What is the best CFM?

mcmillal

Well-known member
What's the concensus on the best carburetor CFM on a nicely built up 200? I have a very nice rebuilt 200; port and polished, enlarged valves, bigger cam, header, etc. I've seen lots of guy on this forum with very similar build ups. I think my problem is the CFM of my current carb. It is somewhere in the 280 range. I am looking for a replacement and am debating between a Weber 38/38 320 CFM and a Holley 2300 350 CFM.

I am looking for performance here. So, what's not enough and what's overkill?

.............Alex
 
Hi Alex,

Seems like everyone here has their own idea of what to do with carburetion on these engines. As you may have noticed, the intake isn't removable.

A few companies (Stovebolt and Clifford) make an adapter that allows you to run a 2bbl carb on the 1bbl intake. I assume this is what you were planning on doing. This has been done by most of the old timers around here at one time or another and can work very well. Unfortunately, while you may have a 350cfm carb, the engine is still trying to breathe it all in through that restrictive 1bbl intake so, while you make pick up a little more power, you will never be able to take full advantage of having a larger carburetor.

Here's a pic of Doug's (Mustang Geezer) setup:

DCP_0005_1.JPG


And here's his page showing how he did it:
http://inlinefever.homestead.com/RamAir.html

Of course, there are other ways of how to mount a Holley or even that Weber. Depends how much power you want, how much money you want to spend, and how much modification/fabrication you can do/afford.

Going with an adapter, I would also recommend to look at a Holley 5200 carb. It's basically a Weber 32/36, but can be found on mid-late 70's Ford 4 cyl cars... easily found, rebuildable, cheap, and a decent performer.
 
Personally, I think there is a lot of overcarbureation going on on the 6's. I mean, I've seen 351W putting out 450HP running at 650CFM Holley.

I think (no physical data to support this) that for a mildly modified log head, you would really want no more then about 300CFM max...I would go about 200-250 CFM.

But that is just me.

Slade
 
Slade, keep in mind that the 4bbl carb you are referring to making 450HP is rated at 1.5" of Hg.... and 2bbl carbs are rated at 3" of Hg.... so it's kinda apples and oranges. A Holley 350 2bbl will suit a mildly warm 200 nicely... especially if it's mounted right to the intake.
 
Thanks guys. I will be really trying to jet a H/W 5200 I have for optimum performance very soon. I am going to install a fuel regulator to control the fuel pumps PSI. Apparently, these H/W's don't like more than about 4psi. My stock fuel pump is putting out 7psi so there is gas dribbling into the secondary.

I am leaning towards the Holley 2300 (350CFM) setup. I really like what Doug has done.

I will let you know the results. (jet sizes, performance, etc.)

...........Alex
 
I agree, a 350 directly mounted to the intake log on a warmed up engine (cam, headers, CR around 9.5:1) is a great carb. I'm not so much refering to a 350 carb, but more for larger carbs.

Slade
 
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