Editing Vortec L31 cylinder head

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==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 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.

==Vortec L31 5.7L head ID==
The L31 5.7L Vortec casting numbers are '''12559062''' and '''10239906'''.

{|
|[[File:062_VORTEC_END_ID_001.jpg|left|frame|Casting number 12558062 Vortec head has 3 small humps, aka "sawtooth", 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.]]
|}

==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 '''[http://www.nastyz28.com/forum/showthread.php?t=56505 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 [http://www.gmpartsdirect.com/performance_parts/store/catalog/Product.jhtmlPRODID=680&CATID=671.html 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.

==Flow rate of L31 Vortec heads==
{| style="color:black; background-color:#ffffcc;" cellpadding="5" cellspacing="0" border="1"
!Lift (inches) !!Intake (CFM) !!Exhaust (CFM)
|-
| align="right" |.1 || align="right" |70 || align="right" |49
|-
| align="right" |.2 || align="right" |139 || align="right" |105
|-
| align="right" |.3 || align="right" |190 || align="right" |137
|-
| align="right" |.4 || align="right" |227 || align="right" |151
|-
| align="right" |.5 || align="right" |239 || align="right" |160
|-
| align="right" |.6 || align="right" |229 || align="right" |162
|-
|}

;'''Sources:'''
:Paul Shufelt, Chevy High Performance (Feb. 2001)

==Upgrading and Compatibility==
The L31 Vortec head will bolt directly onto Gen 1 small block Chevrolets. They will also obviously work on L31 engines (sometimes referred to as Gen1+). They are not compatible with Gen2 (LT1 or LT4) engines. They are also not compatible with any of the current LS engines.

There are however, 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 (and required hardware like springs, valves, retainers, valve keepers, etc)
* Center bolt style valve covers if the heads used previously were perimeter style
** Note: [http://www.crankshaftcoalition.com/wiki/Vortec_L31_cylinder_head#Small_port_Vortec_head_p.2Fn_25534351_.28bare.29_and_p.2Fn_25534421_.28assembled.29 GMPP small and large port Vortec heads] and other aftermarket Vortec heads accept either perimeter or center bolt valve covers
*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 
* 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)
* Head gaskets ([http://www.crankshaftcoalition.com/wiki/Head_gasket#Re-using_head_gaskets generally required] any time heads are re-installed)
* Grinding down valve guides 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. 

==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.

==Valve springs and retainers==
[[File:Vortec beehive.jpg|thumb|left|300px|Straight wound spring, Left; Beehive spring, right]]
<br style="clear:both"/>
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, you must remove the inner damper, otherwise it will bind well before the outer spring does.

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. There are two Comp Cams part numbers for the different spring rates:
*'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=164462240 26915]'''- 105 pounds at 1.8" installed height; 293 pounds at 1.2" (according to Competition Products catalog info); spring rate 313 lbs./in (according to Summit Racing catalog info) 
*'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=1166393320 26918]'''- 125 pounds at 1.8" installed height; 367 pounds at 1.15"

Either of 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:

[[File:787-LEFT; 774-RIGHT (Gen III).gif|frame|left|300px|Retainer p/n 787 left; p/n 774 right]]
<br style="clear:both"/>

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 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. 
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.

==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.

==Valve guide boss==
[[File:900 guide boss1.jpg|thumb|450px|left|Stock Vortec boss is 0.900"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 0.900" to a smaller diameter so aftermarket springs (double or with dampers) can be used. At the same time the boss can be machined to use a commonly available positive seal like 0.530".
<br style="clear:both"/>

===Valve guide boss modification===
[[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 double or those with a damper, the guide boss needs to be modified by shortening and decreasing the OD of the boss. 
<br style="clear:both"/>

===Tooling===
[[File:Tool.jpg|thumb|450px|Comp tooling]]
Crane and Comp Cams 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.
Some Comp Cams part numbers:
*4718- spring seat cutter, 1.440" OD
*4726- valve guide cutter, 0.530" OD
*4732- 11/32" arbor for cutting tools 
<br style="clear:both"/>

;From an article by editor Jeff Smith:
<blockquote>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).
</blockquote>

==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. 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.

Guide plates can also be installed at this time if desired. Consider the Isky adjustable guide plates. If not using guide plates, non shouldered studs can be used instead of studs having shoulders and a hex for tightening (this type of stud is tightened by "double nutting"). <br>
{{Note1}}If using guide plates, non self aligning rockers need to be used. If guide plates are not used, self aligning rockers MUST be used.   

==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.
{|
|[[File:Hard insert seat vortec 906.jpg|thumb|center|400px|Hardened insert Vortec exhaust seat]]
|[[File:Induction hardened seat vortec.jpg|thumb|center|400px|Induction hardened Vortec exhaust seat, note the discolored area around seat]]
|}  

==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; 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:=== 
* 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|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.}}

==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 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.

==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. 

'''[[Vortec_L31_cylinder_head#Upgrading and Compatibility|Return to above]]'''

==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. Due to issues with aftermarket Vortec intake manifold gaskets deteriorating for no apparent reason, it is suggested to either use a genuine GM gasket or a Fel-Pro gasket (part# Q1255).

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:VORTEC GASKET OVER STANDARD INTAKE GASKET.jpg|thumb|center|300px|Vortec intake gasket over standard gasket]]
|}
{|
|[[File:Gmpp vortec tbi intake.jpg|thumb|center|420px|TBI intake p/n 12496821 from GMPP]] 
|[[File:12366573 - GMPP Vortec dual plane intake manifold.jpg|thumb|center|270px|Dual plane GMPP intake p/n 12366573]] 
|[[File:Gmpp 12496822 open plenum.jpg|thumb|center|420px|GMPP p/n 12496822 open plenum intake]]
|}

==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 form Keith Black and others that will work with Vortec combustion chambers without needing any extra work.

[[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"/>

==Vehicles that came with the L31 head==
[[L31 cylinder head sources]]

==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 Rapid Fire Spark Plugs R44LTS 
* AC Delco Rapid Fire 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

==Links==
* Nasty Z28.com forum thread, [http://www.nastyz28.com/forum/showthread.php?t=56505 Vortec Cylinder Heads: The Definitive Guide]
* [http://www.chevyhiperformance.com/howto/97458/index.html Iron Vortec Head All the Details You Need to Know] from the February, 2009 issue of ''Chevy High Performance''.

==Resources==
* [[Valve train points to check]]


[[Category:Engine]]
[[Category:GM]]
[[Category:Cylinder head]]