Offenhauser Dual-Port 360* Intake ~ 'Was It A Gimmick'

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69 Cuda 440

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IMO, Gimmick! Everyone needs a gimmick. I look at this I take and can not buy into it.
I'll design my own.
 
In Theory,

It was supposed to work. As a more 'efficient' Intake that would increase
fuel mileage and improve 'low-end' performance.

They did make these Intakes in both a Square-Bore and Spread-Bore when
they came out in 1971.
 
I put one on a 273 when they first came out. It worked OK but I didn't see any significant difference from the 1966 iron manifold I reamed the bolt holes on to fit my 64. In 77 I put one on a W150 with a 360 and it worked well and, I think, actually made it a bit stronger in low end pulling. (Just seat of the pants observations)
 
They hit the 'scene' in December 1970.

As per my old Offenhauser 'New Product Bulletin'

The smaller runners will provide for more air-speed, increasing velocity.
This will increase Fuel Economy for Daily Driving capabilities.

The Primary throttle bores feed 'straight' down into the 'smaller' Runners
which are located on the bottom plane of the Intake casting.

This creates a'Ram-Effect' as quick as the Speed of Sound. This means,
a faster and hotter Primary feed into the Cylinder Head Intake Ports.

The result is more efficiency at Low-End, and in the early Mid-Range intervals.

Higher velocity in the smaller but separate Primary Ports equals better response
and more Low-End Horsepower.

Damn, it sounded good.
 
Well, I would like to see their dyno chart and I wonder what their test mule was for the dyno data.

Was there ever any independant evaluation/testing done with this intake?
 
A Dyno Chart does exist on the Dual-Port.

Mopar Small-Block Square Bore .. #6005-DP
Mopar Small-Block Spread-Bore .. #6006-DP

Offenhauser stated that the Primary fed the Intake Runners at 3-Times
faster than normal air-speed.

And, that the Secondary air-temperature was 30* cooler, providing for a
more dense air-fuel mixture

Offenhauser added, that the Dual-Port Intake provided anywhere from
15% to 30% more Horsepower than a Stock Intake Manifold.

* Quicker throttle response
* Easier starts in cold weather
* Extended RPM range {300 to 500 RPM's} over a stock manifold
* Reduced exhaust emissions
* Improved fuel mileage
 
For what it's worth, I used to have a pair of them. I ran one on my 383 in my Roadrunner back in the 70s and I put one on my 318 in my crew cab dually.

I was pretty young and dumb at the time I chose one for the Roadrunner. I was just looking for a used aluminum intake to run. Not knowing much about part selection during those pre-internet times, I'd expected to see an ET drop. It didn't make me run any quicker than my stock intake had, but I didn't seem to lose any performance either. One thing that I did notice was a gain in fuel economy though.

Years later when I was putting the dually together I chose many of the same components that I'd run on the 383 even though I had a 318 in it. Once again, I definitely had a noticeable gain in fuel economy as opposed to my stock intake. It may sound hard to believe (and it was a long time ago) but my recollection was that I'd picked up about 2 mpg. The dually was a tow vehicle so there were no track times to compare but performance did improve.
 
Tried one of these on a '72 318 Swinger in '73 with a 600CFM Holley with vacuum secondaries. At a full throttle stomp from idle, it had a massive bog when the secondaries opened that I couldn't tune completely out. If you rolled into the throttle and let things progress at a more sedate pace, no problems, but that wasn't as much fun. Replaced it with a single plane Torker that wound up on 3 more cars...
 
grumpuscreature said:
Tried one of these on a '72 318 Swinger in '73 with a 600CFM Holley with vacuum secondaries. At a full throttle stomp from idle, it had a massive bog when the secondaries opened that I couldn't tune completely out. If you rolled into the throttle and let things progress at a more sedate pace, no problems, but that wasn't as much fun. Replaced it with a single plane Torker that wound up on 3 more cars...
Click to expand...
I never had that problem with bogging. I was also running 600 Vac secondary Holleys. My Roadrunner ran 4.10s and the dually had 4.56s. The amazing thing was that I was running Crower cams with an advertised 300' duration also. I don't have the specs on them anymore but I know that they weren't supposed to develop much torque below 2000 rpm. I know my Roadrunner never launched very hard, but it didn't bog.

I was never able to break out of the 13's with the Roadrunner. The cams weren't the best choice. But like I said, I was young and dumb. Bigger was supposed to be better and 300' was pretty lopey at idle. Although I know that the Torkers were a much better performance choice (and might have helped at the track), I ran pretty good on the street with those Offy 360s.
 
Offenhauser Dual-Port

The Intake gets a 'bad rap', mainly because you had to tweak the Hell out of the
Carburetor.

If the mixture was too lean, the Engine lost low-end power.
 
Frank-n-Head

The Offenauser 360* 'Equa-Flow' Intake was the standard 'Dual-Plane'
High Rise.

The 360* 'Dual-Port' was the gimmick Intake.
 
69 Cuda 440 said:
Yes, two different Intake Manifolds.
Click to expand...

Hmmm, so can you tell which one this one is? It has a "360*" cast int the top, just behind carb. I bought it used from a member a couple years ago. It's in real good shape, I painted it, it was raw.

If my Weiand Action Plus is too tall, I may use this one instead. I don't want to cut my new hood
 

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just look at the runners. If they are divided its a 360 Dual port.
images
 
I wouldn't call it a gimmick exactly. It was no worse than any of the other dual planes in it's class. Certainly not as good as the LD340, but probably as good as the rest.
 
I saw another strange intake at Pomona swao meet years ago, it was a Man-a-Fre 4 2's that had little cast fixed propellers under each carb pad. Whatever sold...
 
Offenhauser 'Dual-Port' 360* Dual-Plane/High-Rise Intake Manifold's

#6005-DP ....... 340-360 'Square Bore'
#6006-DP ....... 340-360 'Spread-Bore'

#GOQO-DP ...... 273-318 'Square-Bore'
#6021-DP ........ 273-318 'Spread-Bore

~ Improvement Trick ~

Cut {grind} out 1" of the Split-Divider in the Intake Runner from the Cylinder Head
side of the Manifold.

Also, smooth out the flashing-edges in the Runner-Ports near the Cylinder Head side of the
Manifold.

A 'definite-must' is to Gasket-Match the Intake Manifold ports, and with a smooth-finish
at a minimum-depth of 1" into the Runner-Ports.

Result, worth an additional {+15 HP} at 4500 RPM's.
 
I like mine and I wouldn't trade it for the world. Are there other intakes out there that might be better because of the dyno slips? Probably.

Better throttle response? Sitting underneath a 3310 I had throttle response like injection. Instantaneous.

The car pulls hard from idle up to 6800.
 
Offenhauser Dual-Port

Worked best, with a Camshaft designed for Low-End Torque and
Mid-Range Power.

In a Small Block > Generally, a moderate Performance Camshaft

Much like the Crane Cams {Grind# HIT-280-NC} 'Hi-Intensity' Hydraulic
Lift ..................... .460"
Duration .............. 280*
Duration @ .050" .. 224*
Overlap ................ 52*
LSA ..................... 114*
Valve Springs ....... #90 lbs. {Valve-Closed} ~ #270 lbs. {Valve-Open}
 
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