Vortec L31 cylinder head
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==Overview== | ==Overview== | ||
| − | The Chevrolet L31 5.7L Vortec cylinder head is the best production head Chevy has made for the Gen I SBC engine to date. Because of this, it has become a very popular swap. | + | The Chevrolet L31 5.7L Vortec cylinder head is the best flowing production head Chevy has made for the Gen I SBC engine to date. Because of this, it has become a very popular swap. |
The name "Vortec" can be confusing because GM used that name for their V6 and V8 truck engines as far back as 1988. But the heads that are being referred to here are from trucks and SUVs produced from 1996-2002. | The name "Vortec" can be confusing because GM used that name for their V6 and V8 truck engines as far back as 1988. But the heads that are being referred to here are from trucks and SUVs produced from 1996-2002. | ||
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* 1996-2002 Chevrolet Express/GMC Savana full-size vans | * 1996-2002 Chevrolet Express/GMC Savana full-size vans | ||
* 1996-1999 Chevrolet/GMC C/K full-size trucks | * 1996-1999 Chevrolet/GMC C/K full-size trucks | ||
| − | * 1996-1999 Chevrolet Suburban/GMC Suburban full-size long | + | * 1996-1999 Chevrolet Suburban/GMC Suburban full-size long wheelbase SUVs |
| − | * 1996-1999 Chevrolet Tahoe/GMC Yukon full-size short | + | * 1996-1999 Chevrolet Tahoe/GMC Yukon full-size short wheelbase SUVs |
* 1999-2000 Cadillac Escalade | * 1999-2000 Cadillac Escalade | ||
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*Heat Risers: No | *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” | *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 | + | *Rocker Arm Type: Self-Aligning |
*Intake Runner Volume: 170 cc | *Intake Runner Volume: 170 cc | ||
*Valve Diameter: I: 1.94”, E: 1.50” | *Valve Diameter: I: 1.94”, E: 1.50” | ||
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*Max. Valve Lift: 0.420” which allows 0.030” retainer-to-seal | *Max. Valve Lift: 0.420” which allows 0.030” retainer-to-seal | ||
*Rocker Stud: Press-in, 3/8” diameter | *Rocker Stud: Press-in, 3/8” diameter | ||
| − | *Spark | + | *Spark plug: 14 mm, 3/4" reach, tapered seat |
==Design limitations and modifications== | ==Design limitations and modifications== | ||
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*'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=164462240 p/n 26915]'''- 105 pounds at 1.8" installed height; open pressure 293 lbs. at 1.2"; coil bind at 1.100"; spring rate 313 lbs./in.; bottom OD 1.290" | *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=164462240 p/n 26915]'''- 105 pounds at 1.8" installed height; open pressure 293 lbs. at 1.2"; coil bind at 1.100"; spring rate 313 lbs./in.; bottom OD 1.290" | ||
*'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=1166393320 p/n 26918]'''- 125 pounds at 1.8" installed height; open pressure 367 pounds at 1.15"; coil bind 1.100"; spring rate 372 lbs./in.; bottom OD 1.310" | *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=1166393320 p/n 26918]'''- 125 pounds at 1.8" installed height; open pressure 367 pounds at 1.15"; coil bind 1.100"; spring rate 372 lbs./in.; bottom OD 1.310" | ||
| − | {{Note1}}The p/n26918 springs were | + | {{Note1}}The p/n26918 springs were updated, Check w/Comp Cams to be sure the specs are correct. |
*'''[http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=26981-16&Category_Code= p/n 26981]'''- 110 pounds at 1.70" installed height; open pressure 292 lbs. at 1.175"; coil bind 1.115"; spring rate 347 lb./in.; bottom OD 1.240" | *'''[http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=26981-16&Category_Code= p/n 26981]'''- 110 pounds at 1.70" installed height; open pressure 292 lbs. at 1.175"; coil bind 1.115"; spring rate 347 lb./in.; bottom OD 1.240" | ||
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On the other end of the cost scale is the use of inexpensive "Z-28/LT-1" springs (or any spring with a ~1.70" installed height and a 1.25" OD) with the damper removed along with the stock retainers that have had some of the bottom ground off to provide more clearance (sometimes referred to as the "ghetto grind"). This will allow more lift (in the area of 0.500") without changing the guide boss height or diameter. | On the other end of the cost scale is the use of inexpensive "Z-28/LT-1" springs (or any spring with a ~1.70" installed height and a 1.25" OD) with the damper removed along with the stock retainers that have had some of the bottom ground off to provide more clearance (sometimes referred to as the "ghetto grind"). This will allow more lift (in the area of 0.500") without changing the guide boss height or diameter. | ||
| − | Chevrolet recommends using the [http://www.summitracing.com/parts/crn-10309-1 Crane Cam p/n 10309-1] drop-in valve spring/retainer kit which is good for .550” lift (this allows about 0.025" between the retainer and seal) with no machining. The spring rate for this spring is 409 lb/in and has a 0.870" ID. | + | Chevrolet recommends using the [http://www.summitracing.com/parts/crn-10309-1 Crane Cam p/n 10309-1] drop-in valve spring/retainer kit which is good for 0.550” lift (this allows about 0.025" between the retainer and seal) with no machining. The spring rate for this spring is 409 lb/in and has a 0.870" ID. |
When retaining the factory boss and seals, be sure the valve seals are driven on all the way. You need to check that they are before installing this kit. Use a 3/8” drive 1/2” socket and a soft mallet to gently drive the seals fully home. | When retaining the factory boss and seals, be sure the valve seals are driven on all the way. You need to check that they are before installing this kit. Use a 3/8” drive 1/2” socket and a soft mallet to gently drive the seals fully home. | ||
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*Comp p/n 981 | *Comp p/n 981 | ||
| + | *Crane p/n 99846: H-11 tool steel | ||
*Crane p/n 144845: Performance hydraulic roller cams, PAC enhanced wire, no damper | *Crane p/n 144845: Performance hydraulic roller cams, PAC enhanced wire, no damper | ||
**OD: 1.265" | **OD: 1.265" | ||
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===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 caution if making the seat larger, there have been a few warnings about cracks developing on heads with enlarged seats. | + | 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. Do not make the spring seat deeper. If more installed height is required, get it from a different retainer, locks, or a longer valve stem. |
==Valve guide boss== | ==Valve guide boss== | ||
[[File:900 guide boss1.jpg|thumb|450px|left|Stock Vortec boss is 0.845"OD]] | [[File:900 guide boss1.jpg|thumb|450px|left|Stock Vortec boss is 0.845"OD]] | ||
| − | For performance use, often the guide boss will be shortened to allow more lift without retainer to seal clearance problems. Along with that, the guide boss OD can be machined down from 0.845" to a smaller common diameter, like .785" of the original Gen1 SBC heads, so aftermarket springs (double or with dampers) can be used. At the same time the boss can be machined from .555" to | + | For performance use, often the guide boss will be shortened to allow more lift without retainer to seal clearance problems. Along with that, the guide boss OD can be machined down from 0.845" to a smaller common diameter, like 0.785" of the original Gen1 SBC heads, so aftermarket springs (double or with dampers) can be used. At the same time the top of the boss where the seal is located can be machined from 0.555" (stock) to a smaller diameter like 0.530" to use commonly available seals. |
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[[File:VORTEC GUIDE BOSS MODIFIED.jpg|thumb|250px|Before (right) and after]] | [[File:VORTEC GUIDE BOSS MODIFIED.jpg|thumb|250px|Before (right) and after]] | ||
| − | In order to fit one of the commonly available smaller diameter positive type valve stem oil seals, the tops of the guide boss needs to be turned down. To fit springs with a smaller ID like | + | In order to fit one of the commonly available smaller diameter positive type valve stem oil seals, the tops of the guide boss needs to be turned down. To fit springs with a smaller ID like doubles or those with a damper, the guide boss needs to be modified by shortening and decreasing the OD of the boss. |
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| − | + | ===Tooling=== | |
[[File:Tool.jpg|thumb|450px|Comp tooling]] | [[File:Tool.jpg|thumb|450px|Comp tooling]] | ||
| − | Crane | + | Crane, Comp Cams and others sell cutters to machine the guide boss diameter using a hand drill. The arbor and cutters should be used with valve guides that are in good condition because the arbor uses the guide to locate the cutters. |
| − | + | ;Comp Cams<nowiki>:</nowiki> | |
| − | *4718- spring seat cutter, 1.440" OD | + | *p/n 4718- spring seat cutter, 1.440" OD |
| − | *4726- valve guide cutter, 0.530" OD | + | *p/n 4726- valve guide boss seal cutter, 0.530" OD |
| − | *4732- 11/32" arbor for cutting tools | + | *p/n 4732- 11/32" arbor for cutting tools |
| + | ;Competition Products<nowiki>:</nowiki> | ||
| + | *p/n 7020 (includes 11/32" arbor)- valve guide boss seal cutter 0.531" OD | ||
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Production L31 Vortec heads come with pressed in 3/8" studs. For high performance and/or solid lifter applications, screw in studs are highly recommended. The pressed studs can be pinned, but this is a stop-gap measure that should be done only in cases where the spring pressures/engine RPM/lobe intensity will not be excessive and/or the budget is limited. Otherwise use ARP screw in studs or their equivalent. | Production L31 Vortec heads come with pressed in 3/8" studs. For high performance and/or solid lifter applications, screw in studs are highly recommended. The pressed studs can be pinned, but this is a stop-gap measure that should be done only in cases where the spring pressures/engine RPM/lobe intensity will not be excessive and/or the budget is limited. Otherwise use ARP screw in studs or their equivalent. | ||
| − | If not using guide plates, non shouldered | + | If not using guide plates, non shouldered straight studs like Pioneer p/n 850001 screw in studs can be used. This type of stud is tightened by "double nutting" instead of tightening it by a hex. |
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===Stud boss modification=== | ===Stud boss modification=== | ||
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