Offenhauser

Is there enough difference between a dual vs single plane Offenhauser intake manifold? I have a chance to buy a used single for about half price so I'm wondering if is an OK deal.

Thanks,

 

Single plane is best suited for high RPM operation, dual plane for real world operation. My experience with a single plane on a street driven SBC was great top end, but poor economy and driveability around town. Of course at the time it was a livable trade-off to a young cruiser, but these days I wouldn't put up with it... my $0.02

 

Unless I was racing my jeep, bwwa ha ha ha, I would not consider a single plane. Are you talking about the split plane offy vs the dual plane offy?. The split plane offy you will have performance very similar to stock with a little loss in the bottom and a little gain in the top. The dual plane offy with the split runners will give a lot more low end power with a minor loss in the top end.

 

I've been happy with my dual plane. But then it was on my jeep when I bought it. It is a good design and well suited to lower RPM driving, like on the trail.

 

The first one I found was a single plane-at least that is what it seems as there is a single divider between the primary and secondary barrels. I'm looking for good manners in typical a driving scenario, not high RPM stuff.

 

Dual plane Offy and Edelbrock


Dual Port Offy

I know they are for different carbs but the Dual Port will be cast into the intake.
A single plane(sorry no pic) will have no dividers under the carb. You will see all 6 runners in the same hole.

 

Ratty, isn't the top pic a single plane Offy? The primaries and secondaries are sharing a common plenum.

 

I assume since the plenum has a divider it would be a dual plane.

 

The division is between the primaries and secondaries. They each have their own separate set of runners (passages). The primary runners are smaller. The idea being that at lower CFM the smaller size will maintain desired greater flow velocity.

I have found that the words "Dual Port" will appear near the thermostat housing and the carb plate has individual openings.
The best way to know is the look at the head ports. It distinctly shows two ports at each cylinder intake.

The picture below is obviously for a V8 application. You can clearly see the dual port at each cylinder intake location.