Exhaust headers - flange size

[David]

Has anyone had the problem of having a set of headers (snakes) with oversize flanges. I have a set with flange holes 3" apart which don't fit my 302 heads. I have seen aftermarket heads with two sets of stud holes. does anyone know if it is possible to drill a second set of stud holes into a standard head to accommodate my wider flanges.

thanks
David

 

[Jac Mac]

Either make /fit new flanges, or preferably buy some better aftermart heads, the extra power if your choose the right ones will be worth it.

 

[Rick]

I have seen flanges made from aluminum that are attached with counter sunk flathead machine screws that have the wider pattern drilled in them. The headers then fit onto the attached flanges.

 

[Jac Mac]

I have seen flanges made from aluminum that are attached with counter sunk flathead machine screws that have the wider pattern drilled in them. The headers then fit onto the attached flanges.

If they are 180° crossovers that wont work with the extra plate thickness.

 

[Rick]

OOps!

 

[David]

I seem to have another problem. When I assemble the pipes in their proper order on the bench and set them up as if they were on an engine, the distance across the flanges is about 1" wider than across my engine at the flange level (hope that makes sense.) It seems as if these headers were made for a 351 block. Before I go looking for another engine, does anyone know of any aftermarket heads that have higher ports and higher flange bolt holes which would provide the same effect on the engine width as a 351 block would do.

Thanks for your replies so far, this problem is driving me crazy. I have a really nice 302 and a nice set of headers and they just won't fit:furious:

 

[Julian]

Sorry to say that if your flanges are for a 351 then they are for a 9.5" (351W) or 9.2" (351C) deck height, whereas a 302 is an 8.2" deck height.

Heads on all three engines are largely interchangeable but no amount of raised port (e.g. C302B head) is going to make up the difference you need because being 90 degree V's the 351W ports are going to be higher 1.3" and wider by 1.3".

If the headers are fairly horizontal at the rear, then you could possibly get away with cutting a section out and rewelding. But in reality you are probably best selling them and getting some money back toward a proper set for a 302. Of course if the headers really are that nice you can always use them as an excuse to upgrade to a 351

 

[David]

Thanks Julian, thats exactly the choice I will make if they are indeed 351 headers. I am going to see a company here in Melbourne who import crate engines from the US. I will take my headers along with me and see whay they will fit. I have had a good offer for the 302 so, as you say, an upgrade to a 351 wouldn't be such a bad thing.

David

 

[Jac Mac]

Wider by 1.84".( spacers 0.92" approx reqd each side )

( 1.3 squared = 1.69. [1.69 divided by 2 = 0.845] sq root of that is approx 0.92, multiply that by 2 to give you the distance further apart, also bear in mind these fitted to a 302 ( 8.200 block ) will sit 0.92" lower with respect to the collectors & primaries where they cross over at the rear.

 

[David]

Looks like the problem is resolved. The headers are built for a 351. I have decided to sell the 302 and build a 351, which is a good indication how highly I prize the headers.

Thanks for all your help.

David