Pontiac V8 engine
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==Heads== | ==Heads== | ||
| + | ===6X (and similar) heads=== | ||
| + | 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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| + | 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. | ||
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| + | 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. | ||
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| + | 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" (the history on them was basically unknown), and they did not in any way 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 or so will be about right for a strong street engine that will run 12's at the drags and can be driven daily, anywhere, without issue. A dual pattern cam like Comp Cams' XE series or a Lunati Voodoo would be good cams to look into. | ||
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| + | 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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[[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.]] | ||
[[File:7K3 Pont HEADS DRILLED FOR HEADERS.jpg|thumb|300px|left|Another view of 7K3 heads drilled for headers]] | [[File:7K3 Pont HEADS DRILLED FOR HEADERS.jpg|thumb|300px|left|Another view of 7K3 heads drilled for headers]] | ||
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