Offenhauser Dual port ??

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4spdragtop

4spdragtop

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I recently bought an old Offy Dual port. What can ya tell me about it? I've never seen one before. From what I've read the front barrels feed one half and the back 2 feed the other half. Im thinking of keeping it for my 340.
Any insight?

Thanks
Steve
 

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You would be better off running a 71 and later stock intake. Only thing would be the weight. Might as well try it if you own it, may get better mpg.
 
The ports are divided.

The primaries feed on the bottom, the secondaries on the top. That way the primaries insulate the secondaries.

It's a great street intake and pulls hard off the line with good fuel economy, but is restrictive above 5000 RPM.

They were made in both square and spread bore.
 
there have been a few magazine dyno tests comparing many intakes. the Offy dual port was an idea that looked good for low end, and was restrictive at over 2000 rpm. the LD340 and Performer rpm has equal low end and best midrange and great top end
 
I had almost forgotten about those, and can recall considering one of those 'back in the day'.... but they proved to be 'long on theory, short on performance'.
 
I knew a guy who got 23 MPG with one of those in a 77 Volare wagon with a 360 4 speed.
 
I disagree that the intake will be a "plug" for anything past 5000 RPM. That will be dependent on the rest of the combo.

I have had many two barrel engines with stock intakes rappin on the 6500 mark. That intake surely flows better than a two barrel.
 
Old Man Mopar said:
Well, look at how much port volume remains after the dividing wall has been added.
Click to expand...

U are correct sir, with the dividing wall going from the carb to the heads, and the extra turns that the flow needs to make, when the secondary of the carb kicks in it is restriction time. the dyno do tell the truth, research it, and back in the day we looked at the cars that went quick-ld340
 
Old Man Mopar said:
Well, look at how much port volume remains after the dividing wall has been added.
Click to expand...

So good or bad with the volume John? I thought the volume/space the dividing wall took away would be bad.
I haven't put verniers too it yet though.

Thanks again for all the info. The thread that gdrill posted has some mods listed that could be done to it.
I agree that how good it is will depend on the rest of the combo
 
I very much remember the published reports on these back in the day, and the top end restrictions were very real. And flow disruptions stepping from the small primary ports to the heads ports when only on the primaries was suspected to be a flow disruptor at lower speeds. There just was no compelling reason to use this concept over other designs, even for economy use and torque, and it quickly died away.

Other manifolds performed better across all RPM ranges.
 
Well, you could maybe plumb the primaries to a small turbo, and the secondaries to a big turbo, with some fancy exhaust plumbing.
Oh wait that was my silly idea.A long time ago.

I always wanted to try one on a big-port headed teener, with some decent compression.
 
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