Offenhauser 360 2x4

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TAG
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Offenhauser 360 2x4

Post by TAG »

So i scored one of those some time back.

Oldsmobile one, to 350 engine. Now, i realise anything newer with one carb outperforms it. But so do modern technology anyways, so why not?
Sometimes the images beats the reality ( as is on many muscle cars, when some boring looking family-car leaves it at traffic-lights).

For those who dont know, Offenhauser 360 dual-quad manifold has both banks isolated from others, but inside bank all cylinders are connected together. Runner shape on intake is straight shot from carb towards bottom, there somewhat radiused ( radiused from bottom, but the upper wall is so-so) 90 degree bent, and then again straight shot to head.

Long story short is that i received these as " great working, straight from the road but stored for 4 years"; well i quessed right.
Carbs were in need of rebuild, and they have soon been. They needed everything, but i feel lucky, since they were rebuildable, and now i have all original, matching pair of Carter Competition series carbs, 4758S and 4761S.

Id like to ask from those who have run such setups, or have more knowledge about the subject.

What should i do to intake? When i received it, it had 1inch OPEN spacers on it? That ruins the whole manifold design from design-point, but is it actually good or bad thing? Another one, should i add spacers to it? Its stamped somehow as low-rise unit per part-number, but from all pics its hi-rise- and if ive understanded correctly, the differences between low-and high-rise intakes were just the height of carb pad. What would it do if i rise the carb-pad height, therefore lenghtening the tract before that 90 degree bend?

Then other minor question. Progressive or straight linkage? I can run whichever since i have whole bank connected together, but which makes more sense at street?

As a side note, from both the Carters and Offenhauser. The casting quality on those is beyond imagination when compared to crap they sell nowadays, when comparing directly Carters to new Edelbrocks, night and day difference, and also Offenhauser to Edelbrock intakes. On Offenhauser all runners are exactly same shape as on original heads, and lines up perfectly. Also exterior is smooth. Edelbrock.. Dont line up too well, runners dont match without work, and overall quality is...
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Re: Offenhauser 360 2x4

Post by Geoff2 »

What should you do with it? Ask yourself why nobody uses them except in show cars. On the positive side...yes,,,beautifully made.
TAG
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Re: Offenhauser 360 2x4

Post by TAG »

I should use it. And asking how should i do it.
Keeping both banks separated, add spacer, is there maybe a real reason it had open spacers?

I have few answers why nobody uses them. They havent been made for decades i quess, for a reason there were way better alternatives even way back then.
One could also ask why many guys sinks 20$k to muscle car when you can go buy relatively new car for same price which drives donuts around you and delivers 30mpg doing that. Because we have a freedom to choose.
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Re: Offenhauser 360 2x4

Post by Walter R. Malik »

They made what they called a "Dual-Port" dual quad intake manifold, also.
A long time ago we found that they worked better with the AFB carbs backwards similar to a Ford FE; (the carb primaries over the secondary manifold bores and the carb secondaries over the manifold primary bores. That certainly would not work with their "spread-bore" type manifolds, though).
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Re: Offenhauser 360 2x4

Post by BigBlockMopar »

I've got both these intakes from Offerhauser (both regular dual carb-360 and Single carb Dual-port).
Don't recall to have used the dual carb Offy, but I have the single carb Dual-port still on a 400ci Mopar bigblock engine.
Had it on a 383ci in the same car, but can't say I'm that much impressed by them. But to be honest, both engines were low cr 'turds'.
(While keeping the stock slugs in the engine) I did try to up the CR in the 'smogger' 400ci with closed chamber heads and steel headgaskets, but the power is not really there.

I have used a low profile, dual quad, marine intake on a 440 years ago, which was a blast to drive.
Carbs were connected non-progressive, which gave it quick and snappy throttle response. The 440 had 11:1cr however.
I ran the intake with 1" 4-holed spacers. This increased the carb's throttle response noticably.

In a 'vague' moment, I even had the plan/idea to match the dualquad Offy intake with a tunnelram 'top', which had pretty much the same carb spacing.

Both Offenhauser intakes can be spotted in this pic; Dual quad as a mockup on the 440ci engine in front, and the single carb Dual Port-intake on the workbench.

Image

Walter,
That's some nice info. Maybe I'll have to try that one day on the 400 engine 8)
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Re: Offenhauser 360 2x4

Post by elwood »

PN 5587 pictured on P21 in the catalog?

http://www.exeterautosupply.com/Docs/Of ... atalog.pdf

usually removing the material between the primaries and secondaries to create a split oval plenum tends to improve overall performance, and a notch between the 2 sides benefits more yet because either side has more access to carb cfm. the 1" spacers would be serving to increase plenum volume and allow full access of all cylinders to full cfm capability. question is whether the engine needs all that cfm or will it perform better overall w/o the spacer plates? spacer paltes are always an experiment as to what any particular likes and how it's used.

as for the linkage, progressive is easier than trying to synch the 2 carbs. the rear carb is the primary carb and opens first off idle, then the front carb joins in. if trying to synch the 2 carbs if they're off just a bit you'll feel uneven accel from a stop, the single carb opening is more predictable
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Post by dwilliams »

TAG wrote: Sun Jul 08, 2018 1:15 pm I should use it. And asking how should i do it.
Keeping both banks separated, add spacer, is there maybe a real reason it had open spacers?
My experience with spacers - some of it with Offy 360 intakes - comes down to "you never know until you try."

If it was my car, I'd start off just bolting the carbs directly to the intake and running it as Offenhauser intended. Then if you try spacers you have something to use as a baseline.
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Re: Offenhauser 360 2x4

Post by cjperformance »

Problem with the 360* equaflow 1x4 and 2x4 is the central divider. Seperating 2 banks of a 90deg v8 crank like that does the same thing to the intake as 'firing order wise' as a V8 with no exhaust X , H , Y pipe.

The open carb spacers help balance the unevenly spaced intake pulses side to side in that intake. This helps it act more like a reasonable single plane intake and not like a half assed dual plane.

Taking the center divider out of them down to the plenum floor actually helps them everywhere.

That said if its just the cool look you want just go with the open spacers and leave the intake stock.

These intakes do actually work quite well with gaseous fuel, LPG or Propane etc even on very basic mild engines.

Walter, interesting you mention reversing the carbs on the Dual Port. We used to run one on a drag car(long and funny story), basic BBF rear engine dragster low budget, hand braking and not enough convertor. Chasing another issue altogether we found reversing the carb the mid range. Im thinking that using the upper port for the primary helped by activating the top of the intake port on the primaries, and / or the cooler charge from the top half of the intake port helped, or a combo of both.
Interesting intake nontheless.
The dial a flow was a good fun novelty but I do like the Port O Sonic.
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Re: Offenhauser 360 2x4

Post by TAG »

cjperformance wrote: Mon Jul 09, 2018 8:54 am Problem with the 360* equaflow 1x4 and 2x4 is the central divider. Seperating 2 banks of a 90deg v8 crank like that does the same thing to the intake as 'firing order wise' as a V8 with no exhaust X , H , Y pipe.

The open carb spacers help balance the unevenly spaced intake pulses side to side in that intake. This helps it act more like a reasonable single plane intake and not like a half assed dual plane.

Taking the center divider out of them down to the plenum floor actually helps them everywhere.

That said if its just the cool look you want just go with the open spacers and leave the intake stock.

These intakes do actually work quite well with gaseous fuel, LPG or Propane etc even on very basic mild engines.

Walter, interesting you mention reversing the carbs on the Dual Port. We used to run one on a drag car(long and funny story), basic BBF rear engine dragster low budget, hand braking and not enough convertor. Chasing another issue altogether we found reversing the carb the mid range. Im thinking that using the upper port for the primary helped by activating the top of the intake port on the primaries, and / or the cooler charge from the top half of the intake port helped, or a combo of both.
Interesting intake nontheless.
The dial a flow was a good fun novelty but I do like the Port O Sonic.
Thanks alot. This along the answers from dwilliams, Elwood and bigblockmopar were kind of asnwers i was wanting to hear.
Real experiences.

Its not just for looks. Okay, i want the look, but i want it to perform as good as possible, no matter what i need to do.
If it involves cutting the center divider down from whole intake, i dont care.
So far what ive gathered, and quess, i think i should "evolve" from no spacer-open spacer- and if it looks promising, cut down the whole center divider.

Thats why im asking - i quess dual quads are lost "art" due to current superiour designs, but they did surpsisingly well decades ago with " inferior dual-quad intakes and carbs".

If you have anything more to add- please do so!
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Re: Offenhauser 360 2x4

Post by elwood »

removing the entire divider is pretty radical, and probably detrimental IMO, we'll just have to agree to disagree on that

look at the Edelbrock Airgap plenum & divider, if chopping more of it out was beneficial they would've done it. that's as far as i would go, recreating the Airgap plenum on the Offy. Holman-Moody did the same thing knocking down the divider a max of about 1" and that was for all day long redline running until the engine gave up. i'm going to guess what's best for a street machine is somewhere in the middle? like the common square divider notch that 99% of all intakes have, or a more conservative front to rear reduction
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Post by dwilliams »

elwood wrote: Tue Jul 10, 2018 3:17 pmremoving the entire divider is pretty radical, and probably detrimental IMO
I had one of the single carb Offys with the collection of different-height center dividers. On an otherwise-stock 283 Chevy with a Carter AFB, the manifold performed noticeably better with the full-height divider in place. Running with no divider made it idle funny and throttle response was a bit soggy; it probably needed more pump shot. Highway fuel mileage was the same (60 miles a day commute then) The notched divider was more like the full divider, and the half-divider was indistinguishable from no divider.

Again, that was a stock 283, other than dual exhaust and an OEM-style AFB. It might have been different with a modified engine. However, the primary purpose of the manifold was to save some weight, since the 283 was swapped into a small foreign car and that was before there were any factory aluminum intakes that weren't exotic racing bits.
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Re: Offenhauser 360 2x4

Post by elwood »

the small displacement is a good example for finding the point of diminishing returns. full divider each cylinder only has access to 1/2 the carb cfm and as you remove more, the more opportunity to over-carb the motor by way of open plenum

larger motors and those with little to no regard to low end will be less sensitive to removing more of the divider and as mentioned above may even show improvements throughout the entire rpm range? only experimentation and possibly a taller recycle pile will tell
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Re: Offenhauser 360 2x4

Post by cjperformance »

Just keep in mind that the 360deg Equaflow is not a conventional dual plane intake. It is divided but just straight down the middle.
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Re: Offenhauser 360 2x4

Post by elwood »

i've always been confused about the Offy 180 and 360 terminology, the pic in the catalog i posted shows what you're describing, like an S.P.2.P. and what i'd call a 180 manifold. and i've seen other Offy's with the 360 logo on them the same way with the full divider. then there are open plenums, not sure i get their marketing deal or if they had some overlapfrom the 180 series to the 360? IDK
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Re: Offenhauser 360 2x4

Post by cjperformance »

When you read Offys blurbs about the intakes you'll quickly see that they were also confused! Some of the things they say are a bit off the wall
PhotoPictureResizer_180711_095138410_crop_706x482.jpg
Read that and imagine what is happening in that plenum following any 90 deg V8 firing order, then re read it !
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