I'm currently running an Offenhauser regular dual with two Stromberg 97's on my 59A flathead. I was thinking of switching over to an Edelbrock super dual, both for a slight performance improvement but mostly for appearance. I recently saw that Vern Tardel sells 4" risers and thought that those might look okay on the Offy regular dual, kind of a poor man's Thickstun. What's the consensus on performance of the regular dual with risers vs. the super dual without risers? I know appearance is an individual thing, but what do you think of the appearance pros and cons of each option? Thanks.
Not enough difference between regular & super for a street-driven car to worry about. Run what you like. Risers will help marginally...
Like Flat Ernie said, not enough difference on the street to make a difference. Is the super better than the regular dual? On a dyno sure, but you'll never feel the "seat of the pants" difference in your car. Matt P.S. My friends would say...."Of course the super dual is better, that's why it's called super and not regular" LOL
Tardel's risers are machined so that it is a single port for both barrels of the carburetor down to the mainifold. Any downside to this versus a riser that's machined for separate ports for each barrel down to the manifold?
The open plenums work just like on a 4bbl intake where single plenum intakes are better suited for higher RPM use and dual planes are better for low-mid RPM. The open plenum risers will weaken the signal to the venturis in the carb. I wouldn't run those on the street. I'm sure there are several folks who've had good success, but I'd prefer to keep a strong signal to the venturi... Again, might not be a difference on the dyno, but this is a case where low-speed driveability may suffer a tiny bit...
Curious, what about the rumor/myth/fact that a regular dual doesn't get the charge equally to all cylinders? This is what a super supposedly corrects. Fact or fiction?
" Weaken the signal to the venturies in the carb."???? I don't understand.. This maybe a problem for the 94s power valves, what else is the issue.. Duane.
Nothing to do with 94 PV. Most flathead intakes are a dual plane design. One barrel on the carb feeds half the cylinders. The venturi works by pressure differential. Air flows faster through the venturi, this lowers pressure, and fuel is drawn out via the jets. By putting a 3" open riser under the carb, the signal (pressure drop) to the venturi is mixed and both venturis see all cylinders. At high RPM, this isn't a factor. At lower RPM, you're diluting the pressure drop seen by each venturi. If you run a two-hole spacer/riser, the signal to each venturi remains the same. Some combinations are more sensitive to this than others and it primarily affects off-idle and low-speed operations - throttle response becomes less "crisp". I've probably not explained it well again...
This is great info guys, thanks I was just asking a buddy of mine the same question this morning on the phone about the difference of performance and look the high risers give vs the lower regular dual design glad i caught this thread today. Thanks, CAB
As another way of looking at it...if engine likes X amount of caruretor flow with a regular 180 separated manifold, it will want less than X with an open plenum design and considerably more than X with an independent runner manifold. In the small block Chevy world, the CFM range on a 350 might run from 650 to 1200 within these options!
Chevy SBG tossed in here because the tech is much better documented and dynoed... Look at some of the posts on 4 carb manifolds on flatheads...how overcarburetion isn't...
To the original question about going from a Offy regular to a Edel super... It'll make a bigger difference in the motor and the engine compartment than just the minimal performance gain... The Edelbrock super doesn't have the generator mount on the front. So if it's on a late motor, you'll have to figure out something for the fan. Also the Edelbrock has the exhaust heat risers blocked. So the exhaust note will change a bit and might sound more 'Hot Roddy'... It won't give you a big seat of the pants change but it might make a pretty big difference in the 'personality' of the car with all the other changes it will bring.
Not 100% true on the Edelbrock. The older versions did have the generator mount and they offered it with or without heat risers. I have one with a gen. mount and heat risers hanging on my garage wall.
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