Vortec L31 cylinder head
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==Overview== | ==Overview== | ||
The L31 Chevy Vortec cylinder head is the best flowing production head for the Gen I SBC engine. They are made of cast iron, have 64cc combustion chambers (actual size is closer to 66-68cc) and 170cc intake runners. | The L31 Chevy Vortec cylinder head is the best flowing production head for the Gen I SBC engine. They are made of cast iron, have 64cc combustion chambers (actual size is closer to 66-68cc) and 170cc intake runners. | ||
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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 heads. | ||
==Design limitations and modifications== | ==Design limitations and modifications== | ||
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==Pushrod guide holes== | ==Pushrod guide holes== | ||
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[[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. | [[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. 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. 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 some means of guiding the push rod. | ||
| − | + | ==New GM Vortec heads== | |
| + | The listing for '''part''' number (NOT casting number) 12558060 cast iron Vortec cylinder head assembly sold by GMPP says in part: | ||
| + | * Completely assembled with 1.94”/1.50” valves | ||
| + | * Uses bare head 12529093 | ||
| + | * 64cc combustion chamber | ||
| + | * Straight spark plugs | ||
| + | * No heat risers | ||
| + | * Requires Vortec specific intake manifold | ||
| + | * Camshafts with more than 0.475" lift require machining valve guide bosses and checking valve seal to valve spring retainer clearance | ||
| + | * Can be machined for 2.02"/1.60" valves | ||
| + | More [http://www.jrgmparts.com/GM_Performance_Parts/GM_Parts_Catalog/GM_Engine_Components/GM_Small_Block_Crate_Engine_Co/Cylinder_Heads_GM_Chevy_Small_/cylinder_heads_gm_chevy_small_.html HERE]. | ||
| − | + | ==GMPP Vortec heads== | |
| + | ==Small port Vortec head p/n 25534351 (bare) and p/n 25534421 (assembled)== | ||
| + | Based on info from GMPP: | ||
| + | GM Performance Vortec small port Bowtie cast iron cylinder heads are machined for 2.00" intake valves and 1.55" exhaust valves and have bronze valve guides. Combustion chamber volume is 66cc nominal, deck surfaces are 0.450" thick, and port volumes are 185cc intake and 65cc exhaust. | ||
| − | + | The valve cover rails are machined for both perimeter and '86-up centerbolt style valve covers. These heads are machined for 3/8" screw-in rocker arm studs, and have valve spring pockets machined for springs up to 0." OD, and will accept up to 0.530" lift camshafts without modifications. They are identified with the Bowtie Emblem on the exterior of the head, below the exhaust flange, and the Vortec logo on top of the intake port area. They also feature the GM logo cast into the bottom of the intake ports. | |
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| − | + | ==Large port Vortec head p/n 25534445 (bare) and p/n 25534446 (assembled)== | |
| − | + | The specs for the large port head is the same as for the small port head except for the port volumes: 215cc intake ports, and 77cc or 84cc exhaust ports, depending on the source. | |
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| − | + | ==Vortec specific intake manifolds== | |
| + | Vortec heads use an intake manifold having 8 instead of 12 bolts. Also, Vortec intake ports are taller and narrower than earlier SBC heads. That means earlier intakes will not match up to the Vortec ports; there's not enough metal above the port (except on "raised port" aftermarket intakes) to allow the head and intake port to match up. Because of these differences, a Vortec-only intake must be used. | ||
| + | The L30 5.0L and L31 5.7L Vortec engines never came with a carb; they all used EFI so did not need a heat crossover port in the heads. GMPP and the aftermarket sell various carburetor and TBI intakes to fit the Vortec heads, though, so using a carb or TBI with Vortec heads is easy and some Vortec intakes have the provision to run coolant through the plenum area to provide intake heat. | ||
| + | {| | ||
| + | |[[File:Gmpp vortec tbi intake.jpg|thumb|center|300px|TBI intake p/n 12496821 from GMPP]] | ||
| + | |[[File:12366573 - GMPP Vortec dual plane intake manifold.jpg|thumb|center|300px|Dual plane GMPP intake p/n 12366573]] | ||
| + | |[[File:Gmpp 12496822 open plenum.jpg|thumb|center|300px|GMPP p/n 12496822 open plenum intake]] | ||
| + | |} | ||
==Vehicles that came with the L31 head== | ==Vehicles that came with the L31 head== | ||
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