Header Flanges, Gaskets

1 7/8" OD Finished Header Flanges - 3/8" thick

1959-76 389-400-421-428-455" Pontiac

(Part Number 20502F38).  Also available with 1 5/8", 1 3/4" and 2" OD
Starter Tubes and flange thicknesses of 1/4", 5/16", and 3/8".
Starter Tubes are approximately 2" long.
Center divider is created from the sides of the starter tubes and multiple
TIG welding passes, then ground and filed to create the center bar.
Center tubes exit away from each other to allow welding access
in area where tubes are close to each other.
Extra metal (which can be ground away) added near center bolt holes
to increase gasket sealing area.
While not visible in the image, the center bolt holes were also grooved
externally with a die grinder to improve ease of header bolt insertion. 

NOTE:  Bypass going to the Home page (which is slow to load) by going directly back to the Header Kits page (or any of the other pages/areas listed above).

CUSTOM HEADER FLANGES:  While the above Header Flange Listing is quite comprehensive, because we do so much CUSTOM designing in this area, one must understand that we offer much more.  Based on already existing header flange patterns, over the years we have made header flanges:  (1)  WITHOUT PORTS for customers using the header flanges to seal the exhaust side of the motor or customers machining the exhaust ports in the flanges to match a reshaped/relocated exhaust port;  (2)  WITHOUT BOLT HOLES because the customer wanted to drill the bolt holes themselves so as to locate the ports in the flange relative to the ports in the cylinder head a certain way;  (3)  WITH SMALLER than normal exhaust ports because the flanges were going to be used as SPACERS (between a header and a head) to add clearance to a starter, oil filter, etc.;  (4)  in Finished Header Flanges, WITH PORTS LARGER than normal relative to a tube size so that a smaller tube size header could be built but with a full size exhaust port in the header flange (one that does NOT block exhaust flow out of the head); etc.  In some cases these design revisions are done at no charge but where custom drilling is performed (some movement of the bolt pattern relative to the standard location), there is a $15-25 extra charge for the time involved.  Where only ONE flange is desired out of a set of two, we charge 75% of the pair price due to the setup time involved just to make the first flange.  We do NOT make PURE custom header flanges (i.e. one of a kind designs where only one or two pieces are needed) due to the development time involved.  Header Flanges are made from Mild Steel Plate - NOT available in Stainless Steel.

¹ Port Size:  ROUND PORTS:  This is the Inside Diameter of the ports in the header flange measured in inches.  ON ALL OTHER PORT SHAPES:  This is the OD of the header tube measured in inches that, when reshaped, would fit into this port size.　 In other words, this dimension does not truly relate to the size of the port  in the header flange but more relates to the tube size specified AFTER being reshaped to approximately match the port in the flange.  Keep in mind that we make many header flanges with several choices of port sizes.  We usually ship the flanges that match the cylinder head port AND the tube size being used as closely as possible.  There are reasons to NOT always ship the best match to the cylinder head port but that is usually due to customer requests or specific needs.  We always ask about this because we see no sense in blocking the exhaust port unless there is a good reason to do so.

To make header building MUCH easier, we supply the header flange with ports (those shaped other than round) sized about 1/16-1/8" oversize from a perfect match so that the tubes do NOT have to be shaped perfectly to be inserted into the port.  Port Shapes:

RD = Round,

OV = Oval,

RE = Rectangular,

SQ = Square,

DD = D-shaped port with flat on bottom in most cases,

SAP = Same Shape(s) As Port(s) in head.

NA = Not Available or Not Applicable

² Header Flanges are priced as a set which means V8 and V6 sets have two flanges (one for each head). Most other engines have just one flange in a set. There are several exceptions to these rules but, where applicable, they are all noted.  Unless specifically mentioned otherwise, all header flanges are 1/4" thick. If you would like thicker header flanges, add $16.00 for 5/16" or $24.00 for 3/8".  All thicker header flanges are made to order and delay header parts shipments about 3-5 days. 　　

Made to order Header Flanges are NOT returnable.

³ Finished Header Flanges and Header Flanges w/Starter Tubes are shipped with a complete set of header bolts.

NOTE 1:  These flanges/cylinder heads have a large center port where two engine cylinders share a single exhaust port and a single header tube. 
On part number 20500CG (Finished Header Flanges), the end tubes are 1 1/2" OD and the center tube is 2" OD.  On part number 20500DG (also Finished Header Flanges), the end tubes are 1 5/8" OD and the center tube is still 2" OD.  If you order the 20500DG, we STRONGLY recommend that you  build the center tube in a "stepped" manner - starting at the head with 2" OD, then use a 3-4" long section of 2 1/8" OD tubing, and then build the rest of the header tube out of 2 1/4".  This is necessary to keep the exhaust gas velocity in the center tube essentially the same as that in the end tubes - to make the exhaust scavenging effects of the header as near equal as possible on all of the cylinders AND still deal with the small size of the center port.

NOTE 2:  These flanges have a large center port where two header tubes are formed into that one single center port.  Where the tubes touch one another in the center part of the port, they must be shaped such that a center divider is created during the welding process.  Often, multiple welding beads must be "put down" in the center to create a wide enough "divider bar" to act as a sealing area against the gasket.

NOTE 3:  These heads are quite rare and are easily identified from the regular cast iron factory "D" port heads by having the two center bolt holes spread very much farther apart.

HEADER FLANGE DESIGN DISCLAIMER: On ANY header flange made to match ANY performance/racing factory/aftermarket cylinder head, due to the fact that the manufacturer - at any time and without notice, might reshape and/or relocate exhaust ports and/or relocate spark plugs and/or change the angle of the spark plugs - we can NO LONGER guarantee port alignment nor spark plug socket clearance. If you are using ANY of these "non-production" heads (or have ported heads) and are concerned with possible port misalignment, we will select the best possible header flange to match your exhaust ports IF you send us a tracing of all ports, bolt holes, and surrounding machined edges.  (Note that FAXing is not often accurate enough for our needs.)  There is a $10.00 labor charge (no discount) for comparing tracings to current flange designs.  There is also a custom flange drilling charge of $15.00 when it becomes necessary to relocate the bolt pattern to align ports to the port tracings as accurately as possible - and NOTE that custom drilled header flanges are NOT returnable!  Otherwise, should port misalignments occur, grind flange ports where needed. If spark plug or spark plug socket interference occurs, then modify flange as needed.

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