Vortec L31 cylinder head
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Unported Vortec’s with the "tricks" can produce 500 HP on well built, high CR, drag race short block. 425-450 HP is more realistic for a killer street engine running on pump gas. | Unported Vortec’s with the "tricks" can produce 500 HP on well built, high CR, drag race short block. 425-450 HP is more realistic for a killer street engine running on pump gas. | ||
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| + | ==Valve springs== | ||
| + | [[File:Vortec beehive.jpg|thumb|left|300px|Straight wound spring, Left; Beehive spring, right]] | ||
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| + | The stock Vortec valve springs are single wound without a damper. The damping is done by the spring ID being a close fit to the guide boss OD; this damps rthe spring without the added cost of an inner flat wound damper seen on the Gen 1 SBC throughout its production. | ||
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| + | The stock springs are not suited for high performance use. There are several replacements for the stock springs, among the best is the beehive spring and retainer combination from Comp Cams. There are two part numbers for the different spring rates: | ||
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| + | ==Exhaust valve seats== | ||
| + | Not long after the L31 Vortec head was introduced, a writer for a car magazine incorrectly stated that the 906 head was vastly inferior to the 062 head because the exhaust flow was so bad on the 904. Despite this myth being shot down many times, it still surfaces now and then. | ||
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| + | Like many things, there's a grain of truth to this. 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 out for best flow using nothing more than a Dremel. | ||
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| + | {| | ||
| + | |[[File:Hard insert seat vortec 906.jpg|thumb|300px|center|Casting number 906 Vortec head with hardened exhaust seat insert]] | ||
| + | |[[File:Induction hardened seat vortec.jpg|thumb|300px|center|Vortec head with induction hardened exhaust seat, no insert]] | ||
| + | |} | ||
==Valve guide boss modification== | ==Valve guide boss modification== | ||
| + | In order to fit one of the commonly available smaller diameter valve stem oil seals, the tops of the guide boss needs to be turned down. To fit springs with a smaller ID, and for using different springs, the guide boss needs to be modified by shortening and decreasing the OD of the boss. Tools are sold (~$100 for the two cutters needed) to do these modifications using a hand drill. | ||
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[[File:VORTEC GUIDE BOSS MODIFIED.jpg]] <br style="clear:both"/> | [[File:VORTEC GUIDE BOSS MODIFIED.jpg]] <br style="clear:both"/> | ||
==Pushrod guide holes== | ==Pushrod guide holes== | ||
| − | [[File:Vortec head p-rod hole enlargement.jpg|thumb|Vortec head enlarging pushrod hole]]Vortec heads have a 7/16" round pushrod hole in the head | + | [[File:Vortec head p-rod hole enlargement.jpg|thumb|Vortec head enlarging pushrod hole]]Vortec heads have a 7/16" round pushrod hole in the head; earlier non self aligning rocker arm equipped heads have a 7/16" x 11/32" ovoid hole in them. |
So what this means is three things- | So what this means is three things- | ||
| − | • Without resorting to welding up the holes to form slots to provide side to side alignment, Vortec heads cannot be used w/non self aligning rockers unless guide plates are used. | + | • Without resorting to welding up the holes to form slots to provide side to side alignment, Vortec heads cannot be used w/non self aligning rockers unless guide plates are used. Heads can use guide slots, OR guide plates, OR self aligning rockers, but only ONE of the three at any given time. |
| − | • If using 1.6 ratio rockers, there's a chance the Vortec's 7/16" hole will not be long enough. A Lewis tool will not work, so the best bet is to use a drill bit larger than 7/16" to open the holes up. Most often a 1/2” bit is used, I would use only as much size as was needed, but 1/2” will work. | + | • If using 1.6 ratio rockers, there's a chance the Vortec's 7/16" hole will not be long enough. A Lewis tool will not work, so the best bet is to use a drill bit larger than 7/16" to open the holes up. Most often a 1/2” bit is used, I would use only as much size as was needed, but 1/2” will work. The push rod hole can also be lengthened with a grinding tool like a Dremel or die grinder. As a last resort this can be done using files. |
| − | • If non self aligning rockers ARE used, they '''''must''''' be accompanied by | + | • If non self aligning rockers ARE used, they '''''must''''' be accompanied by some means of guiding the push rod. |
==Aftermarket Vortec heads== | ==Aftermarket Vortec heads== | ||
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==Recommended spark plugs== | ==Recommended spark plugs== | ||
| − | The exact heat range depends on several factors. This is a guide that will get you in the ballpark. Carefully | + | The exact heat range depends on several factors. This is a guide that will get you in the ballpark. Carefully assess the heat range before settling on a plug for your particular combination. |
•AC Delco Rapid Fire Spark Plugs R44LTS | •AC Delco Rapid Fire Spark Plugs R44LTS | ||
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•Bosch HR9DC | •Bosch HR9DC | ||
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==Links== | ==Links== | ||
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