[Johnny406]

I just picked this up along with a big flippin Holley spreadbore carb. Someone did alot of work on this intake.

[Half-Inch Stud]

Should be good for 11's in a heavy car with highway gears huh.

[Tom Vaught]

It is too bad that the two front runners #1 and #2 look like a house with the roof smashed in by a tree.

Tom V.

[steve25]

Those 360 equal flow Manifolds ARE NOT the ticket for a heavy car as the runners are quite short even when compared to the average single plane Intake!

Offy made both spreadbore and square bore versions of the 360.

The meat they cast those with on the roof also makes for a small sealing area if the heads are gasket matched to a RA4 or SD455 type flange gasket.

There combination of port area and short runners make for a very narrow power band that would be best used with 455 cid motor.

They make a great 471 blower Manifold when machined for a large square plenum and fitted with a adapter plate to bolt the blower onto though!

There is a reason so few of these Manifolds turn up these days and it's not due to them working great freinds!

[taff2]

A mate of mine, with a BBC blowthrough carb turbo combo, switched from a Dart high rise single plane manifold to the BBC version of this Offy manifold to give him a lower hood line and the car actually went quicker! Old school tech eh.

[steve25]

Come on now , your gonna compare the port area of one of these cast up for a BBC to the Pontiac version and in a boosted motor no less!!!!
It would seem that he stumbled on a better Manifold tuned lenght wise for is motor even though it's boosted!
These basically a low rise single plane.

[Half-Inch Stud]

@Steve25 Since i gots one; Offyl made the 360 in Dual Quad too. Just saying. Pretty sure the Non-360 Offyl Dual Quad ran stronger.

[BruceWilkie]

I have one of these too... never used it...think it might be ok with 8 efi injectors and std port heads.

I got a pair of Holley(M/T style) cast valve covers and a 3310 Holley with it for $25.00!

What accessory combo would have required the squished front runners??? The Buick version looks better.

Taff2 fixed his dual quad runners so the fuel doesnt take a a roller coaster ride! Not worth the effort on the single quad.

[steve25]

I know they had made a 2-4bbl version , as I had one for 30 years and never used it. I also had the 1-4bbl version he has and after testing it out for flow balance after I got my flow bench I later sold that one too!

[taff2]

We put the power increase down to the manifold being 'open' inside like a blower manifold- no port dividing walls- so each head port has access to a double width runner which allows the airflow to have a straighter shot to the back of the valve,and also probably a bigger plenum volume compared to a high rise single 4 barrel manifold.
My Pontiac Offy 360 dual quad was modified this way for the very same reasons.
I can't say if the Pontiac version of the Offy 5720 in the pics above has siamesed ports as I've never had one. And now I think of it, the BBC manifold didn't have a centre divider nor squashed front runners IIRC.

[BruceWilkie]

http://www.exeterautosupply.com/Docs...%20catalog.pdf

Page 18 gives a basic inside view of the 5720 intake...lots of plenum(its fairly deep)and almost no runner.

Page 20 is the 5742 q-jet version.

Page 22 is the 5708 hi-rise dual quad... a good working intake but could be better. The front runners take a dip...the Buick version pictured doesnt.

Taff2...post a pic of your "fixed" version.

BTW Exceter is a good source for Offy stuff and some Offy stuff is still being made or can be made .

Too bad they never made a Portosonic for Pontiacs...They made them for alot of others.

[taff2]

My mates manifold looks like the 5766 on page 18, however,he milled the carb mounting pad off and welded on a Domi adapter to take his CSU Domi.
The Buick Offy 5882 on page 22 looks like my modded Pontiac Offy manifold!
As you can see though, mine has siamesed ports (no dividing port walls).