408 ford

Ah, the age old question of what is too much carburetor rears it's ugly head again.  I was wandering through the store the other day and happened to pick up a copy of PHR.  I was interested in the article on the 408 ford in a Fairlane.  I saw where your intention is to put a 950 on a dual plane manifold which is a great idea.  I read further and you mention in the article that there are some out there that feel it will be too much carb. To those individuals I would like for you to contemplate some oversimplified science.  I will use a 302 ford as an example.  The old Holley Carb "bible" has a simple formula for calculating carb size.  This formula will suggest that you run something around 550 to 600 cfm on a 302.  This is for a single plane manifold.  Each cylinder sees all four barrels. On a dual plane manifold though, each cylinder will only see half of the carb.  Each cylinder will only see half of that 600 cfm or 300 cfm.  Now we are undercarbed unless we are trying to get mileage.  In order to get the same cfm per cylinder on a dual plane you would need a 1200 cfm carb.  Interestingly, the Holley Dominator was effectively designed just for that.  It was intended to be run on a small block in Trans-am racing.  

I used to have a 2.0 liter Pinto with a Holley 600 on a dual plane.  It was actually a little under-carbed and I could have used something closer to 750 cfm.  I would hazard a guess that your 408 will be a little under-carbed even with the 950.  Each cylinder will only see 475 cfm which is a little like running a 500 cfm 2 barrel on a single plane.  If you really want to do a test, get an adapter and try a big dominator as well.  The main reason most dual plane set-ups make so much less power in street applications is that most hot rodders fail to size the carb correctly,  

thanks for the info  

Vizard likes to say that if the carb can still meter the fuel, it's not too big.  Put some good boosters, like annulars, and you could run 850, 950, 1050 without any real problems.  

Also, from what I'm hearing about people actually testing HP 950s is that they are really not 950s.  Something less, which varies.  I hear numbers in the 900 range.  A guy on the big block Ford forum flowed a 750DP with a Proform center and IIRC, that carb flowed around 840.  So there are lots of good options.  
1967 Falcon 4 door - 351C
1970 Mustang coupe - 351C
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

Actually we ran a 750 HP on the dual-plane and a 950 HP on the single plane.

The stroker engine LOVED the 950 and the extra air, so I figured why not run it. I agree that as long as the carb can handle fuel metering it can work on a given engine. Most of the time the problem isn't that the carb is too big, but more that it's tuned badly.

The Fairlane engine came out great and I'm pretty happy with the combo (except the non-overdrive tranny).  

Mr. Rupp,

If you could, please e-mail me.  I'm building a '69 Falcon Station Wagon, which has a very similar engine bay.  I'd like to know about your hood clearance with the Vic Jr. intake, and will probably have a few more questions as my build progresses!

BTW, Stan will probably start building my headers in a few weeks :-)

Thanks,
Lee Atkinson  

Actually, with a 4 barrel carb on a V8 with a duel plane intake, half the cylinders see half the barrels on the carb. The reason the carb may seem undersized with a duel plane intake is because of the split nature of the intake. The cylinders feed off of smaller plenums. A larger carb on a duel plane is NOT going to help. A larger carb will be better served on a suitable single plane intake, assuming the engine is set up properly to use it.