Early 273 intake compatibility

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AlaskaJeff

AlaskaJeff

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I've got a chance to pick up an Offenhauser 360 dual quad intake that was made for an early 273 small block. The seller states that it was modified to fit later 318-360 engines. What exactly should I look for? How will the modifications be evident? OR is it even possible?
 
Look for the mounting holes to be drilled out or oblong. Early LA engine used a different bolt size and angle. 65'
 
AlaskaJeff said:
Thanks guys. So the ports size isn't an issue? Just the bolt hole angles?
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The ports are smaller (273-318 size) compared to the larger 340-360 ports. it depends on what heads you're bolting it to.
 
Oooh I dunno what's been "done" to yours, but heres pics of HUGE port mismatch...gasket will last about 30 seconds. 340 gasket on DQ.
**edit** you can see the #5488 on mine, what # is yours?

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From what I understand, a smaller 273/318 port intake works on all small block heads but it's not such a good thing to run the larger 340/360 intake on a smaller port 273/318 head. Although I've never tried any intake that didn't have the head port size window matched. It may not be that big a deal but I can't say. Dual quads! Yay. Low rise or tunnel ram?

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#1 The potential issue is the sealing surface not the ports themselves

#2 the OP doesn't tell us what he is installing the manifold on - 273?, 318?, 340/360???

3# it's not just the bolt size, it's the bolt angle!!! Somewhere here I have a thread that measures the angle mismatch and suggests the beveled washer needed to fix it. I'm on the road so can't take time to look myself
 
It is not the port window itself, It is the runners up to the window. I would not run a small port intake on 340/360 heads.
 
If the intake isn't made for your heads, don't use it.
 
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Well now, there sure is a mixed bag of advise given, running the spectrum from: "Yeah it should be fine" TO "Don't use it" :eek:
Pretty typical with our group here though. I usually take ALL advise and suggestions into consideration and then make up my mind. FYI it would be going on a mild built 360 with cast heads.
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66fs said: "It is not the port window itself, It is the runners up to the window. I would not run a small port intake on 340/360 heads."

FYI- It looks like the 273/318 Offy dual quad being discussed here would appear to work on the MAGNUM heads. The 318/360 Magnum head intake port is considerably smaller than the LA 340/360 port. Factory Magnum and equivalents- not aftermarket HP heads for the Magnum. I have some new EQ Magnum replacement iron heads and the port size difference between the Offy and Magnums is no where near as drastic as with the LA 340/360 head. But one would still have to deal with the bolt angle difference. My heads are drilled with the LA arrangement.
 
The ONLY option for a low profile dual quad intake manifold for the 340/360 LA head is the Modman. Unfortunately- while this intake looks great and is available new it places multi use design over function. At least naturally aspirated function. My research shows the Modman does not work well on a NA street engine. Shame.

modman.JPG
 
I sure don't like the looks of that plenum. I can see fuel puddling.
 
By research I mean reading what people who have used the Modman have encountered. On a typical street engine (typical?- 350-400hp ish) the power down low and in the midrange is not there. But that should not be a surprise when looking at the design. It sure does look fantastic and has the options to run dual 4s, six pack or blower.
str12-340 said:
Can you please share that research?
Click to expand...

modman no top.jpg
 
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