Technical can a Chevy guru explain this intake?

I picked up a 340 hp 327" Chevy engine that numbers wise says it is from a '62 Corvette. Now I know those motors ran an AFB. So looking at the intake, can someone school an ol' fellow on the design purpose? I know they were a good running motor.

 

pretty common design for Chevy high perf intakes from that era. I think the idea was that they wanted the individual carb ports to meet with the runner the same way on both sides...since the runner on the side with the two individual holes is lower, they extended the two carb ports down to the top of the runner.

But that's just a guess.

 

That very interesting 1972 SAE paper 720214 about "Design. Refinement of
Induction and Exhaust Systems Using Steady-State Flow Bench Techniques" talks a little about the difference in flow capabilities of one oval vs two round intake openings. Plus a bunch of other cool stuff.

Based on that paper a reasonable guess is Chevy made the openings different in an effort to equalize the flow in the two planes, and achieve more uniform flow to all cylinders. They make the reasonable sounding claim that is a desirable goal allowing more optimum compression and ignition advance.

By inspection the sharp corners and severely offset runners of that 340 HP don't include any of the high flow/equal flow details in 720214.

The only factory single plane manifold I know of came on Mopar Commando 273 engines. It is interesting to compare its runners to that 340/327 manifold.
The Commando manifold is in the middle here -
http://i727.photobucket.com/albums/ww275/66fs/273intakes001.jpg

 

your somewhat correct with your explanation , it has to do with plenum volume , as the one side is lower thus larger in volume and if left open would cause a fuel stumble , this is why on some manifolds like chrysler RBs with a single plane but dual quad we used stuffer blocks ( epoxied or mechanically added ) in it besides redirecting the flow it kept the volume ( space) low so you had excellent throttle response and no fuel drop out , when you kicked it WOT . the early torquer manifolds we stuffed on the floor in racing to do the same thing , and you could tune the hit to the back tires off the line .

 

Wow, Fascinating stuff, guys. With all of the engineering and technology that went into intakes it's amazing that any of those home-made sheet metal tunnel rams worked at all.

 

Here's an early edelbrock c4b, really a copy of the Chevy intake without the sharp corners Dan Timberlake was referring to. You can see the upper and lower plenum feed the same cylinders as the 340 hp intake.

Dual planes split the air fuel mixture between an upper and lower plenum, typically on a sbc, the upper and lower plenums feed adjacent cylinders. A GOOD dual plane equalize the distribution on adjacent cylinders by plenum and runner sizing.


Second pic shows a single plane with modified runner dividers and a "turtle" intalled. By changing the dividers hopefully on a flow bench, the intake is tuned for equal distribution. The turtle directs the air fuel mixture from vertical to horizontal flow and the ribs also aid in equal distribution.

 

That's a C3B intake.

 

LOL I used to know an induction guy that stated that a certain carb ( I won't step on anyone's toes here) was about as useful as a gas soaked sponge. Yes air would pass though it and fuel would make it into the manifold but that was where it ended.

You could possibly say that same about intake manifolds, some were little more than a place to bolt a carb and others are a real masterpiece of design. On the GM intakes with the oval and two holes I have heard the same thing it had to do with plenum equalization.

There is something that has always disturbed me about those intakes and obviously it is not the problem that it is in my head (or practical application trumps theory). When you are using a 4 hole carb pad as opposed to an open you can effectively increase your venturi length which in turn changes how your carb will function. On these manifolds the oval would represent an open carb pad and the two holes would represent the 4 hole pad so you have two venturis on your carb that have a longer venturi length.

Anyway it is obviously a problem in my head and not a problem in practical application.

 

Thanks guys, didn't know if I would even get an answer but the HAMB always comes through! Guess I was like Porknbeaner, kept looking at the oval versus the two holes and thinking WTF.

 

A Corvette restorer will pay more for that manifold since it is a fairly rare piece. I would suggest that you sell it to someone who wants it for his number matching car. There are plenty of manifolds which will perform as well that can be found cheaply at almost any swap meet.

 

Fritz, you are right, saw them bead blasted and "restored" on evilbay for over a grand! Right now I will hang on to it.

 

Great manifold I ran one on my 64 300hp 327 in stealth mode (orange paint) that and a L79 cam made a great running 300.

 

I don't remember if the winters manifold originally had 4 holes or as it's shown. I have seen many early dual planes modified that way. Any way, adding a 4 hole insulating spacer may help distribution issues.
I'd use it on the ' 62 engine for sure.

 

Great manifold on a 327. Just installed one like this in a 40 coupe-have used a few on 327's

 

I am no guru, but the idea behind these manifolds is to better utilize the primary and secondary from the carb. The individual smaller holes regulate the flow of the primary at lower RPM and idle, while the open slot for the secondary allows for the fuel to be able to dump into the intake at higher RPM where more performance requires more fuel consumption. Being the GM high perf engine it was aluminum for light weight and the design was to have a street-able car at low RPM and still achieve the desired performance of the sportscar at peek performance levels.

 

The problem with your theory is that the primaries are in front and the secondaries are in the back. In your scenario you'd have to turn the carb sideways and that wouldn't work worth a shit. Just sayin...

 

Wingman, that observation is what made me ask the question!

 

Got it, good call. I'll be sure to change my pic file naming.

 

Don't mistake the carb mounting flange shape. If this was true and 1 plenum was meant to run on primary and 1 on secondary, you'd essentially starve half the cylinders on primary.
The plenum is trying to take a vertical column of air and turn it horizontal and divide it evenly, once divided it needs to flow to 8 cylinders. On a single plane this 8 runners, on a dual plane it's 2 into 8 runners. The runners carry into the head and combustion chamber.
The reason the carb mounting flange is larger for the secondaries is twofold. 1) to fit the carb 2) to accommodate the larger volume of air/fuel into the plenum.

 

Well .... all I can say is it makes no sense to slot the venturi on one side of a duel plane manifold. It won't do anything ... unless it was a production line mistake. It would lessen the vacuum signal on that side .... it really makes no sense . . . . and to make my point even stronger, NOBODY has ever copied that design .... it's a dud !

 

I owned a '62 340 hp Corvette, factory 327 with this manifold on it back in the 60s. It came with a single AFB. And that was no dud, for its day it was one good runner. It wasn't copied because the design was refined and improved, by my understanding. And since it was offered on Corvettes subsequently ('62-'65) I doubt it was a production line mistake.

 

no-frame Larry needs this intake...

 

Nice intake and I have used several of them over the years and we sold them over the counter. I never did understand the theory of the design but — it was no wimp. The engines with that manifold ran really well so the design must have had some merit. I will see if I can find a write-up on the theory of the round and oval ports. Old technology but cool looking.

 

I have a NOS 66-67 L-79 intake that has some oem refinements/changes, but the same basic manifold.
The 66 Nova L79 350h.p./327 that Bill Jenkins raced was legendary in mid 60's drag racing.

 

I've got a Chevy intake that according to it's numbers was for the 1962-64 Chevy Corvette. It had a different design with the 4- round holes. See photo.

 

^^cast iron 250hp-300hp intake, I think.

 

you know, I should really try to find an L-79 intake for my '66 wagon, I could mill the septum out like Jenkins did, wouldn't give up much power, and sure would look cool.

 

xhotrodder, The manifold you show is for a 300 horse 327. It is iron and definitely not the same as the 340 horse manifold.

 

Hey George, it's this easy.
Step one: click on ye o'l auction site.
Step two: choose a manifold.
Step three: right check.
Step four: wait by mailbox.
Step five: install said intake manifold.

 

I just looked it up, I was wrong, Jenkins used a C4B with the septum milled out, not the stock intake. Nonetheless, I would love to round up a "490" intake and mill the septum out to run on my chevy II.