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.

==Design limitations and modifications==
Based on info from Gary Penn, of GMPP. This is small 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:

<blockquote>Here is the short version. 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.</blockquote>

==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)

==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==
Both 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 LS 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 retainer:

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

==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 valve seats==
Not long after the L31 Vortec head was introduced, a writer for a car magazine incorrectly stated that the 906 head was vastly inferior to the 062 head because the exhaust flow was so bad on the 904. Despite this myth being shot down many times, it still surfaces now and then.

Like many things, there's a grain of truth to this. 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 out for best flow using nothing more than a Dremel.

From GMPP:
<blockquote> 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.
</blockquote>  
{|
|[[File:Hard insert seat vortec 906.jpg|thumb|300px|center|Casting number 906 Vortec head with hardened exhaust seat insert]]
|[[File:Induction hardened seat vortec.jpg|thumb|300px|center|Vortec head with induction hardened exhaust seat, no insert]]
|}

==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 long enough. A Lewis tool will not work, so the best bet is to use a drill bit larger than 7/16" to open the holes up. Most often a 1/2” bit is used, I would use only as much size as was needed, but 1/2” will work. 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.

==Aftermarket Vortec heads==
The listing for the GM Vortec heads sold by GMPP says in part:

Part number (NOT casting number) '''12558060''' Cast Iron Vortec Cylinder Head Assembly
• 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]. 


==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]]