Offenhauser Dual Port Bore Diameter and Carburetor Clearance

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Torqueflite

Torqueflite

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Does anyone know if the primary butterflies on a Holley 600cfm and 650cfm will clear the bores of an Offenhauser Dual Port intake manifold? The intake bores look small in this photo next to the huge secondaries, but I can't find diameter specs. I assume Offy would have made the intake compatible with both Carter/Edelbrock and Holley since it was introduced in 1970, but I'd like to make sure.

offy.jpg
 
Looks like a Holley 600 or 650 spread bore carburetor would bolt right on that manifold or a thermoquad.
 
Jadaharabi said:
Looks like a Holley 600 or 650 spread bore carburetor would bolt right on that manifold or a thermoquad.
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It looks like either a Holley spread bore or square bore will bolt up no problem, but do you know for sure that the primary butterflies don't have clearance issues?
 
Torqueflite said:
It looks like either a Holley spread bore or square bore will bolt up no problem, but do you know for sure that the primary butterflies don't have clearance issues?
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Personally I don't see any problem with putting a spread bore carburetor on that manifold. A spread bore carburetor has smaller primaries than a square bore carburetor. That manifold is not for square bore carburetors unless you put an adapter on it.
 
:popcorn:Com'on Rusty, don't hold back,lol

The TQ did not come out until 1971. Which implies that Offy didn't factor it in during the design stage...... of a 1970 manifold.
The small TQ has 1.375 bores, the larger IIRC is 1.4375. The AVS IIRC were a tad bigger.
A 600 Holley I think is 1.5625, a 650 is 1.6875

By the time you get an insulated gasket on there, you should have plenty of room
 
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OP,
please,please install that badboy with a spreadbore and report how your engine runs. I acquired one of those last year I think, but currently it is just collecting dust here. I kindof would like to know how it runs on a 318/273 DD, decked out for fuel economy.
 
Is there a part number on the bottom side of that manifold?

There are six different dual Port manifold for the small block Mopar.

6005 DP is for the 340 360 standard 4 Barrel
6006 DP is for the 340 360 with the Quadrajet spread bore
6020 DP it's for the 273 318 1966 and later with square bore
6021 DP is for the 273 318 66 and later with Quadrajet spread bore
6022 DP is for the 273 through 1965 standard 4 Barrel
6023 DP is for the 273 through 65 spread bore

Yours looks to be a 6006DP or a 6021DP to me.
 
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AJ/FormS said:
OP,
please,please install that badboy with a spreadbore and report how your engine runs. I acquired one of those last year I think, but currently it is just collecting dust here. I kindof would like to know how it runs on a 318/273 DD, decked out for fuel economy.
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There’s a member here who just installed one on a 318 in a 1977 Dodge M-886 ambulance along with an eddy 600 and an Isky .400 lift Mil-A-Mor cam. He says it runs really well, and that’s probably a 6000 plus pound vehicle it’s in. But it does have 4.10 gears, and I didn’t ask him about mileage for obvious reasons. He did put 400 interstate miles on it this weekend so I’ll see if he checked mileage.
 
RustyRatRod said:
Get the dial calipers out.
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I don't have the intake manifold, so what would dial calipers do for me? Should I measure the diameter of the air in front of me and compare that measurement to my Holley square-bore primary butterflies? My whole purpose in asking my question is so I don't go buying an expensive intake that won't even work with the carburetor I would like to run. It certainly wasn't to get a response like "well, why don't ya measure it?"
 
Jadaharabi said:
Is there a part number on the bottom side of that manifold?

There are six different dual Port manifold for the small block Mopar.

6005 DP is for the 340 360 standard 4 Barrel
6006 DP is for the 340 360 with the Quadrajet spread bore
6020 DP it's for the 273 318 1966 and later with square bore
6021 DP is for the 273 318 66 and later with Quadrajet spread bore
6022 DP is for the 273 through 1965 standard 4 Barrel
6023 DP is for the 273 through 65 spread bore

Yours looks to be a 6006DP or a 6021DP to me.
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The 1966+ Dual Port 273/318 came in a 6020 for square bore and 6021 for spread bore as you point out. The 6006 has the larger runner. I don't own this intake and don't know the casting number, but I assume it is a 6021 from the spread bores.
 
Torqueflite said:
I don't have the intake manifold, so what would dial calipers do for me? Should I measure the diameter of the air in front of me and compare that measurement to my Holley square-bore primary butterflies? My whole purpose in asking my question is so I don't go buying an expensive intake that won't even work with the carburetor I would like to run. It certainly wasn't to get a response like "well, why don't ya measure it?"
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It was a simple suggestion. Since you didn't say in your first post you did not have the intake manifold, how are we supposed to know? We're not mind readers, plus this is the internet and not everything comes through. It's just text. My apologies. I'll not try to help you again.
 
Must have been a very popular intake manifold design for them to have made six different ones just for the small block Mopar.
What are they wanting for this manifold?
You can put any carburetor on that manifold however it is designed for a spread bore to bolt directly to it. You can use an adapter and put anything you want on it.
What carburetor were you wanting to put on it?
 
AJ/FormS said:
By the time you get an insulated gasket on there, you should have plenty of room
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I tend to agree that with the 3/16" adapter and double gaskets the butterflies should clear. It would be good to get an actual measurement of the intake's bores to be sure.
 
RustyRatRod said:
It was a simple suggestion. Since you didn't say in your first post you did not have the intake manifold, how are we supposed to know? We're not mind readers, plus this is the internet and not everything comes through. It's just text. My apologies. I'll not try to help you again.
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Come on, it was not a helpful suggestion and you know it. If you needed clarification to best assist me, all you had to do was ask, "Do you have the intake in front of you to give us the diameter?" rather than assuming I wouldn't have thought to measure the bores and then measure the throttle butterflies or at the least bolt up the carb and turn the throttle shaft. I'm all for people helping others and appreciate that help, but telling someone "measure it" isn't helpful. I'm sorry if me saying so offends you to where you don't want to help.
 
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Torqueflite said:
I tend to agree that with the 3/16" adapter and double gaskets the butterflies should clear. It would be good to get an accurate bore diameter to be sure.


Come on, it was not a helpful suggestion and you know it. If you needed clarification to best assist me, all you had to do was ask, "Do you have the intake in front of you to give us the diameter?" rather than assuming I wouldn't have thought to measure the bores and then measure the throttle butterflies or at the least bolt up the carb and turn the throttle shaft. I'm all for people helping others and appreciate that help, but telling someone "measure it" isn't helpful. I'm sorry if me saying so offends you to where you don't want to help, but it doesn't sound like you know the answer anyway.
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Dude, I was honestly trying to help. You're the one going off the handle about it. A lot of people sometimes don't think of the obvious. Again, you never said you didn't have the intake so I didn't know.
 
RustyRatRod said:
Dude, I was honestly trying to help. You're the one going off the handle about it. A lot of people sometimes don't think of the obvious. Again, you never said you didn't have the intake so I didn't know.
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I'll take your word that you were honestly trying to help and apologize if I misread and overreacted. As you said, writing lacks the other nonverbal ques that help us figure if someone is being sarcastic or genuine. In my original post, I stated that I did not have the intake bore diameter specs, so I assumed people would understand that I don't have the intake. Next time, I will be more specific.
 
Torqueflite said:
I'll take your word that you were honestly trying to help and apologize if I misread and overreacted. As you said, writing lacks the other nonverbal ques that help us figure if someone is being sarcastic or genuine. In my original post, I stated that I did not have the intake bore diameter specs, so I assumed people would understand that I don't have the intake. Next time, I will be more specific.
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When I'm sarcastic, there's no mistakin it.

With that out of the way, the Offenhauser catalog clearly states those manifolds are made to fit the Carter Thermoquad and the Rochester Quadrajet. I don't know the Quadrajet size right off, but the Thermoquad comes in two distinctly different primary sizes. 1 3/8 and 1 1/2. So there's a "sorta" answer. It will fit at least a 1 1/2 primary size.
 
RustyRatRod said:
When I'm sarcastic, there's no mistakin it.

With that out of the way, the Offenhauser catalog clearly states those manifolds are made to fit the Carter Thermoquad and the Rochester Quadrajet. I don't know the Quadrajet size right off, but the Thermoquad comes in two distinctly different primary sizes. 1 3/8 and 1 1/2. So there's a "sorta" answer. It will fit at least a 1 1/2 primary size.
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:p My issue is I'm deadpan, so your response would have been right up my alley for sarcasm. In the future, I'll expect a more direct approach from your humor, although I hope I'm not the recipient. Again, sorry for thin-skinning on you; it's been one of those mornings.

Your sorta answer is likely close to being the full answer. Holley 600/650 square bore valves are over 1.5", so they'll likely hit without a spacer. I have the opportunity of picking up this model intake locally, but from the feedback here it's likely wiser to wait for a square bore version since it won't do the engine any good to have the air flow out of the larger carb base just to run into a ledge.
 
Torqueflite said:
:p My issue is I'm deadpan, so your response would have been right up my alley for sarcasm. In the future, I'll expect a more direct approach from your humor, although I hope I'm not the recipient. Again, sorry for thin-skinning on you; it's been one of those mornings.

Your sorta answer is likely close to being the full answer. Holley 600/650 square bore valves are over 1.5", so they'll likely hit without a spacer. I have the opportunity of picking up this model intake locally, but from the feedback here it's likely wiser to wait for a square bore version since it won't do the engine any good to have the air flow out of the larger carb base just to run into a ledge.
Click to expand...

OR you could just run a spread bore. There are some dang good ones out there.
 
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