Vortec L31 cylinder head
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Because of the superior port and combustion chamber designs, total timing requirements for maximum power is 4-6 degrees less than the earlier non fast burn heads. | Because of the superior port and combustion chamber designs, total timing requirements for maximum power is 4-6 degrees less than the earlier non fast burn heads. | ||
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| + | ==Vortec L31 5.7L head ID== | ||
| + | The L31 5.7L Vortec casting numbers are '''12559062''' and '''10239906'''. | ||
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| + | {| | ||
| + | |[[File:062_VORTEC_END_ID_001.jpg|left|frame|Casting number 12558062 Vortec head has 3 small humps, aka "sawtooth", on the end of the head.]] | ||
| + | |[[File:906 VORTEC END ID.jpg|right|frame|Casting number 10239906 Vortec head has one large single hump on the end of the head.]] | ||
| + | |} | ||
==Design limitations and modifications== | ==Design limitations and modifications== | ||
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Guide plates can also be installed at this time if desired. If not, non shouldered studs can be used instead of studs having shoulders and a hex for tightening (this type of stud is tightened by "double nutting"). | Guide plates can also be installed at this time if desired. If not, non shouldered studs can be used instead of studs having shoulders and a hex for tightening (this type of stud is tightened by "double nutting"). | ||
| − | ==Exhaust | + | ==Exhaust seats== |
| − | Not long after the L31 Vortec head was introduced, | + | Not long after the L31 Vortec head was introduced, there was much made of the supposed difference in flow between the Vortec heads that came with the hardened exhaust seat inserts as opposed to the heads that had induction hardened seats. This was largely due to an incorrect, though oft-repeated statement made by a car magazine that said in essence the 906 head was to be avoided because of the exhaust seat insert being vastly inferior to the heads with induction hardened exhaust seats. |
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| + | Despite this having been being dispelled any number of times, it still surfaces now and then. But like is often the case, there's a grain of truth to this. On c/n 906 Vortec heads having the hardened exhaust seat insert (not all 906 heads used the insert), there ''can'' be a lip made by the seat where it's pressed into the head. If there's a lip it can be blended and smoothed to improve the flow using nothing more than a Dremel. This is a common procedure that's often done in performance builds- regardless of whether the seats are inserts or induction hardened or unhardened. And also on the 906 heads having the insert, the seat was machined with a single angle instead of a three angle seat as seen on Vortec heads having the induction hardened exhaust seat. The wider seat was used to better transfer heat from the valve into the head/cooling system. Three angle valve seats are the norm these days, done routinely by almost every machine shop. So if the seats are reground during a valve job, the single angle seat can be made into a three angle seat without a problem. | ||
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| + | So both the c/n 906 and c/n 062 heads have virtually the exact same performance potential. In fact the 906 heads having the hardened inserts are actually preferred by some performance engine builders, mainly for marine applications. Later production 906 heads stopped using exhaust seat inserts and at some point, all Vortec head exhaust seats were induction hardened. | ||
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From GMPP: | From GMPP: | ||
:The #906 casting head was available in two versions. One has an Inconel exhaust seat with a single angle grind, and the other has the conventional 3-angle grind on the exhausts as per the #062. The #906 with Inconel seat does not intrude into the exhaust port. It was used primarily on the HD and 1-ton truck applications where sustained towing of heavy loads & weight up inclines could cause eventual damage to a standard induction-hardened exhaust seat from excessive heat. | :The #906 casting head was available in two versions. One has an Inconel exhaust seat with a single angle grind, and the other has the conventional 3-angle grind on the exhausts as per the #062. The #906 with Inconel seat does not intrude into the exhaust port. It was used primarily on the HD and 1-ton truck applications where sustained towing of heavy loads & weight up inclines could cause eventual damage to a standard induction-hardened exhaust seat from excessive heat. | ||
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{| | {| | ||
| − | |[[File:Hard insert seat vortec 906.jpg|thumb | + | |[[File:Hard insert seat vortec 906.jpg|thumb|center|400px|Hardened insert Vortec exhaust seat]] |
| − | |[[File:Induction hardened seat vortec.jpg|thumb | + | |[[File:Induction hardened seat vortec.jpg|thumb|center|400px|Induction hardened Vortec exhaust seat, note the discoloed area around seat]] |
| − | |} | + | |} |
==Valve guide boss modification== | ==Valve guide boss modification== | ||
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