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 64cc combustion chambers (actual size is closer to 66-68cc) and 170cc intake runners.

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)

==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 (one for the keepers, the other 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==
[[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 being a close fit to the guide boss OD; this damps the spring without the added cost of an inner flat wound damper seen on the Gen 1 SBC throughout its production.

The stock springs are not suited for high performance use. 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 LSx engine series. There are two 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"

==Valve spring retainers==
Either of these springs need to be installed using the correct retainer for a Vortec valve- 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"/>

The stock retainers can be reused with aftermarket springs if the OD is the same as the stock springs. In some cases, the retainer can be clearanced to give added lift clearance. This modification is sometimes referred to as the "ghetto grind".

==Rocker arm studs==
Production L31 Vortec heads come with pressed in 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 the budget is limited. Otherwise use ARP #070-134-7221 M8 x 1.25 studs or the equivalent. Unless the builder is well versed in doing this type of work- drilling straight, correctly located holes and tapping them- this is better left to a professional machinist/machine shop.

Guide plates can also be installed at this time if desired. If not, 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").  

==Exhaust 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 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 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 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 exact same performance potential. In fact the 906 heads having the hardened inserts are actually preferred by some performance engine builders, mainly for marine applications. Later production 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 discoloed area around seat]]
|}  

==Valve guide boss modification==
In order to fit one of the commonly available smaller diameter valve stem oil seals, the tops of the guide boss needs to be turned down. To fit springs with a smaller ID, and for using different springs, the guide boss needs to be modified by shortening and decreasing the OD of the boss. Tools are sold (~$100 for the two cutters needed) to do these modifications using a hand drill.

[[File:VORTEC GUIDE BOSS MODIFIED.jpg]] <br style="clear:both"/>

==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.

==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 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==
[[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]]