Actual cfm used vs carb size

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F-BIRD'88
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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Thu Apr 11, 2019 11:50 am

The problem with the 4 qjets on the tunnel ram was the divided plenum. With the plenum divided cylinders 5 and 7 are isolated and fire 1 after the other, 90 deg apart. Thus strong pulsing and reversion on that rear left carb.

If the whole plenum was open the strength of the uneven pulsingbis dampened a good bit just like on any tunnel ram.
A better result would have been if the manifold was a dual plane hirise dual quad intake.
Now the cylinders all fire 180 deg apart.
Could be split plenumnor partial open.
The 4 qJets would work great above a 8-71 blower on this Olds V8.

On the tunnel ram I would have aranged the 2 pairs of QJets a bit different.
Each pair of carbs would be sideways, but inline. (Not back to back)
The front carb's primaries are blocked off and disabled on the front carb of the pairs.
Now there are 6 venturi over each of the 4 paired runners. Common open plenum.
2 central primaries and 4 big secondaries.
4 total primaries and 8 total secondarys in all.
The front carbs of each pair act onlt as secondarys as their primary side is blocked off, not exposed to the plenum at all. 12 venturi in all. 2x Six shooters with symetric venturi layout. Open plenum on the tunnel ram.
Simpler throttle linkage.
The total potential WOT air flow is 2590 cfm @1.5"
If when all air doors are wide open.
The beauty is that the total wide open air flow is completly adjustable by adjusting the air door tension.
Now it is progressive as needed. So is the fuel curve.
By adjusting the 8 sec fuel metering rods and 4 hangers.
A open plenum is much better. On this tunnel ram the split plenum was a mistake.
But again, would have worked much better if the base manifold was a dual plane intake manifold to start with.

Using 4 of the Edelbrock 650 AVS2 carbs instead of 4 qjets would be easier to work with in both back to back and inline pairs configuration. The Divided plenum was a mistake on this one.

F-BIRD'88
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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Thu Apr 11, 2019 12:18 pm

Further they could have saved a ton of money by making the prototype plenum- adapter out of (stacked layers of) wood, FIRST. (Eg: plywood) Allowing easy dissassembly modifications and revisions in the design to work out the bugs. (Like the divided plenum)
When yoy get it right, then cast it or machine from billet aluminum layers.

3D PRINTING lends itself to a plenum/adapter project like this very nicely.

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