Pontiac V8 engine
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==Heads== | ==Heads== | ||
===6X (and similar) heads=== | ===6X (and similar) 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 the "good" 6X head. | |
| + | 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. | ||
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| + | ====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. | 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, [I][B]both[/B][/I] 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. | 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, [I][B]both[/B][/I] 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" [['''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 98 cc 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. | ||
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| + | 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. | ||
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| + | A [url= http://www.wheelspin.net/calc/calc2.html compression ratio calculator] can be used to calculate compression ratios when using different chamber sizes, etc. | ||
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| + | ====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. | ||
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| + | 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. | ||
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| + | ==Cams== | ||
| + | A dual pattern cam like Comp Cams' XE series or a Lunati Voodoo would be good cams to look into. For info on Comp Cams XE series of cams you can contact Butler Performance for good solid info. For info on Crower cams contact Kauffman Racing Engines or Spotts Performance. These shops can be contacted via phone or email. | ||
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| + | ==Intakes== | ||
With the D-port heads, unless they've been heavily ported, an RPM intake is a good choice. It will hit harder off idle and gives up nothing to a single plane at the modest peak rpm the 455 is going to be turning (5000 rpm), built as described here; harnessing the torque by using sticky drag radial tires will give the maximum all-around performance. There might be an argument made for a single plane to "tame the torque". But that might be better left until all other avenues have been exhausted. | With the D-port heads, unless they've been heavily ported, an RPM intake is a good choice. It will hit harder off idle and gives up nothing to a single plane at the modest peak rpm the 455 is going to be turning (5000 rpm), built as described here; harnessing the torque by using sticky drag radial tires will give the maximum all-around performance. There might be an argument made for a single plane to "tame the torque". But that might be better left until all other avenues have been exhausted. | ||
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| + | ==Rods== | ||
| + | There are now 'cheap' but good quality Pontiac rods. Years ago, all that was available were high dollar rods like Miller, etc. or the weak factory forged rods or weak factory cast rods. Neither factory rod is a good choice if the engine will see hard use or high rpm. At the bare minimum, cast rods need to be resized and ARP hardware installed, and the rpm has to be kept under 5500. | ||
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| + | ==Cranks== | ||
| + | The factory cranks are good. But if a crank is needed, it would be worth looking at a stroker to make a 400 into a small journal 455. Smaller main journals of the 400 make it a better foundation for building a high performance 455 than an OEM 455 block. | ||
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[[File:7K3 Pont HEADS DRILLED FOR HEADERS 2.jpg|thumb|300px|left|7K3 heads drilled for headers. [http://www.spottsperformance.com/ Spots Performance] also sells "L" brackets for heads like these that don't have the pad.]] | [[File:7K3 Pont HEADS DRILLED FOR HEADERS 2.jpg|thumb|300px|left|7K3 heads drilled for headers. [http://www.spottsperformance.com/ Spots Performance] also sells "L" brackets for heads like these that don't have the pad.]] | ||
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