Editing Pontiac V8 engine (section)
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==Heads== ;[[Pontiac V8 engine #Parts interchangeability|Return to Parts interchangeability]] ===6X heads=== Casting 6X heads and similar heads from the "smog era" generally all have hardened exhaust seats, screw-in rocker studs and guide plates, with 2.11" intake x 1.66" exhaust valves. See [http://www.pontiacstreetperformance.com/psp/6XheadID.html '''''How to Identify Pontiac's Small Chambered 6X Head'''''] for more info on ID'ing 6X heads. When inspecting 6X head and Pontiac heads in general, check the spring installed height to be sure it is equal between the valves. The spring's seat and open pressure is also important but all but impossible to measure unless the springs are checked w/a spring gauge. There are spring gauges that can be used on an assembled head. When buying assembled heads, demand a receipt showing part numbers. That will not guarantee anything but will cut down on the BS. ===4X heads=== <table border="2" cellpadding="2" cellspacing="0"><tr bgcolor="#DDDFFF"> <td align="center"><strong>Stamped ID</strong></td> <td align="center"><strong>Application</strong></td> <td align="center"><strong>Valve Diameters</strong></td> <td align="center"><strong>Rocker Studs</strong></td> </tr> <tr> <td align="center">1H</td> <td align="center">455 4-bbl</td> <td align="center">2.11/1.66</td> <td align="center">Pressed-in*</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">3H</td> <td align="center">400 4-bbl Manual</td> <td align="center">2.11/1.66</td> <td align="center">Threaded</td> </tr> <tr> <td align="center">4H</td> <td align="center">400 2-bbl </td> <td align="center">1.96/1.66</td> <td align="center">Pressed-in*</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">7H</td> <td align="center">400 4-bbl Auto</td> <td align="center">2.11/1.66</td> <td align="center">Both*</td> </tr> <tr> <td colspan="4" align="center">*All rocker arms studs are threaded beginning with unit number 709986, assembled on or about May 7, 1973<br></td> </tr> </table><br> ===Secondary head code identifiers=== ====1973-'74 4X, 46, 4C, 16/X==== <table border="2" cellpadding="2" cellspacing="0"><tr bgcolor="#DDDFFF"> <th align="center">Stamped ID</th> <th align="center">Head #</th> <th align="center">Chamber Volume<br>(cc)</th> <th align="center">Valve Diameter<br>int./exh. (in.)</th> <th align="center">Valve Length<br>(in.)</th> <th align="center">CID</th> </tr> <tr> <td align="center">'''1H / 1'''</td><td align="center">4X </td><td align="center">112.30</td><td align="center">2.11/1.66</td><td align="center">4.78</td><td align="center">455 </td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">'''2H'''</td><td align="center">46</td><td align="center">96.17</td><td align="center">1.96/1.66</td><td align="center">4.86</td><td align="center">350</td> </tr> <tr> <td align="center">'''3H / 3'''</td><td align="center">4X</td><td align="center">98.21</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">'''4H / 4'''</td><td align="center">4X</td><td align="center">98.94</td><td align="center">1.96/1.66</td><td align="center">4.86</td><td align="center">350/400</td> </tr> <tr> <td align="center">'''5H'''</td><td align="center">4C (AIR)</td><td align="center">96.17</td><td align="center">1.96/1.66</td><td align="center">4.86</td><td align="center">350</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">'''6H''' </td><td align="center">46</td><td align="center">96.17</td><td align="center">1.96/1.66</td><td align="center">4.86</td><td align="center">350</td> </tr> <tr> <td align="center">'''6H'''</td><td align="center">16/X</td><td align="center">110.74</td><td align="center">2.11/1.77</td><td align="center">4.97</td><td align="center">455 SD</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">'''7H'''</td><td align="center">4X</td><td align="center">98.21</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <tr> <td align="center">'''8H / 8'''</td><td align="center">4C (AIR)</td><td align="center">98.94</td><td align="center">1.96/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr></table><br> ====1975 (early) 5C, 51==== <table border="2" cellpadding="2" cellspacing="0"><tr bgcolor="#DDDFFF"> <th align="top">Stamped ID</th> <th align="center">Head #</th> <th align="center">Chamber Volume<br>(cc)</th> <th align="center">Valve Diameter<br>int./exh. (in.)</th> <th align="center">Valve Length<br>(in.)</th> <th align="center">CID</th> </tr> <tr> <td align="center">'''4'''</td><td align="center">5C</td><td align="center">93.74</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">350</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">'''6'''</td><td align="center">5C / 51</td><td align="center">124.51</td><td align="center">2.11/1.66</td><td align="center">4.71</td><td align="center">455</td> </tr> <tr> <td align="center">'''7'''</td><td align="center">5C (AIR)</td><td align="center">100.04</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">'''8'''</td><td align="center">5C</td><td align="center">100.04</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <tr> <td align="center">'''9'''</td><td align="center">5C (AIR)</td><td align="center">93.74</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">350</td> </tr> </table><br> ====1975-'79 6X, 6H==== <table border="2" cellpadding="2" cellspacing="0"><tr bgcolor="#DDDFFF"> <th align="center">Year</th> <th align="center">Stamped ID</th> <th align="center">Head #</th> <th align="center">Chamber Volume<br>(cc)</th> <th align="center">Valve Diameter<br>int./exh. (in.)</th> <th align="center">Valve Length<br>(in.)</th> <th align="center">CID</th> </tr> <tr> <th rowspan="6" >1975-'76</th> <td align="center"> 4</td><td align="center">6X</td><td align="center">93.74</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">350</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">6</td><td align="center">6X</td><td align="center">124.51</td><td align="center">2.11/1.66</td><td align="center">4.71</td><td align="center">455</td> </tr> <tr> <td align="center">6</td><td align="center">6H</td><td align="center">124.51</td><td align="center">2.11/1.66</td><td align="center">4.71</td><td align="center">455</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center">7</td><td align="center">6S (AIR)</td><td align="center">100.04</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <tr> <td align="center">8</td><td align="center">6X</td><td align="center">100.04</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center"> 9</td><td align="center">6S (AIR)</td><td align="center">93.74</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">350</td> </tr> <tr> <th rowspan="2">1977</th> <td align="center"> 4</td><td align="center">6X</td><td align="center">93.74</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">350 / 400 W72</td> </tr> <tr bgcolor="#F1F1F1"> <td align="center"> 8</td><td align="center">6X</td><td align="center">100.04</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <tr> <th >1978</th> <td align="center"> 8</td><td align="center">6X</td><td align="center">100.04</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400</td> </tr> <th rowspan="2">1978-'79</th><tr bgcolor="#F1F1F1"> <td align="center"> 4</td><td align="center">6X</td><td align="center">93.74</td><td align="center">2.11/1.66</td><td align="center">4.86</td><td align="center">400 W72</td> </tr></table><br> ===Valve sizes=== Often, modified Pontiac "X" heads have 1.77" exhaust valves installed in place if the stock 1.66" and this is obviously going to be very easy to determine. As far as the rest of the work that may have been done to the heads, you can visually look to see if they both have at least 3-angle seats (that won't tell you if the seats are concentric, though). The valves can be inspected to see that they have adequate margins, seat widths, and if they've been back cut or have undercut stems. I would suggest measuring the valve guide clearances, too. ===Combustion chamber volume=== One of the most important things that need to be known about the heads is the exact chamber volumes. First, look to see that the secondary identifiers are the same. Even if they are, '''''both''''' heads need to be checked- although doing the end chambers of each head (four chambers total) will be enough to tell that the chambers are equal. This is necessary because there's no way to be sure the heads were '''always''' a pair from day one, onward. Even if they ''were'' paired from birth, one head might have had a bad head gasket that required it to be resurfaced. If '''both''' heads weren't cut an equal amount that can cause the chambers to vary. If the heads were from different engines originally, obviously they can vary due to all the above reasons plus manufacturing and casting differences from the factory. The combustion chamber volume can be changed by milling the head deck. One cc will be removed per 0.005" removed from the deck. All heads can be safely milled 0.050". The 1971 #96 and the 1972 #7K3 heads can be safely cut 0.070" and the 1971-'73 round port heads can be cut 0.085". If 0.030" or more is removed, the intake side of the head should be cut equally to keep the port and bolt holes in alignment. The chamber volume should be rechecked after a valve job; most times a valve job on the same size valve (not replacing a smaller valve with a larger valve) will add 2-4cc to the chamber volume. There were three sizes of combustion chambers on 6X heads. For most builds, the small chamber head is what is wanted. The late large chamber 455 heads on a 400 will put the compression ratio in the 7.8:1 range, even with a 0.040" quench. The small chambered 6X and similar head on a 0.030" over 455 with a 0.040" [http://www.crankshaftcoalition.com/wiki/Quench '''quench'''] will result in a CR of about 9.75:1. On a 400 the CR will be around 9.2:1. *6X-4 and 6X-7: 93cc (have been seen to be as much as 95cc). The 6X-4 heads were found on mid '75-'77 350ci; 1977-'79 W72 400ci (TA "6.6 Litre" option) *6X-6: 124cc, these would have been on a 455 *6X-8 and 6X-9: 101cc *There are also 1973-'74 casting 4X heads that have 98cc chambers and screw-in studs, but the intake port size is about 5cc smaller. *The 1975 casting 5C heads have 101 cc chambers, but they supposedly have about 7cc smaller runners than the 6X heads. Bigger is better, in this case. The 4, 6, 7, 8, and 9 identifiers can be found stamped on one of the vertical ribs on the side of the head. These heads have hardened exhaust seats, screw-in rocker studs and guideplates, 2.11" intake x 1.66" exhaust valves. They can be easily converted to 1.77" exhausts. If nitrous or high rpm is in the cards, this mod should be considered. A [http://www.wheelspin.net/calc/calc2.html '''compression ratio calculator'''] can be used to calculate compression ratios when using different chamber sizes, etc. ===Port volume=== Then there's the port volumes. These heads have relatively small intake ports; the 6X-4 heads used on one 455 build were 158cc "stock" (these ports have also been measured at 153 cc), and they did not look to have been ported. After porting they measured 173cc. These stock sized ports would be like a ~ 125cc head on a 350 SBC. The comparison isn't as bad as it sounds because of the design of the Pontiac head/ports and the 30 degree intake valve angle, but the fact remains- they ARE small. Usually a stock or mildly reworked D-port Pontiac head doesn't need lift in excess of 0.480". That is a little past where maximum flow is reached but before any port stall occurs, given the rpm range of a 455. Combining that w/a duration @ 0.050" of around 234-236 degrees or so will be about right for a strong street engine that will run mid 12 second ETs at the drags and can be driven daily, anywhere, without issue, on 89 octane gas, and using a 2.73 to 3.31 gear ratio is all that's needed. ==="Low compression" heads=== Be aware that published figures often differ. The only sure way to know what the combustion chamber volume is, is to actually measure it. This will take everything into account: previous valve jobs, milling done to the decks, manufacturing and casting tolerance creep/stack up, etc. Obviously an alternative to using the larger chamber heads is to install dished pistons and use any of the smaller chambered performance heads. <br> ===Original head applications=== <table border="2" cellpadding="2" cellspacing="0"><tr><td colspan="5" align="center" bgcolor="#DDDFFF"><font size="4"><strong>CYLINDER HEAD APPLICATIONS</strong> </font></td></tr><tr><td bgcolor="#FFF8DC"><strong>Casting</strong></td><td bgcolor="#FFF8DC"><strong>Secondary ID</strong></td><td bgcolor="#FFF8DC"><strong>Valve diameter (in.)</strong></td><td bgcolor="#FFF8DC"><strong>Chamber volume</strong></td><td bgcolor="#FFF8DC"><strong>Original application</strong></td></tr><tr bgcolor="#F1F1F1"><td>4X</td><td>1/1H</td><td>2.11/1.66</td><td>112 cc</td><td>1973-'74 455ci 4-bbl</td></tr><tr><td>4X</td><td>3/3H</td><td>2.11/1.66</td><td>98-99 cc</td><td>1973-'74 400ci 4-bbl manual trans.</td></tr><tr bgcolor="#F1F1F1"><td>4X</td><td>4/4H</td><td>1.96/1.66</td><td>98-99 cc</td><td>1973-'74 400ci 2-bbl</td></tr><tr><td>4X</td><td>7/7H</td><td>2.11/1.66</td><td>98-99 cc</td><td>1973-'74 400ci 4-bbl auto trans.</td></tr><tr bgcolor="#F1F1F1"><td>4C</td><td>5/5H</td><td>1.96/1.66</td><td>96 cc</td><td>1973-'74 350ci 2-bbl w/A.I.R.</td></tr><tr><td>4C</td><td>8/8H</td><td>1.96/1.66</td><td>98 cc</td><td>1973-'74 400ci 2-bbl w/A.I.R.</td></tr><tr bgcolor="#F1F1F1"><td>46</td><td>6/6H'''*'''</td><td>1.96/1.66</td><td>96 cc</td><td>1973-'74 350ci</td></tr><tr><td>5C</td><td>4</td><td>2.11/1.66</td><td>92-94 cc</td><td>1975 350ci</td></tr><tr bgcolor="#F1F1F1"><td>5C</td><td>7</td><td>2.11/1.66</td><td>99-101 cc</td><td>1975 400ci w/A.I.R.</td></tr><tr><td>5C</td><td>8</td><td>2.11/1.66</td><td>99-101 cc</td><td>1975 400ci</td></tr><tr bgcolor="#F1F1F1"><td>5C</td><td>9</td><td>2.11/1.66</td><td>92-94 cc</td><td>1975 350ci w/A.I.R.</td></tr><tr><td>6X</td><td>4</td><td>2.11/1.66</td><td>92-94 cc</td><td>Mid 1975-'77 350ci; 1977-'79 W72 400ci</td></tr><tr bgcolor="#F1F1F1"><td>6X</td><td>8</td><td>2.11/1.66</td><td>99-101 cc</td><td>Mid 1975-'78 400ci</td></tr><tr><td>6S</td><td>7</td><td>2.11/1.66</td><td>99-101 cc</td><td>Mid 1975-'76 400ci w/A.I.R.</td></tr><tr bgcolor="#F1F1F1"><td>6S</td><td>9</td><td>2.11/1.66</td><td>92-94 cc</td><td>Mid 1975-'76 350ci w/A.I.R.</td></tr><tr><td>51</td><td>6</td><td>2.11/1.66</td><td>124.5 cc</td><td>1975 455ci</td></tr><tr bgcolor="#F1F1F1"><td>6H</td><td>6</td><td>2.11/1.66</td><td>124.5 cc</td><td>Late 1975-'76 455ci</td></tr><tr><td colspan="5">'''*'''Some reported to have a secondary stamp of "'''2'''"</td></tr></table> <br> ===Studs and guideplates=== Heads having pressed in studs will usually have smaller valves than heads having screw in studs, although there are exceptions to this like the 4X-1H 455 head. Pressed stud heads have a tapped hole between the studs for attaching a guide plate on most heads. [[File:Pressed vs screw stud pont.jpg]] ====The bottleneck stud==== [[File:Pont stk stud.jpg|thumb|500px|Stock type Pontiac bottleneck stud]]Pontiac heads like the 6X and practically all other production Pontiac heads likely to be used in a performance-orientated build originally had screw in ''bottleneck'' studs and steel guideplates. There are some exceptions to this, like heads having pressed in bottleneck studs, and the Ram Air IV and "Ram Air II" round port heads, which used a straight 7/16" stud with an adjuster nut/lock nut arrangement. The usual stock D-port arrangement is a "net lash" set-up. Because the rocker stud is 7/16" OD at the bottom, the rocker arm and pivot ball is also made to fit a 7/16" OD stud, so the stock rocker arm and ball can be reused with a straight 7/16" stud. The '''top''' of the bottleneck stud is threaded for a 3/8-24 nut, to be torqued to 15 ft/lb to retain the rocker arm. <br style="clear:both"/> The stock Pontiac net lash lifter preload adjustment may be adversely affected by any of the following: *Block deck height change *Head deck height change *Head stud boss height change *Rocker arm brand/design *Cam base circle size *Lifter design/brand/pushrod seat height *Valve stem length *Head gasket thickness So if any of the above changes are made, the stock Pontiac bottleneck stud/net lash set-up may no longer preload the lifter properly. Unless the studs are changed to allow for an adjustable valve train, different length push rods may be needed to set the lifter preload- but changing the length of the push rod can adversely affect the '''[[valve train geometry]]'''. For that reason it is advisable to use straight studs to replace the bottleneck studs. A good replacement is ARP '''p/n 190-4003''' w/hex nuts, or p/n '''190-4203''' w/12-point nuts. Be aware that there can be clearance issues between the polyloc and valve cover if polylocs are used. Check the clearances carefully; you might be able to use a shorter polyloc. If possible (and the valve cover are so equipped) keep the oil drippers. The oil drippers are a separate piece from the valve covers on the RA II/IV engines. While it is not recommended, the bottleneck studs will sometimes work as an adjustable valve train if a stock SBC lock nut is used and the camshaft is very mild. But this does nothing for the inherently weaker design of the bottleneck stud. The stock Pontiac guideplates are fine to reuse as long as the pushrod diameter is the same as stock or if the pushrod OD is larger, the holes are tweaked to allow the pushrods to fit without interference. ===Rocker arms=== Most Pontiac engines came with 1.5:1 ratio rockers. Exceptions to this were the Ram Air IV engines, which used 1.65:1 rockers. The 1.65 rockers can be used on any Pontiac head but the push rod guide hole in the head has to be carefully inspected/enlongated at the top of the opening. More on rocker arm ratios, including cautions can be seen [http://www.pontiacstreetperformance.com/psp/RockerArms.html '''here''']. ===Valve springs=== Cliff Ruggles has said "We use and prefer the [http://www.summitracing.com/parts/CRO-68404-16/ Crower p/n 68404] (1.6" installed height) or [http://www.summitracing.com/parts/CRO-68405-16/ p/n 68405] (1.7" installed height) for flat hydraulic cams with Pontiac cylinder heads." ===Round port heads=== [[File:D over rnd pont.jpg|thumb|500px|left|D-port #13 heads above a Ram Air IV head]] Round port heads were long favored for high performance. But they are scarce (read ''expensive''), and don't flow all that well, at least when compared to aftermarket heads. But now that Edelbrock and others have come out with affordable aftermarket aluminum heads, the round port heads are all but ignored by the performance crowd. But to restorers, they are still highly sought after. <br style="clear:both"/> ==="Pete's Picks"=== Pete McCarthy did a huge head air flow test that was originally written up in the April and June, 1991 editions of High Performance Pontiac, titled [http://forums.highperformancepontiac.com/70/9029510/the-general-discussion/to-port-or-not-to-port-heads/index.html '''The Ultimate Head: Part I''']. ;The results<nowiki>:</nowiki> *Best performance head: 1970 Ram Air IV *Best intake port: 1969-70 Ram Air V *Best exhaust port: 1968 1/2 Ram Air II *Best D-port head: No.16, No.48, No.12 (tie) *Best low compression D-port head: No.96(1971) *Best low compression post-1972 head: No. 6X *Best balanced head (exhaust to intake): 1963 421 SD *Best low-lift (under .400) head: 1967 No.670 *Worst exhaust-to-intake port ratio: 1969-70 Ram Air V *Worst intake-to exhaust ratio: 1968 1/2 Ram Air II *Biggest surprise: Intake port, No.17 350 head *Biggest disappointment: 1969-70 RA V, 1973-74 455 SD (tie) *Biggest "sleeper": 1975 No. 5C *Most under-cammed: 1963 SD, 1971 455 HO, 1973-74 455 SD (tie) *Most under-exhausted: 1964 GTO (No.9770716) *Most potential for porting: 1973-74 455 SD, 1968 1/2 RA II (tie)
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