What kind of carb does this use???

[Rockfish39]

Oil4kids showed me a picture of this....

I have a couple of questions about it, for anyone who might know...

What application was this intake originally used for ???
What model/size carb does this intake use???
What are the throttle bore sizes ???

I think he's right...other than being a bit beefier around the secondary throttle bores, it looks strikingly similar to the 409 truck intake

Rockfish

 

[CDNpontiac409guy]

Rockfish, I think that's that 340HP 348 alumnium manifold that was missing from my "package" picture of intakes.... and I NEED ONE real bad !
I believe 1960 & 61. Same basic design was used on the first 409's in mid 61.
Uses a Carter AFB similiar to a 300HP 327.

 

[CDNpontiac409guy]

just a blank message

 

[348NUT]

Don't worry Aubrey I'm not going to catch up with you and you're not going to catch up with dq! That looks alot like the aluminum intake on my 61 409. NUT

oh and that sure takes up alot of room for a "blank message"

 

[61stumppuller]

Here is my 2 cents. I think it is a 3767579 used on the 61 305, 340 and 409/360 engines. Look at Alan Colvin's "Chevrolet by the Numbers" pg 121. The blueprint shows the same runner profile for the #2 & 3 cyl. My 61 348/305 has a Carter AFB 3221. This looks like most early 60's vintage AFB's except for an aluminum boss just behind the choke housing. Its about 1/2 inch in dia and sticks out like a sore thumb. It's just part of the throttle body casting. I have seen the same boss on a few other AFB's with two electrical contacts mounted on it. I don't know what they are for or what the application.

There are two other aluminum manifold numbers running around. There is a 3780540 and a 3753748.

 

[JokersBel]

hey nut, you are right, no one will catch up with DQ! lol the man is a machine (or at least always on one!-computer that is )

Aubrey, i'd bet that you can find that intake on ebay soon if you need it. I'd certainly like to own it too, but I don't even own a 409 .... YET! haha Jim

 

[JokersBel]

ooops, i guess I could use it on the spare 348, MAN talk about a blank message - in my head!

 

[Rockfish39]

Hey Stump,
Good observation.... But take a look at the throttle bore arrangement. The primaries seem like they are standard 1.5 in bore, but then closely examine the secondaries. Those bores look to be on the same centerline as the primaries, but they arent. The outer edges of the radius on the secondaries are square with the outer radius on the primaries. But they are not on the inner radius. What this tells me is: that the secondaries are open to a 1 9/16 bore and, because of geometry, are closer together than the primaries are at 1 1/2. Look at the webbing between the bores... It is thinner in the back than the front...The big question is why would it be made that way??? Oil4Kids has to be right... A design like this will keep the venturi velocity on the secondaries higher than normal at the mid-range RPM band. Although an arrangement like this is not well suited for drag racing applications, it would be much better suited on a NASCAR type application. ALSO there is no exhaust port coming up to the base of the carb... Aside from not cooking the gas out of the carb, This design keeps the air density charge at its maximum.

Rockfish

 

[348NUT]

This intake was originally designed for the AFB which is a slight spread bore design. These bores would match the AFB bores. Here's a nice closeup: This intake has a slightly different runner design but I think the carb bores are the same. NUT

 

[dq409]

I don`t think thats the same manifold Nut,,,,,
If you look at the runner coming from the left front hole it runs at an angle and your runs straight forward,,,,,Same on the back runner,,,,
Seams a more even flow to the front and rear cylinders as it has equal length to each side,,,,,
on yours it is offset,,,,
HUMMM,,,,,,,,,

 

[threeimpalas]

I believe that NUT was just pointing out the fact that the bores for the carbs are the same. He does state that the runner designs are (obviously) different between the intakes pictured.

 

[61stumppuller]

This is getting interesting. The photo that 348nut posted shows the 540 casting# behind the secondary bores. I believe the 540 was used on hi-po 1959 /60 cars. The photo that DQ409 posted may be the later aluminum version used on the 61 hi-po 348. It looks to me that the skewed upper runners tend to give equal length runners from the intake bores to the cylinder head port. This is a more sophisticated design than the 540 which does not show equal length runners.

 

[jim_ss409]

It's too bad there aren't any good cheap aftermarket manifolds out there for these engines. I think an up to date style intake would work great on the W engines. I guess there aren't enough of us out here to make mass production worthwhile.

 

[wrench]

Uh oh

Didn't we almost get an intake project started once back on the other message board?

 

[348NUT]

Yes I know dq.

The 540, 776 and all later 409 intakes had these straight main runners. I hadn't seen one with the curved ones before, but notice how the air has to turn around and go backwards a little into #2 and #8! This can't be good, can it? : Could this be why they changed? NUT

Thanks threeimpalas for sticking up for me. That dq can be a real bully!

 

[348NUT]

For what it's worth....

Here's a quote from the 61 HotRod article "409 Biggest Chevy yet":
"The 409 intake manifold is the same as that used for the 340hp 348 engine with one exception; the throttle bore risers have been opened up on the primary side to match the larger 409 carburater. This aluminum four-barrel manifold does not use curved runners to the intake ports of the heads like most 180 degree manifolds, instead a large straight log from each side of the carburater runs lengthwise along the manifold with straight runners taking off at 90 degree angles to the ports. This method of using square corners creates turbulence and keeps the fuel from falling out of suspension as it will sometimes do on sweeping curves."

I'm assumimg this is refering to the 776 intake used on the 61 409 compared to the 540 used on the 348. I'm no expert, but I'd say at high rpm there is little time for fuel to be falling anywhere but into the cylinders and that a nice curved runner would get it there even faster? Correct me if I'm wrong but these straight log intakes don't make sense to me and look funny too. :evil

 

[threeimpalas]

I don't think the way the runners turns back would be a problem, although that bump out thing between the #2 and 3 runners looks like it'd do a nice job of catching some air and causing some unwanted turbulence.

Keep in mind that the new LS1 intakes have runners that loop around in a big (almost) circle and they perform fantastically.

 

[61stumppuller]

I like my Impalas red, without a top, three pedals and AM radios.