Vortec L31 cylinder head

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==Design limitations and modifications==

−

Based on info from Gary Penn, of GMPP:

+

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:

−

Two years ago we undertook an exhaustive (no pun intended) study of the Vortec head in numerous modified states with different valve sizes, throat cuts, valve jobs, port mods, guide mods, etc. We used up about 10 heads, numerous valves, and about $50,000 worth of labor. The study generated 100+ pages of flow and swirl data, which I have at my desk.

+

<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.

−

+

−

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.

−

~~Straight mill up to~~ 0.~~060” safely,~~ 0.~~080” with low CR of 10:1 or less~~. ~~0.100”~~ is ~~living on borrowed time. Always use flat top or dished pistons~~ to ~~enhance flame travel and intake swirl~~.

+

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.

−

~~Angle mill up to 1 degree (about 0.110” off~~ the ~~exhaust side, 0~~.~~000” off intake side) safely for about 12:1 CR with flat pistons with little valve relief. Angle mill to 2 degrees (~~about 0.~~200” off exhaust side) if you like to live on~~ the ~~edge- it has been done~~.

+

−

~~Larger valves increase~~ flow, ~~chamber mods not needed~~, ~~trade off between shrouded verses unshrouded valves not worth~~ the ~~decrease in laminar~~ flow and swirl.

+

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”.

−

~~Throat cutting behind larger valves compliments the larger valves. Open the throat to the seat then remove the edge left by the cutter in the port.~~

+

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>

−

+

−

Blend the seats into the chamber, you don't want an edge here to disrupt flow and create turbulence. "Bowl blend" and shortened guide in port also improves flow. Taper and blend the iron boss. Minimal porting increases flow, too much increase in port size or loss of the benefits of the shape of the stock port will decrease efficiency.

+

−

+

−

Vortec heads (and most others) like straight stemmed valves. Undercut valves create unwanted turbulence and a decrease in intake charge velocity (they add volume- slowing the gases- to the overall "port" volume just behind the valve where max velocity is required).

+

−

+

−

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. This combined with high velocity, lack of turbulence and superior combustion chamber design are where the Vortec’s stand out.

+

−

+

−

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 .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.

+

−

~~'''END'''~~

+

==Valve springs==

[[File:Vortec beehive.jpg|thumb|left|300px|Straight wound spring, Left; Beehive spring, right]]

−

The stock Vortec valve springs are single wound without a damper. The damping is done by the spring ID being a close fit to the guide boss OD; this damps ~~rthe~~ spring without the added cost of an inner flat wound damper seen on the Gen 1 SBC throughout its production.

+

The stock Vortec valve springs are single wound without a damper. 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. There are two part numbers for the different spring rates:

−

*

+

*26915- 105 pounds at 1.8" installed height; 293 pounds at 1.2"

−

*

+

*26918- 130 pounds at 1.8" installed height; 318 pounds at 1.2"

+

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.

+

==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==

Line 44:

Line 36:

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>

{|

Vortec L31 cylinder head

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@@ Line 4: / Line 4: @@
 ==Design limitations and modifications==
-Based on info from Gary Penn, of GMPP:
+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:
-Two years ago we undertook an exhaustive (no pun intended) study of the Vortec head in numerous modified states with different valve sizes, throat cuts, valve jobs, port mods, guide mods, etc. We used up about 10 heads, numerous valves, and about $50,000 worth of labor. The study generated 100+ pages of flow and swirl data, which I have at my desk.
+<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.
-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.
-Straight mill up to 0.060” safely, 0.080” with low CR of 10:1 or less. 0.100” is living on borrowed time. Always use flat top or dished pistons to enhance flame travel and intake swirl.
+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.
-Angle mill up to 1 degree (about 0.110” off the exhaust side, 0.000” off intake side) safely for about 12:1 CR with flat pistons with little valve relief. Angle mill to 2 degrees (about 0.200” off exhaust side) if you like to live on the edge- it has been done.
-Larger valves increase flow, chamber mods not needed, trade off between shrouded verses unshrouded valves not worth the decrease in laminar flow and swirl.
+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”.
-Throat cutting behind larger valves compliments the larger valves. Open the throat to the seat then remove the edge left by the cutter in the port.
+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>
-Blend the seats into the chamber, you don't want an edge here to disrupt flow and create turbulence. "Bowl blend" and shortened guide in port also improves flow. Taper and blend the iron boss. Minimal porting increases flow, too much increase in port size or loss of the benefits of the shape of the stock port will decrease efficiency.
-Vortec heads (and most others) like straight stemmed valves. Undercut valves create unwanted turbulence and a decrease in intake charge velocity (they add volume- slowing the gases- to the overall "port" volume just behind the valve where max velocity is required).
-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. This combined with high velocity, lack of turbulence and superior combustion chamber design are where the Vortec’s stand out.
-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 .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.
-'''END'''
 ==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. The damping is done by the spring ID being a close fit to the guide boss OD; this damps rthe spring without the added cost of an inner flat wound damper seen on the Gen 1 SBC throughout its production.
+The stock Vortec valve springs are single wound without a damper. 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. There are two part numbers for the different spring rates:
-*
+*26915- 105 pounds at 1.8" installed height; 293 pounds at 1.2"
-*
+*26918- 130 pounds at 1.8" installed height; 318 pounds at 1.2"
+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.
+==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==
@@ Line 44: / Line 36: @@
 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]]