I've been building a modified LS2 for some time now. Work is finally finished and the beast is about to go out for a tuning session on the Dyno. Two years ago I was wading through the swamp of available cylinder heads and simply did not know what would fit on which block and, since I was using a 2006 LS2 out of a GTO I was uncertain about the differences, if any. Then I found a 'swap guide' written by Mike Mavrigian . I used it to great advantage and, perhaps some of you can as well.

If you disagree with anything in it, go talk to Mike. It's his work. not mine! Just remember, Mike is an engine builder, author and runs his own shop. He's a nice guy but he knows what he knows ; which means he does not tolerate fools gladly! You can reach him here:https://theshopmag.com/authors/mike-mavrigian


A Look at LS Cylinder Heads

Mike Mavrigian

August 7, 2014


The range of original equipment GM LS cylinder heads offers decent performance out of the box, the mostly notable of which is probably the L92 head.
These heads produce surprisingly good flow and performance and are suitable for power builds.
Pushing the horsepower envelope even further is an array of aftermarket heads from such manufacturers as Trick Flow,
Dart, RHS, World Products, AFR, Edelbrock and Pro-Filer. These aftermarket performance firms take the time to study the OE heads
in terms of port volumes, port angles, valve angles, airflow and combustion chamber design and continue to tweak and improve, taking what GM did to another level.
First, we’ll take a look at the OE cylinder heads designed for the increasingly popular LS platform.
This will provide a basic understanding of the original equipment factory versions. We’ll then discuss performance aftermarket heads.

OEM CYLINDER HEADS CASTING I.D.

LS1 853

LS6 243 (features an intake and exhaust port design change as compared to LS1)

LS2 243

LS7 8452

L92/LS3/LS9 5364

Note: A Mexican LS2 cylinder head, casting number 799, is also available, but features a rougher finish than the U.S. casting.

Factory original LS heads feature PM (powdered metal) valve seats and powdered metal guides, (which feature the lubricity of bronze and the longevity of cast iron guides).
All LS1, LS6 and LS2 heads feature tallcathedral-style intake ports. The LS7, L92 and LS3 heads feature rectangular intake ports.
GM cathedral-style intake ports measure in the range of 3.125 inches high by 1 inch wide. These are easy to identify due to their tall, narrow shape and somewhat radiused top profile.
All LS heads, with the exception of the LS7, feature as-cast chambers and ports, which means that these surfaces are cast to finished form with no extra machining.
The LS7 heads however, feature CNC-machined chambers, intake ports and exhaust ports.
All LS cylinder heads, with the exception of the LS7 heads, are interchangeable among blocks. The LS7 cylinder heads cannot be mounted to other LS blocks, as the wider valve layout would result in valves contacting the bores.
A variety of OE Gen 3 heads are available, including an iron small port (initially used on the 4.8-liter truck engine), the LS1 aluminum head, the LS6 aluminum head with 63cc chambers, the LQ4 aluminum head with 67cc chambers and LS6 heads with larger ports and larger chambers.
Pay attention when interchanging heads and blocks to check for potential valve-to-bore interference.

All OEM LS cylinder heads feature a cylinder bolt layout that provides four bolts at each cylinder location, which provides an improved clamping load,
more evenly distributing the clamping forces around each bore location.
Certain aftermarket racing heads feature a “six-bolt” head to accommodate mounting to LSX and other aftermarket race blocks, for applications that involve extremely high cylinder pressures.Another feature of LS cylinder heads involves the valve cover mounting. Early Gen 3 LS1 heads featured valve cover bolt locations along the perimeter of the valve cover. Later LS cylinder heads feature a center-bolt layout, where special grommeted valve cover bolts enter through the roof of the valve cover.

A Look at Some OEM Heads

The LS3, LS9 and L92 all use essentially the same cylinder head foundation, featuring a four-digit identification number (top of head just outside the valve cover rail) 5364.
The LS7 cylinder head is unique, with identification number 8452. Identifying an OEM LS7 head from the OE LS3, LS9 and L92 head is fairly easy—the LS3, LS9 and L92 heads
feature flat rocker pedestals (to accept separate rocker arm rails), and the ports and chambers feature a cast finish.
The LS7 head features individual rocker arm radiused stands and all ports and chambers display a machined surface. In addition, the LS3, LS9 and L92 heads are
originally equipped with the tapered “beehive” valve springs, while the LS7 head features “straight” valve springs without the beehive taper.
Unlike the LS1, LS6 and LS2 heads that feature the tall, skinny cathedral intake ports, the LS3, LS9, L92 and LS7 heads feature a conventional rectangular shaped intake port style.
Intake port dimensions also vary between the two head versions. The intake ports on the head used for the LS3, LS9 and L92 are 1.250 inches wide by 2.550 inches tall,
while the intake ports on the LS7 head are 1.350 inches wide by 2.40 inches tall.

Head Interchangeability

Which LS heads will physically swap out to the various LS blocks?
Basically, you need to pay attention to the block’s bore diameter. Running a cylinder head intended for a larger bore size can result in valves crashing into the block.
For instance, you cannot install an LS3, LS9 or L92-style head on an LS1 or LS6 block due to valve interference with the block deck. One of the primary reasons that you can’t
simply swap heads willy-nilly is due to the cylinder head’s valve layout and valve head diameter. Heads that were designed for larger bore blocks (such as the LS7,
for example) can easily create valve to top-of-cylinder bore clearance issues. If in doubt, you’ll need to temporarily install the heads (outfitted with light-duty checking valve springs)
and check for valve interference, where the valve head may contact the top of the bore. In this case, you’ll need to notch the top of the bores to provide valve clearance.
So, pay attention when purchasing replacement heads.

Here’s the rundown summary:

· LS1 and LS6 blocks will accept only LS1, LS6 and LS2 heads.

· LS2 blocks can use LS1, LS6 or LS2 heads, as well as L92-style heads, which includes LS3 and LS9 heads.

· LS3 and LS9 blocks can use LS1, LS6, LS2, LS3 or LS9 heads.

· The LS7 blocks can accept any LS head.

Be aware that while production LS1, LS6, LS2, LS3 and LS7 engine cylinder head bolts are 11mm in diameter, the LS9 block uses 12mm diameter bolts.

We’ve discussed intake port styles and sizes already, but here’s a summary of the OE intake port styles: The “cathedral” port was used originally on the LS1, LS6 and LS2.
There are two OE rectangular port styles, including the LS7 style and the L92 style. The LS7 rectangular ports feature 270cc volume.
Since any cylinder head intake port must be matched to the intake manifold port, only an LS7-style (in terms of port shape and dimensions)
intake manifold will work with an LS7-style head. The L92-style ports are a bit narrower and a bit taller as compared to the LS7 ports.
Again, intake manifold selection must match port style and dimensions.

Valves

A few early GM LS engines feature solid stems, while most feature hollow, sodium-filled exhaust stems. The LS7 uses titanium intake valves and hollow sodium exhaust valves.
When buying new valves to complete bare heads or when replacing valves, you can take advantage of high-quality aftermarket stainless steel valves.
The only reason to go with titanium valves is to reduce valve weight, which is only needed for sustained high-revving race engines.

Rockers

Factory production LS rocker arms feature a 1.7:1 ratio for all LS cylinder heads, except for the LS7, which features an increased 1.8:1 rocker arm ratio.
OE rocker arms feature a trunnion bearing at the pivot point, which presents a weak point regarding high-performance use (they tend to fail under high engine speeds).
If you’re building a performance-upgraded or racing LS engine, either have the OE rockers upgraded with a stronger trunnion/bearing setup
or move up to aftermarket units that feature forged/billet high-density alloy bodies and well-oiled pivot bearings or needle bearings.
Performance aftermarket roller rockers are designed for extreme use that involves higher spring pressures and higher and/or sustained engine speeds.
If you want to save some bucks, GM rockers may be upgraded by replacing the trunnions and trunnion bearings with superior components.
The powdered metal rockers are surprisingly strong (and good up to around 450 hp), but the trunnion bearings are a definite weak point.
Note: GM OE rockers are not “full roller” rockers, as they only pivot, or roll, on trunnion bearings and do not feature a roller tip at the valve contact.
Due to valve angles used in various LS heads, rocker arms may be “straight” or offset.
The LS1, LS6 and LS2 heads use a straight rocker (no offset between valve and pushrod contacts), and both intake and exhaust rockers are identical.
On the LS3, LS9 and LS7/L92 GM heads, the intake rocker features an offset (exhaust rockers are the same as used on LS1, LS6 and LS2).
The LS7, as mentioned earlier, features a 1.8:1 ratio (and offset intake rockers).

OEM ROCKER ARM RATIOS

LS1 1.7:1 (intake and exhaust rockers identical)

LS6 1.7:1 (intake and exhaust rockers identical)

LS2 1.7:1 (intake and exhaust rockers identical)

L92 1.7:1 (intake rocker offset)

LS3 1.7:1 (intake rocker offset)

L99 1.7:1 (intake rocker offset)

LS9 1.7:1 (intake rocker offset)

LS7 1.8:1 (intake rocker offset)

OE Rocker Arm Pedestal Rails

Two different rocker arm pedestal rail versions are used. One rail is designed for use on the LS1, LS6 and LS2. The other is designed for the L92, LS3, L99 and LS9.
The rail for the LS1, LS6 and LS2 features the pedestals centered (height-wise) on the rail. Each edge of the rail’s length is straight.
The rail for the L92, LS3, L99 and LS9 locates the pedestals a bit offset, with one side of each pedestal extended out, (one edge of the rail features
individual pedestal bulges, or radiuses that protrude out from the edge).
The rail for the LS1, LS6 and LS2 features each cylinder’s pair of pedestals located 1.901 inches on center from each other.
The rail for the L92, LS3, L99 and LS9 features the pedestal centers located 2.227 inches apart (center of hole to center of hole).
The part numbers on the rails are 12552203 for the LS1, LS6 and LS2 rails and 12600936 for the L92, LS3, L99 and LS9 rails.
The LS7 cylinder heads feature individual radiused rocker stands and do not require the use of a separate rocker arm mounting rail.
Many aftermarket performance cylinder head designs eliminate the pedestal rails altogether and incorporate cast-in machined pedestals
(basically taking the features they like from various GM versions and coming up with a design element combination that works best and that reduces the number of individual parts).
The cylinder head manufacturer will provide recommendations for the specific rocker arms that are designed to be used with their heads.

OE Valve Springs

All original equipment-style LS series cylinder heads feature beehive-shape springs (these feature smaller diameter upper and lower coils
for superior damping of spring harmonics). All OEM spring retainers are steel, even in the LS7.
This single beehive spring design eliminates the need for dual springs, and also allows the use of smaller and lighter retainers.
There is some debate among engine builders regarding the virtues of beehive springs, as some builders prefer to use “conventional” dual springs
that feature uniform top and bottom spring diameters.
If you’re building for performance, as opposed to simply rebuilding an original engine, many builders agree that the use of conventional
single or double springs (with same diameter top and bottom, not the beehive) makes sense.
Availability and pricing is better, along with the advantage of common retainer diameters.
Always base valve spring rates on the camshaft maker’s recommendations. You’ll see valve spring open and closed pressures and installed height specs
on the camshaft data card supplied with the cam. It’s not that there’s anything really wrong with the beehive design, but I really don’t see any big advantage to their use.
To help in reducing valve mass (weight), you can take advantage of titanium retainers, which are readily available from
any of the leading valvetrain manufacturers. The most important aspect of choosing the springs is to always follow the camshaft maker’s spring rate recommendations.

Cylinder Head Gaskets

Early LS engines featured composite-type cylinder head gaskets. Around 2002, GM switched to MLS (multi-layer steel) cylinder head gaskets.
All remaining gaskets throughout the engines are formed elastic seal-type gaskets that are reusable (depending on condition, of course).
The use of MLS cylinder head gaskets is recommended. MLS gaskets provide excellent sealing characteristics and tend to allow a more even distribution of cylinder head clamping.
It’s important to realize that the act of tightening the cylinder head bolts (or nuts on head studs) results in generating a degree of elastic stretch in the fastener (bolt or stud).
This “stretch” creates tension, or compression load, on the head and gasket.
Without proper clamping load, the head gasket won’t seal, and the cylinder head may be subject to uneven thermal expansion and contraction.

Note regarding MLS gaskets: It is very common (on any engine, not just an LS) when using MLS cylinder head gaskets
that you may experience a slight external coolant weeping during the initial engine run. This is normal. The MLS gaskets feature a special
heat-cured coating that will continue to seal during the initial run. Don’t have a heart attack if you see a small bit of coolant weeping out between
the heads and block when the engine runs for the first time. This coolant weeping won’t happen in every case, but it’s not uncommon.
As long as the deck surfaces have been prepared properly and you’ve followed correct assembly procedures, this minor leakage should disappear quickly.

Head Bolts or Studs

The OEM LS1 and LS6 feature two different length hex-head cylinder head bolts (11mm x 100mm and 11mm x 155mm); later LS2, LS7, LS3 and L92 engines
use only the 11mm x 100mm head bolt length, due to the thread depth differences in the blocks.LS9 blocks feature 12mm diameter bolts.
All LS heads also feature additional 8mm x 1.25 x 45mm “pinch” bolts that are located at the inboard edge of each cylinder head.
All LS heads require 10 primary cylinder head bolts, plus five 8mm pinch bolts. All GM OE head bolts are torque-plus-angle and
TTY (torque-to-yield) type, which should not be reused and feature OEM thread locking compound.
All head bolts enter blind holes, so none are open to water or oil. Superior-quality performance aftermarket head bolts are available
that are to be tightened using a specific torque value, eliminating the need to follow a torque-plus-angle method.
The use of studs (instead of bolts) decreases wear on the female threaded holes in aluminum blocks (in terms of repeated disassembly/assembly),
and allows a more precise clamping load, since you avoid the frictional variables of threading into the block as opposed to threading
precision nuts onto precision stud threads.

Note: when installing cylinder head studs, install the studs into the block finger-tight. Avoid preloading the studs,
(in other words, don’t apply a bunch of torque when installing the studs into the block). This can easily result in slight splaying of the studs,
which will interfere with achieving proper clamping load.