@@ Line 3: / Line 3: @@
 The Chevrolet L31 5.7L Vortec cylinder head is the best flowing production head Chevy has made for the Gen I SBC engine to date. Because of this, it has become a very popular swap.
-The name "Vortec" can be confusing because GM used that name for their V6 and V8 truck engines as far back as 1988. But the heads that are being referred to here are from trucks and SUVs produced from 1996-2002.
+The name "Vortec" can be confusing because GM used that name for their V6 and V8 truck engines as far back as 1985. The origin of the term Vortec was for a combustion chamber design with a ramp port which debuted with the 2.0L motor used with the GM J platform (Cavalier et.al.) which twists the fuel mix similar to a tornado vortice, hence the Vortec nomenclature. 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).
@@ Line 26: / Line 26: @@
 *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 or cracked casting, either of which can lead to overheating and cracked heads.
+*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.
-*vehicles that do not have antifreeze receipts or antifreeze or water jugs laying around inside the vehicle. That's another sure sign there was a problem with the cooling system.
 *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.
@@ Line 52: / Line 51: @@
 ==Vortec L31 5.7L head ID==
-The L31 5.7L Vortec casting numbers are '''12559062''' and '''10239906'''.
+The L31 5.7L Vortec casting numbers are '''12558062''' and '''10239906'''.
 {|
@@ Line 60: / Line 59: @@
 ==Technical specs==
-*Valvespring Seat: 1.300” O.D., 0.850” I.D.
+*Valve Spring Seat/Base diameters: 1.290” O.D., 0.852” I.D.
-*Valve-guide Seals: Viton rubber positive seals, total 0.450” retainer-to-seal clearance
+*Valve Seals: Metal jacketed Viton positive type seals on both intake and exhaust
+*Valve Guide Diameter: ID- 11/32" (.343"), Guide OD AKA- Seal Provision: .552"-.555"
 *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”
+*Valve springs: Single .177" diameter wire, No Damper, 1.250” O.D., 0.896” I.D., 80-pound seat pressure @ 1.700” installed height, Open test load- 190 Lbs @ 1.270", Coil-bind @ 1.180”, vortec heads will not accept early SBC springs w/ damper. Max lift for stock spring is .460" w/ .060" distance before coil bind.
+*Max. Valve Lift: 0.460” which provides 0.030” retainer-to-seal clearance (average overall retainer to seal distance is: .490"-.500")
 *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
@@ Line 88: / Line 88: @@
 ==Flow rate of L31 Vortec heads==
 {| style="color:black; cellpadding="2" cellspacing="0" border="1"
-!bgcolor="#DDDFFF"|Lift (in.) !!bgcolor="#DDDFFF"|Intake (CFM) !!bgcolor="#DDDFFF"|Exhaust (CFM)
+!bgcolor="#DDDFFF"|Lift (in.) !!bgcolor="#DDDFFF"|Intake (CFM) !!bgcolor="#DDDFFF"|Exhaust (CFM) !!bgcolor="#DDDFFF"|Exhaust w/ pipe (CFM)
 |-
-| align="center" |0.100 || align="center" |70 || align="center" |49
+| align="center" |0.100 || align="center" |70 || align="center" |48 || align="center" |49
 |-bgcolor="#F1F1F1"
-| align="center" |0.200 || align="center" |139 || align="center" |105
+| align="center" |0.200 || align="center" |139 || align="center" |101 || align="center" |105
 |-
-| align="center" |0.300 || align="center" |190 || align="center" |137
+| align="center" |0.300 || align="center" |190 || align="center" |129 || align="center" |137
 |-bgcolor="#F1F1F1"
-| align="center" |0.400 || align="center" |227 || align="center" |151
+| align="center" |0.400 || align="center" |227 || align="center" |140 || align="center" |151
 |-
-| align="center" |0.500 || align="center" |239 || align="center" |160
+| align="center" |0.500 || align="center" |239 || align="center" |147 || align="center" |160
 |-bgcolor="#F1F1F1"
-| align="center" |0.600 || align="center" |229 || align="center" |162
+| align="center" |0.600 || align="center" |229 || align="center" |151 || align="center" |162
 |-
 |}
@@ Line 185: / Line 185: @@
 <tr class="wbg-blacktext" align="left" valign="top">
 <td class="wbg-blacktext" colspan="7" align="left" valign="top"><span class="wbg-blacktext-12pxB">'''Note''':</span> 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.</td></tr></table><br>
-{{!}} It's unknown at this time why there's a discrepancy in the exhaust flow of the Vortec heads between the two tables.
 ==Upgrading and compatibility==
@@ Line 192: / Line 191: @@
 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"
+* Springs if the cam has a valve lift over about 0.440"
-* Center bolt style valve covers if the heads used previously were perimeter style
+* 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)
 ** 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 [[File:Vortec valve-rocker.jpg|thumb|right|300px|Self aligning stamped steel rockers]]
-*Self aligning rocker arms
+*Self aligning rocker arms (SBC and 4.3L since the 1988 model year use the self aligning rockers and the pushrod holes are round instead of oblong - self aligning rockers do retrofit to the earlier heads but recommended for a stock rebuild
-* Valve cover gaskets
+* Valve cover gaskets (again 87+ centerbolt style)
-* 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 '''[[Vortec_L31_cylinder_head#Using an early style intake on an aftermarket Vortec-type head|Using an early style intake on an aftermarket Vortec-type head]]''' for more info
+* 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 '''[[Vortec_L31_cylinder_head#Using an early style intake on an aftermarket Vortec-type head|Using an early style intake on an aftermarket Vortec-type head]]''' for more info; some applications require the stock SBC intake to have the upper section rewelded with a chunk of metal which covers the intake ports as demonstrated with the SyTy 4.3L or TPI intake base (it is common for the SyTy 4.3L lower intake to be modified with extra material when used with Vortec heads)
 * 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 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 ([http://www.crankshaftcoalition.com/wiki/Head_gasket#Re-using_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.
@@ Line 216: / Line 215: @@
 [[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 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 Vortec valve springs are single wound without a damper and are 1.250" diameter. The damping is done by the spring ID (.896") being a close fit to the guide boss OD (0.852"); 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:
+The stock springs are not suited for high performance use or for lifts above about 0.460" 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:
 *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=164462240 p/n 26915]'''- 105 pounds at 1.8" installed height; open pressure 293 lbs. at 1.2"; coil bind at 1.100"; spring rate 313 lbs./in.; bottom OD 1.290"
 *'''[http://www.compcams.com/WhatsNew/NewsDetails.aspx?ListHistoryID=1166393320 p/n 26918]'''- 125 pounds at 1.8" installed height; open pressure 367 pounds at 1.15"; coil bind 1.100"; spring rate 372 lbs./in.; '''bottom OD 1.310"''' <br>
@@ Line 279: / Line 278: @@
 ==Valve guide boss==
 [[File:900 guide boss1.jpg|thumb|450px|left|Stock Vortec boss is 0.845"OD]]
-For performance use, often the guide boss will be shortened to allow more lift without retainer to seal clearance problems. Along with that, the guide boss OD can be machined down from 0.845" to a smaller common diameter, like 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.
+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 0.852" 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 guide where the seal is located can be machined from 0.555" (stock) to a smaller diameter like 0.530" to use commonly available seals.
 <br style="clear:both"/>
@@ Line 298: / Line 297: @@
 ;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>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 0.555-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>
@@ Line 332: / Line 331: @@
 ==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.
+[[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" oval hole in them.
 ===So what this means is three things:===
@@ Line 371: / Line 370: @@
 ====Large port Vortec flow chart====
 <table border="5" cellspacing="0" cellpadding="5"><tr valign="top" tr bgcolor="#CCCCFF"><td colspan="2"><center>'''INTAKE'''</center></td><td colspan="2"><center>'''EXHAUST'''</center></td></tr><tr valign="top" tr bgcolor="#FFF8DC"><td>'''Lift''' (in.)</td><td>&nbsp;'''CFM'''&nbsp;</td><td>'''Lift''' (in.)</td><td>&nbsp;'''CFM'''&nbsp;</td></tr><tr valign="top"><td>0.200</td><td>128.6</td><td>0.200</td><td>100.8</td></tr><tr bgcolor="#F1F1F1" valign="top"><td>0.300</td><td>188.4</td><td>0.300</td><td>138.6</td></tr><tr valign="top"><td>0.400</td><td>234.8</td><td>0.400</td><td>154.4</td></tr><tr bgcolor="#F1F1F1" valign="top"><td>0.500</td><td>257.2</td><td>0.500</td><td>152.5</td></tr><tr valign="top"><td>0.600</td><td>263.2</td><td>0.600</td><td>163.8</td></tr><tr bgcolor="#F1F1F1" valign="top"><td>0.700</td><td>269.1</td><td>0.700</td><td>167.0</td></tr></table>
-==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.
-===Using an early style intake on an aftermarket Vortec-type head===
-Vortec heads 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<nowiki>:</nowiki>
-<blockquote>
-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.
-</blockquote>
-;Return to '''[[Vortec_L31_cylinder_head#Upgrading and compatibility|''Upgrading and compatibility'']]'''
 ==Intake gaskets==
@@ Line 396: / Line 378: @@
 |}
 {|
-|[[File:Gmpp vortec tbi intake.jpg|thumb|center|420px|TBI intake p/n 12496821 from GMPP]]
+|[[File:Gmpp vortec tbi intake.jpg|thumb|center|420px|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 - some GMT400 light duty trucks and G-series vans including the forward control chasssis will have a hydroboost brake booster in lieu of a vacuum assist power brake booster]]
 |[[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]]
@@ Line 404: / Line 386: @@
 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.
+Off the shelf domed pistons are available from 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"/>
@@ Line 425: / Line 407: @@
 * Bosch HR10BX
 * Bosch HR9DC
+* Bosch 4505
+* Bosch 4458
 ==Vortec water bypass==
 [http://www.hotrodders.com/forum/thermostat-bypass-vortec-conversion-161468.html#post1581704 Thermostat bypass] Hotrodders forum thread
+The L31 (and L30) small block, along with the 4.3L (L35, LU3) came with a redesigned water pump with a threaded boss on the impeller which accepts a fan clutch held with a nut instead of the 4 bolt setup common with 1995 and earlier SBCs. A water pump bypass port was added to the intake manifold where the cylinder block for 1996+ will have the water pump bypass hole eliminated - some 1996-2003 production cylinder blocks will have the bypass hole eliminated and undrilled (visual cue is the RH water pump port where the bypass hole is absent and undrilled - this also includes cylinder blocks with 2 holes undrilled for the timing cover (much like engine blocks casted after 1992 the fuel pump hole is undrilled and unmachined - aftermarket 5.7L crate motor assemblies including the L31 used by Mercury Marine/MerCruiser will have the water pump bypass hole and fuel pump hole drilled out and machined. One solution is the following - use a high flow thermostat or run a water bypass from the heater hose port to the radiator and/or heater core.
 ==Optional GMPP Vortec parts==
@@ Line 566: / Line 552: @@
 <td class="wbg-blacktext" align="center" valign="top">Edelbrock Performer RPM Pro-Flo EFI <b></b>.</td>
+</tr>
+<tr class="wbg-blacktext" align="center" valign="top">
+<td class="wbg-blacktext" align="center" valign="top">2516</td>
+<td class="wbg-blacktext" align="center" valign="top">Edelbrock Performer RPM (Marine application, but allows to bolt on a Quadrajet without an adapter) <b></b>.</td>
 </tr>
@@ Line 729: / Line 723: @@
 <td class="wbg-blacktext" align="center" valign="top">Crane Cams valve spring and retainer kit. Drop-in springs with no machine work needed.</td>
+</tr>
+<tr class="wbg-blacktext" align="center" valign="top">
+<td class="wbg-blacktext" align="center" valign="top">Vsk4h53</td>
+<td class="wbg-blacktext" align="center" valign="top">Alex's Parts valve spring kit. Drop in fit, machine work not required up to .550" Lift, Hyd Roller.</td>
+</tr>
+<tr class="wbg-blacktext" align="center" valign="top">
+<td class="wbg-blacktext" align="center" valign="top">Vsk4h50</td>
+<td class="wbg-blacktext" align="center" valign="top">Alex's Parts valve spring kit. Drop in fit, machine work not required up to .550" Lift, Hyd Flat Tappet.</td>
 </tr>
@@ Line 995: / Line 1,002: @@
 * [[Valve train points to check]]
 * [[Quench]]
+* [http://www.compcams.com/information/Articles/Type/Chevrolet/CC_CHP0201-002.asp  Vortec head chronicles.]
 <br><br>
@@ Line 1,001: / Line 1,009: @@
 [[Category:Cylinder head]]
-*The following information was posted by Bogie on a thread 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 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.
@@ Line 1,011: / Line 1,019: @@
 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."
 Bogie

Vortec L31 cylinder head

Latest revision as of 22:22, 10 July 2020

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