I need to get some collector reducers for my headers, and having no prior experience with headers, I'm a litle confused at the sizing.

I don't know if these are considered 2.5 or 3 inch... The outlet pipe from the headers is about 2.5 inch inside diamter, but it's almost 3in outside diameter of the (sealing surface) flange, and 3 in from hole to hole.

I looked around and most describe the size as the dimension from hole to hole on a 3 bolt flange, but some say it's the inside diameter. The local source for such parts closed a while back, so I just thought i'd get a set from Summit or Ebay.

I just don't know what to get.

No, I do not know the maker of these headers. I did not buy them new.

Thank you, if you can get me the definitve answer...

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

If I understand correctly, they are 2.5". It refers to the pipe OD, not the flange bolt spacing. I think every dual outlet Slant header I've seen is 2.5" collector. Single outlets are 3".

Lou

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Home of Slant6-powered fun machines since 1988

Well, that was my first impression, as well.

I just kept finding these people saying that the bolt to bolt distance was the same as the collector size. Can't be true.

Anyway, thanks. These are long tube, dual outlet low starter truck headers. I consider myself blessed to have found them. They're in good shape ( very old, slightly rusted, but unused) and I had them sandblasted and then I painted with high temp rust preventative.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.