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Old 02-27-2009, 08:48 PM   #1
Imo Apita
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Default Opinions on the Offenhauser Dual Port Manifold

Came across the Offenhauser's on the Summit site.
Apart from being way too expensive what are the good , bad and ugly about them?
They show up on Ebay for anywhere between $40 and $90.
Interesting concept of the dual runners.
Did a search on this site but no real info came up.
From what I understand they seem to work best with a q-jet set up for this kind of manifold.
Seems hard to find info on these such as manifold height, cam suggestions and such.
Anybody currently running these on a mild 350 or 383?
Looking for something a little of the beaten path just for grins.


Click the image to open in full size.
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Old 02-28-2009, 07:31 AM   #2
gkull
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Offenhauser's were the best thing going back in the late 60's and 70's.

Also the GM Lt1 through the 79 aluminum L-82 were also HP adders
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Old 02-28-2009, 10:35 AM   #3
SteveG75
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Quote:
Originally Posted by Imo Apita View Post
Came across the Offenhauser's on the Summit site.
Apart from being way too expensive what are the good , bad and ugly about them?
They show up on Ebay for anywhere between $40 and $90.
Interesting concept of the dual runners.
Did a search on this site but no real info came up.
From what I understand they seem to work best with a q-jet set up for this kind of manifold.
Seems hard to find info on these such as manifold height, cam suggestions and such.
Anybody currently running these on a mild 350 or 383?
Looking for something a little of the beaten path just for grins.


Click the image to open in full size.
Well, that picture is of a Chrysler 383 manifold and won't fit a SBC anyway.

Hot Rod did an article where they did back to back testing of 18 manifolds on one engine (Chrysler 383) and the Offy Dual Port was 30-40 hp and ft/lb down from the more modern dual planes.

Here is the article:
http://www.hotrod.com/techarticles/h...aro/index.html


Here is my plan:
Weiand 7525 combined with a 1" Wilson tapered spacer for the Q-Jet. Still using the Lars tuned original Q-Jet.
Click the image to open in full size.Click the image to open in full size.
Click the image to open in full size.

Last edited by SteveG75; 02-28-2009 at 10:40 AM.
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Old 02-28-2009, 11:30 AM   #4
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Offenhauser was a big name back in the day, old design now. Unless they updated and have some new stuff
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Old 02-28-2009, 02:10 PM   #5
Little Mouse
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Its been many yrs ago but I also saw a test it was a small block chevy using a 360 equal flow offenhauser against a 180 dual plane the rusults were not good for the offenhauser can't remember the exact power difference but the above posters 40 hp loss is about what I can remember it was a big loss in power that I remember for sure.

Now I have an offenhauser manifold but its a cross ram thats basiclly a copy of the crossram chevy used in trans am racing it has a plenium area clear across the entire manifold.

Last edited by Little Mouse; 02-28-2009 at 02:13 PM.
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Old 02-28-2009, 11:48 PM   #6
Imo Apita
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Quote:
Well, that picture is of a Chrysler 383 manifold and won't fit a SBC anyway
I know that, just a pic to show what I was talking about.
Summit website doesn't show the pic for the SBC.
So according to that Hotrod article (thanks for that btw) it's down 40 hp from a tunnel ram intake.
Well, no plans to go tunnel ram for now..
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Old 03-01-2009, 12:03 AM   #7
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Any dual plane intake that will fit under your hood will be down 40 peak HP from a tunnel ram but what about torque throughout the range you run your car in 95% of the time? Don't know about the Offy dual port. It is an old design. The Offenhauser 360 is a good intake and will run right with about any dual plane made. Best thing is very uniform distribution which will help with throttle response and idle quality. I have the tripower Offy 360 split single plane and know I gave up some peak HP. Oh well, so does the hydraulic roller and AFR 195 heads. A well matched combination for your intended use might be a better way to shop. How well does the port on the intake match up with your head ports? What is the operating range on your cam? No sense in having an intake that peaks @ 6500 RPM if your cam is done at 5000. If you look at the results on the article above the Offenhauser dual port averages 411 Ft lbs of torque between 2500 and 4500. The Weiand Team G single plane averages 401 ft lbs in the same range. The motor tested is a built Chrysler 383 with 10.3 comp, iron heads and a pretty nasty solid lifter cam, headers. This is the type of build most would recommend the Weiand Team G single plane for. Suprisingly the stock tripower was one of the best performers across the board. This is a test on a chrysler engine so maybe the result wouldn't be compatable with a SB chevy. JMHO

Last edited by 63mako; 03-01-2009 at 12:33 AM.
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Old 03-01-2009, 12:15 AM   #8
DRIVESHAFT
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Quote:
Originally Posted by Imo Apita View Post
So according to that Hotrod article (thanks for that btw) it's down 40 hp from a tunnel ram intake.
Well, no plans to go tunnel ram for now..
Its also 40hp down from the Performer RPM. 412 vs. 451
Thats a lot to give up for nostalgia.
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Old 03-01-2009, 04:23 AM   #9
Little Mouse
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Quote:
Originally Posted by Imo Apita View Post
I know that, just a pic to show what I was talking about.
Summit website doesn't show the pic for the SBC.
So according to that Hotrod article (thanks for that btw) it's down 40 hp from a tunnel ram intake.
Well, no plans to go tunnel ram for now..
The article I saw was a comparison between a high rise 360
equal flow offenhauser and a high rise 180 dual plane it was
way down in power, no tunnel rams involved in anything.
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Old 03-01-2009, 02:15 PM   #10
63mako
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The only real world test that you can draw a solid conclusion from would be back to backdyno testing. Even then some will pull peak HP in an rpm range you don't use 95% of the time. Some will give up peak HP but show signifigant gains at the bottom end and midrange. Some won't fit your intake ports correctly. Figure out what will accept the carb you want to use. Then, I would match the port size of your heads as closely as possible. That will reduce your choices. Then figure what you can fit under your hood. That will reduce choices more. Then select an intake that operates most efficently in the RPM range of your cam. This will narrow you down to just a few choices, maybe only one or two. Then ask questions here as there is a wealth of information and experience. My choices were limited to an edlebrock dual plane or Offenhauser Split single plane 360. The offy fit my ports better, matched the operating range of my cam better, better distribution and cylinder filling due to the design.

Last edited by 63mako; 03-01-2009 at 02:17 PM.
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Old 08-14-2010, 09:13 PM   #11
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Default Offenhauser 360 dual plain vs 360 dual port pros/cons

I am an old timer and very familiar with both of these manifolds I couldn't post the pictures for the difference. e-mail me if you want.
the 360 dual plain. 360 dual port very different animals. dual plain 1800 to 6500 rpm. dual port off idle to 5500 rpm. These are old school and school requires learning. The small differences in the casting for brackets can cause you great distress if not evaluated prior to purchase. the internal runner ports are so different you have to see it in person. The answer to your question the 360 dual port is different than any manifold on the market.
It requires even more attention to detail for application than most. I run one on my 72 caprice classic 4856lbs turbo400 trans 2.43 rear gear.
and a well tuned Edelbrock 600. 268 h cam Basic RV street strip towing. Be cause the car is mostly ran in town or cruising at 65 the combination works well in. I recommend the 360 dual port for low rpms , heavy cars mild or rv cam towing economy. It will not satisfy high performance , hi rpm, large carburated, heavy or light vehicle, It will make hp and torque at low RPMs <2500. I stress a total realistic approach to selecting either of these manifolds what and how are you going to use it. My caprice 16-17mpg 102 in the 1/4 mile Pulls my airstream and crusies on Friday night hpchuck RFC.
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Old 08-14-2010, 10:14 PM   #12
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The dual port is a completely different animal. There are basically two ports in each runner. They were designed for gas mileage and towing. They never worked well back then except for those two areas *sorta*. I'd look at something else.

JIM
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Old 08-15-2010, 12:00 AM   #13
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I think thats what I said
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Old 08-16-2010, 10:18 PM   #14
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Well I have a 360 dual port sitting in my shed waiting for a motor.
Curious enough to give it a try.
Lots of people already told me it's no good. That's fine, ok with that.
It's not that I don't care, I appreciate all the info but for now I'm going to stick with it.
Not looking for a high winding RPM motor.
I plan on converting a '74 block to roller cam with the e-bay papers I bought for $20. Guy runs his own up to 5500 and advises not to go above that.
The 360 DP is good to 5500 according to the Offenhauser papers.
I am looking for maximum acceleration in short bursts not all out high speed HP. Once all is done I will take it to a 1/4 mile track maybe once,1/8 mile maybe a couple of times. Just to see what it's like to race an engine you built yourself.
Quote:
maximum acceleration in short bursts
is a euphemism btw.
Click the image to open in full size.
  • So manifold is good up to 5500
  • Home brew roller cam conversion is good up to 5500
  • Now the search is for a 1500-5500 roller cam.

Last edited by Imo Apita; 08-16-2010 at 10:29 PM.
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Old 08-16-2010, 10:55 PM   #15
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Here's a shot of the Offy Dual Port runners for those that have never seen one. The idea is similar to the late model stuff with extra ports/valves for high RPM.

Click the image to open in full size.


JIM
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Old 08-19-2010, 09:11 PM   #16
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Yep, that's what mine looks like dual ports.
Plan to do some port matching when I get the heads.
Plan to have some fun with that manifold.....
Need some old style valve covers to make this whole engine look "old".
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Old 08-19-2010, 09:11 PM
 
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