Vortec L31 cylinder head
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They are made of cast iron, have 170cc nominal intake runners, and 64cc nominal combustion chamber volume (actual volumes may vary due to production tolerances and/or modifications done previously, so volumes, especially the combustion chamber volume, has to be determined by measuring, or "CC'ing" the chamber). | They are made of cast iron, have 170cc nominal intake runners, and 64cc nominal combustion chamber volume (actual volumes may vary due to production tolerances and/or modifications done previously, so volumes, especially the combustion chamber volume, has to be determined by measuring, or "CC'ing" the chamber). | ||
| − | 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 30-32 degrees BTDC, or about 4-6 degrees less than the earlier non fast burn heads. |
==Donor vehicles== | ==Donor vehicles== | ||
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|[[File:906 VORTEC END ID.jpg|right|frame|Casting number 10239906 Vortec head has one large single hump 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.]] | ||
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| + | ==Technical specs== | ||
| + | *Valvespring Seat: 1.300” O.D., 0.850” I.D. | ||
| + | *Valve-guide Seals: Viton rubber positive seals, total 0.450” retainer-to-seal clearance | ||
| + | *Combustion Chamber Volume: 64 cc | ||
| + | *Heat Risers: No | ||
| + | *Valve springs: Single wire with damper 1.235” O.D., 0.875” I.D. 75-pound seat pressure @ 1.700” installed height Coil-bind @ 1.150” | ||
| + | *Rocker Arm Style: Self-Aligning | ||
| + | *Intake Runner Volume: 170 cc | ||
| + | *Valve Diameter: I: 1.94”, E: 1.50” | ||
| + | *Casting Numbers: 10239906 and 12558062 | ||
| + | *Max. Valve Lift: 0.420” which allows 0.030” retainer-to-seal | ||
| + | *Rocker Stud: Press-in, 3/8” diameter | ||
| + | *Spark-plug Style: 14 mm, ¾ reach, tapered seat | ||
==Design limitations and modifications== | ==Design limitations and modifications== | ||
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* Head bolts (required only if the original head bolts are either missing or unusable for some reason) | * Head bolts (required only if the original head bolts are either missing or unusable for some reason) | ||
* Head gaskets ([http://www.crankshaftcoalition.com/wiki/Head_gasket#Re-using_head_gaskets generally required] any time heads are re-installed) | * Head gaskets ([http://www.crankshaftcoalition.com/wiki/Head_gasket#Re-using_head_gaskets generally required] any time heads are re-installed) | ||
| − | * | + | * Machining valve guide boss or the use of different retainers and springs, or ghetto grinding the stock retainers, etc., to work with a camshaft having somewhere around 0.450" or more valve lift. |
{{Note1}} The clearance between the retainer and the seal has to be checked during the engine mock up phase of the build to determine exactly what the clearance is with the cam, retainer, valve stem seal, valve locks and rocker arm/rocker arm ratio used. | {{Note1}} The clearance between the retainer and the seal has to be checked during the engine mock up phase of the build to determine exactly what the clearance is with the cam, retainer, valve stem seal, valve locks and rocker arm/rocker arm ratio used. | ||
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*[http://www.thirdgen.org/techboard/tech-general-engine/542295-ls6-valvetrain-vortec-heads.html LS6 Valvetrain on vortec heads] | *[http://www.thirdgen.org/techboard/tech-general-engine/542295-ls6-valvetrain-vortec-heads.html LS6 Valvetrain on vortec heads] | ||
*[http://www.thirdgen.org/techboard/tech-general-engine/562935-rework-vortec-heads.html Vortec valvetrain mods] | *[http://www.thirdgen.org/techboard/tech-general-engine/562935-rework-vortec-heads.html Vortec valvetrain mods] | ||
| − | + | ||
| − | ==Spring seat== | + | ===Spring seat=== |
| − | Use reduced hex head bolts or 12 point fasteners to give more clearance if a larger seat like for a 1.44" OD spring is used. | + | Use reduced hex head bolts or 12 point fasteners to give more clearance if a larger seat like for a 1.44" OD spring is used. Use caution if making the seat larger, there have been a few warnings about cracks developing on heads with enlarged seats. |
==Valve guide boss== | ==Valve guide boss== | ||
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==Vortec specific intake manifolds== | ==Vortec specific intake manifolds== | ||
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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. | 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. | ||
| + | |||
| + | Vortec heads use an intake manifold having 8 instead of 12 bolts. Also, Vortec intake ports are taller 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. An early intake would need at least 0.325" of material above the intake port opening to have any chance of sealing, and that doesn't take the difference in the port width/location. Because of these differences, a Vortec-specific intake must be used. | ||
| + | |||
| + | ;Chevrolet says<nowiki>:</nowiki> | ||
| + | <blockquote> | ||
| + | Do not try to modify either the heads or the intake manifold to try to make the Vortec heads match up to a standard 12-bolt intake manifold. The ports will not match up. You must use a Vortec style intake manifold with any Vortec style cylinder head. | ||
| + | </blockquote> | ||
| + | |||
| + | Due to issues with aftermarket Vortec intake manifold gaskets deteriorating for no apparent reason, it is suggested to use a Fel-Pro gasket p/n Q1255, or equivalent. | ||
| + | |||
{| | {| | ||
|[[File:VORTEC GASKET OVER STANDARD INTAKE GASKET.jpg|thumb|center|300px|Vortec intake gasket over standard gasket]] | |[[File:VORTEC GASKET OVER STANDARD INTAKE GASKET.jpg|thumb|center|300px|Vortec intake gasket over standard gasket]] | ||
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[[File:Vortec dome piston long rod.jpg|350px|left|thumb|KB domed piston for the Vortec head. This example uses a long rod]] <br style="clear:both"/> | [[File:Vortec dome piston long rod.jpg|350px|left|thumb|KB domed piston for the Vortec head. This example uses a long rod]] <br style="clear:both"/> | ||
| − | + | While using a domed piston in a SBC engine is generally avoided, there may be certain circumstances that require their use. One such example is the large port Bow Tie Vortec head; it can only be milled to about 51 cc. This will give about 12:1 CR using flat top pistons. So if a higher CR is required, domed pistons must be used unless the chambers are welded and machined smaller. An engine built with ''unported'' large port Bow Tie heads (FASCAR (Florida Association of Stock Car Racing rules) made over [http://www.chevyhiperformance.com/techarticles/148_0506_gm_bow_tie_vortec_small_block_engine/viewall.html 630 HP/500 ft/lb torque] with 12:1 CR. | |
See the discussion page for more. | See the discussion page for more. | ||
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