Vortec L31 cylinder head

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[edit] Overview

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.

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 30-32 degrees BTDC, or about 4-6 degrees less than the earlier non fast burn heads.

[edit] Donor vehicles

  • 1996-2002 Chevrolet Express/GMC Savana full-size vans
  • 1996-1999 Chevrolet/GMC C/K full-size trucks
  • 1996-1999 Chevrolet Suburban/GMC Suburban full-size long wheelbase SUVs
  • 1996-1999 Chevrolet Tahoe/GMC Yukon full-size short wheelbase SUVs
  • 1999-2000 Cadillac Escalade

[edit] How to find good used heads

Vortec heads have gotten a reputation for cracking easily. The truth is they do not crack any more than ANY modern lightweight production head, although there have been problems associated with leaking intake gaskets on Vortec engines that may have caused more than the usual number of cracked heads.

[edit] Junkyard heads

When buying Vortec heads from junkyards (or any head for that matter), the chances increase that the heads will be cracked. There are ways to tip the odds in your favor, though.

To find heads from an assembled engine that have a better than average chance of being uncracked, look for:

  • heads from a wrecked vehicle. These stand an excellent chance of being good, as long as the other things listed here pass inspection.
  • engines that do not have the thermostat removed. A missing thermostat is an indication the engine was running hot.
  • engines that still have antifreeze in them. Engines with straight water, or without any coolant showing, may well have been losing coolant. No one replaces leaking coolant with antifreeze- they will use straight water "until I fix it". By then, it's often too late.
  • engines with water in the oil or oil in the water. This is a sure sign of a blown head gasket, bad intake gasket or cracked casting, any of which can lead to overheating and cracked heads.
  • Look for heads having a spark plug (or spark plugs from adjacent cylinders) with no unusually colored deposits- or a lack of deposits that were removed by coolant getting into the chamber(s). Head gaskets leaking or a cracked casting that lets coolant into the combustion chamber will make the plugs look a lot different than a normal plug- look for uniformity.
  • Look for engines that do not have evidence of stop leak in the radiator/cooling system. If it has stop leak, it was leaking. If it was leaking there's too big of a chance it overheated and cracked the heads.
    • Signs of stop leak use is a sludgy or copper/silver colored metallic accumulation inside the radiator fill neck, the same thing under the radiator cap, and possibly even in the overflow tank.

[edit] Online or other "sight unseen" sources

Not recommended if from a private seller, especially true if shipping is involved. The cost for shipping a hundred pounds of cast iron across any distance is too high to warrant such a purchase. Very few people sells GOOD Vortec heads online. They're too easy to sell locally.

Buying from a reputable volume/commercial seller might not be as big a risk, but research them fully and carefully before pulling the trigger. And remember, the shipping is on YOU unless otherwise stated in writing by the seller.

[edit] Local private sellers

This can be a good way to get heads. But the provision that they pass inspection BEFORE cash is exchanged should be insisted upon.

Speak to a machine shop beforehand to find out the details (can they inspect adequately with the heads assembled, or do they need to be apart? Does the inspection require being fully cleaned before inspection? How long will this take? How much does it all cost?) before contacting a prospective seller so you can lay out the plans to them. Don't expect the seller to pay for all or part of the inspection- if they fail, consider that as one of the costs involved with using used heads.

[edit] Head inspection

Crack possibly caused by over torquing
400px-Induction hardened seat vortec1.jpg

It is obviously best to have a reputable machine shop inspect your heads for cracks. If you don't have access to the tools needed they can also do the rest of the inspection for valve and valve guide condition, whether a valve job is needed, etc.

Vortec heads tend to crack in the center two cylinders more than the ends. Places to look for cracks are shown above; often between the exhaust and a head bolt hole or water jacket hole, Sometimes the crack will be from the valve seat down into the port. Because the cracks can be very small, using a magnetic particle inspection system will show defects not readily visible to the naked eye.

The image on the right shows a center chamber next to an end chamber, but remember there's a better chance the cracks will be in the center two chambers.

[edit] Vortec L31 5.7L head ID

The L31 5.7L Vortec casting numbers are 12558062 and 10239906.

Casting number 12558062 Vortec head has 3 small humps, aka "sawtooth", on the end of the head.
Casting number 10239906 Vortec head has one large single hump on the end of the head.

[edit] 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 Type: 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: 14 mm, 3/4" reach, tapered seat

[edit] Design limitations and modifications

Based on info from Gary Penn, of GMPP. This is an excerpt from Part 4. Parts 1-4 can be seen in their entirety here, beginning at post #4:

Out of the box, 0.480” valve lift, 350-400 HP dependant on the CR, cam, ring seal, oil control, etc.
More than 0.480” lift cut the guides down to clear the retainers.
Generally speaking, Vortec's stall at between 0.500” and 0.550” valve lift. This is where flow actually begins to decrease. But their true strength is low lift flow which gives more area under the total flow curve. And if you think about it how long are your valves at peak lift? They spend much more time at 0.400” and below, where the Vortec’s outperform most other heads.
Unported, with all the other tricks in place, the Vortec’s will flow about 235-240 CFM at 0.500” intake and 165-170 cfm at 0.500” exhaust, on a 4" bore at 28" H2O, with clay radiused port opening. With some careful porting there is another 5-10 CFM or so to be had. But again the low lift numbers are unsurpassed at 0.100”, 0.200”, 0.300”, etc. lift. For example the Vortec’s flow as much air at 0.400” as 0.500”, and no 23 degree head that I'm aware of can match them at 0.200”-0.300” lift for the combination of flow and swirl. Even the GM Fast Burn head can't touch them at low lift, its ports are too big (flow is similar, swirl is less), it does of course out perform them at lift over 0.500”.
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.

[edit] Flow rate of L31 Vortec heads

Lift (in.) Intake (CFM) Exhaust (CFM)
0.100 70 49
0.200 139 105
0.300 190 137
0.400 227 151
0.500 239 160
0.600 229 162
Paul Shufelt, Chevy High Performance (Feb. 2001)

  Intake Flow Comparison Exhaust Flow Comparison
Valve Lift GMPP
Fast Burn
Vortec L31
Iron 882
Fast Burn
Vortec L31
Iron 882
0.050” 30 40 39 23 25 34
0.100” 61 70 70 53 48 58
0.200” 126 139 125 107 101 108
0.300” 180 190 175 140 121 135
0.400” 221 227 204 167 140 141
0.500” 243 239 205 178 147 142
0.600” 238 229 206 184 151 142
Note: Vortec L31 and Stock Iron 882 flow data where obtained from Car Craft Magazine’s Web site in their Technical Articles section. The Fast Burn (new version) flow data is Chevrolet’s data.

Warning It's unknown at this time why there's a discrepancy in the exhaust flow of the Vortec heads between the two tables.

[edit] Upgrading and compatibility

The L31 Vortec head can be used on any SBC engine from 1955 through the end of Vortec production, with the exception of the Gen 2 LT1/LT4 engines used in some vehicles between 1992-'97. They are also not compatible with any of the current LS engines.

There are some inherent costs associated in swapping from 1995-back heads to the L31 Vortec heads. Here is a list of items to be purchased and/or labor associated with the upgrade:

  • L31 heads
  • Springs if the cam has a valve lift over about 0.420"
  • 1987 to present center bolt style valve covers if the heads used previously were perimeter style (1986 and earlier including the current production Goodwrench 350 crate motor)
  • Self aligning rocker arms
  • Valve cover gaskets
  • Vortec specific intake manifold. While some aftermarket heads have both 12 and 8 bolt intake bolt patterns, the height of the Vortec ports require a tall, "raised port" type early intake manifold (along with porting/port work to the intake manifold and/or head), to even come close to fitting correctly. See Using an early style intake on an aftermarket Vortec-type head for more info
  • Vortec specific intake manifold gasket
  • Vortec specific intake manifold bolts
  • Head bolts (required only if the original head bolts are either missing or unusable for some reason - 1996+ head bolts are torque to yield unlike 1995 and older)
  • 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.

Warning Note: 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.

[edit] Valves

Vortec heads come equipped with valves having a 30 degree back cut to help flow.

Unlike previous SBC valves, Vortec valves have just one groove for the keepers instead of two grooves (earlier valves had one groove for the keepers, the second (lower) groove was for the oil control O-ring); Vortec heads use a positive-type valve stem oil seal and do not use the tin oil shield seen for years on SBC heads, nor do Vortec heads use exhaust valve rotators.

Another difference between Vortec valves and the earlier non self aligning head valves is the tip length. Earlier valves are 0.250" on both intake and exhaust valves. Self aligning head intake valves have a 0.260" groove-to-tip length, exhaust valves use a 0.289" groove-to-tip length. That said, the typical SBC valve tip length of 0.250" will work just fine with self aligning rockers. Like with ANY rocker arm/valvetrain combination, the valve train geometry needs to be verified.

[edit] Valve springs, retainers and locks

Straight wound spring, Left; Beehive spring, right

The stock Vortec valve springs are single wound without a damper and are 1.250" diameter. The damping is done by the spring ID (.880") being a close fit to the guide boss OD (0.845"); this damps the spring without the added cost of an inner flat wound damper seen on the Gen 1 SBC throughout its production. If you have aftermarket springs designed for the earlier heads, you must remove the inner damper because the damper ID will be too small to fit over the guide boss without it being cut smaller. If the boss is cut smaller, a damper should be used.

The stock springs are not suited for high performance use or for lifts above about 0.420" using stock retainers. There are several replacements for the stock springs, among the best is the beehive spring and retainer combination from Comp Cams, originally designed for the LS engine series:

  • 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"
  • 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"

Warning Note: The p/n 26918 springs requires the spring pocket be opened up using Comp Cams tool p/n 4721 or equivalent so there's no binding. The p/n 26918 springs were updated, check w/Comp Cams to be sure these specs are current.

  • 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"

The beehive springs above need to be installed using the correct retainer for a Vortec valve, like Comp Cams p/n 787 (steel) or p/n 788 (titanium), NOT a retainer originally for the LSx engines; the LSx engines have 8mm metric valve stems. Also note the specs are with an installed height of 1.8". The image below shows the difference in installed height when using different retainers:

Retainer p/n 787 left; p/n 774 right

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 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.

Also see:

[edit] Other springs

The following valve springs are single w/either no damper or damper removed. They fit the stock seat, guide boss, seal, and retainer unless otherwise noted.

  • 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
    • OD: 1.265"
    • ID: 0.865"
    • Seat pressure: 120 lbs @ 1.750"
    • Open pressure: 358 lbs @ 1.250"
    • Coil bind: 1.100"
    • Rate: 476 lbs/in.
    • Max net lift: 0.600"
  • Isky p/n 205D
  • Lunati p/n 73943
  • Manley p/n 22410, fit without machining, allow 0.520" lift
    • Seat pressure: 125 lbs
    • Open pressure: 340 lbs @ 0.500" lift
    • Retainer p/n 23652

Warning Note: K Motion K-700 springs have been reported by one member of Hotrodders.com to be breakage prone. Another member (this writer) has had several sets of 1.25" OD single springs with damper (p/n unknown) break the dampers on a 0.480" net lift hydraulic cam SBC application. Whether these problems were transient or ongoing is unknown. If these springs are being considered, research them first.

[edit] Locks

Warning Note: On Vortec and other heads using self aligning rocker arms, using a +0.050" lock can cause interference between the rocker tip and the locks/retainer. Rocker contacting the locks/retainer has been encountered using a combination of c/n 906 Vortec heads, Comp Pro Magnum rockers p/n 1317, Comp retainer p/n 787, Comp spring p/n 26918, and the +0.050" locks.

The engine builder must mock up the assembly and check the clearance closely. In the case there's insufficient clearance, there are a few options:

  • Use non self aligning rocker arms. Requires guide plates be installed.
  • Use longer valves
  • Use a different spring/retainer combo that uses a standard lock
  • If just the locks are hitting the rocker, using a shorter (lash cap compatible) lock like the Edelbrock p/n 9615 may help. This 7 degree lock is 0.050" lower than a regular lock.
  • Warning Use extreme caution if making the spring seat any deeper.

A tool to help determine the installed height using different retainers and/or locks is the Howards Cams p/n 92010, shown immediately below:

Ret height92010.jpg

[edit] Spring seat

Use caution if making the seat larger, there have been a few warnings about cracks developing on heads with enlarged seats. Maximum spring seat diameter is 1.44". 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. 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.

[edit] Valve guide boss

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 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.

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 double springs or springs that use a damper, the guide boss needs to be modified by shortening and decreasing the OD of the boss.

[edit] Tooling

Comp tooling

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:
  • p/n 4718- spring seat cutter, 1.440" OD
  • p/n 4726- valve guide boss seal cutter, 0.530" OD
  • p/n 4732- 11/32" arbor for cutting tools
Competition Products:
  • p/n 7020 (includes 11/32" arbor)- valve guide boss seal cutter 0.531" OD

From an article by editor Jeff Smith
The Comp Cams cutter increases the spring-seat diameter while simultaneously reducing the outside diameter (OD) of the guide boss. The Crane tool also cuts the valve-guide-seal diameter at the same time. Comp sells a separate tool that cuts a new guide seal and reduces the guide height to create additional retainer-to-seal clearance. Both cutters machine the top of the guide down to a 0.530-inch diameter, which is the standard size for positive-type aftermarket seals. This requires purchasing new valve-guide seals, since the factory uses a 0.560-inch guide to locate the seals. Another way to go is to have a machine shop cut the guide boss diameter to around 0.760 inch and reduce the seal height and use either the Crane H-11 tool steel spring (PN 99846) or the Comp spring (PN 981).

[edit] Rocker arm studs

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 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.

[edit] Stud boss modification

If a hex stud is to be used, the stud boss will need to be shortened. The amount to remove varies depending on the stud being used; not all studs use the same radius from the hex to the stud.

If a guide plate is used, add the thickness of the guide plate, the hex, and the stud radius together to reach the amount that has to be removed. This can be anywhere from about 0.320" to 0.375". The main consideration is that the rocker arm trunnion (if a roller rocker) or the rocker slot/pivot ball (if stamped steel rocker) doesn't bottom out on the stud radius. Check with the manufacturer for these dimensions if need be, otherwise the stud and guide plate can be measured with a caliper.

[edit] Guide plates

Guide plates can also be installed at this time if desired. Consider Isky adjustable guide plates. Using guide plates will require the stud bosses to be machined shorter to compensate for the thickness of the plates and the hex on the stud. While home builders have successfully installed screw in studs without specialized equipment, unless the builder is well versed in doing this type of work, i.e. drilling straight, correctly located holes and tapping them, this is better left to a professional machinist/machine shop. At the least, a fixture to guide the drill bit and tap should be used.
Warning Note: If using guide plates, non self aligning rockers need to be used. If guide plates are not used, self aligning rockers MUST be used.

Warning Note: Hardened pushrods must be used with guide plates to prevent excessive wear.

[edit] Exhaust valve seats

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 c/n 906 head was to be avoided because of the exhaust seat insert being vastly inferior to the heads with induction hardened exhaust seats.

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 c/n 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 c/n 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.

So both the c/n 906 and c/n 062 heads have virtually the same performance potential. In fact c/n 906 heads having the hardened inserts are actually preferred by some performance engine builders, mainly for marine applications. Later production c/n 906 heads stopped using exhaust seat inserts and at some point, all Vortec head exhaust seats were induction hardened.

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.
Hardened insert Vortec exhaust seat
Induction hardened Vortec exhaust seat, note the discolored area around seat

[edit] Pushrod guide holes

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" oval hole in them.

[edit] 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 large enough. A Lewis tool will not work, so instead, a drill bit larger than 7/16" can be used to open the pushrod holes up. Most often a 1/2” bit is used, but in any event use what ever size is needed to get the needed clearance. 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. This means guide plates in almost every case, because the pushrod hole is unsuited as a guide.
Warning Warning: Only one form of pushrod guide can be used. If self aligning rocker arms are used, there cannot be a guide plate used. Conversely, if non self aligning rocker arms are used, guide plates are required.

[edit] 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 HERE.

[edit] GMPP Bow Tie Vortec heads

[edit] Small port Vortec head

  • p/n 25534351 (bare)
  • 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 larger than stock (1.25") SBC springs, 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.

[edit] Large port Vortec head

  • p/n 25534445 (bare)
  • 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.

[edit] Large port Vortec flow chart

Lift (in.) CFM Lift (in.) CFM 

[edit] Vortec intake manifolds

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, so using a carb or TBI with Vortec heads is easy. Some GMPP Vortec intakes have the provision to run coolant through the plenum area to provide intake heat.

[edit] Using an early style intake on an aftermarket Vortec-type head

Vortec heads (also applicable to the 4.3L 90 degree V6) use an intake manifold having 8 instead of 12 bolts. Also, Vortec intake ports are taller than earlier SBC heads; there's not enough metal above the port (except on "raised port" aftermarket intakes) to allow the head and intake port to match up. That means earlier 12 bolt intakes will not match up to the Vortec bolt pattern or ports.

Many aftermarket Vortec style heads (including Bow Tie Vortec heads) feature dual bolt patterns allowing the use of the early 12-bolt intakes. This has a very limited use.

Commonly available 12 bolt SBC dual plane intakes do not have enough metal above the port to be ported to match the Vortec port, w/o having a vacuum leak or razor thin sealing surfaces above the ports. 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 into account. Because of the height of the Vortec intake port, only the single plane 'raised port' race intakes have enough height to actually match up to the Vortec head intake port- but even then the ports may be too wide or have other fitment issues.

Because of these differences, a Vortec-specific intake should be used.

Chevrolet says:
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.
Return to Upgrading and compatibility

[edit] Intake gaskets

Due to issues with some Vortec intake manifold gaskets (vacuum and coolant leaks), it is suggested to use a Fel-Pro gasket p/n Q1255 intake gasket, or equivalent.

Vortec intake gasket over standard gasket
TBI intake p/n 12496821 from GMPP - intake does not have the power brake booster vacuum port located on the LH side, needed when used with a 1987-'95 TBI equipped Chevrolet/GMC 305 or 350
Dual plane GMPP intake p/n 12366573
GMPP p/n 12496822 open plenum intake

[edit] Vortec-specific domed pistons

The shape of a Vortec combustion chamber requires a domed piston designed for it if domed pistons are needed. If a small chamber SBC domed piston is used with a Vortec head, the piston could hit if it isn't clearanced.

Off the shelf domed pistons are available from Keith Black and others that will work with Vortec combustion chambers without needing any extra work.

KB domed piston for the Vortec head. This example uses a long rod

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 (drag race/alcohol fuel, etc.), domed pistons must be used unless the chambers are welded and machined smaller.

For reference, an engine using unported large port Bow Tie heads built to Florida Association of Stock Car Racing, or FASCAR specifications, made over 630 HP/500 ft/lb torque with 12:1 CR.

[edit] Recommended spark plugs

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 Rapidfire Spark Plugs R44LTS
  • AC Delco Rapidfire Spark Plugs MR43LTS
  • AC Delco Rapidfire No 3 Spark Plug
  • Accel P526S U-Groove “shorty” Double Platinum (approximately 3/16″ shorter than AC R44LTS)
  • Accel 516
  • Autolite 26
  • Autolite 104
  • Champion RS12YC
  • Bosch HR10B
  • Bosch HR10BX
  • Bosch HR9DC

[edit] Vortec water bypass

8Thermostat bypass Hotrodders forum thread

[edit] Optional GMPP Vortec parts

Intake Manifolds For Vortec Heads
2116 Edelbrock Performer
21161 Edelbrock Performer, Polished 2116
5426 Edelbrock C-26 Dual-Quad
7116 Edelbrock Performer RPM
71161 Edelbrock Performer RPM, Polished 71161
2913 Edelbrock Super Victor, Single-Plane
2912 Edelbrock Victor JR. Sportsman 2V Vortec
7516 Edelbrock Performer RPM Air-Gap Vortec
75161 Edelbrock Performer RPM Air-Gap Vortec, Polished 7516
12496820 With EGR, square and spread bore carb mount
12366573 GM RPM Style, Squarebore Carb.
12496821 GM TBI with EGR
12496822 GM Eliminator Vortec Design (Same as Edelbrock P/N 2913)
------ Holley MPI Commander 950, MPFI Fuel Injection Kits.
3507 Edelbrock Performer RPM Pro-Flo EFI .
2516 Edelbrock Performer RPM (Marine application, but allows to bolt on a Quadrajet without an adapter) .

Note: You can view Edelbrock/Vortec intakes here

Intake Gaskets For Vortec Heads
1255 Fel-Pro Intake Gasket
89017465 GM Intake Gasket(old P/N 12529094)
Rocker Arms for Vortec Heads
12495490 GM Rocker Arms, 1.5 Ratio, Stamped Steel, Self-Aligning
12370838 GM Aluminum Roller Rocker, 1.5 Ratio, Self-Aligning
12370839 GM Aluminum Roller Rocker, 1.6 Ratio, Self-Aligning
1417-16 Comp Cams Magnum Roller Rocker, 1.52, Roller Tip, Self-Aligning
1418-16 Comp Cams Magnum Roller Rocker, 1.6, Roller Tip, Self-Aligning
1317-16 Comp Cams Pro Magnum Roller Rocker, 1.52 Ratio, Self-Aligning
1318-16 Comp Cams Pro Magnum Roller Rocker, 1.6 Ratio, Self-Aligning
10751-16 Crane Gold Roller Rocker, 1.5 Ratio, Self-Aligning
10758-16 Crane Gold Roller Rocker, 1.6 Ratio, Self-Aligning
Camshafts For Vortec Heads
There are hundreds of cams suitable for use with the Vortec head.

Example: 12-235-2 Comp Cam Extreme 4 X 4, flat tappet cam, lift I .447”, E .462”, duration @ .050” 210 degrees Int., 218 degrees Exh.

Strong low end and mid range torque. Excellent cam for RV's and pickups when changing to the Vortec heads.

Note: Valve spring change is required if changing to a performance cam.
Valve Springs For Vortec Heads
10309-1 Crane Cams valve spring and retainer kit. Drop-in springs with no machine work needed.
Valve Covers For Vortec Heads
12355350 GM Chrome With Red Bow Tie In Center
24502540 Valve Cover Adapter, converts center bolt to parameter bolt
10046089 Center Bolt Valve Cover Gaskets

Holley custom cast aluminum valve covers with ball-milled top. The rigid 1-piece aluminum castings combine strength and light weight in a design that provides a tight gasket seal while also acting to reduce valve train noise.


Holley custom cast aluminum valve covers with polished flat top. The rigid 1-pc aluminum castings combine strength and light weight in a design that provides a tight gasket seal while also acting to reduce valve train noise.


Mr Gasket, 1987-up SBC, center hold down, baffled. Included: 2 covers, 1 oil fill cap, 2 PCV/breather grommets.

Head Gaskets For Vortec Heads
10105117 GM Composition Head Gasket, 0.028” thick compressed.
12557236 GM Composition Head Gasket, 0.051” thick compressed.
1094 Fel-Pro Head Gasket, 0.015” thick compressed.
Spark Plugs For Vortec Heads
5613611 R44LTS, set of 8
5614210 MR43LTS, set of 8
25164641 #3, Rapidfire style, set of 8
P526S Accel U-Groove “shorty” Double Platinum Header Plugs approximately 3/16" shorter then R44LTS plugs, set of 8
Miscellaneous Parts For Vortec Heads
12495499 GM Head Bolt Kit
12495491 GM Flat Tappet HD Push Rod Kit
12371041 Factory Roller Cam Push Rod Kit
12550027 GM Intake Bolts Set
134-2002 ARP SBC Vortec, Intake Bolt kit. 6-Point Bolts and Washers, Black Oxide, quantity of 8.
434-2002 ARP SBC Vortec, Intake Bolt kit. 6-Point Bolts and Washers, Stainless Steel, quantity of 8.
134-2103 ARP SBC Vortec, Intake Bolt kit. 12-Point Bolts and Washers, Black Oxide, quantity of 8.
434-2102 ARP SBC Vortec, Intake Bolt kit. 12-Point Bolts and Washers, Stainless Steel, quantity of 8.
8032 Edelbrock Universal Throttle Bracket. For SBC Vortec or Edelbrock E-Tec heads.
Bare Vortec Head
12529093 Same as P/N 12558060 except it doesn’t include intake valves, springs, and retainers.

[edit] Links

[edit] Compression ratio calculators

Warning Note: Some dynamic compression rtatio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. This works OK on older, slower ramped cam lobes, but the faster lobe profiles may need to have 25 degrees or more added to be accurate.

Warning Note: If the intake valve closing (IVC) point isn't known, it can be calculated:

  1. Divide the intake duration by 2
  2. Add the results to the lobe separation angle (LSA)
  3. Subtract any ground-in advance
  4. Subtract 180

This result does not need to have any amount added to the IVC point, like the KB calculator calls for.

[edit] Resources

  • The following information was posted by Bogie on threads that had to do with cylinder heads and I found it so informative that I didn't want it to be lost, so I'm adding it to the bottom of this L31 article....

"The lope sound of the muscle car era is as obsolete as the tube radio. Those cams made more noise than power. If you want to run with the big dogs today, you've got to look for cams with a lot of lift for their duration and fairly long LSA's compared to the old stuff. Big problem today is the inexpensive flat tappet cam is as obsolete as the dodo bird. The flat tappet is very dependent upon low detergent, high zinc/phosphate (ZDDP) oils which except for expensive race only blends, are not to be found anymore. Today's oils are high on detergents and dispersants while low in zinc and phosphate additives. This is because the zincs and phosphates gunk up converters, costing OEM's money for warranty claims, so they've been outlawed. At the same time it is realized that a clean engine experiences less wear, therefore produces less pollution so with the help of 5 micron filters, the detergency is pumped way up. Now there are additives on the shelf to bump the zinc and phosphate levels up in ordinary off-the-shelf oils but these oils are high detergency oils that scrub off the zinc and phosphate coatings so pouring in more from an additive bottle has been proving to be somewhat ineffective. The OEMs went to roller cams in the period of 1985 to 1995 in anticipation of the change in oil chemistry resulting in wear problems between the lobes and flat tappet lifters. In my opinion the day of the flat tappet cam in the hands of the average hot rodder on the street are over. The loss of a flat tappet cam and the secondary damage from all the metal shavings circulating with the oil is so high that it just isn't worth the front end costs that were thought to be saved. So if you're building on a Vortec block from 1995 or later it is at least provisioned for a roller cam if a 95 and from 96 up it has a roller cam. The factory lifters can be used with a more aggressive roller as can the push rods and rockers. The Comp XR264HR has a good midrange with an rolling idle, the XR270HR pushes the power band up the rev range and has a solid stagger to the idle it needs a high stall converter and 3.50 or numerically-higher rear gears.

The production L31 Vortec head is popular because it has a lot of bang for the buck an easy 20 horses to as much as 40 or 50 over previous factory heads with no other changes to the engine except the head swap. There are many heads that are the equal or better but some can get pretty costly. To really make recommendations would take knowing how much money you can put into your project. The factory production L31 is about the low end cost wise but needs work and parts to run with a hot cam. The guides need to be cut down, screw in rockers installed, the factory springs replaced and better rockers are an improvement. All this gets costly. An inexpensive aluminum head that's very effective is the Pro-Comp. But like the L31, if you’re going for a big cam, they'll need at least better springs. Either of these can be built for less than a grand. Best way is to buy them machined but without valves, springs, retainers and studs, then put in what you need for the cam you choose.

The static compression ratio, thus piston crown shape and volumes, the head chamber and the cam's intake closing point all walk together if you want power. Modern tight chambers make power and lots of it even with a less than ideal port feeding it, whereas a poor chamber characterized by everything that predates the L31 style chamber for the Gen I block is ineffective regardless of what you do to the ports compared these new heads. Aluminum lets you push the compression ratio up at least one point over iron and takes 50 pounds off doing it. To get to the compression ratio need to start with the cam, the point where it seats the intake is all important as at that point the piston has risen in the bore and pushed inducted mixture back out. This must be compensated with more compression. This leads you to the concept of Dynamic Compression Ratio which is an adjustment to the Static Compression Ratio for the stroke used up to the point where the intake valve closes. You want a DCR of at least 8.00 to 8.50 for an iron head and 8.50.00 to 9.00 with an aluminum head, so this drives hard on all the volumes in and above the piston crown. Check this out to play with numbers http://www.kb-silvolite.com/calc.php?action=comp2

Flat top pistons will drive you to a larger chamber head, but as long as you stick to recent aftermarket offerings you should find a 72 to 76 cc chamber with all the configurational advantages of the Vortec L31 head. Don’t be fooled, these heads are much different from the early large chamber heads even though they may have similar volumes. The modern chamber pushes the spark plug well in toward the valves, it may favor the exhaust valve to get in even deeper, there will be a significant relief on the intake side between the valve and spark plug and there will be a beak that penetrates from the squish/quench step to between the valves. These are important refinements to getting power out of the chamber by burning everything that gets in, the older chambers threw a lot of fuel out unused or incompletely used which is the "why" for all the emissions gadgets on the engines of the 1970’s and 80’s. A big reason why that stuff is gone today is the new, highly efficient, fast burning chambers you see coming on the LT1 and LT4 of the early 1990’s and the L31 Vortec of the mid 90’s. Other brands did the same thing under different names at Ford it was the GT40 head for the Windsor, at Chrysler it was the Magnum head for their LA block."

They not only out flow but also out burn the older heads. The L31 Vortec used two castings 12558062 which you have uses induction hardened exhaust valve seats for unleaded fuel. The other casting is 10239906 which uses hard seat inserts on the exhaust side otherwise these two castings are the same.

All of these came with self guiding rockers on press-in studs, the conversion to screw in studs would still require self guiding rockers unless there are sheetmetal guides under the studs in which case they can use the older unguided rocker.

The most common issue with these heads is clearance of the bottom of the spring retainer to the top of the guide oil seal. The guides of this head are pretty high when the stem seal is fitted this restricts max lift to .460 to .470 inch. The most common way around this is to tool the guide lower to gain sufficient clearance. The valve springs are 1.25 inch in diameter which is too small for very radical cams. The safest way to deal with this is the use of beehive or conical type valve springs as the with the raised intake port enlarging the spring seat can easily cut into the port roof. The beehive or conical spring use a smaller diameter retainer which also provides some relief with the guide/oil seal to retainer clearance.

Keep in mind that these heads were for a roller cammed engine that uses a shorter 7.2 inch push rod, when they are used with a flat tappet cammed engine you need to go back to those longer push rods. The average kid at the parts store probably doesn't know that so if he looks these up by year or type of head the short push rod is what he'll find, so you have to know that the push rod lenght goes with the type cam not the type head.

The valves of this head are the same 1.94" by 1.50" that Chevy is so fond of. Depending on cam and compression these heads are a 20 to 50 horsepower bolt on. They have very good midlift flow but run flat over .5 inch so going that much or beyond with the lift is of little value without porting them. They very much respond to a 30 degree back cut on the valve's seat, both intake and exhaust, this is very effective on a long duration cam that lifts from .45 to .5 inch at the valve. A split duration cam is also of value as the exhaust flow didn't improve compared to the intake so that side can use a little extra blow down time moreso than extra lift.

The chamber burns fast compared to previous heads, you'll find its happiest with total spark lead of 34 to 36 degrees. The chamber is very detonation resistant compared to earlier chambers many guys run 9.5 or a little more with a squish/quench clearance of 0.035" to 0.040". Flat tops or D dish pistons work best compared to the factory round dish pistons because those have too much of their squish/quench surface contribution too far from the head to be effective.

Have them checked for cracks, they don't like to be overheated, if these are used heads and have been overheated the chances of cracking is super high. They also like 4 corner coolant return, there are kits that make this quite easy to install. A pair of fittings on the rear of the manifold over the coolant return opening of the head that can be connected to the intake's forward return before the thermostat. Or they can be plumbed into the heater/bypass circuit. This prevents coolant vapor bubbles from collecting above the rear cylinders causing them to run hotter than desired. This is almost as good for power as the 4/7 timing swap without the cost of the cam, your valves and piston on number 7 will thank you."

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