you're wanting it to be your street driven car, that's a little out there. you're not going to be able to run even premium fuel, i dont know what the octane rating is in alabama, but here in virginia it's 93 and you don't want to run much more than about 10:1 on it without knocking. Trust me i know. with rising prices, if you can afford cam 2, or airplane fuel, <--hehehe, I wouldn't do it. Not to mention overheating problems. just my .02
With 12:1 compression you will have to run pure alcohol or somuch octane booster that your gas will cost as much as 120 racing fuel. the practical limit for street engines is about 10 to 1. The 250 will respond well to an increase in compression but you are going to have a hard time keeping the head and block straight with 12:1 compression. That long crank is another limitation that hates high compression. You can do anything you want with the 250 but it is going to take lots of money. Almost everything you need to make it work will be custom or made to order. Good luck.
What PaulS said! It would really bite to have a hopped up hot rod that you can't run because you can't get (or afford) fuel for it. My 10:1 engine requires the highest octane fuel commonly available and at $60+ per tank of gas, it hurts to fill 'er up.
I guess I should have read this before building my 331 with 10.5 to 1 compression. But funny how it runs fine on 89 octane fuel. Ditto for the 10.25 to 1 390 in my old 68 Merc. 11 to 1 is possible with 93 octane fuel. 12 might be a stretch, but that all depends on the cam grind and timing you give it.
