Header Flanges, Gaskets

1 5/8" OD Finished Header Flanges - 3/8" thick
Small Block Chev Square Port (rectangular, round, D-port also available)
(Part Number 20312D38).  Also available with 1 3/8", 1 1/2", and 1 3/4" OD
Starter Tubes and flange thicknesses of 1/4", 5/16", and 3/8".
Starter Tubes are approximately 2" long.

Some Small Block Chev header flange designs are also available with 1 7/8" OD starter tubes.
Inner/Outer Header Flange combinations available for tube sizes as large as 2 1/4" OD.

Quality concerns:  When we make these Finished Header Flanges, a drill rod is placed between
the two center starter tubes prior to welding to assure that adequate clearance for tube welding
is maintained.  (If there is little or NO clearance between the ends of the starter tubes, it becomes
almost impossible to weld around the tubes correctly where they are closest to each other!)
Also, because the bolt holes are so close to the ports, we also run a round file through each of the
bolt holes to remove any weld that may have entered the bolt hole during the welding process.
   

    1 5/8" OD Finished Header Flanges - 3/8" thick
Small Block Chev LS engine series (GEN III) D-port version (round also available)
(Part Number 20328DX38).  Also available with 1 3/4", 1 7/8", and 2" OD
Starter Tubes and flange thicknesses of 1/4", 5/16", and 3/8".
Starter Tubes are approximately 2" long.
Flange pictured was ordered with extra metal ("X" in part number) added across the
top to increase its rigidity (see Note 40).  (Standard header flange design
has three cutouts on the top matching the three cutouts on the bottom.)


1 3/4" OD Finished Header Flanges - 3/8" thick
Big Block Chev Factory Aluminum Heads with raised exhaust port floor
(Part Number 20358E38).  Also available with 1 7/8", 2", and 2 1/8" OD
Starter Tubes and flange thicknesses of 1/4", 5/16", and 3/8".
Starter Tubes are approximately 2" long.
  

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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 and all welded items (Finished Header Flanges, Custom Collectors, parts with Welded Flanges, etc. are NOT returnable.

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

NOTE 7: On certain engines, the exhaust side bolt holes are so close to the exhaust ports that it is physically impossible to build larger header tubes due to bolt clearance issues. A combination of INNER and OUTER flanges is now used to allow the construction of larger tube headers on these engines.

The INNER flanges have ports that are on the small side and have to be ground to match the cylinder head. The INNER flanges also have two bolt patterns:

(1) The stock bolt pattern that allows the INNER flange to be bolted to the cylinder head. The stock bolt holes are countersunk so that flat head Allen bolts can be used to hold the INNER flange to the head. The depth of the countersinking is such that the top of the flat head Allen bolts are flush with the outside of the header flange.

(2) The second bolt pattern (seven bolts on the Small Block Chev header flanges is threaded to allow the OUTER flange to be bolted to the INNER flange. This second bolt pattern matches that used by HOOKER HEADERS so header gaskets are easy to find.

While not normally included with plain header flanges, we DO include the necessary bolts with either of these INNER or OUTER header flanges.

Header gaskets are used between the INNER header flanges and the cylinder head and between the OUTER header flanges and the INNER header flanges. Gaskets are NOT included with these flanges.

The 25335 Adapter Flange allows the use of headers built with a flange that has the STAHL seven bolt pattern on a Small Block Chev head with the standard production 6 bolt pattern. The adapter plate has its center ports located to match the center exhaust port locations of standard (NOT spread port) cylinder heads. The Adapter Flange has smaller ports that must be ground to match the head. The plate is threaded to match 3/8-16 bolts (standard coarse thread).

NOTE 14:  These flanges can be ordered with an added horizontal metal "pad" area to make adding a bracket for mounting the alternator or generator much easier.  Must specify which side of engine alternator or generator will be mounted.  Add $15.00 for the extra setup time.

NOTE 15:  Besides the port sizes listed here, we can make finished header flanges with larger ports in the flanges than listed for a particular tube size.  This is important on smaller tube diameters where the listed port size might block the port in the head to some degree.  Add $24.00 when requesting this on round port flanges.

NOTE 16:  Series 311 flanges have tighter radius corners than the series 312, 313, 314, and 315 flanges do.  312 series flanges are closest match to factory port shape.

NOTE 18:  Series 325 flanges have a WIDER six bolt pattern than that used in Production Small Block Chevrolet heads.  Measured center to center, the end bolt holes are 2.48" apart and the center bolt holes are 4.63" apart.  (The same measurements in production Small Block Chev heads are 2.22" and 3.95" respectively.)

NOTE 20:  Some aftermarket cylinder heads for the Small Block Chev engine are offered with a choice of several bolt patterns - the factory six bolt pattern plus two different seven bolt patterns that look almost the same.  Looking at the drawing below:  One pattern matches that used by HOOKER HEADERS where the dimension A = 3 3/16" and B = 2 15/16".  The other seven bolt pattern matches that used by STAHL HEADERS where A = 3 1/4" and B = 3 1/8".  Note that the "B" measurements for the two different patterns differ the most so use those dimensions when double checking bolt patterns on headers or heads when ordering header flanges from us.

350 series:  Round port design with more metal around the exhaust port than is normally found elsewhere. Metal in the bottom of the added area under the port is notched to clear the cylinder head bolts.

351 flange:  2 1/2" round port is huge and can actually extend OUT SIDE of the milled surface of a cylinder head. It can also run into the top of the cylinder head bolts on heads that do NOT have raised ports.

352 series:  The square ports in these flanges match quite well to the square ports found in most of the Big Block Chev Cast Iron heads made by Chevrolet over the past 40+ years.

353 series:  These are flanges with "D" shaped ports designed specifically for the original Dart brand "Merlin" cylinder heads. While not mentioned by the manufacturer, the ports in these heads were moved to the left about .080-.100" and the entire port area and bolt pattern were also moved up about .300". Moving everything up .300" meant that the distance to the cylinder head bolts was increased considerably and we took advantage of that by designing a TOTALLY better header flange for these heads by adding much more metal around the port area to further increase the rigidity of the header flange in that area. This new design makes a standard Big Block Chev header flange actually look "wimpy" by comparison.

354 series:  These are 350 series flanges with relocated bolt patterns that makes the ports align better with the different port location in the original "Merlin" head.

355 series:  These are 353 series flanges with relocated bolt patterns that makes the ports align better with the different port location in the newer "Merlin II" head. This flange also works well on other aftermarket cylinder heads with "D" ports that have been raised at least .300".

358 series:   These are flanges based on the 352 series design but have the floor of the port in the flange raised about a 1/4" to match the raised floor in these aluminum heads offered by Chevrolet.  One issue that must be dealt with is that these heads appear to be wider than other heads as there is a milled notch in the cylinder head near the bottom of the exhaust port that is NOT in other heads for the Big Block Chev engine. It also seems that the area where the cylinder head bolt rests is also higher.  Because of these two differences, we have been told by some customers that they had to grind these flanges to get clearance to the cylinder head bolts.  Keep in mind that this might happen but also that it will happen with ANY Big Block Chev header flange that has not been specifically designed to deal with these two issues!!!!!!!!!!!!!!!!!!!

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, 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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