Bigger Carb

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This may be have already been addressed somewhere else on the forum but here goes.

I am thinking of moving up to a bigger carb on my 69 250. I have the original autolite 1brl. I have heard that the 250s have breathing problems, so how much better is a bigger carb going to be?

If it is going to be that much better, what should I be looking for?

Any help at all would greatly be appreciated.
 
1. The options are based on space needed to have a good air cleaner which doesn't dent the bonnet! The direct mount Holley 2300 series adapor is the hardest to do, as you have to remove the head to fit it, but it is best for bonnet clearance. The shallow variants of Clifford or Stovebolts cheap adaptors can fit the 250 with an amount of reworking. Bonnet space is very tight on Mustangs with the tall 250. If you get the right one, any 2-bbl carb (Holley, Holley/Weber, or any Weber carb will fit on it)

2. With all I6's, Ford purposely undercarbs the engines. I've plotted the degree of carburation from all of Fords sixes, from the first 1941 sixes, right up to the last carb Argentine 221 and Aussie 250's made in the early 90's. The later 1-bbls are quite large, but still don't flow much more than 250 cfm or so.


Best option is the 2300 Holley 7448 or 9117 350 cfm, and the 2300 series Holley 4412 500 cfm, or the equivelent updated Demon or Keith Dorington versions found in the pages of the latests Summit catalogue. They will give you good results.

Nearly as good is the Weber 38 DGAS, which is found on European 2.6 liter Renualt 30 and Ford Capri GT 3000's from 1970 to 1980. It is a very good carb, with an air flow of about 340 cfm at 3"Hg. It has 28 mm venturis, and both throttles open at the same rate. Pierce and others import these, and they are almost exactly the same as the factory Ford 2.3 carbs, but every internall difference gives a 20% performance boost


There are any number of other Weber carbs which can do as good a job. The Us made Holley/Weber 5200 from Pintos and 2.3 Fox Mustangs, Fairmonts and Rangers is a good item, but it has 32 and 36 mm throttles and 26 and 27 mm venturis. It is a little too small for a 250, but can alledgeldy be turned to run okay. It flows 280 cfm at 3"Hg, although there are claims and counter claims that they do 225, 227, 230 or 290 depending on what flow pressure was used, and which one of the 15 versions you can lay your hand on. There are some similar versions found on Chevy Vegas as kits, and standard on 1980 to 1984 Chrysler K-cars and Omnis and suchlike

The 32/36 DGAV or similar Weber is the same kind of carb as the 5200 Holley Weber, but has everything reversed around. its sold by Pierce as a bolt on to early carb BMW's, Ford I6's, Jeeps I6's and flows 290 cfm at 3"Hg pressure.

On a tangent, one of the best carb for the 250 is the Aussie 2-barrel Weber 34 ADM, which has two 34 mm throttles, and two 29 mm venturis. Sensationally economical, it can give 22 to 23 US mpg in 3300 pound four door Fords. Flow is about 320 cfm at 3" Hg pressure, the industry standard for 2-bbl carbs.
 
I just put a Demon 350 cfm on my 1969 Stang w/250...works great so far...I'm still tweaking the air/fuel ratios (I'm rusty at this), and I'm not sure if my distributor timing advance should be routed like factory, or to the carb (has an outlet for that), but I can tell the engine's running a good deal stronger than with my original 1V. My other mods are electronic ignition and Clifford dual headers with port divider.

Regards,
James
 
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