Welding up a 273 intake manifold to work on 340 heads

[Michael Harrington]

This post is about a 273 intake manifold- specifically for a 144 Weiand street blower kit. The manifold I have is an Offenhauser 273 dual quad unit modified to bolt a 144 to it. The Offenhauser 273 dual quad intake can be bolted to the much bigger port 340/360 heads but due to lack of sealing surface material on the 273 manifold this proves tricky, with some failing to get a proper seal. Back in the day- Dyers, Dick Landy and others would buy dual quad Offenhausers (primitive low profile single plane manifolds) and modify them to bolt on a Roots blower. For SBM these companies would weld up the mounting flanges on the 273 Offy unit and after this it would seal with no effort on the 340/360 heads. I have acquired a 144 Weiand blower kit for SBM. The 273 Offy manifold looks like it was done well to mount the little 144 but the intake flanges are the original 273 size design and unmodified. I plan to run this set up on the 340/360 type head. I'm willing to pay the $$$ to have them welded up and then trued up with a cut. Has anyone ever had this done? Any word on cost? I've wanted one of these little blowers for a long time and jumped on the opportunity to but this kit. Top image is a manifold for the 340/360 head. Bottom is the Offenhauser 273/318 head. Much more sealing material on the top unit. Bottom unit needs to have the same sealing meat as the top unit.

 

[Mtrhead]

Very common thing chopping down a intake to make a blower manifold usually it's the cheapest method

 

[Michael Harrington]

For fun, here is an untouched Offy unit alongside the same unit but modified to mount a Weiand 144.

 

[PRH]

Can you take a pic of the lower intake with a 340 gasket on it?

 

[perfacar]

i used the felpro 1243 gasket on my 273 with 360 heads, have no problems at all. 273 intake / 360 heads

 

[4spdragtop]

I've a thread here with pics showing the drastic differences on an offy dual quad with the 2 different felpro's, 1213 and 1243. Drastic lol, altho someone that can weld aluminum can build up/add to the sealing area to make it work. I bought the DQ initially to put on 340...nope..

 

[33IMP]

I have a tm7 440 intake that was welded up at the top of the ports, to match a max wedge port. I did not have it done, bought it at a swap meet cheap, cause it was hogged out too big for a standard 440 head. Mine was a challenge to get sealed to iron max heads. Several homemade valley pans didn't work. You probably won't have that problem with a sbm. You can see the slug of aluminum welded at the top of the ports.
So, I'm sure it can be done..... but I'm betting it won't be cheap.

 

[Michael Harrington]

Here is a 340/360 gasket on the surface of the 273 manifold. From the sealing surface side it doesn't look bad. But the OTHER side shows the problem created with the lack of sealing material on the 273 manifold design. The placement of the gasket and the manifold must be perfect for a proper seal. I want things less challenging so I will ask the machine shop in my area if they can build up with weld beads then true the gasket surfaces.

 

[Michael Harrington]

i used the felpro 1243 gasket on my 273 with 360 heads, have no problems at all. 273 intake / 360 heads

I believe you. My preference is to have more margin for error when aligning the unit for an airtight seal.