Pontiac V8 engine
m |
m (Minor clean up) |
||
| Line 2: | Line 2: | ||
==Overview== | ==Overview== | ||
A look at one of the more popular GM engines. | A look at one of the more popular GM engines. | ||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
==Bore and stroke== | ==Bore and stroke== | ||
| Line 17: | Line 12: | ||
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. | 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. | ||
| − | + | ===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. | ||
| Line 37: | Line 32: | ||
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. | 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. | ||
| − | + | ===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. | 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. | ||
| Line 102: | Line 97: | ||
==Cranks== | ==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. | 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. | ||
| + | |||
| + | ==Ignition== | ||
| + | [[File:PONTIAC CCW ROTATOIN ADVANCE WEIGHTS.jpg|thumb|300px|left|CCW orientation of mechanical advance weights and cam]] | ||
| + | <br style="clear:both"/> | ||
| + | See [[Hot rodding the HEI distributor]]. | ||
==Original build information== | ==Original build information== | ||
Your Privacy Choices